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D&G 5" vs AP 130 f/6

Started by adamsdp, 03/14/2004 03:06PM
Posted 03/14/2004 03:06PM Opening Post
I was very fortunate to purchase a used D&G 5" f/10 a few months ago and have been very happy with the views. The optics in the D&G are outstanding and really pull away from several of the Chineese refractors I have at high power. I am wondering how much difference there is between a D&G 5" and an AP 130mmf/6 on planetary/lunar viewing.

I put myself on the wait list for an AP 130 f/6 and know that I will never be sorry in getting one. I am just curious how much of an improvement it will provide over the D&G I have. I have a Baader Contrast Booster filter which acts as a minus violet filter but haven't felt the need to use it yet. I am going to try that out and think about getting a chromacorr. I have done more reading
about refractor optics and it seems spherical aberration is more important than the chromatic aberrations and that really good achromats like the D&G do a better job at limting chromatic aberrations than the Chineese refractors. That being said, the D&G is a really nice scope and I am tempted to get a 5" f/10 or f/12 just to get the upgraded AP focuser and adjustable lense cell that mine does not have.

Dave Adams
Posted 03/14/2004 06:49PM #1
I would'nt get one if you want the AP focuser anytime soon. My friend just bought a D+G 5" f 12, had to wait a few months for the scope, and now has been waiting a few months for the AP focuser. It appears that they are on back order (what at AP in not on back order) so they gave him a synta type focuser for the mean time.
Other then that it is an excellent scope and is what convinced me to eventually purchase a refractor myself (TV102). The views of the planets through the D+G have been very good and it is deffinently a sharp scope.
We had a real amazing view of Jupiter last night when we viewed Jupiter with the D+G using a binoviewer.
Posted 03/14/2004 07:45PM #2
I think I can answer this question. I have owned a D&G an 6 inch f -12. And currently own a Zeiss APQ 130 an f 7.7 triplet apochromat like the AP.

While the D&G will have excellent smooth optics and a lovely star test the amount of residual chromatic aberration for a 5 inch at f 10 will mean low contrast markings will be harder to see in this scope compared to an apo. The AP will reveal sharper more well defined planetary images.

It will still do a tremendous job but in terms of image contrast on fine planetary detail it will be slightly less impressive than an AP 130.
My brother has recently sold his 5 inch f 15 D&G after acquiring a 715 Maksutov. His scope was fairly close to the point where secondary colour does not hurt the fine detail to the extent of a shorter focus achromat.

I have recently built an AS 80 f 10.5 short flint achromat of a high quality which has significantly less false colour than a standard achromat. It is effectively like an f -15 3.1 inch achromat. I have tested it beside an ED doublet (semi)apochromat and it holds up well, possibly being better at rendering fine detail on planets than an ED. Using this as an example and knowing how good D&G achromats are I would say an f 20 or 25 D&G 5 inch doublet would approach the apo performance in terms of planetary detail seen at the eyepiece. In short if you get to a focal length 4 -5 times the aperture in inches false colour starts to be barely visible and a non issue with respect to performance.
Deep sky and double performance would match an apo at f 15 with a 5 inch D&G, possibly f-12.

5 inch D&G's are excellent and vastly superior to the average short focus Chinese mass produced scopes. They are a much better value at less than 1500 US in an ota than the $5000 or so for an AP.

One last point, I am convinced long focus doublet achromat's have the potential to approach or even out perform short focus triplet apo's for visual use. A bit like the argument for planetary eyepieces and how monocentrics and orthoscopics seem to be the best. Less glass and potentially superior polish etc.

Best wishes


Attached Image:

Kevin Barker's attachment for post 77495
Posted 03/14/2004 08:26PM #3
Hi Dave,

Maybe this will be a kind of answer by analogy: I owned a 6" D&G F/15 for a couple of years and found it to be an excellent performer. There was some color but nothing to write home about. Planetary images were sharp and filled with detail. Liked it so much, I bought the 8" D&G. In the mean time I ran across an Astro Physics 6" F/12 Superplanetary APO. While I do not have both 6" scopes to compare side-by-side, I can tell you that the images in the AP are essentially color-free in focus and better in terms of low contrast detail on Jupiter and the globe of Saturn than the 6" D&G. The difference on low contrast features is subtle but clearly something you would notice. And it is not that the AP is "sharper", rather all of the visible light is in the image and not around it so you can pick up more subtle shadings and features. Having said that, during the recent approach of Mars I had the 8" D&G and the 6" AP out on several nights and a lot of folks looked through each. The D&G was definitley a crowd pleaser and drew the most "wows!" from the viewers. The image of Mars was sharp and detailed in both. The extra light in the larger scope made thing easier to see but at it's peak brightness there was false color around Mars. Funny thing was that none of the folks who looked through the two scopes was bothered by it. I actually pointed out the "purple halo" and to a person they felt it was not an issue even when 10 feet away the AP was "color free."

On the Moon there is a bluish hue through the D&G while through the AP the lunar surface is almost white. Again, the difference is subtle but you would see it. The question really is one of personal taste and finances. An AP 6" is right at $7,000 if you could get one ( I am on the list too!) A 6" D&G is around $1700 last I looked and available YEARS sooner. Forgetting the wait, is the difference in performance worth the difference in cost (for a visual observer)? Only you can answer that one!