TOA + BORG Reducer/1.4x Teleconverter

Following are my friend’s test shots by his TOA150 + BORG 0.7x super reducer (#7870) and 1.4x teleconverter (#7215). Both were taken by modified Canon 500DH and  single frame without dark and flat.

with 7870

Basically he got 7870 as a part of his 71FL F3.9 astrograph system. So he was curious how 7870 would work with his TOA150. Result? not bad. Not perfect though. We can see hot spot at the center and coma at each corner. Hot spot was as anticipated. Basically reducer’s front opening aperture should be too small for 6″ objective.  So it’s hard to make the illumination curve flatter without flat frame. I think it should be minimized when flat frame is applied. About coma. TOA150 looks a bit too long focal length(1100mm). 7870 is basically optimized for from 300mm to 1000mm. So this is out of the range which allow to adjust reducer’s lens placement based on focal length. If 1mm or 2mm spacer rings are added between camera and reducer, coma should be gone and hopefully hot spot might be a bit reduced. It will be worth re-testing with spacer ring. BTW, fortunately 7870 can reach focus without special adapter. BORG 72mm adapter (7912) allows to connect onto the end of drawtube. Accordingly it should be same with TOA130 and TSA etc as well and  moreover it should work better because of shorter focal length and smaller objective sizes.

with 1.4x teleconverter (#7215)

This is as expected. Very flat. Unfortunately the speed is very slow for DSLRs though.

Shooing with TOA150 might be toughest test in the aperture and focal length. In any cases, TOA150 shows super clean image even it was used with 1.4x teleconverter. I believe his TOA150 must be made as designed. Wonderful scope!!


~ by tedishikawa on July 19, 2012.

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