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| equipment & techniques
Equipment
For most of the astrophotos taken before January 2001, I used the A-P refractor mounted on a Losmandy side-by-side plate with an A-P 80 mm, f11 guidescope, all on the Losmandy G-11 mount. Guiding is with an SBIG ST-4 guider via the guidescope. Since January 2001, all photos have been made using an A-P 1200GTO or A-P 900GTO mount. The G-11 had only one modification: adding handles to the clutch knobs (pictures here). The Losmandy knobs-with-handles seemed a bit pricey, so I drilled and tapped the knobs for 1/4-20 bolts (angled like the Losmandy handles) and used 1/4-20 bolts cut off to the right length as handles. (You can buy hex-head bolts with about 3/4 inches of thread and 2 inches of smooth shaft.) The handles on the dec axis clutch knob have to be the right length and angle to prevent them from hitting the RA drive motor. The extra torque from these handles makes a tremendous difference in stabilizing the head of the mount when it's not quite in balance. I like the Losmandy side-by-side plate for mounting two scopes separately and have used it regularly with the A-P refractor, placing the 80 mm f11 guide scope on the second plate. A few photos were taken with the Takahashi reflector, using the same guiding and mount arrangement. The RC scope is too large and the focal length too long to guide with the guide scope on the side plate, so for this scope I mount the guide scope on top of the main OTA to decrease flexure. I am currently experimenting with an OAG for guiding the RC scope. The A-P 1200 GTO mount is installed on the permanent pier in my observatory. I use the A-P 900 GTO for my portable mount. Both A-P mounts are beautiful pieces of machinery and works of art. The majority of the photos were made in Sonoma County, California, in a backyard observatory with a permanent pier (described in the Observatory link) at latitude +38° 34.7', longitude 122° 50.1' W. This site is moderately light-polluted, and I find that photos made without a light pollution filter get overexposed at 40 to 50 minutes at f4.5 or 6. With an IDAS (Tokai) light pollution filter Kodak E200 or Supra 400 film can tolerate exposures of 90 minutes (I haven't tried longer) without getting overexposed backgrounds. I have not yet quantitated the background fog density. I also have a handy home-made eyepiece holder on the pier. My cameras include a 35 mm Nikon FM2N and a Pentax II 6x7 medium format camera. I have just begun to use the Pentax and do not yet have a scanner capable of better than 1200 ppi on medium format film, so experience to date is very limited. Techniques Astrophotography (taken as both film and CCD imaging) can be uncomfortable, frustrating, and expensive. It has been compared to standing outdoors on a very cold night burning up 100 dollar bills. It doesn't always work that way, fortunately, and when a beautiful image comes out of the printer it all turns out to have been worthwhile. It does involve learning habits that go beyond the daylight snapshooter's bag of tricks. For emulsion (film) astrophotography, selecting the film can be the first problem. Not all films follow the reciprocity law when exposures extend into the many minutes or hours needed for faint astronomical objects. Furthermore, reciprocity failure may not be equal across the visible spectrum. As a result, some colors of an object may end up exaggerated or suppressed because of the inaccurate response of the film. The most important colors for astro imaging are the spectral emission lines indicated in bold in this table. All film is processed by a local processing specialist shop. These people use machines rather than dip and dunk processing but are knowledgeable and cooperative about the needs of astrophotographers. My general approach to working with the processed film starts with scanning of the 35 mm negative or slide with an HP PhotoSmart scanner (old model). I always scan at maximum resolution (2400 ppi) and avoid changing the automatic exposure settings unless the preview is excessively dark. Color balance usually automatically sets to neutral but if the HP is confused (more common with negative scans) I usually set it to neutral. Because of the lack of clear image boundaries on astro negative strips I often have to move the image selection box around to cover all of the negative. I then do a final scan into a directory named for the date of the photo session. I next read the file into Photoshop and do a preliminary examination with the Brightness/contrast sliders to see how much can be pulled out of the film image. If it looks promising, I use the Levels or Curves sliders to improve the color balance and contrast as much as possible without washing out highlights or increasing grain excessively. I try to avoid letting the sky go to jet black, following the advice of Jerry Lodrigus and Chuck Vaughn and try to keep it at a level of at least 20. I then write the file out as a tif file. If I have more than one image of the same object (the usual case), I then combine them in RegiStar (http://www.aurigaimaging.com/) using the Find stars, Register, and Combine procedures. I then write the output file (with a new name) into the appropriate dated directory. Back in Photoshop, I enlarge the image to 8x10 inches or more and examine it for flaws and grain. Airplanes and satellites get retouched out (if possible) using the cloning (rubberstamp) tool. Minor levels of grain are treated with Gaussian blur in Photoshop, using a 0.5 to 1 pixel setting. If the grain appears obnoxious, I try running the file through bigsmooth, Axel Mellinger's superb program for selective grain reduction that avoids degradation of stars http://canopus.physik.uni-potsdam.de/~axm/articles.html. See here for a sample of the results of a bigsmooth grain-reduction operation. Input and output from bigsmooth is in tif. Usually settings of 5 (radius) and 20 are adequate in bigsmooth. I then bring the file back into Photoshop for final adjustment of color, contrast, and size. If it looks acceptable, I run out an inkjet print. I try to save the original raw scan (at 2400 ppi) and the final 8x10 enlargement (at 300 ppi) files and sometimes, intermediate files as well. All this adds up to lots of megabytes on the hard disk and I periodically download each dated directory onto CD-ROM. I have a TDK veloCD CD-RW burner that writes CDs at 12x and out of more than 100 tries has not yet failed a single burn. Compared to my previous CD burner, that is amazing! I currently use an Epson Photo Ex inkjet printer. This printer produces near photo-quality prints up to 11 inches wide, so I can generate an 11x14 or 11x16 print if the image is really good. I use Kodak Glossy Photo Paper almost exclusively because it gives me the best final print quality, retains no "pizza wheel" impressions, and has the weight of heavy photo printing paper (52 lb). It has one major disadvantage, namely the black ink on prints remains tacky for several days after printing, so prints must not be stacked for at least that length of time. (Last updated 2001-07-30)
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