FF/FR not very FF - Help!

[mackiedlm]

So, despite getting my new short and fast refractor and NEQ6, I have spent some time trying to get my venerable old 8" LX200 GPS to take an image longer than 20s. I've put it on a wedge, done the Petersons Bucks Gears upgrade and added guiding through a guide scope. I got my first image from the set up on Sunday and I think while its promising there are still a few issues I need to resolve. Its noisy and I need to start dithering to get rid of some of the banding. I think the guiding was not awful (total RMS around 1.2" most of the time) but I know I can improve on that.

The biggest problem is what looks to me like horrible field curvature and coma. (Is that what I'm seeing or is it something else) I have a Meade 6.3 FR/FF in place and had really hoped it would be better but I'd like to hear your thoughts. Is this is good as I'm going to get in terms of flattening, or can I adjust (spacing for example) or do I need to tighten up my colimation. Any thoughts anyone?

Anyway, looking for advice.

8" LX200GPS f/6.3 FR/FF, wedged LX200 mount
EOS 1100D (un moded)
Guided in PHD2, Processed APP (this is not a full process - a very slight crop to remove some ragged edges and a quick run through APP- I think it could be improved but I'm not sure its worth the effort)
49 X 180s ISO800

 

So, thanks for looking and any suggestions or advice you can give (preferably not "stay with the 80ED and stick that hulk in a dumpster". I'm Scottish and therefore am genetically programmed to not throw things away! )

David

[Davey-T]

Could be collimation and spacing although the spacing is pretty forgiving with the .63 f/r, how have you got the camera connected ?

The DSLR sensor is quite large so will aggravate any problems in the corners, I use an Atik314L on mine with reducer and also bin 2X2 to get a more sensible image scale.

The wedge also benefits from a 3D balancing system as I find mine needs different balancing depending on whereabouts it's imaging.

Dave

[mackiedlm]

51 minutes ago, Davey-T said:

Could be collimation and spacing although the spacing is pretty forgiving with the .63 f/r, how have you got the camera connected ?

The DSLR sensor is quite large so will aggravate any problems in the corners, I use an Atik314L on mine with reducer and also bin 2X2 to get a more sensible image scale.

The wedge also benefits from a 3D balancing system as I find mine needs different balancing depending on whereabouts it's imaging.

Dave

Thanks Dave.

The camera is attached to the FR with the Meade variable ccd connector using one extension (I think its 30mm)

I had expected to have some problems in the corners but this is coming way in - probably nearly half way.

rgds

 

David

 

 

[michael8554]

Hi David

The Coma is worse on the left side suggesting tilt, which is surprising as you have good screwed connections for the FR, Meade Connector, and DSLR. 

But there is overall Coma, have you got the FR 105mm from the DSLR sensor? 

Canons have 44mm back focus, plus 10 or 11mm for the T2 Adapter, so you need 60mm extension,  30mm is incorrect. 

A stacked image is not best for examining star shapes, a single sub, stretched if too dim, is best. 

Michael 

[mackiedlm]

5 hours ago, michael8554 said:

Hi David

The Coma is worse on the left side suggesting tilt, which is surprising as you have good screwed connections for the FR, Meade Connector, and DSLR. 

But there is overall Coma, have you got the FR 105mm from the DSLR sensor? 

Canons have 44mm back focus, plus 10 or 11mm for the T2 Adapter, so you need 60mm extension,  30mm is incorrect. 

A stacked image is not best for examining star shapes, a single sub, stretched if too dim, is best. 

Michael 

Thanks for that Michael. i'l get the ruler out tonight and see what i have got.