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
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.
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
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
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.
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.
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
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.
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.
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
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.
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.
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 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
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
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.