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I am looking for a Barlow lens for my 76/700mm reflector to use for lunar and planetary imaging. Now, I know that this probably isn’t the best scope for the purpose but it’s a present from my wife and has some sentimental value. So please bear with me  I have a cheap 2x lens that came with the scope but it’s rubbish. I realize that a 3“ mirror has limitations in resolution so I am wondering which is the most reasonable Barlow to buy: 1.5x, 2x or 3x magnification? Without Barlow I am 1 arcsec/px scale on my camera. Thanks a lot for any tips! |
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Hi Jesco, I get what your saying about the 3" scope. Given that it's an F/9.2 it is probably of medium to low quality, but you can still have some real fun with it if you stay within its limits. At best you can get about 50x magnification per inch of aperture up to an atmospheric limit of about 400x (varies a lot). Most nights you will be limited to ~2 arcSec/pix, which if you do the math will lead to the same place. So your looking at about 150x as your maximum useful magnification. The magnification will be approximately 700*B/D where B is the Barlow factor and D is the diagonal of your imager's FPA. The same magnification limit applies if your use an afocal setup (scope with eyepiece, more complicated, probably not useful here due to the magnification limit). Hope this helps. Clear skies, Tim |
