Astrophotography is a fairly complicated hobby, and there's a lot to learn! One of the most important aspects of astrophotography is picking the correct camera for your lens or telescope (and vice versa!) For all my fellow photographers out there, we are very familiar with focal length, and how that affects our images. As you'll learn though, focal length is just the tip of the iceberg! In this article I will break down all the major points, and simplify things as much as possible.
Of all the images I've taken, this is still one of my favorites! I used a Tokina 100mm Macro lens, Nikon D750, and an iOptron SkyTracker Pro to take a single 60 second photo.
Let's start off with focal length, since this is the easiest to understand. More focal length means more zoom, and any objects you are photographing will appear larger in the frame. This can be hard to quantify when it comes to deep space astrophotography though. Thankfully, I've got plenty of sample images to give you an idea of how the different objects will look. For the rest of this section, I will be focusing on focal lengths with a Full Frame camera, like the Canon 5D or Nikon D850. We'll cover crop-sensors, and how they affect focal length, later on.
Now that I've photographed most of the large objects in the night sky with a variety of lenses, I've got a pretty good idea of how the focal length will change the composition. I recommend using at least 250mm. At this focal length, even the largest objects (like the Andromeda Galaxy) will be fairly small in the frame. You will need to crop in quite considerably to get a great photo. If you have a lower-resolution sensor, this crop will cause problems with the image quality. However, if you've got a high-res sensor like the Nikon D850, you can crop in quite close and still retain a lot of detail.
This comparison shows the Andromeda Galaxy at 150mm, 200mm, 300mm, 400mm, 500mm, and 600mm. The original photo was taken at 500mm and edited in Photoshop. I then scaled it to show the galaxy would look at these various focal lengths. The Andromeda Galaxy is also one of the largest objects in the night sky.
I personally like shooting between 400mm - 600mm for most of the deep space objects. Let's be clear, when I say deep space objects I'm referring to the brightest and largest objects in the night sky. For a full list, check out my Deep Space Course, which focuses on 12 different objects. Once you get to 400mm, you should be able to fill most of the frame with these objects. As the zoom in further, and the objects get larger in the frame, you will be able to pull out more details. However, there is a drawback to consider.
The more zoom you have, the more accurate your tracking has to be. Instead of shooting 2 minute exposures at 250mm, you will be lucky to get sharp stars at 30 seconds when shooting 400mm+. Of course, this largely depends on your polar alignment accuracy, balance, the tracker itself, and whether you have an auto-guider.
Before I purchased an auto-guider, I was limited to 30 second exposures with my Tamron 150-600mm lens. This was never enough time to capture the light that I needed. Even if I took 100 photos and stacked them, I would still have problems baked into the final image. Most notably, there's an ugly purple glow at the bottom of my photos. Once I started using an auto-guider though, I could easily shoot 2+ minutes with sharp stars! For more information on auto-guider, check out my article here.
As I was doing research for this article, I learned about a great resource - telescopius.com This website allows you to input your focal length and sensor size to get an accurate view of how large the objects will appear. Now you can quickly see how an object will look with any give combination of camera and lens!
Once you get to the Telescope Simulator page you can select any object you plan on photographing. You'll want to make sure you input your focal length and sensor size in the appropriate boxes. If you're not sure what your sensor size is, this website should tell you. A Full Frame sensor is usually 36mm x 24mm. This is a great way to try different combinations and determine what focal length or sensor size you should consider buying.
If you have a 70-200mm lens, you may also have a teleconverter laying around. These usually come in 2 versions - 1.4x and 2x. The 1.4x teleconverter will give you a small boost in focal length, but you will also lose a stop of light. That 70-200mm f/2.8 lens will now act like a 98-280mm f/4 lens. That's not much more zoom, and you're capturing half the amount of light you were at f/2.8! The 2x teleconverter will go much further, but also cost you 2 stops of light (that's 4 times less light)! That lens will now act like a 140mm - 400mm f/5.6 lens. That might sound pretty good, essentially equivalent to a 100-400mm f/5.6 lens. However, teleconverts aren't designed for astrophotography. Therefore, you may see severe star distortion and chromatic aberration, among other problems. if you have one, feel free to try it, but I would not recommend buying one specifically for astro.
Just to recap, I generally recommend 400mm - 600mm for most of the objects that we can capture with a DSLR. If you only have a 70-200mm lens, most of the objects will appear quite small in the frame. This causes them to lose that "wow" factor. If your budget allows it, I'd recommend getting something like a 100-400mm or 150-600mm lens.
This photo was taken with a stock Nikon D750, William Optics Space Cat, SkyGuider Pro, and ZWO ASIAir. This combo is very portable and lightweight, and provides excellent results! The only downside is the relatively short 250mm focal length of the Space Cat, but it worked nicely for this composition
Almost all of my deep space images have been taken with camera lenses, usually the Tamron 70-200mm G2 or the Tamron 150-600mm. These both do a surprisingly good job! The best part is the versatility. I can use these lenses for landscapes and wildlife photography during the day, and astro at night! Therefore, I highly recommend starting off with whatever camera lenses you currently have. There are a few things you need to watch out for though.
Since camera lenses aren't specifically designed for astrophotography, they may exhibit some problems. The two big ones are chromatic aberration and coma. Chromatic Aberration is a colored line around high-contrast areas, like stars. This may manifest as a bright blue or purple glow around your stars. In some cases the chromatic aberration is so bad, it completely ruins a photo. Telescopes can also have this problem, especially cheaper ones. One trick to reducing chromatic aberration is "stopping down the lens". Rather than shooting wide open, at f/2.8 for example, you can intentionally use a smaller aperture like f/4. You'll capture less light, but the stars may appear sharper and have less chromatic aberration. It is possible to remove chromatic aberration in post-processing, but the results will vary from lens to lens.
Coma is a unique star distortion that will change for every lens. I recommend reading this thorough analysis of the various types of coma. I honestly don't see too much coma with most telephoto lenses, this is mainly a problem with wide angle lenses between 35mm - 85mm. Coma can usually be corrected fairly easily by stopping the lens down. For example, my Sigma 35mm f/1.4 ART lens has terrible coma at f/1.4. The stars look like birds! The only way to fix this problem is by using f/4. At that point the stars are finally sharp. However, f/4 captures 8 times less light than f/1.4!
To be honest, I don't really have much experience with telescopes. The only telescope I actually own is the 250mm William Optics Space Cat. It does a nice job, but it's not exactly a big fancy telescope. Therefore, I can't give any real recommendations. I would recommend checking YouTube and the CloudyNights forum before you buy any telescope. Both platforms are great repositories of sample images and user feedback. I'd recommend reading this article for more information on the different types of telescopes..
I have much more experience with camera lenses, but there are still too many to choose from! My general advice would be to get a 100-400mm lens, or a 150-600mm lens. These will both provide enough zoom to capture incredible photos! I really like the Tamron brand of lenses, they've come a long way in the past few years. Their latest lenses rival the first party options from Canon, Sony, and Nikon, for a fraction of the price!
If you are thinking of buying a new lens or telescope, there are two main factors to consider - Aperture and Focal Length. I'd recommend at least 400mm for the focal length. This should be enough zoom for most of the big nebulae and galaxies in the night sky. I would not go higher than 800mm though. This will be overkill unless you have a high-end "Go-To" telescope mount. Just keep in mind that the size, weight, and price of a lens / telescope will increase along with the focal length and maximum aperture.
My final recommendation really depends on your current setup. If you're like me, and have a DSLR, telephoto lenses, tripod, and a star tracker, then there's really no need for a telescope. You might as well stick with your current lenses, or consider buying a new telephoto lens. You can use it for both astrophotography and your "normal stuff" - portraits, wildlife, landscapes, etc... I would only recommend buying a telescope if you are also considering a dedicated astrophotography camera. In that case, you'll probably want to get a higher end mount too.
This photo was taken with the William Optics Space Cat telescope. Since it was only 250mm, the Andromeda Galaxy was fairly small in the frame and I had to crop quite a bit to get this final image. I've gotten better photos of this galaxy using a standard camera lens like the Tamron 150-600mm. In most cases, telescopes aren't magically better than a telephoto lens. They may be cheaper and lighter though!
The two most important camera settings for astrophotography are aperture and shutter speed. The shutter speed depends on a few factors - your polar alignment accuracy, whether or not you are using an auto-guider, the build quality of your star tracker, your focal length, and how well balanced your setup is. If you have everything perfect, you could probably shoot up to 10 minute exposures at any given focal length. Realistically though, I'm happy if I can get 3 or 4 minute exposures at 400mm+. A longer shutter speed is one of the best ways to get higher quality images. As the total exposure time increases, your camera's "white noise" will become less apparent. This white noise is visible in your photos when you don't capture enough light. On my D750 it mainly manifests as a purple glow at the bottom of the photo. This was a nightmare to deal with, until I began using a star tracker and taking longer exposures. Once I was able to shoot 3+ minute exposures, the problem completely disappeared! Taking longer photos is one way to reduce the your camera's "white noise", and increase the detail in your photos.
A wider aperture is another way to capture more light, and reduce any visible "white noise" generated by your camera. I use a Tamron 150-600mm f/5 - f/6.3 lens for most of my deep space astrophotography. As I zoom in, the lens captures less light. At 600mm I only have an f/6.3 aperture, which does not transmit much light at all. Therefore, I need to shoot longer exposures to overcome the small amount of light transmission. There are some lenses that have a fixed aperture, like the Nikon 200-500mm f/5.6. A fixed aperture passes the same amount of light through regardless of the focal length.
You can also get a telescope or lens that is a fixed focal length, like a 500mm f/4. The downside of a fixed focal length is that you cannot zoom in or out. If you're trying to find a distant galaxy or nebula without a Go-To tracker, a fixed focal length can make your life much more difficult. When I'm trying to find my objects at night, I start at 150mm and take test photos until I see the object. Then I can zoom in, focus, and recenter the object again. A zoom lens is a nice thing to have at night! Meanwhile, all telescopes will be fixed focal length.
Let's do some quick math problems. As a reminder, here are the main aperture values. As we go up or down the list, we either double or halve the amount of light. So f/4 will transmit twice as much light as f/5.6. Let's say my Tamron lens is at 400mm with an aperture of f/5.6. If I were to go out and purchase a 400mm f/4 lens, I have now doubled the amount of light that will pass through to my camera. That's pretty good! Instead of having to shoot a 4 minute long exposure, I can get the same results in just 2 minutes now! Instead of spending 2 hours capturing photos at f/5.6, I can spend 1 hour capturing photos at f/4 and get the same amount of light. If I were to go even further, and buy an f/2.8 lens, I would capture up to 4 times more light than the f/5.6 lens! That means even shorter exposures, and less time to spend on an object.
So you might be thinking "Great! I'll just run out and buy a 400mm f/2.8 lens then!" Not so fast. First, those lenses usually cost more than a car! Second, they are usually very large and heavy. If you have a SkyGuider Pro or Star Adventurer, it will not be able to handle such a big lens. If you have a legit telescope mount, then you could probably make this work. Although, you may be better off investing in a telescope rather than a big 500mm f/4 lens. They are usually much lighter and cheaper.
This also brings me to a small point about Fresnel lenses. This is a special type of glass, like you'd see on a lighthouse. It is much lighter than normal glass, and can drastically reduce the size and weight of a lens. However, due to the glass design, it deforms the stars. You wouldn't want to use a Fresnel lens for any astrophotography. Here's an example of a fresnel lens - the Nikon 300mm f/4 PF.
For most people, the best thing you can do is take longer exposures. This will have a big impact on your overall image quality, without needing to spend thousands of dollars on a new lens or telescope. Although, you may need to get an auto-guider to make sure your star tracker is accurate enough to shoot 30+ second exposures at 400mm+. If you've got the cash though, it might be a good idea to invest in a faster lens. If you can get down to f/4, that would be great! I wouldn't stress about getting down to f/2.8. Just remember, the lens can't be too large and heavy! I wouldn't get a lens heavier than 6 lbs. The SkyGuider Pro and Star Adventurer can handle "11 lb payloads", but I wouldn't push it that far. At most, I would put about 8 or 9 lbs on them. That includes your camera body, L-Bracket, lens, auto-guider, guide-scope, and whatever else you may have attached. If you have a legit telescope mount that can handle a large payload, then go for it! If your mount can handle 20lbs+ you might as well invest in a quality lens or telescope.
The biggest problem I faced as an amateur astrophotographer was the purple glow caused by a lack of light. This purple glow was always visible in my astro images, and I had to go to extreme lengths to hide it. That's why a lot of my earlier images had strange color balances like you see here. This color scheme did a good job of hiding the purple color at the bottom of my images. Once I got a star tracker, I realized there was a simple fix - just take longer exposures! Now I take 4+ minute photos and I no longer have to deal with ugly, grainy, purple photos at night.
There tends to be some confusion around crop-sensor cameras, especially when it comes to focal length and astrophotography. Let's start off with the basics first. A crop sensor Nikon DSLR, like the D3500 or D5600, will magnify the image by a factor of 1.5x. Therefore, your 70-200mm lens will have a Field of View (FOV) similar to a 105mm - 300mm on a Full Frame camera. For Canon shooters, you'll need to multiply your focal length by 1.6x. Therefore, that same lens will look like 112mm - 320mm. As you can imagine, this magnification drastically increases with higher focal lengths. A Tamron 150-600mm lens on a Nikon D5600 will look like a 225mm - 900mm lens.
The outer image was taken with a 14mm lens on my full frame Nikon D750. I had a very wide Field of View that allowed me to capture a nice foreground and sky. The inner image was taken with the same 14mm lens, but placed on a crop-sensor camera. Since the crop sensor magnified the image by a factor of 1.5x, I have a narrower Field of View equivalent to about 21mm. This is not ideal for Milky Way photography, where we want a wider Field of View.
While crop-sensors aren't ideal for Milky Way photography, they are a good idea for deep space astrophotography! If you use a crop-sensor camera with a telephoto lens, you will automatically crop out most of the vignette and star distortion. That's because of the image circle. Full Frame lenses produce a large image circle that's designed to cover a full frame sensor. However, your crop sensor is much smaller, so it only sees the center of the image circle. The center usually has the sharpest stars, and minimal vignette.
I took 2 photos, one with a Nikon D5600 and one with a Nikon D750. Both were taken with the William Optics Space Cat telescope (250mm). As you can see, the D5600 image only fills the center of the frame. Therefore, all of the vignette and star distortion in the corners is automatically cropped out. I don't have to worry about taking flat frames now! Plus, the additional magnification of the D5600 will allow me to get closer to the Orion Nebula.
Next, let's talk about using DX mode on a Full Frame camera. This is a setting you can enable in your camera's menu. Once you turn on DX mode, the camera will automatically crop the photo by a factor of 1.5x. To be clear, this is not the same as actually using a crop-sensor camera. This might make more sense if you look back at the images above. Both the Full Frame D750 and Crop-Sensor D5600 have 24 megapixel sensors. If I turn on DX mode on my D750, I will now capture what you see in the center photo. However, I will have lost quite a bit of resolution due to the crop. Meanwhile, the D5600 is starting off "zoomed in", and it has the full 24 megapixel resolution. Since the starting point is already zoomed in, I can crop even further and retain more detail. Hopefully that makes sense!
The DX mode automatically crops your photo after you take it. You could do the exact same thing in post-processing. In fact, that's what I recommend! Why crop in-camera and lose that data forever when you could just crop later on? If you turn on DX mode in-camera you will be reducing the resolution of the file, and limiting yourself in the future.
All of the deep space photos you've seen on my website were taken with a Full Frame camera. If I had an unlimited budget, I would likely buy a crop-sensor camera too. The crop-sensor would allow me to get a bit more detail out of the smaller objects in the night sky with any given lens. To be honest though, the results would be marginally better in most cases. If you are ready to take things to the next level, you'd be better off investing in a dedicated astrophotography camera. I'll cover this further down in the article.
I decided to use a Nikon D5600 (crop-sensor) during the Lunar Eclipse, rather than my Nikon D750. The 1.5x crop factor caused the moon to fill more of the frame, and create an impressive image.
If you've made it this far without getting completely lost, congratulations! Now we're going to get a bit more technical.
Pixel Size is one of the most important factors to consider when buying a camera for astrophotography. The pixel size of your camera and focal length of your lens/telescope are the two main factors that determine how large an object will appear. I recommend using this website to find your own camera's pixel size. The main field we are interested in is "Pixel Pitch", which tells us how large the pixels are. As you can see here, my Nikon D750 has a pixel size of 5.95 micrometers. That's pretty big for a DSLR! Meanwhile, the Nikon D5600 has a pixel size of 3.89 micrometers.
If you compare the crop-sensor Nikon D5600 with the full-frame Nikon D750, you'll notice a few important differences. The Nikon D750 has a much larger sensor, this extra surface area translates into more light gathering capabilities. In other words, the full-frame camera is able to capture more light and perform better in low-light scenarios. On the other hand, the crop-sensor camera has smaller pixels and a higher pixel density. This translates into more detail and resolution when photographing distant nebulae and galaxies.
If you are purchasing a dedicated astrophotography camera, like the ZWO ASI 1600mm, you should be able to find the pixel size on the main spec sheet. In this case, the ASI 1600mm Pro has a pixel size of 3.8um. I also want to point out that the ZWO ASI 1600MM has a "micro four thirds" sized sensor. This is even smaller than APS-C. A 4/3" sensor will magnify the image by a factor of 2. So a 300mm lens placed on a ZWO 1600MM would have a similar field of view as a 600mm lens on my full frame D750.
Larger pixels will be able to capture and store more light than smaller pixels. Larger sensors also have more surface area, and can capture more total light. This is why I highly recommend a good full-frame camera and wide angle lens for Milky Way photography. You get the best of both worlds - a wider field of view and less grain!
Crop Sensor cameras are generally better for deep space astrophotography. They usually have smaller pixels and a 1.5x crop factor, which will make the objects appear larger in the frame. This should allow you to pull out more fine details. The only downside is that the smaller pixels will capture less light, and the smaller sensor will have less total surface area to capture light. That means you need to shoot longer exposures, and more of them, to overcome the camera's inherent "white noise".
Hopefully this concept makes sense now. Milky Way photographers will definitely want a full-frame camera with large pixels, paired with a sharp wide-angle lens. This will provide excellent results when using a star tracker and my recommended shooting techniques. If you would rather focus on deep space astrophotography though, then a crop-sensor camera or even a dedicated astro camera may be a better choice. You'll need to take more photos, and have better tracking and guiding, but you should be able to pull out more detail.
The Pleiades fill the frame in this photo, taken with my Nikon D750, Tamron 150-600mm, and SkyGuider Pro.
It's finally time to put everything together, and figure out how your camera will perform with any given telescope or lens. We'll be using a fairly simple equation, but you'll need to know your camera's pixel size in micrometers and the focal length of your lens or telescope. If you forget what your camera's pixel size is, visit this website and find your camera. The main field we will be using is "Pixel Pitch".
(Pixel size / focal length) x 206 = arc-seconds per pixel
Let's start with my Nikon D750 and Tamron 150-600mm, which is one of my favorite combos.
(5.95um / 600mm) x 206 = 2 arc seconds per pixel
Now let's try my Tamron 70-200mm and Nikon D750.
(5.95um / 200mm) x 206 = 6.1 arc seconds per pixel
Okay great, we know the "arc-seconds per pixel", but what does that actually mean? Very simply, you want the number to be between 1 - 2. The higher the number, the worse your images will look. The stars will appear blocky and many objects will look small in the frame. This corresponds quite well with focal length. As I mentioned, I like using 400mm - 600mm on my Nikon D750. This gives me an "arc seconds per pixel" rating between 2 and 3. If I were to use less focal length, from 200mm - 300mm, I just wouldn't have enough zoom to create a "wow!" image. My arc second rating would be between 4 and 6.
This table was taken from Atik, an astrophotography camera manufacturer. This is a very easy way to figure out what focal length will work best for your camera. If you don't know your camera's pixel size is in um, click here to find out. The field you are interested in is "Pixel Pitch". My Nikon D750 has 5.95um, so my recommended focal length is around 600mm. If I was using a D5600 though, which is 3.89um, I would only need a 400mm lens for ideal results. Smaller pixels require less zoom, while larger pixels require more zoom!
If you've ever used PHD2 or the ZWO ASIAir, you may have seen the term "arc seconds", in regards to the guiding accuracy. Arc Seconds are a measurement, and are routinely used in astrophotography to measure accuracy. For example, in this PHD2 screenshot you can see a graph with a blue line. The graph has +2", +4", and +8" above the center line, and -2", -4", and -8" below the center line. These are arc seconds. If I was using my 150-600mm and Nikon D750, my Arc Seconds Per Pixel rating is 2 (if I'm at 600mm). Therefore, I'd want the blue line to stay between +-2". If the line starts going +-4" or higher, my stars will likely lose their sharpness. If I was using my 70-200mm though, I could be between +-6" in most cases, and not notice any problems with the stars.
Click here to see the full size image. If you look closely, you'll see 2", 4" and 6" above the center graph line, and -2", -4", and -6" below the center line. The blue line represents our tracking accuracy. In this case, the blue line stays between +-2" in most cases. If I was using my Tamron 150-600mm at 600mm, I need to make sure the blue line stays between +-2". If I see it start jumping up higher than that, the movement will likely show up in the photo. However, if I had my Tamron 70-200mm lens, I can have the blue line move around between +-6", and it wouldn't show up in the photo. Remember, the more zoom you have, the more accurate your tracking has to be.
If you're a little confused (or completely lost!) let me simplify this as much as possible. Remember back to focal length, and how that affects things. We generally want more zoom, so the objects appear larger in the frame and we can see more details. However, more zoom also requires more accurate tracking. If your star tracker isn't up to the task though, you'll quickly see star trails. That's basically the same idea with arc-seconds.
For Arc Seconds, we generally want a small number, between 1 - 2. In most cases, 2 is considered the sweet-spot. We determine this "arc-seconds per pixel" number by the equation: (Pixel size / focal length) x 206 = arc-seconds per pixel If this number is 5 or higher, you probably don't have enough zoom for the best results. You can either buy a camera with smaller pixels, or get a larger lens/telescope. Either way, it will lower your "arc-seconds per pixel" and give you better results.
I want to be clear here, I would only worry about "arc seconds per pixel" if you want to photograph deep space objects - like nebulae and galaxies. If you want to photograph the Milky Way with a 70-200mm lens, or something similar, you can get some great photos! All this arc seconds talk is really for people who want to take things to the next level. In most cases, they'll be purchasing a dedicated astro camera, high-end mount, and telescope. In my own experience, I've found myself wishing I had a better "arc-seconds per pixel rating" when photographing some of the nebula in my Deep Space Course. I find that I can't capture the fine details nearly as well as other folks, who are using cameras with smaller pixels.
When it comes to guiding, arc seconds represent tracking accuracy. Again, we want a low number here. Ideally, the RA line on our PHD2 / ASIAir graph will stay around the center line - which represents 0" or perfect tracking. Realistically though, the line will jump up and down between +-4" in most cases, if not higher. I usually try to match my camera's arc-seconds per pixel rating with the guiding accuracy. In other words, if my camera rating is 2", I want to see the line on PHD2 stay between + or - 2". If it goes to +-4", or even +-8", then I know I'll likely have blurry stars. I either need to figure out what's going wrong, or just shoot shorter exposures.
I'm still surprised how cool this photo turned out! I took this image from a fairly light polluted area in Northeastern Ohio last winter. I used a D750, Tamron 150-600mm, and SkyGuider Pro. There were quite a few things that went wrong during the shooting process. I forgot to double check the focus throughout the night, and found that all of my photos taken after about 20 minutes had blurry stars. This was likely due to the cold air shrinking the lens slightly, and throwing off the focus. I did not have an auto-guider when I took this photo either, so I was only shooting 30 second exposures. Remember that ugly purple glow that is always present in my D750 photos? It was here too, but I managed to edit the image in a way that suppressed it. All things considered, it's a miracle I was able to get such an awesome shot with such terrible data! If you want to learn how I edited this photo, check out my Deep Space Course.
Most people start off using a DSLR camera for their astrophotography. DSLRs have a lot of benefits: high-resolution images, RAW capabilities, huge lens selection, rear LCD screen, easy controls, and more! However, DSLRs do have some notable problems when it comes to astrophotography. The three big problems, in my opinion, are the Bayer Array, IR Cut Filter, and the heat that builds up on the sensor.
If you've ever taken a photo longer than one minute, you may have noticed a bunch of bright dots all over the image. These are called "hot pixels", and they are usually caused by the sensor overheating. These hot pixels can ruin an amazing photo, especially if you are taking an 8+ minute photo during the day, using ND filters. Thankfully, there's an easy fix!
Long Exposure Noise Reduction is a camera setting that can be enabled on most newer cameras. When LENR is turned on, your camera will automatically take two photos - a light frame and a dark frame. (It will only do this when shooting 1+ second exposures) The Dark Frame will have the exact same settings as your normal photo, but the shutter will stay down. This prevents any light from reaching the sensor, and allows the camera to map out the hot pixels in the photo. Once the camera has both a dark frame and a light frame, it analyzes them for hot pixels and automatically removes them.
From a photographers perspective, turning on LENR will double your shutter speed. Once you begin taking a 30 second photo, you will need to wait a total of 60 seconds before you can use the camera again. The first photo will go like normal, but during the second photo (dark frame) the camera may say "Job Nr", and prevent you from pressing any buttons. Once it finishes taking the dark frame, the camera should become usable again. Keep in mind, you can always turn off the camera in the middle of the dark frame, if need be. This will kill the second exposure, and prevent the camera from removing the hot pixels. It shouldn't hurt anything though. I sometimes do this if I know my photo got screwed up by someone's headlamp. No point standing around wasting time on a ruined photo.
As you can see from the photo above, this process works very well! However, there is one major downside. Remember, LENR will always take two photos. Therefore, if you take a 4 minute long exposure, the camera will take a total of 8 minutes to complete the image. (4 minute light frame + 4 minute dark frame). This can drastically slow down your workflow, especially at night. Instead of shooting dozens of compositions at night, you may be limited to just a few. I only use LENR when I'm photographing my foregrounds for Milky Way photography, or when using ND filters during the day.
You may also notice some strange artifacts when using LENR, especially with a wide-angle lens and star tracker. Please read my Nikon D750 article for more information on this problem.
I want to be clear, I do not recommend using LENR when doing deep space astrophotography. When we are photographing deep space objects, we tend to take dozens (if not hundreds) of photos and stack them together to reduce grain. If you had LENR turned on, you'd be wasting half of your night taking dark frames. As you'll learn in my Deep Space Course, we can automatically remove hot pixels during our normal photo stacking process. No dark frames required!
Every DSLR has a Bayer Array filter, think of a checkerboard with Green, Blue, and Red squares. These squares are little color filters that cover every pixel on your camera's sensor. The green filters only let green light through to the sensor, blocking most of the red and blue light. Likewise, the red filters block green and blue light, only allowing red light through. Same with Blue. This is what allows your camera to "see" color! However, the design does have some problems.
Since green is one of the most prominent colors here on Earth, the Bayer Array usually has 50% green filters. That only leaves 25% for red and 25% for blue. Therefore, a lot of the light that reaches the sensor at night is not being used. Remember, most of the red light that hits a blue or green filter is largely blocked from reaching the sensor.
While the Bayer Array has made color photography easy, it tends to cause problems for astrophotography. During the day, there's plenty of light entering the camera. Who cares if some of the red or blue light doesn't reach the pixels. At night though, we need every photon we can get! Also, think about the various nebulae you've seen. Do you recall seeing much green?
A Bayer Array will definitely reduce the light gathering capabilities of a sensor, but it's not a huge problem. Newer sensors have truly amazing designs that funnel more light into the actual pixels. The Bayer Arrays also don't block 100% of the light that hits a wrong colored filter. However, a monochrome sensor, with no Bayer Array, should always produce cleaner results. I'll explain monochrome sensors further down in the article.
There's one last thing to consider when photographing nebulae. What wavelengths are they actually emitting? By now you've probably heard of Hydrogen Alpha (H-Alpha), which is basically the color red. The specific wavelength of H-Alpha is 656nm. Unfortunately, most cameras block this end of the light spectrum, which leads us to another problem with DSLRs - the IR Cut Filter.
Every DSLR has its own filter that blocks UV and IR wavelengths from reaching the sensor. This "IR-Cut Filter" is a small piece of glass that is placed on top of your camera's sensor. If you've ever opened up your camera, this is probably what you saw inside. Every IR-Cut filter is a little different, but the main goal is to limit the wavelengths reaching the sensor to 350nm - 650nm. This should capture the full range of color - from Violet to Red. It will also block out the unwanted UV and IR wavelengths, which can cause problems for photography. The human eye is able to see from roughly 400nm to 700nm, so it makes sense that our cameras should see the same wavelengths as us.
As I mentioned earlier, H-Alpha (656nm) is one of the most prominent wavelengths being emitted by nebulae. This wavelength is usually blocked by most IR Cut filters. In other words, your camera is unable to see the red light coming from the nebula! Only a very small amount of that light will actually reach the pixels on your sensor. If that H-Alpha light hits a green or blue filter on the bayer array, it will be mostly blocked too. As you can see, these various DSLR problems are starting to add up. This is where dedicated astrophotography cameras come in.
Rho Ophiuchi is a fun object to photograph in the summer. I took this photo with a Tamron 70-200mm, Nikon D750, and SkyGuider Pro. One problem I noticed is that my Nikon D750 is unable to capture the beautiful red colors that were present. At best, I have some dim purple light, but not the beautiful H-Alpha light I would have liked to see.
One of the most common questions I get asked is "should I have my camera sensor modified?" If you're unfamiliar with sensor modifications, let me explain. The most common DSLR mod is an "H-Alpha conversion", where your camera's IR Cut filter is replaced with a new one which passes more of the 600nm - 700nm wavelengths through. If you haven't seen them already, please look at these graphs. As you can see, most IR Cut Filters block the red H-Alpha light from reaching your camera. The average DSLR is only able to capture about 20% of the H-Alpha light being emitted by a nebula. A modified IR Cut Filter will allow much more red light through.
There are also specific camera models which include a modified IR Cut filter by default, like the Nikon D810A and the new Canon EOS Ra. These cameras are usually much more expensive than the standard DSLRs, but tend to have special programming that will make your night easier. For example, the Nikon D810A has extended shutter speed options, allowing you to select past 30 seconds. You can also zoom in further during Live View. I've considered getting an astro camera like the EOS Ra, but decided that a real astrophotography camera may be a better investment. We'll cover that in the next section.
If you are considering modifying your DSLR, be aware that there are usually two options. We've already discussed the first option - H-Alpha. The second option is called Full Spectrum, and it will completely change the way your camera works. If you get the Full Spectrum mod, your IR Cut filter will usually be replaced with a clear piece of glass. This glass does not block any UV or IR light. Therefore, your camera can now see Ultraviolet, Visible, and Infrared wavelengths! This has multiple benefits and drawbacks.
Let's start with the benefits of a Full Spectrum mod. First, you can do UV or IR photography! This can be a fun way to use an old camera, and capture unique photos. Just be aware, you will need to purchase special filters. These various filters will block visible, IR, and/or UV light, allowing you to focus on specific ranges. If you don't use a filter, all of your images will have a strange purple color cast and you may have a hard time focusing. All things considered, I'd generally recommend avoiding a Full Spectrum mod, unless you know what you are doing.
All of the photos you see on my website were taken with a stock Nikon D750, which does a terrible job of capturing H-Alpha light. I've considered getting an H-Alpha mod, but ultimately decided against it for a few reasons. First, I only have one DSLR and I need it to perform great for landscapes, wildlife, portraits, etc... Second, I'd rather save that money and put it towards a dedicated astro camera in the future. My Nikon D750 does well enough, especially with a few editing techniques. Lastly, I've seen very heavy color casts with modified cameras. These color casts can be a nightmare to remove, especially if you do wide-angle nightscapes. All things considered, I don't see the point in getting my DSLR modified.
Most of the nebulae I capture have a purple color cast, since my DSLR is unable to see the red H-Alpha wavelengths. If you get your camera modified, be warned! You may now have a heavy red color cast in all of your photos, due to the abundance of H-Alpha light!
I get quite a few questions on mirrorless cameras, so I figured I'd include a section in this article. Overall, I think mirrorless cameras do a good job, but they have some problems.
A lot of people love the digital viewfinder. It can show you a real-time preview of how your photos will actually look, you can see the zebra pattern to make sure your image is focused properly, you can view your playback images easily on sunny days, and much more. However, I think the display usually looks like a cheap old CRT TV, not very pleasing to look at. I've tried out various Nikon, Sony, and Canon mirrorless and they all seem to have the same quality viewfinder display. If this doesn't bother you, than you'll probably love having a mirrorless camera! I'd rather use the old optical viewfinder, so I'm fine with my DSLR for now.
If you've got a DSLR, and have been considering a mirrorless camera, don't forget about the different lenses! Nikon uses a new Z-Mount, which is much larger than the old F-Mount. Therefore, you need to buy a special adapter to utilize your lenses with the new camera body. This adapter will add extra weight and bulk to a mirrorless setup. If you want to get a new Z-Mount lens though, you'll be paying quite a bit more!
I'm sure you've also heard about the infamous Sony Star-Eater bug. Basically, the noise-reduction algorithm would accidentally target stars (thinking they were hot pixels or grain) and remove them from the photo. To be honest, I try to do this in post-processing, since it can help make nebula, galaxies, and dust stand out better from a "noisy" background of bright stars. However, many people were rightly disappointed because it affected RAW images, which shouldn't have any noise reduction applied anyway.
One of the best reasons to get a mirrorless camera for astro is the improved Live View. With most new mirrorless cameras you can actually see the Milky Way in real-time when using Live View. It really is amazing the first time you see it! If you currently have a DSLR, then you know how hard it is to see anything during Live View at night. At best, we can see a few bright stars. If you've got bad eyes, a mirrorless camera can certainly make things easier for you at night.
There's one other thing to consider when choosing a mirrorless camera for astrophotography - sensor heat. When you use Live View, the sensor is exposed to light and a signal is continually being sent to the camera's LCD screen. This process generates a lot of heat! Now, with a DSLR we don't have to use Live View, although it is very helpful for focusing and composing a shot. A mirrorless camera will always be using some sort of Live View, either in the viewfinder or the rear LCD screen. Therefore, a mirrorless camera will run hotter than a DSLR in most cases. With all that being said, I wouldn't worry about the Live View heat too much. If you take a 1+ minute photo your sensor will begin to overheat anyway, and hot pixels will begin to show up in your photos. This is true of both mirrorless and DSLR cameras. I normally take 4+ minute photos, and my photos are always covered in hot pixels. This is why I use Long Exposure Noise Reduction to automatically remove them. I want to reiterate though, I do not use LENR when doing deep space astro, only for foreground photos at night.
So, what's my final word on mirrorless? I've considered getting one, but due to the lens selection, mediocre digital viewfinder, and bad ergonomics, I've held off. If you plan to just use the mirrorless camera for astrophotography, either Milky Way or Deep Space, I think it will do a great job in most cases! I'm fine with my DSLR for now though.
Sometimes you may want less zoom. In this case I used a ~350mm focal length to capture both the upper and lower portions of the Veil Nebula. Alternatively, I could have zoomed into 600mm and focused on a single piece.
Once you've mastered a DSLR for astrophotography, you can take things to the next level with a dedicated astrophotography camera. These are quite different from DSLRs - they lack an LCD screen, there are no buttons, they have much smaller sensors (usually), and they don't even look like a camera! Take a look at the ZWO ASI 1600MM, which is currently a popular astro camera.
I remember the first time I saw these little astro cameras, I was pretty confused! Why would you want a small sensor? Why are they so low-res? Where is the screen? How do you even take a photo?
Let's start with the most obvious problem - how do you take photos with a CCD-style camera? The short version is that you'll need a laptop to control your camera. Once your dedicated astro camera is connected to the laptop, you can use one of many different applications to take your images. Alternatively, you could use the ZWO ASIAir, which will allow you to do a polar alignment, auto-guiding, and even take photos all from one app on your smartphone! ZWO is currently (as of December 2019) preparing to release a new version of their ASIAir, but here's an overview of the original device. Regardless which route you go down, you will be controlling everything from your laptop / smartphone application. This can be both good and bad.
I normally spend 6 months living out of my car each year. When I do astrophotography, it's a very involved process. I'm always standing out there with my gear, making sure nothing goes wrong. This sucks in the winter! I'd rather not get frostbite standing around waiting for my camera to capture images. This is where dedicated astro cameras will make your life a lot easier! You can now sit inside your house, or car, and relax while the camera is hard at work outside. Whether you are using a smartphone app or laptop connection, you can monitor how the photos look, adjust settings, and even switch filters around electronically, if you have a filter wheel.
I'd recommend checking out Chuck's Astrophotography on YouTube, he has taken some incredible photos from his backyard in Detroit! That's really the main selling point of dedicated astro cameras - you can capture amazing photos any time, any where! This is revolutionary if you're accustomed to a DSLR, where you can only shoot during the New Moon and at a dark sky location. If you've ever tried photographing a nebula from a big city, or during a full moon, you know that it's a pretty much a waste of time. The extra light in the sky completely washes out the fine details, and you're lucky if you can even see the object you want to photograph. Meanwhile, a dedicated astro camera can get Hubble-quality photos during a full moon in downtown Los Angeles! How?
The answer is Narrowband Filters. These are designed to block out all light, except for a very specific wavelength. This opens up a whole new world of possibilities! However, it does complicate the workflow. The normal process for a DSLR is to take one set of photos, then stack them together. This is fairly easy. However, Narrowband filters will require you to take at least 2 sets of photos, if not 3 or 4! To make things even more confusing, these images will likely be monochrome. You need to do some extra steps in post-processing to actually create a color image.
A dedicated astro camera will generally come in two variants - monochrome and "one-shot-color" (OSC). ZWO uses a specific naming convention to differentiate the two. Monochrome cameras are always labeled "MM", while color cameras are usually "MC". Here are two ZWO cameras that are nearly the same, except that one is monochrome and the other is color. Monochrome sensors are usually more expensive, which I find a bit odd. You'd think the complexity of a Bayer Array would increase the price of color cameras...
The color cameras have a similar design to a DSLR - they include a bayer array. This allows them to capture color photos. Since these are dedicated astro cameras, they should perform a bit better at night. For example, look at this graph from ZWO on their ASI 183MC camera. Notice how much more light the camera captures, including the H-Alpha range? As I understand it (and I may be wrong), most dedicated astro cameras do not have an IR Cut Filter. Therefore, you will capture more H-Alpha light, but you may also have problems with star bloat. Even though you have a color camera, you may still need to invest in filters that will block IR and UV light.
Alternatively, you can buy a monochrome camera, which will only capture black and white images. Now you might be thinking, "why would I want to take black and white photos of nebula?". Well, the main reason is the increased sensitivity to light. A monochrome sensor does not have a Bayer Array, so more light can reach the pixels. However, you will need special filters to ultimately create a color image. Click here for a great article on how filters work with monochrome cameras.
Once you purchase a monochrome astro camera, you will also need a set of filters to go along with it. Let's start with the traditional Red, Green, and Blue filters. As you can see here on Astronomik, there are various sizes to choose from - 1.25", 2" (M48) etc... You will need to pick the correct size based off your telescope or filter wheel. If you have no idea what I'm talking about, you may be familiar with UV ("Protection") filters for your camera lens. These come in different sizes based on the filter thread of your lens. For example, my Tamron 150-600mm has a 95mm thread, while my 24-70mm lens has a 77mm thread. It's basically the same concept as the astro filters. You need to make sure the filters will screw into your telescope or filter wheel.
*Caveat - I'm still new to this realm of astrophotography, so not everything in this section may be 100% accurate. I'm explaining the process as I understand it. I've never actually used a dedicated astro camera with filters yet, but I plan to in 2020.
Now that you've got your RGB filters, you can begin the new workflow. This is going to be much more complex than a typical DSLR workflow though. Let's do a quick recap first. With a DSLR (or "One Shot Color" astro camera) you take a series of photos of your desired object. Once you've captured at least an hour's worth of images, you should have enough total light captured. You can now bring those photos to the computer, stack them, and edit the final image. That's all there is to it!
If you have a monochrome camera though, you're going to need at least 3 sets of photos. For example, we'll attach our Green filter and take an hours worth of images. Then we can swap to a Blue filter and take another hours worth of photos. Next, we'll switch to a Red Filter and capture another hour of photos. You may also want to capture some Luminance photos. Once you have your different sets of photos, you can now stack them and calibrate them in special software. I believe you need to stack each color separately. Once you have all your clean, stacked photos you can bring them into a program like Photoshop. At this point you can finally create a color image! You'll need to map the Red stack to the Red color channel, Blue to Blue, and Green to Green.
I almost forgot! You'll also need to take Dark Frames. Although, these will be much easier now that you have a cooled camera. You could theoretically take your Dark Frames whenever you want, just make sure the sensor temperature is the same as it was when you took your light frames. These dark frames should be included with each color stack, to "calibrate" them and help reduce any grain, amp glow, and hot pixels.
If you will be using Narrowband filters, rather than RGB filters, it's going to be the same general workflow. Instead of swapping between RGB though, you'd swap between an H-Alpha filter, Oxygen filter, and Sulphur filter. Those are the common ones anyway... Since you are capturing such a small amount of light, literally just a few nanometers, you will need to take even longer exposures, and more of them! Once you've got your photos stacked, you can map the images to color channels in Photoshop. But what color is Oxygen? Or Sulphur? Well, that's where the "Hubble Palette" comes in.
If you want to make the leap up to a dedicated astrophotography camera, you'll want to make sure you do things right! I'm currently in the process of buying my first astro camera, so I can let you know what I've learned so far.
First, I want a good monochrome camera. I realize this will complicate my workflow considerably, and take a lot more time to create a final image. I'm hoping the results will be worth the extra effort! I'm currently thinking of getting either the ZWO ASI 1600MM Pro or the ZWO ASI 183MM. There are literally hundreds of other options, but these seem like a good choice for me. I don't have a big telescope, so I can get away with using my 250mm Space Cat telescope for now. The smaller pixels of either camera will help me to pull out fine detail in the nebulae and galaxies I want to photograph. I could even buy a special adapter and use these cameras with my DSLR lenses.
A monochrome camera will also require a set of filters. I'm planning on getting both RGB and Narrowband so I can image throughout the lunar cycle. There are a lot of different filter companies to choose from. The more money you spend, the higher quality the filters will be. Cheaper filters will cause the stars to bloat and distort, among other problems. I'm considering getting the new ZWO filters, since they are a reasonably priced, but I've heard the quality could be better. You could also go with Astronomik, who make good products. If money is no object, then I hear the Astrodon filters are the best on the market. Before you invest in filters, you also need to consider which filter wheel you will be using.
A filter wheel can usually hold 4 different filters, if not more. This will make swapping between filters much easier at night, especially if you use all ZWO equipment and have the ASIAir! Here's one example of a filter wheel, the ZWO EFW Mini. Note how the filter size is 1.25" or 31mm. The 1.25" filters can be installed by screwing them onto your telescope or into the filter wheel. However, this may cause some vignetting. Therefore, you may want to spend a bit more and get the 31mm filters. These will produce less vignette, but I believe they're a bit more cumbersome to install. I recommend reading this article for more information on filter wheels.
Just to make sure you're thoroughly overwhelmed, ZWO also makes a special variant of both the ASI 1600MMGT and the ASI 183MMGT. Both models have a built-in filter wheel, which should reduce the overall size of the camera. I'm also considering getting one of these, rather than the standard models that require an external filter wheel.
You could get everything I've discussed so far in one easy bundle. This should give you a clear idea of what you'll need. That's assuming you've already got a lens or a telescope that's good for astrophotography. Of course, you'll need a telescope mount or star tracker too! At this point, we're starting to get into Chuck and Trevor's territory. I'd recommend watching some of their videos to help wrap your mind around everything we've discussed today.
If you managed to make it all the way to the end, congratulations! I know this was a long read, and it may have taken you a few days to get through the whole thing. We covered a lot of topics in this article, so I want to recap the most important points and give you my recommendations.
First, I recommend using the Telescopius Telescope Simulator to see how your various lenses will work with your current camera body. You can also input different camera sensor sizes and lens focal lengths and get an idea of how the objects will look before you buy anything! I recommend looking at multiple different objects like the Andromeda Galaxy, Orion Nebula, Pleiades, North American Nebula to get a good overview. If you decide you want to upgrade your camera or lens, you'll now have a much better idea of the results you can get!
I want to stress that I am a photographer first, so my point of view is a bit different than others in the field. I also have minimal experience with dedicated astro cameras, telescopes, go-to mounts, and filters. Everything I've done so far has been with a stock DSLR, telephoto lens, and a small star tracker. I think I've shown quite definitively that you can get great photos with a modest setup. You don't need to run out and buy a big telescope, heavy tracking mount, high-end monochrome camera, and multiple sets of filters. However, if you are thinking of upgrading some of your components, or getting into the hobby more, I would recommend checking out both Chuck and Trevor over on YouTube. They have a lot more experience with telescopes and dedicated astro cameras than me, and can provide more insight.
Again, I want to stress that you don't need a new camera! Even if your current camera is not ideal, you can capture a lot of great images with it! This will also allow you to practice the workflow of astrophotography, before investing more money into the hobby. The only time I would highly recommend getting a new camera is if your current one exhibits serious sensor-level problems. I've seen some cameras have terrible banding issues, potentially caused by a defective or dying sensor. A few small problems aren't a big deal, as you've seen with my images. But if you've got thick purple lines running across your images, it might be time to upgrade!
If you decide to get a dedicated astro camera, be aware that it will greatly increase the learning curve and difficulty. I would not recommend going this route until you've mastered astrophotography with a DSLR and telephoto lens. I've spent countless hours over the past few years learning about astrophotography, and even I had a hard time wrapping my head around the complexities of a monochrome camera and RGB / narrowband setup. Not only will the shooting process be more involved, you'll also need to step-up your post-processing skills. You may need to start using more complicated programs like PixInsight for the best results.
The main takeaway of this article is pretty simple. If you have reached the limits of your current gear, then you have a few different routes you can go down. You could upgrade your lens / telescope, you can upgrade your camera, or you can upgrade your tracking mount. Of course, if you've got the money you can do all three! My main problem is that I don't have enough zoom, unless I use my big 150-600mm at 600mm. I can't feasibly get a new lens, since my SkyGuider Pro cannot handle much more weight. I could invest in a nice "Go-To" telescope mount, but I still travel too much. There's no way I could fit a giant mount in my car that I'm living out of. My best choice is to get a new camera with smaller pixels, which will translate into more fine detail in my deep space images. I could buy a crop-sensor DSLR or mirrorless camera, or possibly even a modified camera like the Canon Ra. However, this wouldn't take things to "the next level". Therefore, my best bet is to go all the way and invest in a monochrome camera with both RGB and Narrowband filters.
If I decide to make this jump though, I need to be ready for the intense learning curve. There will be a lot of headaches along the way, but I suppose that's a requirement for this hobby!
In closing, I hope this article helped you out! If you have any questions please leave a comment and I'll try my best to answer them. I would also recommend checking out other astrophotography resources. They'll have much more insight on picking your first telescope, mount, and astro camera than me. I come from a photography background, so I do things a bit different. I'm still using a DSLR, telephoto lens, and SkyGuider Pro but I'm looking forward to making a big leap in 2020!