Saturday, February 20, 2016

Common Questions About Analog Astronomical Photography

As a photographer who works with film, I often get inquiries on various social media as to how the images are done. This is especially true of my long exposure images. The most common questions have to do with exposure, equipment used, and how do I get those stars to be pinpoints if the exposures are an hour or more.  This blog post is my answer and I will link those that ask to it.

Astrophotography used to be the domain of amateur astronomers; astronomers did astrophotography. With the advent of the digital workflow, photographers have entered the domain, at least with what can now be done with a fixed tripod and camera arrangement. Professionals especially are well suited to produce excellent results with digital cameras. They have the resources at hand and workflow experience in post processing to best the work of what the astrophotographers of old used to struggle to accomplish with film.

Enter film based astrophotography. This is how it was done just fifteen to twenty years ago. There was really only one way to capture Milky Way vistas - with film.

The Sagittarius Milky Way Pentax 67 with 400mm SMC Takumar - Superia 100

One dispute over many professionals is experience. They are not astronomers, but many are bright enough to pick up on the basics of how the sky works. Some are truly gifted sky enthusiasts and as such produce superior work.

Personally, I do not recommend those just starting out with their interest in capturing the night sky photographically to use film. Digital is faster, easier, and encourages beginners to continue their efforts. Film based work can be unforgiving. I've tutored a few individuals who attempted it and were discouraged right from the beginning. There is so much that can go wrong.

So why film? I use film simply because it is what I have always used since I learned the craft in the early 1980's. In 2007, instead of switching to digital, I stepped up to medium format film. In 2016 I am still using film, although I have done some digital work. My other reasons for using film are aesthetics, continuity with traditions started by early astrophotographers such as E.E. Barnard, Max Wolf, and more recently, David Malin, to name but a few.

The nigh sky view from the observatory
Successive images overlapped to show fields captured with 400mm Takumar

For me this is an avocation and I can please myself with what I do, such as there still people who paint or sketch. When I perform my best work, I get great remarks but they are often mystified by my use of film despite my doing well with it. This seems to be the default nature of modern photographers. It prompts the question as to why? This also presupposes that there is no advantage to film, only disadvantages. But this simply is not true.

The Milky Way of Taurus and Perseus

Bright and dark nebulae populate this wintertime target

Pentax 67 105mm f/2.4 @ F/4 Kodak E200 - 1 Hour Exposure

Film images exist. I can show them to you. They are not virtual images or a representation of a kind. Original images exist in tangible form. They are imperfect, and they are vulnerable to the years following development.  Done properly, noise is never an issue in long exposure work with film.  Color films such as Kodak E200 deliver high fidelity red sensitive portraiture of the night skies.  Most digital cameras, DSLR's namely, need to be modified for extended red sensitivity.  Finally, rendition.  The look of film is unique.


The crux of this essay is to convey just how it's done. Analog astrophotography requires patience, years of practice, and perseverance before anything else. Good cameras, the proper films, and a way to share them in online communities are also required. The act of the image taking process itself is a sort of art.

The basics:

Access to dark skies away from city lights, good weather, and no Moon dictates where and when to do the exposures.

A properly aligned equatorial mount with provisions to compensate for the Earth's rotation is also a requirement. This may be the hardest part for many. I use a permanently mounted fork mounted telescope permanently aligned with the celestial pole. The celestial pole is the point in the sky where the Earth's axis point towards. Aligning the polar axis to this point allows the equatorial mount to work in parallel with the Earth's own polar axis. Alignment to within a few arc-seconds will allow extended tracking without trailing of star images during the exposure.

Heavy lifter!
Pentax 67 and 400mm SMC Takumar Riding Piggyback an 8" SC Telescope

A second part of this tracking mount is the clock drive. It's job is to rotate the polar axis counter to the Earth's rotation. It also needs to be accurate. Being a mechanical worm gear with a period of rotation of its own brings forth periodic error. No gear is perfect compared to the precision of the Earth's rotation, so we also need to correct this as time goes by. To do this we incorporate a drive corrector. The drive corrector allows the photographer to monitor a guide star as a reference to the Earth's rotation and manually correct via a small hand controller to speed up or slow down the clock drive when appropriate. This is called guiding.

The Small Sagittarius Star Cloud -Messier 24 Region
Pentax 67 400mm SMC Takumar @ f/5.6 Fuji Acros 100 1 hour Exposure

One can employ a small CCD camera in place of the guiding eyepiece to monitor the guide star and do the corrections automatically. This is called an auto-guider. It does the labor of constantly correcting the drive as needed. I do not use one, as I monitor the guide star (through the telescope the cameras are attached to) and correct manually. This is tedious work. Discouraged already?

A session goes like this:

At dusk, the camera is loaded with film (if not already) and mounting shoe to attach to the telescope is mounted to the 1/4-20 threaded tripod socket on the camera body, or telephoto lens mounting plate.

The telescope is exposed to the sky as the roof is rolled back at the observatory. Optics are checked, guiding eyepiece is installed and prepared to receive the camera.

The Piggyback mounted Pentax 67 with 165 f/2.8

The mount is made by Losmandy

The camera is mounted atop the telescope (this is called piggyback mounting) and locked into position at the proper balance point of the arrangement.

An area of the sky is selected for exposure. This involves lens selection for framing of a particular field. Lenses routinely used for this range from 105mm to 400mm focal length for the Pentax 6x7.

Once the field to photograph is established and the telescope is locked in place, a suitable guide star is centered into the double cross-hair eyepiece. This eyepiece is of the proper magnification to offer guiding corrections less than 10 arc-seconds. The star is centered at the same time the camera shutter is ready to be opened. Focus on all my Pentax 67 lenses are set at infinity stop as this seems to be true infinity. Lenses are stopped down to usually f/4.8 or f/5.6 for fully illuminated fields.

The exposure begins...................... The guide star is monitored and hand corrected for accurate guiding during the exposure. This can range from a short exposure of twenty minutes, to long exposures of an hour or more. Ninety minutes is the longest I've used in practice. One hour is typical.

In the Observatory with setup for a nights session of film based astrophotography!

Once the exposure is done, the shutter is closed and next frame advanced if another exposure is to be taken that night.

During exposure the sky needs to be scanned visually to make sure aircraft do not enter the photographic field. Gently capping the lens while the aircraft (or satellite) passes by, then removed to resume exposure. I've often capped the lens for five to seven minutes on a one hour exposure during busy aircraft times.

Wind. A windy night prevents most work from being done with longer lenses. Wider angle lenses can usually be employed with such conditions.

Dew. Nighttime moisture tends to build up on optics and this needs to be prevented or the lenses will fog up, causing stars to have halos. A small hair dryer works well. Gently “spray” the lens with the warm stream of air every 10 minutes on moist nights. Heating tapes can be purchased for such use as well. I use a hair dryer.

Developing films. Color and B&W films can be processed normally or push processed to bring out faint details. Only two currently produced films work well for astrophotography, Fuji Acros and Fuji Provia 100F. Legacy films such as Ektachrome 200, Superia 100, and Fuji 400F work great!

The Milky Way of Southern Ophiuchus
Fuji Acros 100 Produces fine astrophotographic images.
Pentax 67 400mm @ f/5.6 Fifty-Minutes Exposure

A scanning workflow is best done at home. With experience, more details and tonality can be elicited from your films. Post processing in Photoshop and astrophotographic softwares is of great benefit to film images.  Transparencies and negatives contain much more information than you might expect. Film has the added benefit of having less noise than digital captured sub-frames, so detail is high given proper exposure and proper guiding under ideal conditions.

Film based astrophotography has been a rewarding pastime. I've enjoyed the long hours under the starry dome, slowly building up photons on photographic films.  If anything, it has been a meditative process. Slowing down and doing it the old fashioned way, it is still a great way to capturing the heavens.

Flanders Pond Observatory

A shelter and a permanent setup  makes it all possible.  

More images at my Flickr site.  You can monitor my efforts, both film and digital on my Facebook page.  Twitter fans can find me on my Twitter feed.