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Post by stargate on Sept 2, 2011 5:18:20 GMT -5
Hello all,
I'm curious as to how this ( non R-30/60) lens would compare to the other ( F/5, F/5.9 and F/6.5) available WF Achros out there?
Thanks!
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Post by Mike on Sept 2, 2011 15:23:37 GMT -5
Let's say an 127 F12 for the sake of simplicity. An R30 has the characteristics of a scope with 30% more focal length (in terms of chromatic aberration and smaller spot size). So an 127 F12 R30 would have the reduced CA of a F15.6. This moves it in line with the Sedgwick rule of 3X the aperture in inches for the false color to be at an acceptable level. Pretty simply once it's explained. Just think of the shorter length and lighter weight tube. The difference in F12 and F15 can make or break the use of popular mounts ie Celestron CGEM. The F12 is still going to be fairly close to the ground but unlike the F15 you won't have to lay on your back while looking at the zenith  Mike |
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Post by Mike on Sept 2, 2011 15:42:13 GMT -5
I should add that we have a nice Wide Field scope (WFT150-5). It's great for scanning star fields at low power. The scope itself is far superior in quality to the big two cookie cutter scope makers. You get a CNC machined tube that is well made and machined absolutely square on the ends, your choice of focuser etc. It looks and feels like a custom made scope that was handcrafted. However it, like any achro scope at F6. exhibits large amounts of CA when pointed at the moon or bright stars. You are also limited in magnification. No super short focal length eyepieces trying to magnify Jupiter. It depends on what you want to do with it. I'll tell you the scope I'm excited about, the new Asteria AT 127-12 R30. This is going to be a hit at under $2000 for a custom built scope. It will show very little or no noticeable CA and be around 54" long. Which means less than 30" below the mount's head leaving sufficient ground clearance. Not to mention all the benefits of long focal length. I want one of these for myself.
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Post by Ales - iStar Optical on Sept 6, 2011 5:11:57 GMT -5
We have JUST released info on ISTARs new Asteria WFT 150-5 R30, check our web site under Comet Hunters. Images of this scope coming in about one month time, first production run lenses are due to be finished in two month time, OTAs can ship just in time before Christmas. This new Black-Red beauty runs at F/4,8. We will keep everyone posted on the actual star testing, level of CA and related issues.
Cheers,
Ales P. Krivanek
ISTAR Optical, owner
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Post by tonybegg on Jun 17, 2012 14:16:37 GMT -5
I am afraid ISTAR has just appeared on my radar having just seen them in stock at OPT (I did see the Mt Stromlo post-fire replacement scope's objective was an ISTAR APO). Last night I was thinking of the 8 in f/5 and what it would be useful for and it occurred to me that serious imagers who like fast focal ratios also for the most part photograph through filters which might mitigate the CA. Which would make the 8 inch f/5 at $3330 the most bang for the buck telephoto lens available. The luminance channel might be a bit tricky, but am not an imager yet so don't know.
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