Cosmology 101 Items',
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
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 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.
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.
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
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.
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.
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
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
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.
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.
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
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
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.
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
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
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
a Motorized Barn Door Tracker for instructions on how to build a simple
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.
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.
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:
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.
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
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
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
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
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, 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.