Last updated on
4/11/2006

You are visitor number

 

A 35mm camera with film is the classic method used by amateur astrophotographers.  You can attach a 35mm camera body (without the lens) to your scope with an adapter, essentially using the scope as the camera�s primary lens. This is called prime-focus photography.

This method takes a lot of perseverance because a telescope, as a camera lens, is not very fast optically (usually an f/10 telephoto lens for Schmidt-Cassegrains or f/15 for Maksutofs) while most astral objects other than the moon, Jupiter, Saturn, or the sun are very faint. So you�re looking at very long exposures, typically 30 minutes or more, and you will need to delve into specialized techniques in treating the film (hypersensitizing) if you want to shoot many deep-sky objects.  (Hypersensitized film is treated in a bath of [mostly] nitrogen gas that reduces reciprocity failure - film�s tendency to not accumulate any more light after a certain period of time.) You also will need to manually correct the scope�s alignment during this length of exposure time, since very few (if any) commercially available mounts can track so well that they hold an object stationary for that long a time.  Get ready to watch the object and guide the scope for a half-hour or more, a process that re -defines the meaning of the word tedious.  In fact, many astrophotographers using 35mm film purchase a small CCD camera and connect it to the scope�s drive electronics to use it as an autoguider.  It can automatically correct the scope�s drive to keep a star stationary, and this is an easy (albeit not particularly inexpensive) setup to do with most GoTo SCTs.

Nevertheless, despite the technical hurdles posed by deep-sky photography on film many of the best astrophotographers use 35mm (or even larger-format) film because they believe the printed image from a film negative produces the finest result. The basis for this view is that a 35mm negative acquires far more information that today�s digital CCD chips can acquire.  (You would need a 10 megapixel CCD chip to equal a 35mm negative, although the bad news for film is that a fine-grained 35mm film has a much lower sensitivity to light than a CCD chip.) The difficulties associated with using film with a scope should motivate you to appreciate even more, the images some folks have produced this way.

Should you decide to use a 35mm camera with your scope, there is one major issue to be aware of: you need a single-lens-reflex (SLR) camera (where you see through the lens when you look through the camera�s viewfinder), and it actually needs to be an older camera. Newer SLR cameras use the camera�s battery to hold the shutter open during the 30 to 45 minutes of the exposure. This drains the battery, after which you can�t take any more pictures (or worse, the shutter snaps shut most of the way through a long exposure). In this case, automation and progress is a real problem.  Older SLR cameras didn�t use the battery to hold the shutter open - for long exposures with them the shutter is held open by using a cable release that can be locked to keep the shutter release button depressed. However, some folks have found a way to replace the battery in a newer SLR with a piece of wood dowel, at each end of which is fastened a wire that leads out of the battery compartment and into a larger-capacity battery with the correct voltage. The larger battery will hold the shutter open a lot longer.

If you only want to shoot the sun or the moon, long exposures aren�t needed and any SLR camera will work (although being able to lock the mirror up is an uncommom SLR feature but a major vibration-reduction advantage leading to better focus).  You just need a T-adapter (made by Celestron, Meade, Orion, or other vendors) and a T-ring to fit your camera.  Note that not all SLR cameras have a T-ring adaper available*. 

The most popular 35mm camera for this type of astrophotography is the Olympus OM line of SLRs - they do not use battery power to keep the shutter open during long exposures and they are very light-weight compared to most SLRs, which is an advantage when you work on balancing a fork- mounted scope with the camera attached. Used OM camera bodies are readily available and the older versions such as the OM-1, are not very expensive.  However, there are two accessories for these cameras that are commonly used by astrophotographers.  The first is to replace the standard split-image focusing screen with a plain matte screen .  This is because the standard split-image focusing screen requires a lot of light to work; for terrestrial use plenty of light is available but for astrophotography most photo subjects are too dim to illuminate the split image - a plain matte screen works better. (Not all older SLRs are set up to allow changing the focusing screen but it can be easily changed in the Olympus OM series.) The second accessory has to do with the camera�s viewfinder. When a 35mm camera is attached to your scope and the scope is aimed upwards, it�s rather inconvenient to sit on the ground and try to look through the camera�s viewfinder to focus the camera.  Some SLRs have an accessory �right-angle� viewfinder available - this accessory clips onto the camera�s viewfinder and has a right-angle prism in it that allows to sit in a comfortable position and still see through the viewfinder.  For Olympus OM cameras, this accessory is the Olympus �Varimagni� which is expensive (around $150 if new) but it has quality optics and does also include a magnifying lens that you can use to achieve more precise focus.  Used Varimagni�s do show up on Astromart occasionally but they are snapped up very quickly. Another right-angle finder option for OM cameras was actually made by Pentax - astrophotographers say that the Pentax Refconverter fits on an OM viewfinder as long as you get the M or A version of the Refconverter. These also show up in the used camera accessory market; they are less expensive than the Varimagni but they are no longer manufactured so they are more difficult to find (Olympus does still manufacture the Varimagni).

You can also use a 35mm film camera with a telescope eyepiece in what is called eyepiece- projection photography, using an adapter made for this purpose. The ScopeTronix adapter discussed on the Scopetronix Threaded Adapter page works for this.  I note on that page that the number of eyepieces that will fit in such adapters is somewhat limited, but using an eyepiece will allow you to fit a wider size range of objects onto the 35mm film.  To get proper exposures you will need to know the effective focal ratio (f-ratio) of your eyepiece-projection system. See the F-Ratio for Eyepiece Projection Photography page for the formulas to calculate the effective f-ratio.

If you want to try 35mm film astrophotography I strongly recommend that you purchase Michael Covington�s book or Robert Reeves� book (see the Photo Basics page) to get started. Note that Robert Reeves also has a Web site that lists the results of his tests of many 35mm films for their suitability for astrophotography.  Go to Robert Reeves Celestial Photography and click on the �Testing Films for Astrophotoghraphy� link (these results are the ones described in his book). For astrophotography I also recommend that you get a flip-mirror to help center and focus the image - proper focus is CRITICAL!

A good source for film-photography equipment and accessories is B&H Photo.  They maintain a very large inventory of hard-to-find accessories, so their prices are not the very lowest around, but they are reputable, helpful, and fill orders quickly.  A vendor with the very opposite business model is Smile Photo, who will tell you an item is in stock when it is not, and then keep you on hold for long periods of time when you try to call and find out why you haven�t received what you ordered - caveat emptor.

Should you wish to digitize your 35mm photos (for example, to e-mail them to your friends), there is a film scanner on the market that sells for less than most. Pacific Image Electronics has a Prime Film 1800 film scanner that scans negatives or slides at 1800 dots per inch (dpi), connects to your USB port, and sells on the street for a little less than $200 (their Web site includes links to mail-order vendors).  It works well although it is wise for you to calibrate it for the film you use.  The resolution is not as high as the 2400 dpi film scanners on the market, but its price is much less than those scanners.  But make sure you download the latest driver for the 1800 from their Web site. __________________________________________________________________________

* Typically, T-rings are available for the following SLR mounts: Canon manual-focus (FD), Canon autofocus (EOS), Minolta MC/MD bayonet, Minolta Maxxum bayonet, Nikon, Olympus, Pentax screw mount, and Pentax bayonet mount.  If you own an older camera with a thread mount, it might accept the Pentax thread mount T-ring.  If you have a new camera with a bayonet mount not listed above (Ricoh, Cosina, etc.), it most likely accepts the Pentax bayonet mount T-ring.  Your camera�s instruction manual may have more detailed information.
__________________________________________________________________________

Note that you can shoot wide-angle photos of constellations and the Milky way simply by mounting a 35mm camera on top of a scope, using the scope to guide the camera.  (For longer exposures, to avoid star trails the scope will need to be mounted on an equatorial wedge.) This requires a �piggy-back mount� that screws to the top of the rear cell of your scope and holds the camera. Celestron and Meade both sell these for their respective SCTs; Celestron�s is $35 and Meade�s (shown here on the right holding a camera) is $39 for an 8� SCT and higher for their larger SCTs.

Note that mounting a camera atop your scope will require that you add weight below the scope to retain balance. See the Balancing an SCT page for more information on this.
 

Back to Astrophotography Basics
 

___________________________________________________________________________________