Guiding Woes sorted at last... :-)

[JohnP]

oh yes you are right... not worth it for £75+£5 delivery - Bern is selling for £94 delivered so may as well get new.

Thks anyway,  John

[RobertM]

How much backfocus does the OAG take up and are you using it with your Atik or a DSLR ?

Thanks
Robert

[JohnP]

The brightstar takes up 32mm. I am using with Atik (I don't image with DSLR).

I did some more tests on Tues night on DSO's. I did some quick images of m101 - total 6x10min subs - When I stacked them the log file shows total movement between first & last frame as following:

dX = 0.08, dY = 0.74, Rotate = -0.03 Deg, Scale = 1.00

Measurements in pixels - so avg per frame in Y was .74/6 = 0.12 pixels - this may have been down to Polar alignment - Anyway it was essentially no movement & I could easily stack all 6 frames with no star alignment & stars were still round..

For a laugh I also moved to m57 (totally different part of sky) - again finding a guidestar was no problem & did 2 subs of 20mins each (my first time to ever attempt such long exposure) & they downloaded straight on top of each other again. Again no alignment necessary to stack.

Hope that helps,

John.

PS - The only thing I'll say (I think I have already said this once) is that the guidstar is not so much a star as a straight line - terrible coma because it is on edge of light cone. However, the guide prog still seems to be able to find centroid & guide successfully.

[RobertM]

Those figures look pretty impressive John.  I'm assuming your measurements are in pixels, what was the pixel scale in arcsec/pixel ?

32mm is quite short.  Is the Brightstar very strong, also what length is the 2" push fit adaptor and can it take different camera adaptors?

Thanks
Robert

[JohnP]

Robert will take a picture of setup & send to you. Not sure about the lengths I will need to measure. I have just ordered one from Bern - I am currently borrowing Jim's - so if you speak to him nicely you never know he may let you borrow to try out on your setup...

With regards pixel scale as you know my atik16ic is only 640X480 pixels - In fact this was the main reason for trying to sort this - I always have to display my images full size because there are so few pixels so any egg shaped stars etc. really show up whereas people with DSLR's or 3,000 pixels sensors normal reduce image size for display so it is not as noticebale. 10 pixel drift to me is a lot to loose around the edge of a frame as well

Sorry getting back to field of view/ resolution my chip images at 2.54 arcsec/pixel which yields a FOV of approx 28 X 21 arcmins.

Cheers, John