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Everything posted by bendavidson

  1. This was so useful - been using the Celestron 6.3 focal recucer for a year and disappointed it only increased my FoV on the 9.25" SCT from about 20' to 30'. I didn't realise you positioned it BEFORE the visual back!! Looking forward to getting more like the 80' mentioned above and not having to splash out (yet) on the Hyperstar... Thanks! Ben
  2. What a brilliant beginner's guide - thank you so much Ian. A couple of questions re the pixel scale calculations. I have a Canon EOS 700d, similar to the one you used as an example here. Your EOS 500d has 15.5 megapixels (15.1 effective megapixels) and a chip size of 22.3 x 14.9mm. That's a chip size of 22,300µm x 14,900µm = 332,270,000µm2, divided by 15,500,000 pixels, comes to 21.44µm2 per pixel (or 22µm2 per pixel if you're only counting the effective ones). Yet you say the chip's pixels are 4.7µm2. 1/ Your number looks like the square root of mine. Is that right and, if so, why? 2/ Also if so, how come you are using the effective number of pixels rather than the total number? Thanks in anticipation. Ben
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