Tumbleweed Observatory's

Astronomy Hints




How to Choose a Camera for Astrophotography

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Astrophotography Options

The Flexible SLR

As far as cameras go, the world is going digital, that's for sure, as indicated in the Amateur Astronomy Survey camera's used result. But digital cameras with the flexibility of the 35mm SLR are still very expensive. The SLR (Single Lens Reflex) camera is by far the most flexible camera in the astrophotographer's arsenal. The good news is, for star photography the 35mm camera remains an excellent choice.

Pictured above is my trusty EXA SLR (Single Lens Reflex). I purchased it for lunar, planetary, and general astronomy photography because it was an SLR, but an amazingly affordable one. It was affordable because it had a simpler shutter mechanism and only 4 shutter speeds. I remember paying about $35 for it new when other brands were selling in the hundreds. No longer made, the camera is still available at used camera outlets.

An SLR, among other advantages, has a view finder that looks directly through the camera lens. Because of this the SLR is ideal to use with a telescope. The focus of the telescope can be directly seen through the view finder. Typical snap-shot cameras have a view finder separate from the lens, so one cannot tell if the image is focused on the film plane or not.

The EXA shown has a waist-level view finder that focuses on a ground glass. In the days when I used this with my telescopes to take lunar and planetary pictures, the ground glass image was a great benefit for precise focusing. For star use, it isn't as handy as the more common penta prism. An EXA was used to take the moon image below through a 50mm refractor. Other images taken with the EXA and 50mm telescope are on the 2 inch lens page.

I mentioned that the EXA was a minimalist SLR. By that I mean it is an intro model, having few shutter speeds, and not even possessing a focal-plane shutter. In non-solar system astrophotography, you are usually making exposures several minutes long, so a 1/1000 of a second shutter speed is of no value.

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Removable Lens

Another advantage of the SLR is that is has a removable lens, as shown in the above picture. This opens the door for some incredible astrophotography options.

It gives options to the general photographer also, which is a big reason that the 35mm had such a vast following (and still has, for that matter). The EXA shown has what is called a bayonet type of lens mount. That is, it has three areas spaced around the lens that slide and lock into position with a twist.

Many other camera models also use bayonet mounts, and it's a type of attachment I like the best. Don't assume, however, that one brand's bayonet mount lens will fit another brand's camera. That almost never happens.

Other camera models use a screw-on attachment. With this type, the lens barrel of the lens is threaded, and screws into the camera body. Again, be aware that most brands have unique thread sizes, so only the same brand of lenses will fit the cameras.

Interchangeable Lenses

Shown in the above picture is one of the advantages of having a camera with a removable lens. In this case, the original camera lens has been replaced with a 135mm telephoto. Given that the original lens was a 50mm, the telephoto magnifies images by the ratio 135/50, or 2.7 times.

The 135mm is a common moderate power telephoto. Conventional lenses are available up to 400mm, or even greater. More elaborate configurations of telephoto lenses are also available, using Maksutov optics or other telescope configurations for higher magnifications.

The Hale Bopp comet photo on the 2 inch lens lens page was taken with this 135mm lens. The image is also shown below.

Hale Bopp Photo
Comet Hale Bopp

It illustrates the type of images that can be obtained with modest equipment. To get the picture, I made use of the ability to replace the basic lens with a 135mm Telephoto lens, and mounted the camera on a Piggyback Mount. This is one of the simplest ways to get into astrophotography. With a piggyback setup, you view through the clock-driven telescope to keep the target in position as the camera, with shutter locked open, collects the time exposure.

piggyback astrocamera
SLR in Piggyback Mode

Even More Flexibility

The picture shown above illustrates yet another advantage offered by being able to remove the lens. Shown is a simple snout that fits into a 1.25" eyepiece holder, and an adapter.

I mentioned before that each camera manufacturer has it's own type and size of lens mount, and most aren't compatible with other manufacturers. But there is a simple, standard type of thread mount called a T mount.

I say simple because the T mount lenses usually must be manually controlled, since they have no automatic connections to any particular camera body. That means that if you use a T mount lens on a camera that normally can auto select a lens setting with a built in photo cell, the automatic feature won't work when using the T lens. T lenses are used in what's called a preset mode. The operator must manually set the focus and f stop of the lens prior to making an exposure.

Not a bad compromise really, given that the T lenses are usually much less expensive than the automatic, camera specific variety. The 135mm in the previous picture is a T mount lens.

When a T mount lens is used, an adapter must be also used that accepts a T mount lens and fits a specific camera's body. Adapters like this are available for virtually all popular SLR's.

Telescope Ready

This picture above shows the EXA with the eyepiece snout mounted to the camera with a T adapter. This makes for a very handy technique of taking photographs through a telescope.

I simply insert the snout into the telescope focuser instead of the eyepiece, and focus the telescope while viewing through the camera. This gives of the most precise focus, and mounting couldn't be simpler.

More magnification can be obtained in a couple of ways. You can purchase an eyepiece projection attachment, which fits between the telescope and camera. It will allow insertion of an eyepiece, which then projects a larger image onto the film.

I just insert my Barlow lens, then the camera. This also projects a larger image onto the film, and makes for a very compact unit. The image below shows the EXA with snout attached, and the camera and snout is inserted into my NexStar 5SE.

35mm attached to NexStar 5
EXA at Prime Focus of NexStar 5SE

Such an arrangement can be used to take photos through a telescope without the chance of light leaks ruining the exposures. I used such an arrangement years ago with my EXA and my 50mm Refractor, which at the time was mounted on a homemade pipe-fitting mount that had a Jaeger's clock drive attached. I still have the telescope, but no longer have the old cobbled together mount. The contrived arrangement worked, however, to provide me with some pretty nice 2 Inch Telescope Astro Photos. Below is shown an example, using the EXA plus Barlow lens looking through my 2 inch refractor:

35mm Image of Lunar Apennine Mountains
Lunar Apennine Mountains

The above lunar image was taken years ago through a lowly 50mm refractor and my trusty Exa. It took advantage of the steadiness possible with a small telescope, and the advantageous aspects of the SLR.

Webcam Astrophotography

Still another camera choice is a modified webcam. You can make your own Webcam Astrocamera, or purchase one ready made, like discussed on the Celestron NexImage page. These make very light and small cameras, as the image of the Celestron NexImage camera below illustrates. The camera is shown alongside a ballpoint pen to get a sense of size.

Celestron NexImage
Celestron NexImage

These cameras have a snout the diameter of a standard 1.25 inch eyepiece, and thus slip right into the telescope focuser in place of an eyepiece. Or, they can slip into a Barlow lens that is in the focuser, in order to get more magnification. Below is an image of my Celestron NexImage coupled to my ETX 90 telescope.

Celestron NexImage with ETX 90
ETX 90 with Webcam

Webcams are only useful for lunar and planetary photography, but they are very good at it. The way most people use them is to take movies of a few seconds long of a target, then later use an image stacking program like RegiStax to create an enhanced image. The stacking procedure can't give more than the telescope can resolve, but can help get close to that limit. The following image of the lunar crater Copernicus was obtained with such a camera and my ETX 90. More such images are on my ETX 90 astrophotography page.

Copernicus Crater
Copernicus with ETX 90

Some Personal Notes

It is true that the "through the lens" aspect of an SLR is also available with most digital cameras. If you focus by looking at the LCD display, you are looking through the lens. The difficulty with the more affordable digital cameras (up to a few hundred dollars) is that the camera lens cannot be removed.

This leaves only the afocal type of telescope photography as an option. In afocal, the operator must use an eyepiece and focus the telescope for the eye. Then a camera set to an infinite focus can be mounted behind the eyepiece to get a telescopic image. I made a device to hold a once owned digital camera to the eyepiece, shown at this Digital Mount web page. The page shows some images taken with this kind of setup, and has a link to a commercial camera mount that's better than the one I cobbled together.

On a couple of occasions, I've even setup a camera on its own tripod, placed just behind the eyepiece of my telescope. This was to get short exposure photos of a Mercury transit and a Venus transit. It's a difficult procedure, but by placing the camera on its own tripod, the shutter movement didn't cause the telescope to vibrate, which would have ruined the shots. Below is an example of this awkward afocal setup. I used a Pentax on its own tripod, set next to the eyepiece of my 2 inch telescope which had a solar filter over the objective. I able thus to get a decent shot of the Venus transit in 2012.

Venus Transit
Venus Transit, 2012

I don't care much for this procedure because an eye focus may not be properly focused for a camera, given that eye lenses also have anomalies. Also, if using an inexpensive digital camera, you may not be able to set image brightness or camera focus, so the precise control of image quality isn't available as it is with an SLR.

Given that, I admit that I don't use the SLR much for lunar and planetary imaging anymore. I use a modified webcam. It also gives me direct focus control and some brightness control. In addition, I can combine several digital images into one better image using a perl script I've written.

But for comets and stars, I still find the 35mm my best option. Used 35mm cameras are cheap (some new ones are even cheap compared to a digital SLR option), as are used telephoto lenses. Camera adapters are also available, as well as eyepiece adapters.

Whatever you do, I wish you luck. Stay tuned as I'll be working this summer to produce some more star pictures with my handy 35mm SLR.