[clive milne]

Originally Posted by Peter.M

Its sad that being a young person on this forum I can't tell if Clive is trolling or not.

Hi Pete, I find myself with a rare idle moment so I'll take the time to clarify a few things. The reply that Paul submitted also warrants a response which I will include as well.

The image presented by Dave is on a different level acquisition wise (probably due too factors Paul mentioned), however the processing leaves a lot to be desired.

The point that myself and Mark have been making is that no one on the web has published images taken through an RC12 that demonstrates the limit of its native resolution at prime focus. Paul's list of mitigating factors doesn't invalidate what we are saying, if anything it strengthens our argument. As for the processing, we aren't discussing the relative aesthetics of the images, just the acquisition of the raw data which is on a different level as you noted yourself.

Pauls image is also his first effort with the RC12 (i believe)

I may be wrong, but I think it is the ONLY image taken through Paul's RC12 visible on his web page. The question that others have asked is is there something to this? After all, word has it that Paul was given a discount on the purchase price on the understanding that he would put it through its paces and post a thorough review of the telescope.... After two years, his best (only?) result by his own admission suffers from focus &/or tracking errors.

it was guided with an external guide scope,

Paul's web page suggests a QSI OAG + Orion starshoot autoguider.

and no flatterer was used.

Ritchey–Chrétiens have strong field curvature, this is true.
It is also true that they are diffraction limited for a good portion of their field (axially). So this cannot be used as an excuse for a reduction of image sharpness in the centre of the field.

Those factors alone would contribute to the image capture quality.

Contribute, perhaps.... anyway, here is a bit of an introduction to the effect of field curvature in RC's... You will quickly see that this isn't the problem with Paul's image:
http://www.dreamscopes.com/pages/pro...4/ccvrc-07.htm
(The orientation and magnitude of the blur circles are not consistent with field curvature)

Now, on to Paul's reply.
Here it is in full (for context):

That is funny Clive. This goes to show little you actually know about imaging.

First off, that scope is close to 20K and I never said these scopes were as good an RCOS. Secondly, and importantly this image was taken with an AO-L. My image is taken without an AO-L. If you knew what an advantage this has in imaging at long focal lengths you would not have embarrassed yourself Clive. He also uses focusmax for his focus. I did not do that for my image and am working on this for my RC12 now. Not only that this image you put up has had a lot of deconvolution applied to it and I can see it because I know how to process images, not seen you do that before. For the equipment David uses go to this site. Off you hop now and go back to where it is you came from.

Now deconstructed.

That is funny Clive. This goes to show little you actually know about imaging.

Paul doesn't actually know how much I know about imaging but invites you to believe he is an authority figure on the subject. Implicitly, the substance of our words is irrelevant. Paul is to be considered a trusted source of information... clive is not.

fwiw) If you have followed this forum over the last year or so you may have come across threads where Peter (Ward) and myself have held differences of opinion. Notwithstanding the intensity that the discussion oft times reaches (spirited would be one way to describe it) Peter has never once resorted to an appeal of authority even though he is one of the most experienced and skilled imagers in the country (if not the world) But I guess Peter has been around long enough to know my background on the subject.

First off, that scope is close to 20K and I never said these scopes were as good an RCOS.

Well, until we see an image that taken with an RC12 that is accurately focussed and accurately guided (yet to happen) we can't actually know how good they are..... My point from the beginning.
Incidentally, I actually do believe that an RC12 (assuming the optics are even half way reasonable) should be able to produce an image indistinguishable from an RCOS 12. I think the difference is in the fact that the RCOS will do it straight out of the box, the RC12 has mechanical issues that hold it back.

Secondly, and importantly this image was taken with an AO-L. My image is taken without an AO-L. If you knew what an advantage this has in imaging at long focal lengths you would not have embarrassed yourself Clive.

'dog ate my homework'
The truth of AO is that (unless the mount has gross drive errors) it will tighten your star images by 20- 30% at best.
ie):
http://www.optcorp.com/pdf/SBIG/AOvsNoAO.jpg
The deviation between Paul's image and the theoretical performance limit of a 12" RC is of too great a magnitude to attribute to 1 - 10 Hz seeing variation... . period.

I might also point out that the star images in Paul's image are uniformly ellipsoid across the image. The blur circle has a long side (~130%) perfectly aligned to the Right Ascension axis... there's a clue...
Ergo, it aint an optical quality, field flattener, focus or seeing issue.

He also uses focusmax for his focus. I did not do that for my image and am working on this for my RC12 now.

Two years without a properly focussed image?
Seriously?

Not only that this image you put up has had a lot of deconvolution applied to it and I can see it because I know how to process images, not seen you do that before. .

You are invited to believe that unless you post a heap of pretty pictures on the internet, you cannot be possessed of the ability to analyse them.
Now the irony in this is that Paul has used similar language dismissing the comments of the only professional optician subscribed to this forum who has actually built a Ritchey Chretien.

Off you hop now and go back to where it is you came from

To try and win an argument on the basis of being a self imposed authority figure isn't graceful, flavoured with condescension it is even less so.
But, when the argument is without substance.... well that is just pure comedy.

~c