Deep Space Astrophotography for Beginners -

As you may have read in my earlier post “How to get into Astrophotography“, there are many different types of astrophotography.

Deep space astrophotography is by far the most challenging but also the most rewarding, in my opinion.

If you are going to go down this rabbit hole, there’s a lot to know, so I will cover deep space astrophotography from A-Z in this post.

I’ll give you an idea of what an example setup looks like, explain each component in-depth, and provide you with some different options for each piece of equipment.

Let’s dive in.

Table of Contents

Example Set up

The most important component of your deep space astrophotography rig is the mount. I would anticipate spending around $1500 or more on an entry-level setup with a go-to mount. Of course, the total price will vary depending on whether or not you are buying equipment new or used.

The items listed in bold are not technically required, but they are in certain instances. For example, autoguiding is required for Narrowband imaging.

A Go-To equatorial mount
Camera (DSLR or astronomy camera)
Telescope
Field flattener or coma corrector
Dew Heaters
Autoguiding equipment- A guide scope and camera

Add-ons to consider

bahtinov mask for precision focusing
Filter wheel and filters (for monochrome/narrowband imaging)
Power management components (usb hub/pegasus powerbox)
Individual filters (dual narrowband for OSC cameras)
Imaging laptop (nothing fancy required)

Mounts

To capture deep space objects, we need our equipment mounted on something that counteracts the earth’s rotation.

Why? Because as the earth rotates, so does our target. If we don’t mount our equipment on an equatorial mount, we will eventually get what’s known as field rotation.

To better understand this, think of the constellation Cassiopeia.

When you look at Cassiopeia in the night sky at 6 pm, it may look like the letter W. Look at again at 11 pm, and it will look like the letter M.

Equatorial mounts differ from altazimuth mounts which just move up and down and left to right on a horizontal base. Instead, equatorial mounts sit on wedge, angled so that it’s aligned with the earth’s pole.

This polar alignment allows equatorial mounts to keep the camera’s perspective on your target the same throughout the course of the night.

By doing this, we can ensure that the object never rotates in any of our images.

If the way I explained this didn’t make sense, please visit this link. It offers one of the best explanations I have ever seen.

Things to consider:

When buying a mount, consider the payload capacity, tracking performance, and weight. A general rule of thumb for starting off is to half the manufacturer’s payload capacity.

This isn’t a rule that is set in stone, but you will create unnecessary challenges as a beginner if you max out the payload capacity.

More weight equals more strain on the mount. This will be especially problematic if you are trying to guide a long focal length to start out.

Another thing to consider is the weight of the mount itself. Figure out how much payload capacity you need now and consider the future if you upgrade. A mount like the EQ6 R pro is one that you may never outgrow, and it’s a great mount.

It’s also a heavy mount, so it may not be ideal if you’re someone that has a bad back or portability at the top of your priority list.

In this case, the iOptron CEM40 may be a better option. It has the same payload capacity but weighs half as much because of the mount’s center-balanced nature.

Below are beginner mounts under $1800 that are considered good for astrophotography:

iOptron CEM26
Orion Sirius EQ-G and SkyWatcher HEQ5 Pro
SkyWatcher EQ6 R Pro (Same thing as the Atlas II and vice versa)
Orion Atlas EQ-G
Sky-Watcher EQ6 (Discontinued, same thing as the Atlas EQ-G)
Orion Atlas II EQ-G

Note: I would resist the temptation to buy lower-class mounts than these for astrophotography.

They may be advertised for astrophotography, but the motors and gears often don’t have the precision required for it.

Furthermore, mounts in a lower class than the ones listed here typically have higher gear slop and backlash levels and will most likely lead to a lot of frustration when it comes to imaging.

Mounts can be difficult to come by in new condition right now. However, you can save a lot of money by buying used on cloudynights if you are in the U.S.

Cameras

DSLRs

DSLRs are the best budget way to get started in Astrophotography. DSLRs are considered OSC cameras which stands for one-shot color.

In OSC cameras, a Bayer matrix is used to assign photons to a particular color. This color filter mosaic consists of tiny filters that overlay your camera’s sensor and allow the pixels to render color information.

When you take a photo with these cameras, all of the RGB channels are combined into one single image. DSLRs will work just fine with some targets, but they also have their downsides.

These downsides include the inability to regulate the sensor’s temperature and a decreased sensitivity to hydrogen-alpha in stock cameras.

If you already have a Canon/Nikon camera with interchangeable lenses, use it (except if it can’t be computer-controlled). A used DSLR is the most cost-effective way to photograph DSOs.

I wouldnt recommend spending more than $350 on a DSLR unless it is modified for astrophotography. Cameras should be purchased used if possible since there are minimal benefits to buying it new.

If you can’t find any deals in your area, look for used cameras on websites like eBay. Many of the cameras below (except the T6i and T7i) can be found for less than $350 second-hand.

When buying an astrophotography camera, the two most important things to consider are the software and hardware compatibility and the sensor used in the camera.

DSLR recommendations:

Canon

SL2 / 200D
SL1 / 100D
T7i / 800D
T6i / 750D
T5i / 700D
T4i / 650D
T3i / 600D

Nikon

D5300/D5500/D5600 (All of these cameras have the same sensor)

This is not an all-inclusive list. Other camera models will work fine for astrophotography that I have not put in this guide.

Suppose you can find an Astro-modified version of any of the cameras listed above. In that case, you should buy that instead because it will give significantly better performance on certain targets.

Nikon or Canon DSLRs are highly recommended for astrophotography because they have by far the most compatibility with image acquisition software compared to other brands.

However, Canon cameras support a wider variety of software and hardware than Nikon, so consider that too.

OSC Astronomy Cameras

Astronomy Cameras offer two variants, OSC and Monochrome.

The OSC astronomy cameras are more efficient than DSLRs in many ways. One is that they don’t contain the same filters that limit the camera’s sensitivity to hydrogen-alpha.

The other is that they can be cooled, which reduces the noise in your images considerably. Cooled cameras also allow you to build a library of dark frames, which means you can take them once and never have to worry about them again.

OSC vs. Monochrome within the realm of astronomy cameras is a matter of personal preference. Some people like the one-shot color appeal because it makes image processing a bit easier for a beginner.

This is because you don’t have to separately process or combine your channels like you would with a monochrome camera.

Some people also think that less imaging time is required with OSC cameras. This is a debated subject, but my personal opinion is that this is not true.

Four hours of OSC integration should be the same as one hour each of LRGB with a monochrome camera. Monochrome may even be more efficient specifically because of the Luminance filter.

Examples of commonly used OSC Astronomy cameras. Please note that MC does not stand for Monochrome. The MC models are the color version, and MM indicates monochrome.

If you are not sure which camera to get, note that its important to properly pair it with the telescope that you plan on using.

You want to make sure that you are properly sampled based on the cameras pixel size, and the telescopes focal length.

Camera Name	Color or Mono	Sensor	Sensor Size	Pixel Size
ZWO ASI 294 Pro	Both MM and MC	IMX429	4/3 CMOS	4.63
ZWO ASI 1600 Pro	MM only (MC Discontinued)	MN34230	4/3 CMOS	3.76
ZWO ASI 533 Pro	MC only	IMX533	1″ CMOS	3.76
ZWO ASI 183 Pro	Both MM and MC	IMX183	1″ CMOS	2.4
ZWO ASI 2600 Pro	Both MM and MC	IMX571	APS-C CMOS	3.76
ZWO ASI 2400 Pro	MC only	IMX410	Full Frame CMOS	5.94
ZWO ASI 6200 Pro	Both MM and MC	IMX455	Full Frame CMOS	3.76

Monochrome Astronomy Cameras

Monochrome cameras don’t use a Bayer matrix and basically image in black and white.

Instead of a Bayer matrix, you need individual filters placed in front of the camera sensor to capture the different color channels. These channels are then combined in post-processing to make a single-color image.

The biggest advantage that Monochrome cameras offer over OSC is that they can be used with narrowband filters.

Narrowband filters restrict the light that’s captured by the camera to a very specific bandpass. These most commonly include Hydrogen, Oxygen, and Sulphur.

These filters also allow you to capture emission nebulae in ways that you simply couldn’t without them. It’s worth noting that you can also use dual narrowband filters with DSLRs and OSC astronomy cameras which isolate two emission lines simultaneously.

These also make an incredible impact on your photos and the ability to pick up signal in the hydrogen and oxygen channels. The other major advantage of narrowband filters is that they can overcome even heavy light pollution.

Light pollution gets worse and worse as time goes on, and many sites aren’t nearly as dark as they were 10 years ago. So if you live somewhere like New York City and want to pursue deep space astrophotography, you will want a mono camera and a set of narrowband filters.

Keep in mind that not all targets can be imaged in narrowband, and it is best suited for emission nebulae. In addition, because these filters only allow light from specific wavelengths to enter the camera’s sensor, you are cutting out all of your broadband signal.

Telescopes

The fact that we need so much integration time also means that the type of telescope or camera lens that we would want to use is very different than it would be for planetary astrophotography.

For DSO astrophotography, we are much more concerned with the focal ratio of the telescope and less concerned with aperture.

The focal ratio is the focal length divided by the telescope’s aperture and measures the telescope’s speed.

When I say speed, I mean the amount of time required to capture signal and collect light. The lower the number, the faster and more efficient the telescope is.

If you use a slow telescope, the amount of exposure time you will need increases exponentially compared to a fast telescope. Doubling your focal ratio increases the imaging time required by 4.

In other words, you would need to spend 4 hours imaging a target with an f/10 telescope to achieve the same result as an f/5 telescope in just 1 hour.

The best telescopes for DSO astrophotography are typically refractors or Newtonians, and as mentioned before, you can even use a camera lens.

You likely wouldn’t use an SCT for this unless you used a focal reducer because SCTs tend to be slow compared to the others mentioned.

Many people are surprised that you can use a camera lens to capture DSOs, and that’s because they don’t necessarily realize that some DSO’s are absolutely huge.

For example, if you could see the entirety of Andromeda with the naked eye, it would take up as much space in the sky as about 5 full moons.

The enormous size of some of these objects means that you wouldn’t necessarily want a long focal length to image them. If you choose too long of a focal length for a large DSO, you can’t fit the whole object into the telescope’s field of view.

Having said that, many galaxies appear incredibly small because they are unbelievably far away. These are best captured with longer focal length telescopes like dedicated imaging Newtonians.

Reflector suggestions

The benefits of reflectors over refractors are that they are much cheaper and have no chromatic aberration.

If you get a reflector for astrophotography, make sure it’s advertised as an imaging Newtonian. For Skywatcher telescopes, this is noted by “p-ds.”

Their models noted with only a “p” are for visual purposes, and attempting to use one of these will likely result in issues reaching focus.

Refractor Suggestions

A small apochromatic refractor is going to be the best choice for the majority of beginner astrophotographers. They are the simplest telescopes to use and do not require any collimation or other maintenance required by reflectors.

The optics in Apochromatic refractors are made from special glass that will almost eliminate chromatic aberration. You will commonly see three different types of refractors: doublets, triplets, & flat field.

When you see the term flatfield or Petzval, these are quadruplets. The benefit of flatfield telescopes is that the field flattener is built-in instead of being purchased separately.

A doublet is a telescope that uses two glass elements to correct chromatic aberration; a triplet uses three. As a result, a triplet will outperform a similarly built doublet in terms of color correction.

If it’s in your budget, get a triplet telescope. Most doublet refractors are well color corrected, but there is still residual chromatic aberration and star bloat.

Most apochromatic doublets are perfectly fine starter telescopes. However good triplet will give you tighter stars, and chromatic aberration will not be noticeable at all.

The spreadsheet below compares all commonly available refractors. It lists the prices and additional information for different countries: Telescope Database

Field curvature and flatteners/reducers

Note: Newtonian telescopes suffer from coma rather than field curvature. You’ll need to use a coma corrector instead of a field flattener.

Refractors use glass to bend light and do not have a completely flat focal plane. The focal plane is curved, which causes the stars on the edges of your frame to be distorted.

Technically you can image without a field flattener, but it’s not advised. Field flatteners will dramatically improve the quality of your images.

Examples of field curvature:

Some field flatteners also act as reducers, which will simultaneously reduce the focal ratio and focal length of your telescope.

Reducers are great for increasing the speed of your telescope (or decreasing the amount of time required to image your target). They can also make a long focal length telescope easier for your mount to guide.

Field flatteners range in cost from $100-$250 USD. I suggest buying the dedicated one made specifically for your telescope. However, many flatteners are generic and will fit any scope that meets their specifications.

Autoguiding

Autoguiding is something that you will want to quickly upgrade to once you begin deep space astrophotography.

It will allow you to maintain sharp stars, dither, and image with narrowband filters. In general, it is the most cost-effective way to improve an astrophotography image.

Of course, it will not turn a bad mount into a good one, but it can correct for a certain amount of periodic error. It also makes perfect polar alignment less crucial.

Guiding works by using a secondary camera and telescope that monitors one or more stars in the general region of your target.

If the guiding software detects that the star has moved out of position, instructions are sent to the mount to bring it back to its original position.

There are two main ways to pick up the light coming from a guide star. The first is by using an often-smaller secondary telescope called a guide scope.

Guide scopes are typically mounted to your primary telescope; piggybacking it on the tube rings is a common way to do it.

The second option is a small prism/mirror that reflects some light entering the main telescope to the guide camera. This second option is known as an off-axis guider.

Guide camera

Monochrome guide cameras are used more commonly than color because they have higher levels of sensitivity.

A ZWO ASI120MM mini paired with a generic 50mm Amazon or eBay guide scope will work just fine with telescopes under 750 mm focal length.

The next step up would be an ASI290MM mini, which is only necessary if you use an off-axis guider.

It’s also worth noting that I use an ASI224MC, which has worked great and doubles as an excellent planetary camera.

Guide scope / Off-Axis Guider

For DSLR users, guide scopes are usually the only option because there is not enough space to insert an off-axis guider.

Guide scopes should be rigidly mounted to prevent differential flexure.

This is when the guide scope or main imaging camera moves independently from one another. The guide camera will detect this movement, try to correct it, and ruin the exposure.

In comparison, an off-axis guider gets inserted into the imaging train and does not need to be supported in other ways.

If you are using a guide scope, I would definitely avoid attaching your guide scope to the finder shoe bracket. Doing it this way will more than likely cause flexure and bad guiding.

Please see the thread below for good examples of how a guide scope should be mounted: https://www.cloudynights.com/topic/561217-game-plan-for-newbie-rig-keep-me-off-the-guardrails/page-4

Another factor to consider is that the guide scope needs to be protected from dew, just like your main telescope.

Therefore, a secondary dew heater is required to prevent your guide scope from dewing up and losing your guide star. An off-axis guider, on the other hand, is inside the telescope.

As a result, it does not need dew protection.

I always suggest buying the cheapest 50/60mm guide scope you can find because they are all basically copies of one another. Paying more for a guide scope won’t give you better performance.

Conclusion

Well, there you have it; in this post, I did my best to explain deep space astrophotography in its entirety.

In this particular type of astrophotography, everything is more or less a la carte. You pick and choose which individual pieces of equipment you want to build your rig.

Therefore, I would highly advise against buying anything that is marketed as a packaged astrophotography setup.

The telescope is often oversized for the mount, and the mount itself is often designed more for visual use than astrophotography.

If you stick to this guide and the suggestions that I have laid out, I’m confident you will have everything you need to take some incredible photos of deep space objects.