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The Flexible SLR
The SLR (Single Lens Reflex) camera is by far the most flexible camera
in the astrophotographer's arsenal. The world is going digital, that's
for sure, but digital cameras with the flexibility of the SLR are still
very expensive. The good news is, for star photography the 35mm camera
remains an excellent choice.
Pictured here is my trusty EXA SLR. 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.
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If you're in the market for a used or new SLR, now available in both film
and digital versions, check out:
Calumet Photo,
a large source of cameras of all types.
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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 quick picture 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 images on the 2 inch
lens page.
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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 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 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.
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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. Which 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.
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Interchangeable Lenses
Shown in this 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 more. More elaborate configurations of telephoto
lenses are also available, using Maksutov optics or other telescope
configurations for higher magnifications.
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The Hale Bopp comet photo on the 2 inch lens lens
page was taken with this 135mm lens. It illustrates the type of images that
can be obtained with modest equipment.
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Even More Flexibility
The picture shown here 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.
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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.
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Telescope Ready
This picture shows the EXA with the eyepiece snout (that is a T thread)
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.
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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.
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Another Model
Another SLR that is a good candidate for astrophotography use is
the Zenit, shown here. It is also a minimalist SLR, though it does sport
a few more features than the EXA. For example, it has more shutter speeds,
making it a better camera for general use.
It also has a true focal plane shutter, which allows better use of
telephoto lenses. And finally, it has a penta prism view finder, where the
operator looks forward through the lens, instead of looking down at a
ground glass as with the EXA.
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Almost any SLR will do a good job as an astro-camera. I mention these two
models because I happen to have them. I purchases them with astrophotography
primarily in mind, and didn't need or want to pay for features I wouldn't
use.
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Still an SLR
As shown in this picture, the Zenit also has the all important feature
of having a removable lens. This Zenit also uses a bayonet type lens
mount. The Zenit is an interesting model. It is inexpensive, as was the
old EXA, but it uses a lens mount compatible with the popular Pentax
camera.
There are many supplemental lenses available for the Pentax, and with
a Zenit, you can make use of them. A caution: Pentax has models with both
bayonet and treaded mounts, as does Zenit. If you have in mind some
lenses, be sure you pick the right version of Zenit.
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Hale Bopp Through an SLR with 135mm Telephoto
This image is an example of what can be done with an inexpensive SLR
under the proper conditions.
For this image, an EXA with an inexpensive T-mount 135mm lens was mounted
piggyback on a Meade 90mm refractor. The Meade (a Chinese import) had a minimal
clock drive, but enough to let me take the photo, about a 5 minute exposure.
Check out how to make a simple piggyback camera mount at Piggyback Mount.
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Kodak color print film was used, and gave a nice rendition of Hale Bopp, showing both the ion trail (blue) and the dust trail.
The dust trail is residue shed from the comet, and shows it's travel history.
The ion trail shows the direction of the Sun, as the Sun's energy blows ions away from the comet.
Some Personal Notes
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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 digitals (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 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, most inexpensive digital cameras don't allow the operator 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.
If you want to obtain a inexpensive SLR to try some asto photography, I
suggest you look at Calumet Photo. They
have new cameras, and good stocks of used ones.
If you have some familiarity with what you are looking for, eBay Stores
 is another good choice.
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.
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