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RICHARD COFER

VdB 141 Ghost Nebula

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Posts Made By: Roland Christen

July 22, 2006 06:21 PM Forum: CCD Imaging and Processing/Solar System

Color Shift Problems

Posted By Roland Christen
SCTs have sphero-chromatism due to the nature of the corrector plate. Assuming that the scope was fully corrected for green light, then the blue end of the spectrum is undercorrected, and the red end is over corrected. This spherical aberration manifests itself as a slight out-of-focus halo and will be enhanced when using shorty Barlows, which themselves have sphero-chromatism. If you can take 3 seperate R,G and B images, you can minimize this by slight refocusing of the red and blue images, but there will always be a bit of softening, especially in the blue end.

By the way, the new "RC" corrected SCTs from Meade will have even more sphero-chromatism than a standard all-spherical SCT, so the effect will be more pronounced, especially if you intend to Barlow the image with a "shorty".

Roland Christen

July 24, 2006 06:20 PM Forum: Equipment Talk

Malco 360 deg Rotating Pier Plate for AP 900/1200

Posted By Roland Christen
They are two different things, even thought hey have the same name. The AP unit allows the mount to be firmly attached to the pier top and allows fine adjustment of the azimuth angle without loosening the 4 attachment bolts. It will not rotate any more than the standard azimuth adjustment that comes with the mount.

The Malco is not for fine adjustment of the azimuth. It is intended for 360 degree rotation so you can rotate the entire mounting without having to place the pier in a North-South orientation.

Roland Christen

July 29, 2006 05:30 PM Forum: Refractors

21 inch APO - any idea what it might cost?

Posted By Roland Christen
I have no idea. Markus could probably give you a better guess since I would think only the Russians he deals with would be able to make something that large at a reasonable cost.

Rolando

July 31, 2006 02:51 PM Forum: Equipment Talk

FC-100: what glass is the front element?

Posted By Roland Christen
The color curves that Tak published suggest that the element is KzF2. Normally fluorite is coupled with KzF2 in order to achieve a lens that is well corrected with all spherical surfaces. This gets you pretty good color correction with some error in the violet. One can also use KF3 with fluorite to achieve all-spherical design, but with less good color correction. BK7 would not be a good match unless the focal ratio is long (F12 or longer) or unless the BK7 is split into two pieces to form a triplet lens.

Roland Christen

August 5, 2006 03:56 AM Forum: CCD Imaging and Processing/Deep Sky

Tiny Bubble(s)

Posted By Roland Christen
And here's a closeup of the little bauble.

Rolando

August 7, 2006 11:49 PM Forum: CCD Imaging and Processing/Deep Sky

H-a filter

Posted By Roland Christen
I use a 10nm Ha filter. This allows me to find bright enough guide stars to work with.

Roland Christen

August 9, 2006 05:44 PM Forum: Mounts

Orion Atlas aka EQ6 vs CGE or GM-11

Posted By Roland Christen
Everyone always wants to scrimp on the mounting and put most of their money into the optics. For astrophotography, the mount is the single most important item. If you shoot with a long focus SCT like your C9.25, you will want a mount with smooth periodic error. Otherwise you will not be able to make use of the resolution capabilities of the scope.

When I say smooth, I don't necessarily mean low. Smooth means a mount where the peiodic error does not vary rapidly over a short time period, i.e. 5 - 10 arc sec or more error over a period of 10 - 30 seconds. These kind of errors are virtually impossible to compensate with PEC, and they really affect autoguiding. With the C9.25 you will capture errors on the order of 1-2 arc seconds, so your mount should be able to track smoothly for short periods of time to that accuracy.

Rolando

August 17, 2006 09:42 PM Forum: CCD Imaging and Processing/Deep Sky

Western Veil

Posted By Roland Christen
Super nice!

Rolando

August 19, 2006 06:16 PM Forum: CCD Imaging and Processing/Solar System

Bay of Rainbows!!

Posted By Roland Christen
That is pretty incredible!

Rolando

August 23, 2006 08:56 PM Forum: Astro Binoculars

Looking for the Best Big Binos

Posted By Roland Christen
I will be getting a pair of 20x100 right angle binoculars in my next shipment for evaluation. These are made to the same internal specs as our smaller binos. If they work as well as I expect, we will sell them also. I evaluated a straight thru model of a 4" binocular, but I feel for such a large device the right angle eyepieces are the only way to go. The 4" binos are really really big (like holding a 6" RFT refractor on a small tripod), and with the straight thru eyepieces they end up having to be placed high up in the air - too high for most tripods to be stable. With a right angle bino, you can sit comfortably on a low stool and have the binos at a more reasonable level without extending the tripod legs to wobblidomcity. Only drawback is that a right angle bino requires more costly prisms and mechanics, which increases the price.

Rolando

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