Improving field flatness

[MG1]

Hi guys,

Having seen a few peoples posts recently about CCD inspector I though I'd give it a go and try and see if the various tweaks I've done to the optical system have made any difference.

I put through just over 150 images taken over the past two years and exported the reults to excel to create a graph showing the changes to field curvature, collimation offset and x/y tilt.

I've included the FWHM curve too just to see how this maps against the others. The FWHM and tilt figures are at a base+100 just to raise them up the graph a little for clarity.

I'd be interested to see what you think...it certainly has shown me the difference the feathertouch has made to the stability, but also made me wonder why I'm not getting a flatter field than 7-10% at its flattest.

Any suggestions as to where I might look to make these improvements?

Cheers everyone....hope you enjoy the graph and apologies for being a bit geeky in the quest for sharp, flat field.

Michael

[MG1]

....and now the rugby's finished here's a screen grab showing one of the latest flatness graphs. This is about the flattest it has shown, but is it possible to get flatter?

[robbieince]

Hi mike

Looks pretty flat to me.

Collimation is a tad off centre which wont help but you may not be able to do anything about that.

Is it worth playing with the spacing even if you think you have it as spec?

If you are using filters I have heard these can affect optimum

Optical path length. Ie you need slightly shorter spacing when using filters (half filter thickness?).

Regards

Rob

[MG1]

Hey rob, how's things up there...hope you've not had this nasty wintery blast that the scots have had!

I think I may have to try and learn a little more about the physics of lenses....it may be easier that fettling more aluiminium down only to find I need to make it bigger!

Just imagine....take of a thou' wait for a clear night to test it....process images, take off another thou'.....I could be a qualified optical engineer in the time!

I guess what I'm saying really is how do these figures compare with what everone else is using to image with?

My subs look pretty good to me, and I may be at the limit of what this kit can do...if so then I'm not sure I have it in me to squeeze the last 7% out!

I'm going to start saying I have an 83% flat field, and that's got to be A* in new money by anyones standards eh?

Anyway, would be good to see what people have.

If anyone would like me to put through say half a dozen raw files then they can PM me and I'll send you my email address.

I just need to know the following extra info too:

Camera

Sensor Type (ie mono or Bayer Matrix)

pixel size

& if possible saturation level (ADU)

The images need to be uncropped fits, sbig or tiff's...although it also seems to work with canon RAW files (mine were from the 5dmkii)

go on Rob, send me some from your new toy.... I dare you!

[robbieince]

Hi

Yep been grotty since kielder - tonight is first decent night and been committed with family duties - sigh. Debating going out now to try and tune in the ag8.

Will send some fits when I get a chance.

Have you seen the variable t extenders from telescope service - easily tuneable - I have one on order.

[MG1]

Any other volunteers to email me a raw or fits file to run through CCDinspector?

Might be a good comparison of what is achieveable with different setups....just a thought.

I don't want to post my email up here, but PM me and I can send you it.

Go on...could be interesting....and I've not got that many day's left on the trial...!