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roughplanet wrote: Firstly, let me say that although I have read many books on astrophotography, I am a rank amateur in terms of experience. From what I have read (and it is, I suspect, common sense anyway), most astro photographs, or at least many, are shot with the lens wide open. But almost all lenses are sharpest in the middle of their f-stop range, and something I knew nothing about until recently; 'bokeh' or background blur, is prevalent (and in fact, desirable in portrait photos) in lenses with larger apertures. So which lenses are the most suitable for astrophotography, given the above, as obviously the uncorrected aberrations & bokeh present in (say) f1.4 50mm or f2.8 135mm lenses would be quite undesirable for astrophotography. Thanks in anticipation of your help. "Robb Spring" wrote in message ... Bokeh is best seen in a catadioptic lens. (the "cheap" 500mm lenses, on ebay, that look like mak-cassagrain telescopes). This is because the lens has a fixed focal ratio, usually F8, and a factor of the mirror design, I believe. With normal camera lenses, say an F1.4 50mm (a good overall lens), the image will have problems around the edges of the photo, at 1.4 Fstop. Im not certain why, I have read about it, but not experienced. (I am learning astrophotography, too.) You compensate by setting to F4 or F5.6, and increasing exposure length. The 135mm will work too, but you will likely have to increase to similar aperature settings. Best overall webpage I found, for astrophotography, is the following: http://www.darkskyimages.com/ The following page, is good, as well. http://www.geocities.com/CapeCanaveral/Lab/6529/ Finally, read the following document at kodak's webpage. http://www.kodak.com/global/en/consu...Contents.shtml God bless, -Robb Thanks for the web sites. All of them have quite a lot to offer, and have saved me wading through dozens of others. Google can be such a pain nowadays, with 100's of sites for even the simplest ask. What we need is a 'Condensed Google'; something similar to the Readers' Digest's Condensed Novels :-). Laurie |
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