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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 shown above. 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, as digital cameras take the forefront, 35mm cameras are getting cheaper, and for star photography the 35mm camera remains an excellent choice.

Pictured above is my trusty EXA SLR (Single Lens Reflex). I purchased it years ago for lunar, planetary, and general astronomy photography because it was an SLR, and an amazingly affordable one. It was manufactured in various configurations by a German company named Ihagee up until 1976 when the company was disbanded. Ihagee's flagship camera was the EXA's big brother, the Exakta, a fine SLR camera. The little brother EXA was affordable because it had a simpler shutter mechanism and only 4 shutter speeds: 1/30, 1/60, 1/125, and 1/175. It also has a Bulb setting with the ability to lock the shutter open, a perfect option for star field time exposures.

If you are into cameras, you'll probably notice that the 1/175 shutter speed is unusual. It amounts to a 1/2 stop in exposure. Apparently that's the highest shutter speed achievable with the simplistic shutter mechanism of the EXA. 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 piggyback star photography 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.

Moon Craters through 50mm Telescope
Moon Through 50mm Telescope

I mentioned that the EXA is 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 seconds to a few minutes long, so a 1/1000 of a second shutter speed is of no value. Not only are the EXA's shutter speeds limited, it also has no other frills, like no light meter, no timer, etc. But as simplistic as the EXA is, it has rather precisely the attributes I desired in an astronomical use camera -- a light-tight film box, popular sized film, and a removable lens with the ability to take other lenses and attachments.

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A few years ago I noticed an ad for an inexpensive SLR brand that I wasn't familiar with -- Zenit. Below is a picture of the Zenit 122K camera that I decided to purchase more or less as a backup to my beloved years old EXA.

Zenit 122K Camera

You might notice that it too is kind of a stubby model, about the same size as the EXA. The Zenit happens to be a camera manufactured in profusion by the old Soviet Union. They made millions of the cameras in various models, and even though they've been out of production since around 2005, unused cameras of the model shown above can still be had in their original boxes.

The Zenit shares many similarities with the EXA, though it has some notable differences. Like the EXA, it also has a limited set of shutter speeds, though adds one more: 1/30, 1/60, 1/125, 1/250, and 1/500. It too has a Bulb setting for long exposures, and also offers the ability to lock the shutter open without continually holding down the shutter button. Perfect for astronomical pictures.

While the shutter speed range is similar to that of the EXA, the shutter type is different. The Zenit has a more traditional focal plane curtain shutter. It is this more common SLR shutter design that gives the Zenit an additional shutter speed. Even so, it is limited to the 1/500 shutter speed where some focal plane shuttered cameras can reach 1/1000 of a second or even faster..

Unlike the EXA, the Zenit has a built in light meter that indicates correct exposure with red and green led's. But, alas, the light meter is notoriously inaccurate, so I just leave out the batteries and operate the camera as a pure manual model, the way I operate the EXA.

Zenit 122k Timer

The Zenit also has a timer option that is missing from the EXA, which allows you to set up the camera, trigger the exposure, and have a few seconds to get into the photo yourself before the shutter is actually tripped. Of course, for astronomical work neither the light meter, even if it was accurate, nor the timer are of any particular value. So you see, such a simple and basic SLR, while perhaps panned by serious photographers, is actually a perfect instrument for astronomical picture taking.

Removable Lens

The SLR 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 the screw 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.

Shown above is the Zenit in a similar pose, with its lens removed. It like the EXA uses a bayonet mount. Rather uncommonly but conveniently it uses the Pentax K mount. So it can in fact directly make use of Pentax lenses with the K mount.

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.

In this case, the lens isn't one specifically manufactured to fit the EXA bayonet mount. It's a lens manufactured to fit a somewhat industry standard T-thread mount. Many lens are made with this mount with the intent to make them usable on almost any SLR camera. And you can get a T-thread adapter for almost any camera model. That's what I've done here, purchased a T-thread adapter for my EXA so it can accept any T-thread lens. As you might expect, I also have a T-thread adapter for the Zenit.

Zenit 122k w/telephoto

Above you see the Zenit using the same 135mm T-thread telephoto. As with the EXA, the telephoto attaches via a T-thread adapter which in this case converts the T-thread into the camera's bayonet mount. So I can use whichever of these cameras to do the same astronomical work.

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.

Usually a few minutes exposure will give great results. In my backyard, there's enough light pollution that after about 3 minutes of exposure I start to get background fogging in the images. But a minute exposure with today's films works wonders.

piggyback astro-camera
SLR in Piggyback Mode

The Hale Bopp photo illustrates how a camera, in just a few minutes of exposure, can bring to light what you could only otherwise see with a sizable telescope. Below is another illustration. It is a photo of the vast nebula region in the constellation Cygnus. This isn't a great photo, but it does illustrate again how modest equipment with a bit of time exposure reveals wonderful hidden treasures.

Cygnus Nebula
Cygnus Nebula

Barn Door Mount

Star pictures, if you don't require the flexibility of removable lenses, can actually be taken with any camera. I'd still recommend a film camera for this work because of the ability to have long exposures. Digital cameras, unless very expensive, provide little support for long time exposures.

You can simply put your camera on a tripod, point it to the section of sky you are interested in capturing, and lock the shutter open for up to a few minutes. With this simple technique, you won't get the light integrating advantage of you camera in that the earth's rotation will cause the stars to drift across the film. What you'll collect are called star trails -- streaks left by the stars as earth's rotation moves them across the film plane.

The star trails themselves are interesting in their own right, however. Pictures taken near the pole will show stars moving in a great circle, the center of the circle being where the earth's pole is aligned. Pictures taken in a non-pole direction will show straighter lines.

To get the advantage of the light integrating potential of a time exposure, you need a way to keep your camera pointed at the same point in the sky. The images of Hale Bopp and Cygnus shown on this page were taken with my Piggyback Camera Mount. The telescope has a clock driven mount, so the camera, taking a ride on the telescope, was kept pointing at the same position in the sky even as the earth was rotating.

But if you don't have a telescope with a clock driven mount to use as a base for a piggyback mount, you can consider building a barn door mount, sometimes called a hinge mount. These simple mounts use a few common things you likely have in your garage or workshop plus maybe a couple more. There are motorized versions and manual versions.

The idea of such a mount is to have a simple device that can sit on a regular camera tripod and track stars well enough for a camera to collect great star photographs. You can't use a telephoto on such a camera with much luck, but you can get wide field star pictures that are impressive.

Check out the Build a Hinge Tracker site for how to construct a manually driven model, and the Build a Motorized Barn Door Tracker for instructions on how to build a simple motorized tracker.

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" telescope eyepiece holder. Like the 135mm telephoto, the telescope adapter has a T-thread, so it connects to the camera through the T-thread adapter. Likewise, I can use this telescope adapter arrangement with the Zenit.

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 in place of the eyepiece, and focus the telescope while viewing through the camera. This gives 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

Web cam Astrophotography

Another camera choice of moderate cost for photographing through a telescope is a modified web cam. You can make your own Web cam Astro-camera, 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 Web cam

Unlike the long-exposure capable SLR cameras, Web cams are only useful for short exposure 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 detail 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

In the above image, Venus is the large, dark, round spot. It helps put the size of the sun in perspective I think, remembering that Venus is nearly the size of earth. Look how much bigger the sun is than Venus. The scattered smaller and less defined spots on the image are sunspots.

I don't care much for this photographic 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 web cam. 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 Yorick program 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.