Posted 09 May 2007 - 09:17 PM
Recently I've done some critical observations of Venus as it's well placed. I think it the most severe test for Chromatic abberation. My little 2.4 inch f/13 Lafayette and Polarex 3 inch F/16 truely yielded what I would qualify as APO performance. In focus it was almost pure white with no distracting color. Not bad for achromats but also not unexpected for the long focal ratio's.
Both of these classics have yielded excellent results and sharp views of doubles.
I also have the original Tele Vue Genesis f/5 4 inch. I consider it a classic as it began the interest in short focus refractors. I bought it in 1989 I think. I recently sent it back to Tele Vue as I detected mold on the internal surfaces of the objective. I treasure this scope and didn't want to attempt a clean up myself.
Tonight I put it thru some tests. Venus...wow compared to my old classics it showed lots of blue color, but hey it's a f/5. Cranking up the power still showed the blue but the planets gibbous disk was sharp as a tack and way surpassed the smaller scopes despite the color.
Next was Propus...Very tough as it was low in the sky but yet it showed the secondary...I see this couple as Reddish and Green. I've detected the secondary in the 3 inch but most likely thru imagination knowing its position angle.
Delta Gemini was next and the f/5 made easy work of it.
Saturn was high and the little Genesis with a 2.6X Dakin barlow combined with a 4.8 Nagler (270X), just blew my socks off. No detectable false color and a very sharp view of the equitorial belt, Cassini division, polar cap shading etc. Not bad for a scope that is only about 2 feet long and weighs in at less than 10 lbs. Just extremely happy with my refurbished Genesis scope and wanted to share my recent tests. Bonco
Posted 10 May 2007 - 07:21 AM
Last night I compared my Pronto to the WO66SD, even with a minus violet filter the Pronto has very noticeable false color. The WO, essentially none. The ED-80 is even better...
And to keep this appropriate to this forum... My 60mm is an old Asahi-Pentax from the 60's and it does a nice job on Venus as you found...
RV-6 and 12.5 inch Meade RG both are color free...
I have a triplet of Meade 80mm F/11s from the early 80's, these show some false color but it is much less than the Pronto.
Venus is a favorite of mine, I have been spending more time on Venus than Saturn.
Posted 10 May 2007 - 08:08 PM
Totally agree about the RV6 it's s superb planetary OTA, no false color..
The long focus classic achromats did better than I expected on Venus which I consider a critcal color test. Other than Venus and blue white stars like Vega/Rigel etc. the original Genesis provides exceptional views. I did view Vega with a Genesis SDF and it was virtually color free. I'd love to hear some reports of venus color in classical 4 inch F/15's and/or the new Antares as I'm considering buying one.
Posted 10 May 2007 - 08:32 PM
I have several long-focus 'classic' OTAs (Tasco, Unitron, Pentax) as well as one of the new Antares Elite 105/1500s.
I've been very pleased with the performance of the Antares scope. It shows me less color with more contrast than my Unitron -- which doesn't really surprise me. The coatings on the Antares are so much better than my Unitron's (I have a fairly late Unitron, so I'm pretty sure it has coatings). My Pentax 102/1200 shows a tad more color, but it also is a very crisp, contrasty image (indicative of good coatings as well, IMO). My 80mm and 76.2mm f/15 OTAs are very good, low color images.
Not surprised about your Genesis findings. I have several shorter refractors that use ED or better objective glass that yield near/color-free images on Venus. Of course, they're a bit more expensive.
Posted 10 May 2007 - 09:03 PM
Thanks. I've been looking for reports on the Antares 105/1500. I think I'll buy one as the Unitron's are beyond my price range. I'd like to get one with a standard rack and pinon as the scope looks much more like a classic than the crayford duel speed focusers. Wanna sell yours, hehehe.
Posted 10 May 2007 - 09:10 PM
At F/15 the depth of focus is enough that a Crayford would probably seem slow. Of course one would hope the R&P is of good quality, not TV but better than the average Synta refractor.
Posted 10 May 2007 - 09:20 PM
I *really* like that Crayford on the Antares. It's nice to be able to be sure you're getting precise focus without any rack slop.
And I'll be happy to sell you my Unitron OTA. Seriously. PM me if you want to talk about it.
Posted 10 May 2007 - 09:59 PM
Posted 12 May 2007 - 09:07 PM