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- Discovery 17.5” Split Tube Dobsonian Telescope
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What's the best 35mm SLR camera for astrophotography
"What's the best 35mm camera for astrophotography", is a question I've heard asked hundreds of times over the years. The answer is that almost any 35mm SLR camera can be adapted for use with a telescope. The best camera is the one which makes the job of astrophotography the easiest…the one which has the best combination of features for ease of use with a telescope. A combination of DESIRABLE FEATURES, AVAILABILITY, PRICE, SIZE/WEIGHT will determine the best camera.
The fundamental prerequisites for an easy to use astro camera are interchangeable lenses and a mechanical shutter with a "bulb" setting. Since many 35mm cameras have these features in common, even those dating back to the 50's, your choices for a suitable 35mm camera (based only on these requisites) is huge. The list ranges from the exotic leicas and Nikons to the private label cameras sold by JC Penney and Sears. While any one of these cameras are capable of producing fine astro photos, some are more capable than others and a few have the camera functions which make them ideal for astrophotography. Following is a list and a discussion of the most desirable camera functions for astrophotography:
The shutter must be completely mechanical/manual with user selectable shutter speeds and a "bulb" setting. This describes most 35mm SLRs built and sold prior to the late 70's, as this was the "state of the arts" during that time period. During the 80's, camera manufacturers started to add more electronic sophistication to their products…producing automatic, electrically activated, state of the arts shutters, which effectively took control of shutter speed selection (some also took control of the lens aperture) leaving the user with virtually no guesswork and limited control. Several of these cameras have a selectable "manual mode", but the shutter is still activated electrically.
The problem with an electrically activated shutter, even if used in manual mode, is that the shutter will drain the small batteries (watch type batteries) during long duration exposures. Some guided astro exposures require that the shutter remain open for 30 minutes or more. The small, camera contained batteries do not have the reserve power for too many of these exposures. When the battery drains, the camera is dead and your exposure is ruined.
This issue can be side stepped on some cameras, but it is far easier to use a camera with a mechanically activated shutter. The Canon AE-1, as an example, has an electrically activated shutter with a selectable manual mode. The camera contained battery (1.5V) can be removed and wired with a jury-rigged lantern battery. If you are not certain whether your camera has a mechanical or battery powered shutter, use this simple test. Remove camera batteries and activate the shutter. If the shutter works, you know it's mechanical.
The ideal astro camera must have removable lenses. Whether you choose to photograph piggyback, prime focus,
afocal or projection photography, removable lenses is necessary in all but the piggyback method.
Piggyback - Camera mounted on tracking telescope but optically independent of telescope.
Prime Focus - Using telescope as camera lens.
Afocal - Using the complete telescope optical system including eyepiece and complete camera optical system including camera lens.
Projection - Using the camera body only and telescope with eyepiece (positive projection) or without eyepiece (negative projection).
This feature is very nice to have but not an absolute necessity for good astrophotography. All reflex cameras
have a mirror between the lens and the shutter to divert the light path so that the user can see the actual image.
When the shutter is activated, the mirror flips up and out of the way allowing an unobstructed light path to the
film. The motion of the mirror as it slaps to its up or clear position is quite abrupt and creates camera vibrations.
Camera motion can spoil the exposure…making the recorded image appear fuzzy or out of focus.
Mirror lockup is the ability to move the mirror to the up position before the shutter is activated…thus eliminating vibration. As I said, this feature is nice to have but not an absolute necessity. Absence of this feature can be side stepped by using the "hat trick." Prior to activating the shutter, cover the scope aperture with a hat or suitable shroud. Open the shutter and allow a few seconds for the vibrations to die…then remove the hat.
Interchangeable Focus Screens:
This is a very important feature, particularly if you plan to photograph very dim objects such as galaxies,
nebula and star clusters. Most cameras are equipped with matte focus screens…perfect for most terrestrial applications
and okay for bright objects (moon and bright planets) but very poor for dim celestial objects. While some stock
focus screens are better than others, the problem here is that the focusing screen effectively restricts light
to the user's eye. When dealing with very dim objects such as galaxies, the focusing screen could render the object
nearly invisible and impossible to focus.
A camera with interchangeable focus screens allows you to use that screen which is best suited for your application. Some screens (made for astrophotography) allow up to 400% more light to the user's eye, making the task of focusing much easier.
The above desirable features narrows the field considerably as only a hand full of cameras can boast of all these features. Certain models made by Nikon, Olympus, Lieca and Pentax have all above functions and other manufacturers such as Minolta, Yashica, Contex and Ricoh are missing one or two of the necessary camera functions.
Most of the candidates for the best astro camera were built and sold during the 70's and early 80's. Some were
built later and a few are still in production. The earlier models such as the Nikon F series and the Olympus OM
series, are widely recognized as the best cameras for astrophotography. In my opinion, the Olympus OM-1 and the
Nikon F (although often pricey) are among the best astro cameras. I prefer the OM-1, as it has all of the required
features and has the additional advantages of being very compact, readily available and reasonably priced.
A good specimen of the Olympus OM-1 (completely functional & cosmetically clean) sells for up to $250 on the used market…I have seen them sell for as little as $125. Often, a specimen with a non-functioning light meter will sell for less. If you plan to use your camera for astrophotography only, an OM-1 with a non-functioning light meter may prove to be a good buy. The light meter circuit is never used for astrophotography so you will not be sacrificing any important camera function.
Whether you buy an expensive Nikon HP or a $25, 40 year old Practica, get a camera to use with your telescope…it's fun and it's rewarding! There is no other telescope accessory available, which costs so little and delivers so much. No other device is capable of increasing the seeing power of your telescope to the extent that a camera can in the hands of a capable user.