Astrophotography - My Beginning

Location: Hannover/Germany - 9°46'e 52°22'n
Date: 29.12.2001 - ~20:00

I used my Sigma 600mm mirror lens on my Manfrotto 055 tripod, pictures were taken with my Canon T90 on Fuji Sensia 100. I scanned the slides on my Olympus ES-10 and performed image processing with Photoshop.

Finding a correct exposure is quite easy: The moon is an object illuminated by the sun so the good old "sunny 16" rule can be applied when the sky is clear. f16 at ISO100 with 1/100s exposure time should give a correct exposure. The fixed f8 of my lens (effictive aperature should be around f10) gives a shutter speed of about 1/250s. The results proof that assumption for fullmoon when skies are clear. I would even underexpose the fullmoon next time one step(1/500s) to get better scanable slides and to minimize tripod shake effects.

Location: Paderborn/Germany - 8°45'e 51°42'n
Date: 03.01.2002 - ~7:00

Problems

• Seeing
  Without knowing any better I took the images from an open window. Warm air emerging from the room into the winter night caused an blurred and wobbling vision resulting in unsharp images with lack of contrast and distortions.
  The overall seeing might have been suboptimal as well.
• Focussing
  Accurate focussing on the matte std focussing screen of the T90 is quite a guess. Split image and microprism ring doesn't help much either. The focussing screen is too course grained to resolve the fine structures of the moon surface which isn't too contrasty.
• Camera/tripod shake
  600mm focal length is a challenge for a photo tripod. The Manfrotto 055 is quite sturdy but at 600mm extreme caution is necessary in order to get sharp images. It's a good idea to use a cable release or the self timer of the camera. In most cases mirror pre-lock is more a hype but for this application it's worth a try. I will use my Canon EF with mirror pre-lock next time.
• Resolution of
  • Film
    Even with 600mm focal length, the full moon covers only a smaller area on the slide/negative. The diameter of the moon on the film calculates like:
    
    I can measure exactly that value on the slides. With that diameter, the moon disk covers only 23,76 square mm on the slide - only about 2,75% of the complete frame of 35mm film. On this small area, even the fine grain of modern ISO100 slide films affects image quality.
  • Scanner
    The resolution & scan quality of the Olympus ES-10 is not sufficient to project all details of the slides especially on that small film area of interest.
• Dynamic range of scanner
  The Olympus ES-10 has been a film scanner targeting the home user. It should be out of production for some time. The dynamic range and color resolution it's able to capture is quite limited. As a consequence, fine shaded areas in the slide result in flat colored squats in the scan without texture.

Digital image processing

• Scanning
  Images have been scanned at max. scanner resolution of 1770 dpi.
• Channel alignment
  The green channel of the scanner has a noticable shift of 4-6 pixels compared to the red and blue channels at max. resolution.
• Level adjustment
  To get better contrast an adjustment of the brightness levels (range compression) has been made.
• Resize & cropping
  The images have been cropped to the areas of interest and resampled to 25% of the scan resolution.
• Unsharp mask
  To enhance structures on the moon surface, heavy filtering using "unsharp mask" has been performed. As a result the very flat detail contrast is enhanced but also the edge of the moon to background gets an unnatural "burned out" effect and the moon surface gets quite grainy.