Achromats

I do not mean to start a war on brands or designers or manufacturers or anything like that.
I am considering buying a 6" achromat in a lens cell. I have personal reasons to avoid the chinese refractors the world is flooded with at the time being (I don't like the f/ ratios, in the first place).
I would love to go f/12 or f/15 (with the latter being the preferred one but not for "portability" ...).
I would appreciate your comments and reviews about D&G's and TMB/APM's Fraunhofers.

I have used an f/12 D&G 5", and it is a very fine lens, both on planetary and deep sky. They specialize in making what you want. The TMB's are, as I remember, of lower focal ratios, but should also be very well made. Bob Royce also makes 6' f/12 and f/15 doublets, they would be very good as well. They are big scopes and require considerable mounts.

Hi Andre,

There have been several threads on the subject- one is to be found if you do a forum search under "D&G 6-inch f/15 Refractor". I have owned two D&Gs, currently an 8" F/12, and would be glad to share my impressions with you.

Larry

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I will add my own endorsement for D&G. I've viewed through several 5- and 6-inchers since '93, and all were *very* fine, well-figured and -polished objectives.

I'd have absolutely no qualms directing my efforts towards AP/TMB or Royce, either. I expect their quality and performance to be comparably superb.

Mounting is *definitely* an important consideration. Most of the D&Gs I tried utilized alt-az mounts similar to this one (attached .jpg -- courtesy Dale Keller).

Best wishes.
-Dan

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well this is my baby 6-f/12 d&g, it don't get no better. john

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My new D&G 5" f10 just saw first light last night.

I am sorry to say that my results were not very encouraging after more than a 15 month wait from order date to finaly obtain the last piece (an A-P focuser which was on backorder). Not sharp at focus at modest powers (120x), and some false colour on Jupiter.

I will troubleshoot, as it could be collimation (which didn't look too bad on casual star testing) or perhaps squaring off of the focuser (unlikely as it threads perfectly into the back of the OTA), but as it stands my 3-inch Takahashi is a superior planetary scope to my 5" D&G achromat, and the Takahashi is actually cheaper ($1100 vs $1600).

I am crossing my fingers that the problem is not the optics but rather my assembly of the OTA (the lens cell ships separate fom tube). I'll update you after I've tinkered with collimation, etc., but for now I'm not a particularly happy camper.

About those mounting requirements for long focal length refractors....

(D&G 8" F/12, Parallax HD150 on a 60" tall pier)

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