If I had any hair left i'd be ripping it all out by now! (aka Now Whats Wrong?)

[timetraveller]

hiya TJ I'm no expert on this but are you sure your not getting digital delay between the two imaging camera's maybe its a delay between them that is causing a drag effect in the motors it wouldn't be noticeable over a small number of images but over much larger numbers the effect might be accumulative regards PETE

[Whippy]

I don't think that's helping Tim, I reckon the calibration and the guiding exposure times have to stay the same. I normally go for 1 second and go longer (1.5 or 2 secs) if I can't find a star and stick with that.

Tony..

[Tim]

I have tried getting into Starks yahoo group to ask the question but that is one messed up process, i give up on that. Anybody happen to be signed up already?

[Tim]

Great article by Craig Stark here with a technique for identifying flex;

http://www.stark-labs.com/blog/files/category-ask-craig.php

[Tim]

Just had this reply from Craig Stark, thought it might be useful to post.

Opinions or extra advice on the pixels etc bit? I dont really understand enough about that and could do with reading a tutorial or something?

Is he in effect saying, dont bother with F10, go for f6.3 and enlarge the image in photoshop for the same result?

???

Thanks

TJ

[MartinB]

That's very true Tim because at 2000+mm f/l in with normal size pixels the seeing just isn't going to be good enough to give extra resolution...unless you use active optics.

As far as guide star exposure goes - you want the best signal to noise ratio you can get without over saturating the star. Guiding is based around the centroid and this will be calculated with best accuracy between 1/3 and 2/3 saturation. This also applies to calibration to some extent. The time saved by choosing 0.2 vs 2 secs is around 9.2 seconds. Just how much of a hurry are you in Tim!!! So your exposure time has to be determined by the brightness of the guidestar. If you use an over saturated star your guiding will be poor.

[MartinB]

Ah! just read the Craig Stark piece so my last reply is completely redundant :oops:

[MartinB]

This is the best guiding article I have ever read. http://aajonahfish.com/autoguiding.htm

[steppenwolf]

This is the best guiding article I have ever read.

I agree - I like the way the guy has researched and written the text, especially the S/N simile

[Tim]

Seem to of missed the reply out there somehow, here it is;

No, that shouldn't affect things. I'd lay money you're looking at differential flex, but I've not looked at your logs or anything. I'm swamped (and beyond) at the moment, but that is a LONG focal length for AP work and you're on a moving-mirror scope. I'm not sure what camera you're on but if it's got a typical pixel size of about 7 microns you're at about a half an arcsec per pixel. Unless you've got an adaptive optics unit, and/or *ultra* pristine seeing, you're not going to gain anything by running under 1 or even 2"/pixel. If you want a "close up" of the Crab there, you're really not doing any better (and maybe worse) going at prime vs. just blowing the image up in your photo editing software.

Craig

[Psychobilly]

Thought there was somethign missing TJ

I actually experienced (or maybe it was becasue i was lookign for it) the same drift in deck inthe stacks that wasn't apparent on DSS is shows up as a a gradient along the top and bottom edges of the stacked image (more noticable on the bottom) I did take some RA DEc at the start and End of Each 270 min set and will have a look at them later..but realised I have turned the logs off in PHD doh...

Possibly for widefield it might be a good thing as it helps with the drizzle process.

Billy...