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RICHARD COFER

VdB 141 Ghost Nebula

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Posts Made By: Roland Christen

February 28, 2005 09:33 PM Forum: CCD Imaging and Processing/Deep Sky

Pleiades - M45 from Utah

Posted By Roland Christen
>>No Pleiades image that I have seen can compare to Jeff Hapeman's beautiful recent post of this object, which sets the standard IMHO.>>

Where was that one posted. I musta missed it.

RC

March 3, 2005 08:40 PM Forum: CCD Imaging and Processing/Deep Sky

Selecting a CCD Camera

Posted By Roland Christen
In my opinion the ST10XE is extremely nice for the money - high resolution, high sensitivity, fits almost any situation from wide field deep sky to super planetary imaging.

Roland Christen

March 4, 2005 02:39 AM Forum: Equipment Talk

So, Interferometer or Foucault?

Posted By Roland Christen
>>If the mirror is great the images will also be great. If the mirror is poor the views will also be poor. If the finish is rough the contrast will suffer. If the figure is poor then the images will suffer>>

What is great and what is poor? I'm willing to bet that you cannot see the difference between a 1/4 wave mirror and a 1/40 wave mirror in an 18" size.

Today there is software available that allows you to determine the wavefront error of your telescope. Basically it requires that you take two out-of-focus images of a star using a 16 bit CCD camera. These images are then analyzed and calculations of P-V, RMS and Strehl are done. Send me a pix of a star out of focus both inside and out, 16 bit Fits image, defocused to 150 pixels. I need to know the focal length and aperture.

Roland Christen

March 5, 2005 08:10 PM Forum: Equipment Talk

So, then we are wasting our money?

Posted By Roland Christen
It may be that one of your scopes has a severe turned edge and the other one is clean to the edge. In that case, you will see the difference for sure regardless of size and almost regardless of seeing conditions. The turned edge scope will look soft and never really snap into focus, even though the stars may look relatively clean.

A 1/4 wave evenly spread over the aperture and smooth will be quite sharp in an 18" aperture, but that same 1/4 wave defect concentrated at the edge will have a very much higher negative effect on contrast and sharpness.

In fact, I can see the effects of turned edge in many astrophotos that people have published, so it is not an uncommon thing to have. It is probably the single most prevalent defect in poor mirrors besides astigmatism.

Take the two out-of-focus images with a CCD camera for the Roddier test that I described earlier and send me the Fits images. I'll be able to tell you right away what you have in those two mirrors.

Roland Christen

March 7, 2005 04:34 PM Forum: Reflectors

Re: Tom Scott Mirrors

Posted By Roland Christen
Tony Hallas has a Tom Scott 14" F8 Cassegrain.

Roland Christen

March 7, 2005 08:19 PM Forum: Equipment Talk

Clarifying methods used for Interferograms on Anta

Posted By Roland Christen
I am not accusing anyone of manipulating their data. I am trying to educate you guys on what to look for under the hood, so to speak. Sometimes data is incomplete, and as far as these flat interferograms, I would not accept them myself if I were buying this item from an unknown vendor. I have been led down the garden path too many times, plus I know a bit about testing and what I would like to see in the data.

Do not read more into what I say than what I say.

If you all are uncomfortable with any of this, then say so and I will say no more on the subject of optical quality, optical testing etc. God knows that Peter Ceravolo has tried so many times in the past to elevate this subject among amateurs, and then be rebutted and shat upon by some who always seem to know better.

Roland Christen - heading out to Hawaii for R&R.

April 4, 2005 10:23 PM Forum: Equipment Talk

OK, I tried sand paper to remove the coatings...

Posted By Roland Christen
>>Does anyone know of a solvent of some kind that will remove coatings from a lens and leave the glass intact? >>

I probably have posted about anti-reflection coatings on 150 different occasions on a dozen or more newsgroups. For some reason amateurs think that AR coatings are like mirror coatings, in that they can be removed with some kind of chemical process. The fact is, the only process that will remove a modern multi-coating is to GRIND it off. Think about that for a minute, and what effect this might have on the underlying glass 8).

Roland Christen

April 13, 2005 07:08 PM Forum: CCD Imaging and Processing/Solar System

Sunset on Maui

Posted By Roland Christen
Green Flash with same setup as previous image.

Roland Christen

April 23, 2005 12:13 AM Forum: CCD Imaging and Processing/Deep Sky

FS152 Omega Centauri

Posted By Roland Christen
Does your camera automatically clip the histogram, or did you do this when you processed the image?

Roland Christen

April 25, 2005 04:55 PM Forum: Equipment Talk

Feedback, Mewlon/AP/TEC

Posted By Roland Christen
The 210 would probably fit very nicely on your GM8. The 160 AP would severely overload that small mount. This scope is very different from the 210 Dall-Kirkham. The 160 refractor is primarily a CCD imaging scope which can also be used for high resolution visual. If you want mainly a visual scope, go for a light weight Cass. It will be easier on your mount and your back.

Roland Christen

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