D&G 6" f/12 Refractor
Posted 26 January 2006 - 11:07 AM
Posted 26 January 2006 - 11:27 AM
Thanks for the excellent article - I enjoyed it quite a bit.
Posted 26 January 2006 - 03:34 PM
Posted 26 January 2006 - 05:18 PM
Posted 26 January 2006 - 07:28 PM
It put a smile on my face in the midst of all this rain in the NW.
Oh yeah, it reaffirmed my wanting one of those fine refractors!
Posted 26 January 2006 - 10:42 PM
Posted 26 January 2006 - 11:12 PM
Because those with large $$ "normally" go for big APOs these days, it doesn't mean everyone does - or even wants to. Small APOs, sure - big APOs, not so sure..........
On an absolute basis, the very, very finest APOs can "potentially" give the very finest visual images in the best of conditions (no temp drift), with the most light focused in the airy disc.
That said, D&G doublets are still preferred by some, price no object. Why? Well, as a highly regarded former director of ALPO once told me: "A D&G doublet is worth the wait no matter how long - - one from anyone else is likely not worth the wait no matter how short". (a couple of other quality american makers have joined the scene since that comment was made to me 12 years ago).
Here's what keeps 'em coming back:
When it comes to practical observing with LARGE refractors, an air-spaced doublet has distinct advantages over an oil-spaced triplet, perhaps less so over an air spaced triplet. When you go out to view, if you live in an area like me (Kansas) where temps drop and keep dropping 'till dawn, an air-spaced Achro like the D&G equalises very quickly and the design is optimized to make temp changes less noticeable at the eyepiece than triplet designs. This means that while the APO-man is often waiting for the slight softness in the image to "go away", the achro-man is getting maximum performance from his lens.
And with maximum performance in a long focal length doublet, carefully optimized for most color-free possible with spherical correction to 1/10 wavefront (not just surface ptv) or better, what you have is a perfectly corrected lens which has the capability to perform, big time!
A 5" doublet of this quality will often have planetary images preferred by most over the highest quality 7" Maks, for instance (and that's assuming the Mak has temp stabilized). Contrast does not always beat greater aperture for what you want to see, but it does do so often enough on planets, the moon, doubles and open clusters.
With only two elements up front and as few as three in the eyepiece, you have the potential of superb contrast which more glass or reflections can hardly match and blackest contrast is what some of us CRAVE.
Another virtue of this design is the very long focal length which makes for a scope that an owner takes such pride in as it "looks" like a real scope. I don't think too many of us realize the pride of showing off one of these long boys -- a point "visitors" certainly DO appreciate - it creates a sense of anticipation in them that makes their (often long awaited) time at the eyepiece doubly rewarding.
Long focal length, as we all know, but most of us seem to forget, allows higher powers without normally using barlows. This scope type simply puts the least amount of glass between you and the universe - think about it.
Great designs for relatively inexpensive roll-roof observatories have never been better or cheaper to build.
Put one of these in your backyard with a scope like a D&G in it and many could call that good enough - for life.
Want a little better even - get a chromacor corrector instead of that next Nagler or two and you will reduce what tiny chromatic aberration is remaining by as much as 60%.
Everything is a compromise of performance objectives when it comes to scopes. I don't think you'll find many who would trade a large, perfectly figured doublet scope for anything else.
It performs when sometimes the great names are "too hot" to handle and most of us don't have time to wait. Do you?
Wishing all the best of scopes under perfect skies!
p.s. I hear the nay-sayers - the ones who need to justify buying that huge APO instead of putting their kids through college saying things like - :"well, put that scope on Venus or Sirius and..." - Hey, get Serious! Fact is, a touch of color "may" be seen by some, but not by all. And if your idea of astronomy is looking at Sirius all night -- I'm sure we'd find it "interesting" to read an article about your observations.
Posted 27 January 2006 - 02:59 AM
I have to admit that I've been curious about D&G refractors for some time now, especially in the larger apertures...
Now please, somebody lash me to the mast!!!
hearing the siren's call..
Posted 27 January 2006 - 08:34 AM
Posted 27 January 2006 - 09:49 AM
Thanks for a very enjoyable report Tom. I loved the picture, I've got/had quite a few different types of scopes, but theres no denying theres something special about a big, long refractor.
Posted 27 January 2006 - 10:21 AM
I have not been on cloudynights lately, however after reading your review I was compelled to say it's one of the nicest I've read. I love when people just simply speak from the heart and say it like it is. I am working on two 6" F-15 D&G's at the moment which unfortionatly will be a little longer than yours is. Pons is helping with the designing of the tubes. One tube is being made of wood while the other will be metal. I will just be getting the lenses in their cells and doing the rest.
A long time ago I built a Zeiss replica case for a Telementor. About 3 years later the customer called me back and said he'd give me a completed D&G lens in the cell, an AP focuser and a Zeiss 50mm F-11 doublet lens for the finder in exchange for a wooden tube for his 6" F-15. I agreed and I'm working on them now since the lenses are still being made. I plan to use and ATLAS mount with custom wood legs, so we'll see how it goes.
I should also mention that at these focal lengths with good glass, the color correction is great on the D&G's and another thing many color correction fanatics forget is how sharp these long scopes are. They are really tack sharp! with gorgous black backgrounds. Good job!
Posted 27 January 2006 - 12:25 PM
Posted 27 January 2006 - 12:58 PM
Posted 31 January 2006 - 01:41 AM
Posted 31 January 2006 - 01:53 AM
It would be great to read a comparison on the D&G F12 vrs F15 visually, and if the extra length really makes that much difference, with considerations to the mount.
Posted 31 January 2006 - 07:47 PM
Posted 31 January 2006 - 08:21 PM
Thanks for the review. For me it is quite timely as I am considering acquiring one of these refractors.
To be honest, my current 'scope quest' has been going on for about a year. I do most of my observing with my 18 Obsession, and I expect that will continue even after the next scope arrives. But, I have been longing for something nice to use for lunar and planetary studies... OK, open clusters and doubles too.
I had a very nice Intes MK-66 6" Mak-Cass (that I wish I still had) that served me quite well. I especially liked its performance with Denk II binoviewers on the Moon.
Questions I have are:
Any current D&G owners using a binoviewer?
What about mount requirements?
I am thinking of getting an Orion Atlas with the pier extension. Will this work out with a 6" f/12 model? I am undecided as to whether I'll get a 5" or 6", but it will be f/12. To me this is more appealing than the last scopes being considered, all 4" apos.
All comments appreciated.
Posted 31 January 2006 - 08:24 PM
Posted 31 January 2006 - 08:50 PM
Posted 01 February 2006 - 11:05 AM
Posted 16 July 2006 - 10:08 PM
Posted 17 July 2006 - 04:03 PM