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Old 23-05-2012, 11:27 AM
swannies1983 (Dan)
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swannies1983 is offline
Join Date: May 2006
Location: Adelaide
Posts: 781
Image scale: barlows/powermates and extension tubes

I'm sure this has been asked but I couldn't find anything when doing a search. When it comes to planetary imaging, is there any difference in stacking barlows/powermates versus using a powermate/barlow + extension tube?

Also, I have a 2x powermate and an old 2x barlow. The glass in the barlow isn't the best so I have taken it out and have been using the tube as an extension tube. The overall length of the tube isn't that long (~50mm). This increases the image scale but how do I know how much by? Is there a formula to calculate the increase in image scale based on the length of extension tube? I would like to know how long an extension tube I need to increase image scale to ~4x when used in combination with my 2x powermate.
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