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Sep 22 2015 01:41 PM by turbo399
6" D&G F/12 Refractor
I recently built an OTA around a 6 inch f-12 D&G lens for my twin brother Kevin's Zeiss IB mount. I've had 2 occasions to use the scope and felt a commentary with later updates could be useful to anyone enquiring about the performance of the scope.
The tube is 8 inch ali with a 3.2mm wall thichness and it is beautifully powdercoated white. The tube ends are powdercated black along with a dovetail tube-ring combination a result of my own imagination.
The mount is similar to a C-11 in terms of solidness and just manages to control the 17 kilogram monster.
A crayford focuser made by a local friend out of stainless steel has a Zeiss adaptor threaded into the end so a superb 2 inch Zeiss prism diagional can be employed with .96 1.25 and 2 inch adaptor rings.
After finishing this scope I drove over to Westland (250 km) with a friend to personally deliver the scope. It also happenned to be a very dark night and we quickly got the big refractor mounted balanced etc ready for action.
First light was on M42 and I did the honours with the first peek thru a 24.5mm Meade Wide Angle eyepiece. I was not disappointed the 5th and 6th star of the trapezium stood out easily! No sign of any chromatic aberation at this power anyway. The nebula showed amazing contrast and definition. It was immediately apparent this scope was no lemon.
I had my Celestron 8 with me for comparison. It is a very good example of a SCT and predictably was slightly brighter on all objects viewed. However it was obviously losing on the contrast stakes and NGC2070 the Tarantula Nebula and M46 with the lovely planetary proved this. Contrast was superb although the image wasn't brighter the sky was darker and more could be seen in several nebulous objects viewed.
Despite the limited aperture and long f ratio this scope is a real punchy deep sky performer. Stars are pinpoints very similar to my own 5 inch f-15 D&G refractor. There is only slightly more longitudional chromatic aberation in the 6 inch than the 5 which was quite a relief to us all as we feared it could be a problem. It clearly wasn't.
Gamma Centauru 1" easily split with black space between the components.
Startesting on Canopus -0.7 the in and out diffraction patterns were very nice on both sides. This was at 200 X! The lens snapped into focus and the image was very pleasing. In focus at high power stellar images were sharp and lean as one would expect from a high quality refractor. At one point we suspected very slight astigmatism in the lens however this has proved to be nonexistent.
Kev has used the scope on several clear nights since the first light and he is very happy with the performance especially on the moon. He has found it easily copes with 450 x with a zeiss 4mm ortho and virtually no false colour is visible even at this power. Save for some minor false colour this scope is a superb performer and would seriously push a good few top end apos.
We are both keen observers and Kev also owns a superb Zeiss APQ 100/1000 he picked up on tender for a steal when Zeiss went out of the telescope business 5 years ago. He sold an 8 inch Newt after getting annoyed at the fuzzy images and the fact the Zeiss easily performed better on planets. We both have been keen stargazers for over 20 years.
D&G optical sell these superb lenses for around $900 US. I believe there is no better value out there in terms of a high quality planetary scope. It can take time to get the lens 6 months in thsi case but the wait is worth it.