Posts Made By: Allen Tracht

Conventional focal reducers rarely work with Newtonians because they lack sufficient in-focus. Still, I'd like to increase the field of view of my CCD, which is about 10mm corner-to-corner. Three-fold would be nice.

So, I propose putting two eyepieces front-to-front, with their eye lenses separated to make their exit pupils coincide. One, say a 35 mm would be in the normal position in the telescope, converting the real image formed by the primary into a virtual image at infinity. The second, say 12 mm, would focus the image at infinity down to a new, real image of 12/35 the size of the original, focused on the CCD which would be placed at the position of the 2nd eyepiece's field stop, which must be accessible.

With a 10mm final field diagonal, the eyepieces would need a good 45-degree field of view.

I hope that using both eyepieces at their infinity focus will minimize image defects.

Can anyone suggest the (probably obvious) defects in this idea? Will there likely be problems with vignetting or field flatness?

If this is a good idea, does anyone make and sell them?

Does anyone know of a good Appleply/Europly distributor within a couple of hours drive of Pittsburgh, PA? The local "distributors" all seem to want to special order entire "units" of 40 or so sheets!

Allen

There have been some very favorable comments regarding the Starmaster V8, and now I see that a V11 (or V-11) model is due soon. Rick Singmaster replied to my email saying that it would be a few weeks before they would be available, but so far I haven't had much luck getting basic dimensions (weight, especially) from him.

Rather than bother Rick (I'm sure he's very busy), I'll ask this forum: do any of you have preliminary specs on this new scope?

Thanks,

Allen

I put Parallax rotating rings on my G11/Gemini Newtonian scope so I could view comfortably regardless of the orientation of the OTA. It works great. However, when I rotate the OTA, the image shifts. This really keeps the goto from working well, as its alignments are subject to seemingly random errors as I rotate the OTA to view the alignment objects.

Has anyone else fought this problem and come up with a reasonable solution?

Allen

I'm playing around with a large reflex finder design that uses a mirror rather than a lens. So, I'm looking for a parabolic mirror about 3-6" in diameter at F/1.25 to F/1.5, without a central hole. The optical quality need not be anywhere near diffraction limited: a molded design is probably fine.

Can you suggest a source for such a mirror?

Thanks,

Allen

Scott,

You graciously offered to make me a deal on a mirror, but I haven't been able to reach you. Please let me know how I might reach you, either through this forum or a private message.

Thanks,

Allen

I'm nearly sold on a Starstructure Dob, but I'd like to see one in person before I buy. Michael Zammit isn't aware of any near my area (within about a half-day drive of Pittsburgh), but one may have been resold, moved, or even passing through the area.

If you have one, and wouldn't mind my taking a look, please let me know.

Thanks,

Allen Tracht

Perhaps this will inspire:

http://www.astromart.com/classifieds/details.asp?classified_id=352778

I use JMI Wheely Bars that include leveling feet.

-- allen

Does anyone have the TFOV and weight, including the supplied rings, for this finder? Thanks. -- Allen

I'd appreciate your suggestions for a wide-field scope that would complement (and maybe piggyback on) a C9.25, primarily for visual work. I'm thinking about a Televue NP101, with a reasonable aperture and wide FOV, but I'm open to suggestions.

Allen