Using the Schmidt
The 12-inch camera Jason uses is a true Schmidt design like the famous 48-inch Schmidt on Palomar Mountain in California. The camera possesses a focal length of 670 millimeters and operates at f/2.2. This produces a 4.5° by 5.5° field of view on a 6 by 7-centimeter negative using 120 format film. The camera uses single exposure film “chips” that must be individually loaded into the camera’s film holder. The holder is then magnetically mounted at the camera’s focus through a door which opens on the side of the tube.
Being a true Schmidt, the primary mirror is larger than the corrector plate, spanning 16 inches to the corrector’s 12 inches. This gives the camera a distinctive step-tube appearance in contrast to the straight tube of the classic Celestron/Epoch Schmidt which uses an equal-sized corrector and mirror. The corrector is smaller by design to eliminate vignetting of the extremely wide field. Since the corrector must be mounted twice the instrument’s focal length from the mirror, the 12-inch Schmidt is a long instrument compared to a regular Schmidt-Cassegrain telescope.
The huge Schmidt is carried on an equatorially aligned Meade 16-inch SCT LX-200 fork mount that is more than adequate for the camera and its refractor guidescope. Although the camera normally comes with a 7-inch guidescope and CCD autoguider, Jason deliberately chose to use a smaller 5-inch f/9 guidescope so it could be mounted off-axis in adjustable Losmandy rings. This allows him to center comets in the Schmidt’s field of view while guiding on the nucleus. He has recently added a larger, stiffer set of rings that enables using filters during long exposures.
To locate his target fields, Jason uses a transparent template which he lays over the pages of the Uranometria 2000.0 star atlas. Because the magnetically mounted Schmidt film holder can be rotated to any framing angle, multiple objects can be oriented as needed within the field.
Once the Schmidt is properly aimed at the desired celestial coordinates, an easy task with the LX-200 controls, the camera’s large size often makes it awkward to reach the film loading door. To make it easier to install the film holder, the Schmidt’s controls have been modified to include the “load” command. When invoked, this command will slew the camera from the desired direction to a position where the film loading door on the side of the tube is easily reached. Once the film is loaded, the controls automatically reposition the camera’s aim on the original celestial coordinates.
Stray light, even from feeble LED displays, can noticeably fog today’s high-speed color emulsions. The film is most prone to fogging while loading the camera’s film holder. Jason performs this operation in a light tight-box on one wall of his observatory, but he has found that circumstances can still conspire to fog the film unless precautions are taken. Black tape is used to cover the LEDs on the telescope mount while other illuminated devices such as the music CD player, battery charger, and autoguider controls are covered. Jason even changes into all-black clothing to prevent stray light from reflecting off himself and onto the film holder while he is handling it. The latter results in a scene reminiscent of “Ninja Astronomer,” but Jason’s end results justify his efforts.
Humidity more than stray light is actually the film’s chief enemy. Because the 120-format film used in the 12-inch Schmidt has such a large surface area, it can actually swell and buckle if it absorbs moisture from the air during the exposure. This will ruin the critical focus achieved by the Schmidt mirror optics. To combat the humidity problem, Jason uses the same trick I popularized 10 years ago with my Schmidt camera; he floods the interior of the camera with a continuous slow flow of dry nitrogen gas. To stabilize the film before use, Jason bathes the emulsion in the same atmosphere it will encounter inside the camera and even purges the film-loading dark box with nitrogen. This will prevent moisture from warm hands from degrading the hypersensitized film emulsion.
A number of different films are used in the Schmidt, including Kodak’s Ektar 25, PPF 400, Technical Pan, and Fuji 400. Jason hypers his own film using an Edmund micron-range vacuum pump, a homemade hypering chamber heated with a modified Radio Shack temperature alarm, and 8 percent forming gas. He vacuums color film for 30 minutes before hypering while black and white receives 60 minutes of vacuum, followed by three-PSI forming gas at 48° Centigrade. His hypering times for Kodak PPF and Ektar 25 are 3 and 12 hours, respectively.
Image enhancement technique
The real secret of Jason Ware’s astrophoto success is in the stack and copy technique to enhance the images. In this process, Jason actually shoots three identical images of each target. The two best exposures are then selected for negative stacking. For this process, each image is exposed to a point just short of where sky fog begins to show on the negative. With Jason’s current film of choice for the Schmidt, 120-format Ektar 25 (which he laments will soon be discontinued by Kodak), the exposure is 17 minutes. Each exposure is not as dense as a single negative can be, but without the degrading sky fog, two shorter exposures stacked atop each other have a higher combined contrast than a longer, single sky-fogged exposure.
Exposing the initial negatives in the Schmidt camera is actually the easy, relaxing part of the astrophotographic process that Ware employs. The time-consuming work really begins in the darkroom where he estimates it takes about six hours and twenty dollars worth of copying materials to go through the steps that produce a final enhanced high contrast printing internegative. But once these steps are complete, the image can easily be printed again and again from the final internegative. Jason uses all-Kodak darkroom materials, finishing the process by printing on Ultra color enlarging paper.
Through the use of fine-grained large-format film, Ware can obtain the high-resolution wide-field celestial views he desires. Jason explains that digitally enhancing the contrast of a single negative with his Photoshop computer program enhances grain, while stacking two negatives in the enlarger tends to cancel grain. He admits that digital enhancement techniques can achieve a similar level of detail with perhaps better contrast and saturation than chemical darkroom techniques, but the digital requirements for medium format have mostly deterred him from using electronic techniques. Scanning, processing, and outputting detailed medium-format images require an enormous amount of computer memory and cost.
By judiciously shopping the used equipment market, Ware has assembled an advanced professional-quality color darkroom at a very modest expense. His secret is patience in waiting for the bargains to appear instead of buying equipment at full retail price. He thus enjoys the use of items such as an automated Jobo film processor and color negative densitometer that are not normally found in darkrooms.
Today, film astrophotography is almost exclusively the domain of the amateur astronomer since the professional astronomer relies mainly on electronic data gathering. In fact, the best amateurs produce better celestial images than the professionals, given equal equipment. The exceptional images produced by astrophotographers such as Jason Ware prove that, in spite of the declarations of CCD aficionados, film is not dead in astronomy.
The observatory roof slowly rolled back, flooding the formerly dark room with sunlight. As my eyes adjusted to the sudden brightness, the gleaming white Meade 12-inch Schmidt camera seemed to awaken and beckon for a loving touch. As I ran my hand over its cannon-like barrel, I couldn’t help but reflect on the maturing of amateur astrophotography over the four decades that I have practiced this art. The amateur can now routinely operate powerful large-aperture Schmidt cameras, once only the realm of professional astronomy, and produce exquisitely detailed wide-field celestial images that rival those from professional instruments.
One person who routinely does such astrophotography is Jason Ware. He operates a 12-inch Schmidt camera from his Wild Duck Observatory, located a 90-minute drive north of his Dallas, Texas, home. From this 12 by 12-foot observatory, Jason enjoys 6th-magnitude skies while imaging not only the showcase objects and faint targets, but also wide-field groups of objects, making high-resolution images suitable for framing.
At age 37, Ware is a youngster in the field of advanced astrophotography where practitioners are typically older. Jason considers it an honor to use the large Schmidt. Noted mainly for his astrophotography, Jason is also an avid visual observer, having earned his Messier and Herschel certificates. But in astrophotography, where beginners are ecstatic to achieve any image at all, Ware has become such a perfectionist that he considers each of his twice-monthly photo sessions a success if he achieves only one publication-quality image. On average, he actually obtains three completely successful images per trip.
I have used a smaller 8-inch Schmidt camera for the past 20 years and was eager to get my hands on the larger 12-inch camera. I was thus delighted to accept an invitation by Jason to accompany him to his observatory for an evening with the optical marvel. I was equally anxious to see how he processes his exceptional images, because unlike many of today’s skyshooters, Ware does not digitally enhance his celestial pictures. Although he has recently started doing some digital imaging, most of Jason’s work is prepared entirely the old-fashioned way, in a photographic darkroom.
