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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
I think you missed a step, to take out the gradients induced by your optics. Generally this involves taking a frame of a uniformly lit white background and subtracting the gradient present in it from your other frames, dark and light. Then again analytic astrophotography may be different from artistic. Other sky gradients are best just avoided altogether(by not being near cities or other light pollution, or taking exposures during the right time of night).
Gradients can be removed by both taking "flat" frames as you stated (using your actual optical path) or by producing an artifical "flat" frame and then subtracting this out. There have been some pretty advanced programs developed that can synthesize artificial "flats." There are also light pollution filters which work pretty well which cut-off light at the various wavelengths that are common in lighting.
Vigilatny Registered Member #17
Joined: Thu Feb 02 2006, 02:47PM
Location: NL
Posts: 158
EastVoltResearch wrote ...
Gradients can be removed by both taking "flat" frames as you stated (using your actual optical path) or by producing an artifical "flat" frame and then subtracting this out. There have been some pretty advanced programs developed that can synthesize artificial "flats." There are also light pollution filters which work pretty well which cut-off light at the various wavelengths that are common in lighting.
As I suspected. I'm pretty sure such "fixes" would be unacceptable in many scientific situations. A better solution, at least from a measurement perspective would be to use a filter to isolate the wavelength you wish to measure(like H-alpha, etc.).
When you take a color picture do you just use the camera's color sensor? Or is there an option to turn that off, and use filters? The was the only part of color astrophotography that was tricky, calculating exposure times for each filter to make it look close to true to life.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
As I suspected. I'm pretty sure such "fixes" would be unacceptable in many scientific situations. A better solution, at least from a measurement perspective would be to use a filter to isolate the wavelength you wish to measure(like H-alpha, etc.).
Yes, i would agree. Fortunately, i'm not out to reproduce science and am more interested in inspiring others with these cool images.
wrote ...
When you take a color picture do you just use the camera's color sensor? Or is there an option to turn that off, and use filters? The was the only part of color astrophotography that was tricky, calculating exposure times for each filter to make it look close to true to life.
There is no option to take a monochrome image with a DSLR. The bayer matrix is built into the CMOS sensor and no way to separate it, although some have experimented with creating artificial LRGB channels using the RAW color filter array (CFA) information from the cameras.
Dedicated astro CCDs (i.e. SBIG) are still far superior, but the Canon DSLRs are a much more cost effective solution. Considering an almost full-frame Canon DSLR (modified) is about $1600.00 (Hutech modified) vs. a full-frame SBIG CCD (ST11000 series) which costs almost $15,000 once you factor in the filter wheel, etc...
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Astrophotography / Astronomy Photos
