Eric: You're wrong about the optics here. The Airy disk and diffraction rings are a result of the small aperture of the refractor not the lack of central obstruction or tube currents. I have seen beautiful Airy disk and diffraction rings in a 90mm Mak that Siegfried brought to SPOC once. The Mak has a huge central obstruction and is famous for internal tube currents. The airy disk and diffraction rings disappear in a large aperture reflector because they are so much smaller that they get lost in the seeing. It's an old myth that has persisted for decades. You can split stars with a reflector just fine. DT From: "erikhansen@thebluezone.net" <erikhansen@thebluezone.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, June 21, 2011 3:04 PM Subject: Re: [Utah-astronomy] Celestron Edge HD
You still will not get the airy disks, yes a stop will help but you still have tube currents to deal with. A refractor will out perform a reflector on double stars. Have you ever looked through the big AstroPhysics Refractors? Just the opinion of a #$*#$**##.
On the other hand, if you make an offset mask for a large reflector, you
now have a refractor buster. Cost is free if you have some black poster board laying around.
Mat
-----Original Message----- From: utah-astronomy-bounces+mat.hutchings=siemens.com@mailman.xmission.com [mailto:utah-astronomy-bounces+mat.hutchings=siemens.com@mailman.xmissio n.com] On Behalf Of erikhansen@thebluezone.net Sent: Tuesday, June 21, 2011 4:36 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Celestron Edge HD
Of course any scope with a central obstruction will have problems on the planets, only a refractor yields those airy disks.
I just checked Cloudy nights and it seems Celestron is having some quality
control problems. Here is the review.
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4644922 /page/0/view/collapsed/sb/5/o/all/fpart/1
Debbie
On Tue, Jun 21, 2011 at 10:43 AM, Steve Fisher <iotacass1@hotmail.com>wrote:
Debbie: Bill Cowles and I had a chance to observe through several different size HD's at RTMC in 2009. This was the last RTMC that Bill and I attended and the first roll out of the Celestron HD series. I honestly don't think the HD would be significantly different than another C-8 or larger except for imaging. The HD was designed for a flatter field across the
entire
field much the same as the Meade ACF although a different path to get there. If you are thinking about imaging then the HD would be an improvement with the flatter field and the vented OTA but if you are just using for visual use, not so much in my opinion. That is of course "just my opinion".Steve > Date: Tue, 21 Jun 2011 09:33:42 -0600
From: astrodeb@beyondbb.com To: utah-astronomy@mailman.xmission.com Subject: [Utah-astronomy] Celestron Edge HD > Has anybody looked through one of these? I wondered how doubles would look through this telescope? I think globulars would look good. It seems like 8 inches is the minimum aperature to resolve globulars. Any thoughts about this scope?
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