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Photography, Digiscoping & Art
The Birdforum Digiscoping Forum
Photography using 'Astro' telescopes
Comparison of teleconverters & barlows
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<blockquote data-quote="David Ellsworth" data-source="post: 1850730" data-attributes="member: 40206"><p>As I understand it, moving the camera farther from a barlow or TC will result in more magnification. I'm rather foggy on whether anything else changes, and I'm not sure how to interpret your explanation as to answer my question of whether the corners are sharper because of the extra "cropping/zooming" or if it is an unrelated effect. (I would experiment myself, but I have no barlows yet, and I don't have any DSLR extension tubes so it would be really hard to experiment with a teleconverter and increase TC-to-camera distance while keeping a parallel focal plane.)</p><p></p><p>So, either for the sake of argument (a thought experiment) or as an experiment to try for real:</p><p></p><p>* Take a photo at minimal camera-to-barlow distance, and call this Photo A.</p><p>* Take a photo with some extra distance between camera and barlow, keeping all else equal, and call this Photo B.</p><p></p><p>Now, crop Photo A to match the magnification of Photo B; call this Photo A'. Downsize Photo B to match the magnification of Photo A and call this Photo B'. If necessary, sharpen Photo A' a little more than Photo B, to compensate for the extra effect of the camera's anti-aliasing filter in Photo A (or the reduced effect of the AA filter in Photo B, depending on how you look at it).</p><p></p><p>How does Photo A' compare to Photo B'? Does Photo B' have sharper corners?</p><p></p><p></p><p>Here is a test done a while back in which the Televue Powermate seems to lose by a huge margin: <a href="http://photo4fun.zenfolio.com/p231550804" target="_blank">http://photo4fun.zenfolio.com/p231550804</a></p><p></p><p>Would the Powermate do a lot better with extra camera-to-barlow distance? And would those astigmatic corners be improved without being completely "cropped/zoomed" away?</p></blockquote><p></p>
[QUOTE="David Ellsworth, post: 1850730, member: 40206"] As I understand it, moving the camera farther from a barlow or TC will result in more magnification. I'm rather foggy on whether anything else changes, and I'm not sure how to interpret your explanation as to answer my question of whether the corners are sharper because of the extra "cropping/zooming" or if it is an unrelated effect. (I would experiment myself, but I have no barlows yet, and I don't have any DSLR extension tubes so it would be really hard to experiment with a teleconverter and increase TC-to-camera distance while keeping a parallel focal plane.) So, either for the sake of argument (a thought experiment) or as an experiment to try for real: * Take a photo at minimal camera-to-barlow distance, and call this Photo A. * Take a photo with some extra distance between camera and barlow, keeping all else equal, and call this Photo B. Now, crop Photo A to match the magnification of Photo B; call this Photo A'. Downsize Photo B to match the magnification of Photo A and call this Photo B'. If necessary, sharpen Photo A' a little more than Photo B, to compensate for the extra effect of the camera's anti-aliasing filter in Photo A (or the reduced effect of the AA filter in Photo B, depending on how you look at it). How does Photo A' compare to Photo B'? Does Photo B' have sharper corners? Here is a test done a while back in which the Televue Powermate seems to lose by a huge margin: [url]http://photo4fun.zenfolio.com/p231550804[/url] Would the Powermate do a lot better with extra camera-to-barlow distance? And would those astigmatic corners be improved without being completely "cropped/zoomed" away? [/QUOTE]
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Photography, Digiscoping & Art
The Birdforum Digiscoping Forum
Photography using 'Astro' telescopes
Comparison of teleconverters & barlows
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