SKYSHOOTING COMETS - A CHALLENGE FOR ASTROPHOTOGRAPHERS IV By Chris Schur This is the fourth and final part in the series on skyshooting comets. There will be of course many more lectures on this subject, including the mathematics of offset tracking, special darkroom methods, and special cameras for comet work. In this lecture however, we will discuss actual films and optics to choose from to obtain the best results. It must be pointed out that these recommendations come from a variety of sources, including actual experience of many of our local club members. There may be some films in this lecture that might be difficult to get in your area. With time however, additional films will be tried and further recommendations will be made available. RECOMMENDED LENS/FILM COMBINATIONS FOR SOME TYPICAL CASES a) Faint Comets. A typical case would be the famous Comet Encke. With an orbital period of 3.3 years, this one will be back for skyshooters soon. Typically 9th magnitude and fainter, a 10" to 16" scope is recommended and a high resolution film such as 2414 or hypered Kokak Pro 400 is recommended. b) Average Comets. The infamous Comet Kohoutek will not be back in our lifetimes with an orbital period of 75,000 years. Its brightness was in the range of 6 - 8th and was easily seen in binoculars. For this type of comet, use a 200mm - 400mm telephoto lens of f/3.5 to f/6 focal ratio. Also, 6" to 16" of aperture will reveal fine details in the inner coma. 2415 film, T-Max 400 and Konika 400 is recommended. c) Bright Comets. The well observed Comet Halley was in this class. Ranging in brightness from 3rd to 5th magnitude, a much wider range of films and lenses could be employed. Here, and lens from a lowly 50mm to a 400mm telephoto could be used to an advantage. Focal ratios from f/2.8 to f/6.3 is recommended. As with average brightness comets, 6" to 16" of aperture will reveal inner knots, rays and other near nuclear phenomenon. Films such as 2415, Kodak and Fuji 400, TMax 400 is best. Slide films such as Kodak P1600 and Fujichrome 400 have been proven in the field to be superior to all others. For Schmidt camera users, 2415 and hypered Kokak Gold 100 is best. d) Brilliant Comets. Comets West, and Bennet, and Hyakutake will always be remembered as especially beautiful objects that could be seen in a dark sky without too much twilight interference. Brilliant comets are typically brighter than 2nd magnitude at their finest, and nearly any film or lens combination will work. 35mm wide angle to 200mm telephotos will allow you to keep all or most of the tail in the picture even with a speed as slow as f/6.3. 4" to 16" prime focus shots will reveal a wealth of details not seen in average comets. Even slow speeds such as f/8 will work fine here. Recommended films for best results are Fuji super G 400 with its low halation characteristics, Kodak 2415 for the furthest reaches of the tail, and Kodak Pro 400 ppf for the best overall shots. Schmidt cameras however rein king for this type of work. Kodak Gold 100 and 2415 is the only choice. e) Twilight comets. Comets Okazaki-Levy-Rudenko or Broresen- Metcalf come to mind here as recent examples. Buried in twilight, special methods were needed to extract them. 135mm to 400mm telephotos best, f/4 to f/11. Kodak 2415 with a wratten 29 filter will help here, also in the 4" - 16" scopes stop down to f/6 or f/8 to reduce twilight fog. Fuji 400 Super G Plus, Kodak Pro 400 ppf, and 2515 proved to be best here. f) Comets with anti-tails. The best example is Comets Arend- Roland in 1957, however a recent comet, Bradfield displayed a remarkably similar appendage. Short focal lengths such as 135mm - 400mm telephotos are best, and a fast f/2.8 to f/3.5 is needed. The ONLY film to use here which has sufficient contrast to record this very elusive phenomenon is Hypered Kodak 2415 and a 50cc Yellow filter. Schmidt cameras have again proven superiority in this field. g) Split Tail Comets. As mentioned in a previous lecture, Comets Halley and West exhibited dual tail structure each with a different color indicating the composition. But there are many comets that reveal subtle colorations in the regions near the front and center of the coma. One film comes to mind as being the best for accurate color renditions and good color saturation. The film is Kodak Pro 400ppf. We have also had good success with the Fuji 400 super G plus and Kodak Gold 100 films. CONCLUSION If you have a simple tracking mount, and some assorted short focus lenses for your 35mm camera, you will be all set for the bright comets which can occur several times per decade. With the addition of moderate to long telephotos, or a small Newtonian/Refractor a whole new world of comets, perhaps 2 - 3 per year opens up to you. And with a ten inch or larger aperture, dozens of objects per year are possible. Whether you choose to use fast film and short exposures at the expense of fine detail, or go for the high resolution tech pan (2415) and use offset tracking, skyshooting comets can be simple or as complex as you like. These celestial wanderers can be among the most beautiful objects in the sky if you own only a simple camera or an elaborate astrophotographic instrument. The challenges and rewards will be waiting for you.