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Old unused 1.25" barlows/extension tubes
I'm getting into some saturn imaging with my 8" f/6 newt plus unmodded toucam. I do have a 1.25" 2x Televue barlow and another older 2x barlow, allowing me to image at f24 (assuming that's correct?) I had some good seeing last night (despite the predictions of skippy weather) and I probably could push my image scale even higher if the conditions are right. Anyone have any unused 1.25" extension tubes or old barlows with damaged glass that I could take out and use the tube as an extension tube?
NOTE: how do I calculate what length extension tube gives me what f-ratio? Say I use the 2x Televue giving me a f-ratio of f/12, what extension length is required to increase it to f/30?
Last edited by swannies1983; 11-05-2012 at 11:36 AM.
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