Odd stars on one side of image

[spillage]

I am hoping that someone will be able to give me insight to this issue.  I have tried adjust the spacing in my mpcc, making sure the camera is flat when attached to the scope and collimated the scope many times. I feel that this is collimation and that my collimation skills and not good enough but with some many possibilities I am pulling my hair out.

Guiding with this image was around 0.6" and PA was done using a polarscope.

The stars on the left look very odd like small triangles and the stars on the right hand side look okay.

If anyone has any ideas it would be more than appreciated.

L_Light_2018-08-06_23-28-48_Bin1x1_180s__-20C.fit

[Thalestris24]

You probably have some tilt somewhere. Which scope was it?

ps it's better if you post jpegs so that people can see an image without having to download and save a file...

Louise

[spillage]

This is on the sw quattro. I only had the .fits file to hand but will post up the .jpg. I will have a look at the adjustment available on the focuser tomorrow. This is the only thing I have not looked at yet.

[Thalestris24]

This might be of interest

 

[Oddsocks]

As above, tilt is the problem, quite significant too. 

CCD Inspector gives 34% tilt for your posted single image 'though CCD Inspector gives more accurate results when averaging ten or more images and ideally only star fields, no nebula or galaxies in the image as these can skew the results and introduce localised distortions (small humps or sags in the curvature and 3D maps).

 

[spillage]

Thank you both for your input. I have stripped the focuser and found it was not central so hopefully this is now resolved. Tonight is looking a bit cloudy but if I get any chance at all I will take some test shots.

That curvature is worrying as I am using the mpcc. Just been out to check and from the sensor to the m48 shoulder is 58.5mm. Should the curvature be this bad?

[Oddsocks]

2 hours ago, spillage said:

That curvature is worrying as I am using the mpcc. Just been out to check and from the sensor to the m48 shoulder is 58.5mm. Should the curvature be this bad?

I think that is not unusual for a non-dedicated flattener Mark. 

The MPCC is designed to suit a wide range of focal ratios and will be at it's most effective in the middle of it's quoted range. As you approach the limits of it's designed f/r range (f3.5 to f6.0 for the Mark III MPCC) then it's performance is reduced a little.

There is a dedicated Aplanatic flattener for the Quattro which would give a flatter field, quite expensive, though not as costly as the Wynne Corrector for my OO UK f3.8 AG8 which retails at a little under £1000 when the VAT is added.

I did have a MPCC mark II somewhere but haven't seen it around lately, I think I may have sold it off with an old scope. I seem to remember that the distance from the M48 shoulder to the sensor should be 57.5mm (or 55mm when the T2 ring is attached) and at the Quattro f/r a mm out either way will have a big effect so you should try to get the correct 57.5mm distance and measure the field flatness again. Add or subtract distance under test until you get the best performance the MPCC can deliver.

There used to be a free trial for CCD Inspector so you might find it useful to download a copy and trial it to set up your system.

William.

[alacant]

Hi

Yeah, I think it's the cc at the limit of what it can do. LHS has astigmatism and with the camera tilted  too far away from the cc. I'd recommend this cc which copes with tilt without having to fuss with spacing and stuff.

HTH and clear skies.

Here's a jpg: