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Re: [APML] Tele Vue & Field Flatteners for Refractors?
Thanks very much John,
In my opinion you "under post". Have been meaning to get that message out
for some time. I learn something new with nearly every writing. It has the
effect of raising the SNR considerably, which is often so badly needed.
(What can I say, I tells 'em like I see 'em.) Too many of the upper echelon
are far too silent. Mostly bored I figure, tired of rehashing.
The M101 looked excellent, but I'll go with the 0.8x version too. I've
gotten pretty used to a little vignetting in my 35mm world. 8)
Sincerely,
Jim Vineyard
>From: "John Boudreau" <jeboud@comcast.net>
>Reply-To: Discussion of Film Astrophotography <astro-photo@seds.org>
>To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
>Subject: Re: [APML] Tele Vue & Field Flatteners for Refractors?
>Date: Tue, 3 Feb 2004 20:22:22 -0500
>
>Hi Jim,
>
>As Chris mentioned, the "Ranger" 1.1x version induces chromatic aberration.
>The Pronto/TV85 .8x flattener is APO and so produces sharper stars, but
>does have somewhat more light drop-off towards the corners since it's
>reducing the light cone. But both are restricted to a clear aperture of
>only about 37mm due to the I.D. restriction of their male T-thread end,
>which is the main source of the vignetting in each.
>
>Much of the "blue halo" part of the chromatic aberration from the Ranger
>unit can be greatly reduced by use of a UV-cutoff filter like the 2"
>versions available from companies like Baader, Astronomik, Schuler, and
>others. If you use an IDAS LP filter, it also cuts off in the blue end at
>about 410nm, so it acts as an effective UV-cut also.
>
>Additionally, if you have RegiStar, you can realign the individual RGB
>channels to further reduce the lateral component of the chromatic
>aberration of the Ranger flattener:
>http://home.comcast.net/~jeboud/xchrom.htm
>Unfortunatly, RegiStar can have a problem with some starfields, and *at
>times* may not realign the channels as well as it usually does. But it's
>always certainly worth the effort--- I even use it to realign the RGB shift
>due to atmospheric dispersion in images of somewhat low-altitude subjects
>taken with the APO Pronto/TV85 flattener.
>
>This image was taken with a TV85 using the Ranger flattener, _no_ filter,
>just RGB aligned with RegiStax:
>http://home.comcast.net/~jeboud/m101wdfld.htm
>
>A real pain about the Ranger flattener is that it's female end _isn't_
>T-thread, so you'll have to also buy the 2" adapter from TeleVue that mates
>up to it. I also found that adapter to have the smallest O.D. of any 2"
>accessory I ever owned, and so it was a sloppy fit.
>
>In the end, I found myself shooting only with the Pronto/TV85 .8x
>flattener. It gives better images and I can live with the vignetting.
>
>John Boudreau
>http://home.comcast.net/~jeboud/astro.htm
>
>----- Original Message -----
>From: "Jim Vineyard" <mojjv@hotmail.com>
>To: <astro-photo@seds.org>
>Sent: Monday, February 02, 2004 7:31 PM
>Subject: [APML] Tele Vue & Field Flatteners for Refractors?
>
>
> >
> > Hello All,
> >
> > I'm trying to figure out the *real* difference between the "Ranger"
>and
> > "Pronto & TV-85" field flatteners. Both are described on Tele Vue's
>page as
> > follows:
> >
> > http://www.televue.com/engine/page.asp?ID=169
> >
> > I'd much prefer to use the "Ranger" version, both for price ($84) and
> > because it does not reduce the focal length but actually increases it
> > slightly by 1.1x. The thing is, it is listed for use on quote: "the
>Ranger,
> > Pronto and TV-85."
> >
> > The "Pronto and TV-85" version costs $265 and reduces the f.l. by 0.8x
> > *BUT* is listed for use on ANY brand refractor from 400mm to 600mm.
> >
> > I want to use a flattener on a non-Tele Vue brand scope of simular
> > aperture, 600mm f. l. with a 2" focuser integrated T-thread adapter. I
> > don't want vignetting, or I'd at least like to reduce it to a minimum on
> > 35mm film. This'll be my first refractor since my first-ever scope some
>12
> > of them ago! It's a semi-apo.
> >
> > So can I get away with using the "Ranger" field flattener?
> >
> >
> > Mucho - Thanks In Advance (M-TIA) for any guiding wisdom, or even an
> > alternative brand which might work!
> >
> >
> > Jim Vineyard
> > www.deepskyphotos.com
> >
> > (I'm once again behind some 2 to 3 hundred APML postings and need to
>catch
> > up! Plus there's that CCD list. I don't know how you guys do it, fast
> > computers and speed reading?)
> >
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>
>
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