Choosing your first Dedicated Astro Camera

If you are considering purchasing your first astro camera, you’re probably overwhelmed!  Do I want a monochrome or color camera?  What brand should I go with?  Do I need filters?  How do I even use this camera?  We’ve got a lot to cover, so let’s get started!

*Before we get into all the details, I want to mention that I have no affiliation with any company, so I don’t really care what you buy.  My main goal is to help you make an informed decision.  I don’t have experience with every camera out there, so I can’t give specific recommendations on this camera or that camera.  I always recommend doing your own research on a specific camera model before you buy it.  CloudyNights and YouTube are great resources to hear feedback from fellow astrophotographers.

Brands

There are a number of astrophotography camera manufacturers, including Atik, ZWO, and QHY.  I’ve only ever used ZWO products, so I can’t give any first hand knowledge of Atik or QHY.  However, I’ve heard from many people that QHY cameras tend to have driver problems and compatibility issues with lots of computers.  Atik seems to be a very reliable and high-quality manufacturer, arguably one of the best in the market.  ZWO is one of the most popular companies in the astrophotography world right now, and for good reason.  They make a large variety of products targeting all the various interests – planetary, deep space, high-end cameras, entry-level cameras, auto-guiders, and more.

The main reason I chose ZWO was their ecosystem of products.  They’ve taken the Apple approach, and made a wide range of products that all work together fairly seamlessly.  For example, ZWO makes the ASIAir.  This device allows you to control your camera, auto-guider, and filter wheel all from your smartphone!  That means you can sit inside your warm house on a cold winter’s night and relax while your camera is outside doing the work.  In the past, I had to leave an old laptop sitting outside with my gear.  Every 15 or 20 minutes I would go check everything out and make sure there were no problems.  This wasn’t very practical.  Now, with the ASIAir, I can instantly see if there’s a problem!

The Galactic CoreA detailed look at the Milky Way galaxy, the Lagoon Nebula and Trifid Nebula can be seen as well You can capture some amazing photos with a simple DSLR and lens!  This was taken with my Nikon D750 and Tokina 100mm Macro lens

DSLR vs Dedicated Astro Camera

If you are a DSLR user, then you are already used to the color camera workflow.  We normally take a series of exposures, stack them together, then edit the final image in Photoshop.  All things considered, it’s a fairly straightforward process.  While DSLRs make astrophotography easy, they do have some notable flaws.  These include the Bayer Array, IR Cut Filter, and lack of cooling. 

The Bayer Array is what allows a color camera to actually capture color photos.  I’d recommend reading this article for a succinct overview of the Bayer Array.  The downside of the Bayer Array is that it limits the light gathering potential of a camera sensor.  It also lowers the color resolution in a photo.  

The IR Cut Filter is designed to block UV and IR wavelengths from reaching the sensor, while allowing the visible color wavelengths through.  The visible light spectrum ranges from 400nm (violet) to 700nm (red).  Ultraviolet light is found below 400nm, while Infrared light is found above 700nm (roughly anyway).  Unfortunately, the IR Cut Filter tends to block the red color emitted by many nebulae in the night sky.  The main emission is Hydrogen Alpha, which is the color red.  Many nebulae produce a lot of H-Alpha light, but the IR Cut filter blocks up to 90% of it.  This is why some companies have started offering camera sensor modifications.  They will replace the stock IR Cut Filter with a modified one that will allow more of those near IR wavelengths through.  That means more red colors and less noise! 

DSLRs tend to overheat very easily when doing astrophotography.  We normally take 1 – 5 minute long exposures, and the sensor generates a lot of heat during this time frame.  The use of Live View will also heat up a camera sensor.  All of this heat tends to generate hot pixels, brightly colored dots that appear all over the image.  There are ways to remove hot pixels, both in-camera and in post-processing, but it would still be better to cool the sensor down.

Dedicated Astro Cameras solve all three of these problems!  A monochrome camera will not have a Bayer Array, which means it will be more sensitive to light and produce higher-quality images.  In most cases, these astro cameras do not have an IR Cut Filter either, so they are more sensitive to near Infrared wavelengths.  Finally, dedicated astro cameras tend to have built-in cooling, so you can keep the sensor cold and limit the amount of heat-related noise!

There are some downside to using a dedicated astro camera though, especially if you are used to a DSLR.  Most notably, the astro cameras do not have an LCD screen or buttons!  That means you’ll need to control everything from a laptop or your smartphone.  This can be a nice benefit though, depending on how you look at things.  Astro cameras also tend to have lower resolution sensors than DSLRs.  That means your images won’t look as great if you want to print out large photos.  With that said, astro cameras are quickly closing-in on DSLRs, and ZWO recently announced a full-frame monochrome camera!

I used a DSLR for 5 years, and I was able to capture some incredible photos!  However, I eventually started to reach the limits of my DSLR and I wanted to take things to the next level.  Once I reached this point, my biggest dilemma was what type of astro camera to buy – monochrome or color?

Picture saved with settings embedded. A monochrome camera should allow you to capture very clean, detailed images with lots of great color!  

Monochrome or Color?

Astro cameras usually come in two flavors – monochrome or color.  Depending on which option you go with, your workflow will be completely different.  Monochrome cameras require more work, and money, but they should provide higher quality images.  Color cameras are much simpler to use, but the results won’t be as good.

If you want to keep things simple, and cheap, I would recommend starting off with a color camera first.  This will limit the amount of additional gear you’ll need to buy, and your post-processing workflow will be much simpler.  To be honest, I have not used a color astro camera yet, so I can’t give any first-hand recommendations.  However, there are plenty of online resources who can point you in the right direction, including AstroBackyard and Chuck’s Astrophotography. 

If you are ready for a new challenge, and you’ve got the cash, then I’d recommend jumping into the deep end with a monochrome camera.  That’s what I did.  The first thing to understand is that monochrome cameras will only take images in black-and-white, they will never be able to take a color image.  To be clear, if you use filters and special post-processing you can ultimately create a color photo.  The camera itself will always produce monochrome images though.

LRGB Filters

Very simply, you’ll need to buy at least one set of filters to get the most out of your monochrome camera.  The most common is “LRGB” – Luminance, Red, Green, and Blue.  These filters will attach to your telescope or filter wheel, and they only allow a certain range of wavelengths through.  For example, the Red filter will let between 600nm – 700nm through to the camera sensor.  The images will still be monochrome, but you will have captured only red wavelengths.  You can then swap to the Blue filter and take another photo, this time only capturing blue wavelengths.  Same with Green.  The Luminance filter will allow you to capture between 400nm and 700nm all at once!  This Luminance filter is mainly designed to capture the detail of a nebula.  Once you have the separate Red, Green, and Blue color channels, as well as the Luminance, you can create a color photo!  There are a few different ways to do this, but we’ll get to that in a later article.

It’s important to understand that you’ll need to take 4 sets of photos with the LRGB filters.  If you had a color camera, you could take one set of photos, stack them, and begin your processing.  Therefore, a monochrome camera can take up to 4 times as long to create an image!  You'll also need to stack each color channel independently, which will increase the editing time.

Picture saved with settings embedded. If you use a monochrome camera, you only technically need two different filters to create a full color image.  This photo was created with just H-Alpha and Oxygen filters.  (I can reuse the Oxygen data for both Green and Blue color channels.  H-Alpha stays on Red)

Narrowband Filters

You can also buy a set of Narrowband Filters, which will allow you to use your monochrome camera in light polluted areas, or even during the full moon!  Narrowband filters will only allow a very specific wavelength through.  The three narrowband filters are usually – Hydrogen Alpha (Ha), Oxygen (OIII), and Sulfur (SII).  Since these filters only allow a very small range of wavelengths through, all other light will be blocked, including light pollution and moonlight!  Once you’ve captured photos with at least two of these filters, you can create a color image in post-processing.  However, these won’t be “real” colors.  You can use a variety of “color palettes” when editing your photos, and change how the final image will look.  I recommend reading this article for more information. 

Pixel Size and Sensor Size

The pixel size and sensor size are very important, and they will change what you are able to capture with your camera.  You must pick a camera with the proper pixel size for your current telescope or lens.  If you mismatch the two, you will not get good results.

Sensor Size 

Let’s start with sensor size, since this is a topic DSLR users are familiar with.  A full frame camera sensor is 36mm x 24mm.  This is quite large!  Full frame cameras generally perform better in low-light, which is why they are recommended for Milky Way photography.  Full Frame cameras also do not have any crop factor.  This allows you to get a wide Field Of View with a wide-angle lens.  I’ve been using a full frame Nikon D750 for the past 5 years, and I really like it!

As the sensor size gets smaller, the low-level light performance usually suffers, and there’s a crop factor that must be accounted for.  APS-C is the most common crop factor, and is found on most entry-level Canon, Sony, and Nikon cameras.  An APS-C sensor is 23.5mm x 15.6mm on Nikon, and 22.3 x 14.9mm on Canon.  Since the sensor is smaller, the images will be magnified by a factor of 1.5x on Nikon and 1.6x on Canon.  Therefore, you must multiple the focal length of your lens or telescope to get the proper Field Of View.  A 500mm lens placed on an APS-C camera will have the same Field of View as a 750mm lens on a full frame camera.  (500mm x 1.5 = 750mm)

As I'm reading through this, even I'm getting confused with all these numbers and equations.  Thankfully there's an easy way to visualize everything.  Check out Telescopius, and the Telescope Simulator.  You can change the focal length and sensor size to match any camera/telescope you plan on buying.  This will help you to see the types of images you can capture.  You'll just need to do some research on your camera's actual sensor size (in mm), to input the correct data into the telescope simulator.

Most dedicated astro cameras have 1” sensors, or Micro Four Thirds (4/3”) sensors.  The 1” sensor has a 2.7x crop, compared to a full frame camera.  That means a 500mm lens placed on this sensor will have the same FOV as a 1,350mm lens on a full frame camera!  Meanwhile, the 4/3” sensor has a 2x crop.  As you can see, these small sensors will have a massive impact on the photos you can capture!

Arc Seconds Per Pixel

Before we get into this, I’d recommend looking at this graph.  It sums up everything I’m about to explain very clearly.

In order to get the best results with your astro camera, you need to pair it with the proper lens or telescope.  Thankfully, there’s a simple equation that will quickly tell you how your proposed setup will work.

(pixel size / focal length) x 206 = arc seconds per pixel

As you are looking at the different astro cameras, you should see a spec sheet which includes the camera's pixel size.  It's usually listed in micro-meters, or μm.  For example, ZWO lists all the relevant specs near the top of the page.  In this case, the pixel size is 3.8um.

The focal length should be fairly easy to find for your current lens or telescope.  Just make sure it’s the actual focal length.  For example, the William Optics RedCat 51mm.  The 51mm refers to the diameter of the lens, not the focal length.  The focal length of the RedCat is 250mm.

Once you’ve found the camera's pixel size and the lens' focal length, you can plug in the numbers and figure out your “arc seconds per pixel” rating.  Generally, you want this number to be between 1 – 2.  As you get above 2, the higher the number, the worse the results.  The technical term is undersampling, in other words, you don’t have enough zoom.  You can either buy a lens/telescope with more focal length, or buy a camera with smaller pixels.  Either way, it should lower the “arc seconds per pixel” rating and give better results.  On the other hand, if the number is below 1, then you are oversampling.  You have too much zoom!  Don’t forget to look at the graph I linked to earlier in this section for a quick idea of what will work best.

Just to be completely clear on this section, use the formula: (pixel size / focal length) x 206 = arc seconds per pixel  Either use your current gear, or the gear you plan to buy.  If the number is higher than 2, you need more zoom or smaller pixels.  Realistically, most people won't get a number below 1, unless they have a huge telescope already.  
 

Final Recap

There’s a lot to consider when purchasing your first astro camera!  The first thing to determine is whether you want a monochrome or color sensor.  A color sensor will be much easier to use, and the workflow will be similar to a DSLR.  A monochrome camera will require much more time, effort, and money.  You'll need to buy at least one set of filters, usually LRGB.  I'd also recommend getting a filter wheel, which will hold all of your different filters.  (I'll be explaining this further in next week's article.)  If you decide to get a monochrome camera, you'll be spending at least $500, if not $750+, just to have the equipment to create a color photo.  You also need to take photos with each filter.  Rather than spending one hour photographing Orion, you may need to spend an entire night!  It will also take much more time to process and edit those photos into a color image.

After you've decided between color or monochrome, you need to think about the pixel size and sensor size.  These will have a massive impact on the compositions you are able to capture.  For example, I usually recommend 400mm - 600mm on a full frame camera.  This allows you to fill the frame nicely with some of the most beautiful objects in the night sky - Orion, Andromeda, Pleiades, Horsehead Nebula, Rosette Nebula, etc...  If you have a smaller sensor or smaller pixels, you won't need as much zoom.  A micro-four/thirds or 1" sensor would only need about 200mm - 400mm to get similar results.  

No matter which brand or type of camera you choose, the pixel size is critical!  You must match the pixel size to your current telescope or lens.  If you do not, you may get mediocre results and ultimately waste money and time.  Remember, you want the “arc seconds per pixel” to be between 1 – 2 for the best results.  Once you get to 3, 4, 5+, you will be severely undersampling.  In other words, you don't have enough zoom.  You'll either need to buy a bigger lens or telescope, or get a camera with smaller pixels.  

For more information, be sure to watch this week's video: