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Articles

Choosing The Ideal Setup To Begin Your Astrophotography Journey

by JayTee

This article should be used as a reference source for the ideal setup needed to educate those that would like to start their Astrophotography (AP) journey or anyone switching from visual astronomy to AP. This article is an opinion article and contains one of many possible solutions about what to gear to purchase to start AP. My opinion is based on wasted money and hard-won knowledge and is the generally accepted path to enter AP.

Cheers,

JT

Choosing The Ideal Setup To Begin Your Astrophotography Journey

The intent of this paper is to explain the 3 different branches of astrophotography and the factors that determine what gear will give you the very best results using an ideal, high quality, entry level setup for each branch. This paper covers ONLY the gear you will need, it does not cover the methods, procedures, techniques, theories, and lesser expensive, not as capable imaging gear. The gear I’m recommending gives you an ideal entry level setup using high quality gear for imaging within the different AP branches. These recommendations are my opinion of what is best to use. It is an opinion based on hard won knowledge that was gained by the wasting of hundreds and hundreds of dollars on unsuitable gear (cameras, mounts, telescopes, focal reducers, etc) for whatever branch of AP I was pursuing.

Lastly, the first two branches can be accomplished with a point and shoot camera or even a smartphone. Even though you will have limited success with this approach it is still a great teacher of basic AP concepts. This is how I started so if this appeals to you then by all means please use whatever gear you currently have available until such time that you want to spend the money necessary to acquire the gear listed here. The gear listed below gives you your greatest chance for success in acquiring stunning images.

The Three Branches of Astrophotography (AP) Arranged By Easiest And Cheapest To Accomplish

  1. Widefield/Nightscape - This branch is characterized by capturing as large an area of the night sky that your current lens/equipment will allow.

    1. It also accommodates a more artistic approach by capturing an area of interest, like the Southern Milky Way, the Big Dipper, the Orion constellation or the sky around the star Polaris with landscape features included if you so choose.

  2. Planetary/Lunar/Solar - This branch is pretty straight forward, you select the solar system object you want to image then do so.

  3. Long Exposure Deep Sky Object - This is the most challenging, costly, infuriating, and humbling of the 3 branches. This branch entails imaging galaxies, diffuse and emission nebula, planetary nebula, and various star clusters, both globular and open. These objects are collectively and affectionately called “faint fuzzies”.

The Factors That Determine What Gear Is Best Suited For Each Branch

Widefield/Nightscape -

The goal is to take images that span large sections of the sky. No telescope is designed to do this but your stock camera with its kit lens is.

In its simplest form this is all you need.

  1. Photo tripod
  2. Your camera with a wide angle lens ≤50mm (18 - 35mm preferred)
  3. An intervalometer, cable shutter release, or IR remote shutter release
    1. Additions that give you greater capability
    2. Any polar aligned tracking mount to increase the exposure duration. An Alt-Az mount will not suffice
    3. But an Alt-Az mount on a wedge will, also a “Barn Door” tracker, or any of the commercially available Star Tracker type camera mounts

Southern Milky Way 20 x 3 minutes images (1 hour total exposure time). Canon 500D and the 18-55mm kit lens set at 20mm at 1600 ISO on a Celestron GT Alt-Az mount on a wedge.

Planetary/Lunar/Solar -

This can be further broken down into planetary and lunar/solar, but the imaging gear mostly remains the same. Planetary imaging is carried out by shooting a video file of a small bright object (one of the planets). Because planets are bright, we use a video file versus still frames because we want to shoot several thousand frames in hopes that 10-20% of those frames will be taken during a short period of still air, this is called “lucky” imaging. Whereas, lunar/solar involves imaging a much larger and even brighter object and although still images can work here, we still tend to want to use the video format to cash in on lucky imaging. In order to capture planetary images we use a very long focal length to give us an image size large enough to reveal planetary detail. Also, the larger the aperture of your telescope, the finer the detail you will reveal in your images. So ideally you’d like a long focal ratio telescope (f/10 or greater) with a fairly large aperture 8” or greater..

Here is the ideal gear you need for planetary imaging.

  1. Telescope - An SCT or Mak-Cass with a focal ratio ≥ f/10. The larger the aperture the better
  2. A small pixel (2.75 - 3.75µ ), fast frame rate (up to 60 fps) CMOS planetary videocam. with a small sensor, 9 - 15 mm diagonal measure
  3. Any accurate tracking mount either EQ or Alt-Az
  4. A laptop computer to power the camera and run the imaging software

Of all the solar system objects to image, the moon is by far the easiest and is usually where most folks begin their AP journey.

For simple, inexpensive lunar imaging this is what you’ll need.

  1. A camera with the ability to zoom in,
    1. The zoom capability should be equivalent to a 200mm or greater telephoto lens. Which is equivalent to about 8X. All of the following cameras will work.
    2. A smartphone or
    3. A point and shoot or
    4. A DSLR
  2. Tripod

Or you could just hold your camera (or smartphone) up to your eyepiece of your current telescope, then snap away!

For solar imaging all the above gear will work, just remember you need to filter out 99.9% of the Sun’s heat. Any approved “white light” filter will allow you to image the Sun. Additionally there are specific solar telescopes and solar eyepieces that can give you small band pass capability centered on the Hydrogen alpha (Ha) emitted wavelength to reveal amazing solar detail. These are very expensive pieces of gear.

10,000 frames, top 10% used. Taken thru a CPC 1100 with 2X barlow giving a focal length of 5600mm, using an ASI 120MC camera and Fire Capture software

Long Exposure Deep Sky Object Imaging -

There is a good reason why this is the most difficult and expensive branch of AP. To image the Faint Fuzzies, you need a polar aligned tracking mount (specifically an equatorial mount) that can also be computer controlled which allows for auto guiding. The reason for using an equatorial tracking mount is that so few photons emitted by your object of interest actually make it onto your camera’s sensor. This requires that we leave our camera shutter open for as long as possible. Sometimes as long as 10 minutes. For this branch of AP do not use an Alt-Az mount because that configuration suffers from an effect called field rotation which makes the stars look like little curved arcs in your image.

For this section to make more sense let’s get some terms straight

  • Tracking - accomplished by the motor on the Right Ascension axis on your EQ mount negating the rotation of our planet keeping the desired object in the field of view of the camera.
  • Guiding - this is what the mount and you do, using the motors on both axes of your mount, to keep the desired object in the field of view absolutely motionless within the field of view. These adjustments are made concurrently while the mount is still tracking the object
  • Auto Guiding - this is what the mount and your computer do to keep the desired object absolutely motionless within the field of view.

AP Mount Considerations.

Because the size of the pixels in our cameras are measured in microns, this then is the scale of error allowed by our telescope mounts when they are tracking the object. Guiding tries to minimize the errors encountered in our tracking (there are several anomalies that can introduce these errors) but guiding can never negate all of them. These tracking errors are seen by the camera sensor and they are additive in nature. The longer the exposure, the more errors the sensor records. This requires a telescope mount with a high level of precision, and this level of precision is not cheap.

Just as in business the mantra for success is “location, location, location, with long exposure AP our mantra for success is the mount, the mount, the mount. This is further illustrated by the fact that a cheap scope on an expensive mount can take great images, whereas an expensive scope on a cheap mount will take crappy images.

You want a mount that is rated for a decent amount of payload weight (25 - 30 lbs or 11 - 14 Kg). This payload rating pretty much ensures that the mount is of high enough precision that the tracking errors will be small enough for the auto guiding to significantly smooth out those errors. Lastly, weight, it is our enemy in long exposure AP. An increasingly greater payload put on the mount will generate more frequent and larger errors in tracking. For this reason it is always suggested that you do not load up your mount with more than 50-60% of its maximum payload capacity. This is often referred to as the AP load. And why we want a mount that has a max capacity of 25 - 30 lbs. This gives us an AP payload (for the 30 lb max) of only 15-18 lbs.

Imaging Telescope Considerations.

When starting out in long exposure AP, using a short focal length smaller aperture refractor is by far the easiest way to proceed. It has two main advantages:

1) A shorter focal length gives us a brighter image because the camera views a bigger chunk of sky. A brighter image allows for reduced exposure times. The chunk of sky we are imaging is measured in degrees, arcminutes and arcseconds. So if our mount exhibits tracking errors of only 1 arcsecond in size but each pixel on the camera’s sensor attached to our short focal length refractor can only see a piece of sky no smaller than 3 arcseconds then our mount’s tracking errors are much more difficult to detect and in some cases they are just flat out undetectable on our image. This is the desired goal in long exposure AP, keep your tracking errors smaller than the amount of sky each pixel sees!

2) Because we are using a smaller aperture refractor it is lighter in weight. So we can stay within the AP load for our chosen mount.

Guide Scope Considerations.

When starting out in long exposure AP, I recommend that you use a separate guide scope to accomplish your guiding. The other alternative is to use what’s known as an off-axis guider (OAG). Because of its design it works best on a larger aperture telescope than the small refractor I’m recommending. A small inexpensive refractor works best as a guide scope. We need this guide scope (along with our guide camera) because we need to produce an image on the computer that our guiding software can use to calculate then implement the guiding commands.

Imaging Camera Considerations.

There is now a lot of latitude in the products available for your use. Up until about 3 or 4 years ago it was recommended that all beginners start their AP journey using a DSLR camera. The reason being is that they are a color camera, they are much less expensive than the dedicated CCD “Astro” cameras, plus it was highly likely you already owned one. Nowadays you have a whole range of affordable CMOS “Astro” cameras from which to choose many of which have a cooling system for the sensor. If you choose to go with a DSLR camera be advised that they suffer from heat noise (noise - our other enemy) because the DSLR sensor is not cooled this means the longer the exposure, the hotter the sensor gets (more heat = more noise). Features a beginner should look for in a CMOS camera: I recommend you start with a color camera because it simplifies the entire process, then as large a sensor as you can afford (13 - 26 mm sensor diagonal measure) and one that has relatively large pixels (4.0 to 5.5µ) and a cooling system for the sensor is preferred. Cooling means much less noise. The reason for using a large sensor is that a larger sensor can image a larger piece of sky and because its physical size will accommodate more or larger pixels. Remember, the larger the piece of sky the camera sees, the more arcseconds each pixel will have to image which helps mask tracking errors.

Guide Camera Considerations.

This camera only needs to be a mono CMOS videocam with medium to large pixels (3.75 to 5.5µ). Cooling this sensor is not needed.

Computer Considerations.

A comuter is required to run the auto guiding and image acquisition software also for storing your images out at the scope. It does not need to be fancy, your basic Dell business laptop has more than enough features and computing power to run everything you’ll need to plug into it. The vast majority of AP software is written for Windows so going with a PC means a lot fewer compatibility headaches.

After all that discussion here is your shopping list for an ideal high quality, entry level setup for long exposure deep sky object AP

  1. A computerized equatorial mount with a capacity of at least 25 - 30lbs (11 - 14 Kg) check this post for an attached list of mounts ranked by payload capacity Telescope Mount Payload Capacities
  2. The imaging telescope should be a short focal length refractor with an aperture of 60 - 80mm, f/5 to f/7. An APO refractor is best but an ED glass achromat will also do.
  3. The guide telescope should be a smaller aperture short focal length refractor (to save weight). A simple achromat works well here.
  4. The imaging camera
    1. a CMOS “Astro” color camera with pixels between 4.0 to 5.5µ and sensor size diagonal measure between 13 - 26 mm -- or --
    2. a DSLR either Canon or Nikon because of their compatibility with image acquisition software
  5. The guide camera
    1. a smaller less expensive CMOS mono astro camera or your planetary videocam if you bought one already
  6. A laptop computer, PC based
  7. A table
  8. A chair - it seems obvious, but I just wanted to give you a complete list.

NGC 3372 (Carina nebula) 33 X 3 minute exposures (total time of 99 minutes). Canon 600D attached to an ES 80mm APO refractor on a Celestron AVX mount using Astrophotography Tool (APT) as the image acquisition software and PHD2 as the guiding software

Conclusion

I hope this article gave you some insight into the concepts and reasons for the gear I recommended for each of the three branches of astrophotography. If any of these concepts were not clear and understandable for you, please don’t hesitate to ask questions in the AP equipment forum on TSS.

Lastly, do not hesitate to start with just a camera and tripod or a camera hooked up to the focuser of your telescope to see what results you can achieve and never be afraid to experiment with all the image parameters: exposure times, ISO settings, and f-stop settings. You may surprise yourself at the image you can obtain.

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