Flats and CCD Inspector concerns

[Droogie 2001]

Note sure what to make of this. I was watching a video on improving flats for my WO Star 71 and using CCD Inspector to help with this.
I downloaded the free trial and performed a Flat analysis on one of my Flat frames.
I was fairly alarmed by the results because when I looked at them in SGP they looked fine.
CCD Inspector appears to show at least two issues. One is the centre of optical illumination is quite a way out from the centre of the CCD chip (KAF8300)

Also not sure if the high percentages around the image are an issue? Though they seem to be fairly consistent though.

When I perform a high stretch on a Light frame the image in SGP does seem to follow the off centre illumination issue.
I have looked at other settings on CCD Inspector but have to say I am not too sure on whether the results I get back are good or not.

How or do I need to adjust the optical illumination train to be more central? Is this a massive issue?

Basically I have the CCD camera fixed with extension tubes to allow me good focus with not much drawer tube extension (11mm). It is a good fit with no slack.

I have included a picture of one of the flats.

Thanks

[theastrodragon]

How are you taking your flats? It could be the flat field isn't fully uniform, and/or suffers from vingetting (which might explain the data)

[Droogie 2001]

Using a flat panel with SGP flat calibration.

[theastrodragon]

I'm not familiar with SGP, are you working on the flat before using CCDInspector? If so, try an analysis of the raw flat

[Droogie 2001]

Hi ,

Yes capturing them with SGP Flats calibration tool which times how long it take to reach a set ADU.
Are you are suggesting I capture in CCD Inspector and then inspector the captured flat? I can understand the logic in this.

Thanks

 

[MattJenko]

With flats, as long as they are taken with the same off center as the lights, is this a real issue?

[Droogie 2001]

The processed images have a distinct light gradient when stretched. (Admittedly high stretching) Also surely not having the core light zone in the centre means I am losing detail of sorts? As I say i know next to nothing about CCD inspector but  understandably seeing my optical track not correctly aligned is worth investigating?

[theastrodragon]

Does CCDInspector show anything off-centre with a starfield rather than the flat? This would help show if its an issue with the flat, or the setup.

 

Also, a flat field cant remove everything. Gradients due to light pollution wont come out as they vary with the time of exposure, especially if you have bad light pollution or the object is low. What a good flat can do is remove vingetting and donuts, which makes dealing with the gradients a lot easier.

[Droogie 2001]

Sorry for the late responses. I have tried it on a Star field, though it does have some small galaxies within it. Also I understanding that it should just be a star field but I do not currently have the ability to perform this yet (cloud out)

That said it still shows off centre with these star field images.

I will be looking at taking flats via CCD inspector (if I can get it working with the camera) this week and will see what this yields. I fully expect it to be off centre by about 14% which is what it is at currently.

 

[theastrodragon]

Having some stuff other than stars shouldn't be a problem as CCDI is supposed to ignore these.

The main issue is getting enough stars in the field (300+ according to their site as a minimum). If you don't have enough stars, the algorithms give inaccurate results.

[Droogie 2001]

Took a look at CCD inspector last night and managed to get the application to pickup flat images which I was taking with SGP. Basically you point CCD Inspector at a folder for it to monitor and it then pickups any new FITS files that are added to that folder, simple.

That's about all I can do with the flats. Still shows the same off centre image which is no surprise as the 3rd party application (SGP) is the same one as before.

The next step would be to get outside and take an image of a star field but all of this relates to collimating and as I am not looking to collimate but just want to get my Optical centre lined up with the CCD centre. That is get the two crosses to overlap or as near overlap as possible. Then it looks to me that some sort of adjustment is required, if indeed this is possible?

I will email WO and see if it is possible to adjust the optical path as I know from this You Tube video that this is the solution to my issue (14mins in) but in that video the scope is a Sky Watcher and not a WO Star 71

https://www.youtube.com/watch?v=SX9Iz9FQRtU

Has anyone carried this out on a William Optic Star 71? There are two silver Allen key nuts underneath as well as a lot of small nuts but I have no idea what each does. Clearly I need to check before I start messing with them...