Off Axis Guider test

[Rocket Pooch]

Hi,

Like the 8" newt I got around to testing my OAG tonight for the 1st time, its a little fiddly to setup the 1st time, but blimey its good.

Here's the complete setup, look no guide scope or second set of dew hears.



Here's a full frame of M51 with this setup, non processed

http://farm3.static.flickr.com/2705/4522224226_3f09f7caf6_o.jpg

Here's the centre full sized crop, look how round the stars are, there was about a 6 pixel shift over 100 minutes, I think this was the focuser bending a little.....

[MarkS]

Good result Chris - you must be really pleased - the whole setup is unbelievably compact now.

Was it difficult to find a guidestar?

[RobertM]

That's impressive SD.  It'll be good to see it in action on the newt.

Must be great having dark skies all the time - I'm looking forward to some great images from down there!

Robert

[Rocket Pooch]

Hiya,

Mark, guide star is not a problem the mirror is about the size of the chip and a was getting guide stars with 1 second exposure at 15k ADU much brighter than the main camera, infact the guide camera seems to be 4x as sensitive as the main camera.  The fiddly bit is focusing the OAG, what I did was to get the OAG near the camera, and focus the main camera on a tree 200meters away then focus the OAG.  This gave me approx focus when I did the imaging, a little tweak and it was done.  The only thing which will throw this out is a change in filters, so I ensure all my filters Ha, SII, O3, LRGB are all parfocal, well nearly.

Robert, the newt is going to get a 3" focuser when I sort out the optics, this setup is really heavy now and I don't think the standard focuser on the newt will work, the skywatcher one is ok, but I need to do a slight pip with it, that involves polishing the flat plate and applying some alchohol to the rubber (oh err missus).

The biggest thing here is the camera, it a babe, but all this wide field imaging is odd, I really would recomment people stick to 314L type camera's unless they want to get into a new world of pain

So chuffed I am, that chuffed I'm going to make some new dew heaters for the 8" ARC and give this a go with the OAG.  This should be a perfect setup for small objects....

See you all at the weekend, although apparently transparency will be crap, something to do with a volcano?

Chris


P.S. There is a bug in AA where it instantiates a new ASCOM connection and therefore the ASCOM guiding did not work, if it had the guide cable would also be missing, I might switch to Maxim, but I was getting .02 RA and .10 DEC guiding, this is well in the sub pixel (dispite the note below).

P.P.S. Also dont leave an additional 7.5kg on the mount when you change scopes the mount goes click click when it get at horizontal hopefully I have not done anything bad.....

[MarkS]

P.P.S. Also dont leave an additional 7.5kg on the mount when you change scopes the mount goes click click when it get at horizontal hopefully I have not done anything bad.....

Eeek! 

I agree regarding large chip imaging.  The tolerances required are very exacting. Collimation and CCD alignment really have to be spot on.

[RobertM]

3" focusers aren't cheap and may be a bit overkill for what you want.  Did you use the 'newt' design prog to check the vignetting?

The guide chip is ahead of the main camera/filters so that may account for such a large discrepancy in the sensitivity.  It may also not have an UV/IR blocking filter which would also make a big difference.

Robert

[MarkS]

Did you use the 'newt' design prog to check the vignetting?

Sounds interesting.  What is it?

[RobertM]

It's a very simple ray tracing program to help design Newtonian systems.
http://www.dalekeller.net/ATM/newtonians/newtsoft/newtsoft.htm

[JohnP]

mark - try this

http://www.simtel.com/product/view/id/26652