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equipment & techniques

A rotation gauge for positioning a CCD camera on an A-P holder.

Vanes for producing diffraction spikes with a refractor.

See Sources & Sensors  page for data on emission lines, films, and CCDs.

See work  page for tracking tests and work in progress.

Optical Imaging Equipment

(Listed in chronological order of purchase)

  • Meade LX200 Schmidt-Cassegrain 8 inch f10 and 90 mm ETX (old model)

  • Astro-Physics (A-P) Starfire EDF  refractor 130 mm f6
  • Takahashi Epsilon hyperbolic Newtonian 160 mm f3.3
  • RCOS  Ritchey-Chretien Cassegrain 12.5 inch f9
  • Nikon cameras and lenses
  • Pentax 67 II camera and lenses (sold July 2003)
  • Canon 10D digital 6.3 megapixel camera (purchased July 2003)
  • Canon 1D mark II 8.3 megapixel camera (purchased January 2005)

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 guide scope, all on the Losmandy G-11 mount. Guiding is with an SBIG ST-4 guider via the guide scope. 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 before I sold it: 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 guidescope on the side plate, so for this scope I use a Lumicon Newtonian-type OAG or with the built-in guide chip on the ST-10XME CCD camera. 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 emulsion 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 (purchased from Hutech)  Kodak E200 or Provia F400 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. I have not used negative film since Kodak discontinued the "old" Supra films and introduce newer types.

Cameras

My film cameras include a 35 mm Nikon FM2N (used exclusively for astroimaging) and one other Nikon (used primarily for terrestrial work).  My first CCD camera was a Meade 416 XTE, with the Meade 616 color wheel. I then added an SBIG ST-10XME camera and SBIG CFW-8A color filter wheel and have the Meade on hand as a backup camera. A  recent camera acquisition (February 2003)  was a Philips ToUcam 740 Pro webcam. This $80, egg-shaped device is made for sending pictures of yourself and your family to others over the Internet but it works very well as a moon and planetary imaging device. The newest items in this group are a pair of Canon digital cameras (see equipment list above). I  use these primarily for terrestrial work but have found them easy and convenient to use for star trails as well. I have noted great results with similar digital cameras on the web but have not found the software for using these one-shot color cameras as simple and easy to manage as that for monochrome CCD cameras. One of the major problems with the software is the lack of printed (hardcopy) manuals. 

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.

Film

For emulsion (film) astrophotography, selecting the film can be the first problem. Few, if any, 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 either 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. Because of this problem and the need for very long exposures, I switched almost entirely to CCD digital imaging in 2002.

All of my film is (more accurately, was) processed by a local processing specialist shop. These people use automated  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); more recently with a Polaroid SprintScan 35+. I always scan at maximum resolution (2400 or 2700 ppi) and avoid changing the automatic exposure settings unless the preview is excessively dark. Color balance usually automatically sets to neutral. I then do a final scan into a directory named for the date of the photo session. My experience with the Polaroid scanner suggests that more exposure control is useful with this machine than with the HP scanner. 

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 Lodriguss and Chuck Vaughn and try to keep it at a level of at least 15-20. 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 on screen 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 or the selective Gaussian blur noise reduction program,  SGBNR (http://www.pleiades-astrophoto.com/software/en.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 to 10 (radius) and 20 to 50 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 2400-2700 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 (2002) or DVD (2005). 

CCD

For CCD imaging I use MaxIm DL/CCD version 3.x (version 4.x as of 2005) for camera control and initial image processing. After more than two years of intermittent struggling with Meade software for  my Meade CCD camera, I gave up and switched to MaxIm. It is far superior! I also prefer MaxIm to CCDSoft (the SBIG software) for use with my ST-10, but that is because I'm already  familiar with MaxIm. Most imaging of dim objects is done with 5 minute exposures (5 or 7.5 minutes for blue) to avoid blooming of bright stars. Dark fields are collected during periods of repositioning of the scope and locating guide stars through the guidescope. Flats are generated with the T-shirt technique for the refractor and skyflats for the RC reflector. After a night of imaging, I download all the raw CCD files onto a CD disk and transfer them to my desktop computer for processing. Initial data reduction and compositing of averaged or median combined images for each color is usually done in MaxIm. I then equalize the backgrounds for each composite and create an RGB composite using the color combine facility in MaxIm. I then  write the files out in tif format. The tif files are then read into Photoshop and, if I have a luminosity image, combined using Layers. The separate layers are then adjusted as described above for film, with blurring (if any) applied to the RGB layer and sharpening to the L layer. The image is then flattened and saved as a tif (or JPG for the website) file. 

I began doing my own digital printing with an Epson Photo Ex inkjet printer. This printer produces near photo-quality prints up to 11 inches wide, so I could generate an 11x14 or 11x16 print if  the image was really good. I used Kodak Glossy Photo Paper almost exclusively because it gave me the best final print quality, retained 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. I obtained an Epson Photo Stylus 1280 in 2003 and this printer exceeds the quality of the Photo Ex. It allows me to make 13 inch wide prints and is faster than the older printer. I use Epson Premium Glossy Photo Paper with this printer. It has quality equal to that of the Kodak paper and dries faster. In 2004 I purchased an Epson 2200P printer. This printer uses pigment- rather than dye-based inks and provides for much greater longevity of the printed images. I currently use the 1280 for most of my proofing and the 2200 for final, display prints. I'm extremely satisfied with the color results from these printers. For terrestrial images, I still like the occasional black and white print and I find that the 2200 can produce very impressive B&W results with the appropriate handling. I plan to upgrade the 2200 to an Epson 2400 in the near future because of its even greater facility with B&W printing.

(Last updated 2005-11-11)

 

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