Do you think my vignette is uneven?

[swag72]

Following on from this thread (towards the middle), it once again came up about my uneven field in my images. Kev and Billy suggested between them, 4 flats, each one with pressure on the 4 sides of the camera. So that is what I have just done. Below is a screen grabl of the 4 flats just taken. Top left pressure towards the left, bottom left pressure towards the top, top right pressure towards the right and bottom right pressure towards the bottom.

I know that it's not the best image in the world, but to my eyes, the vignette doesn't appear to move. If you agree that suggests that the issue is somewhere else in my setup.

While I was putting it together for these flats I realised that I hadn't been tightening my screw in reducer and that it had some movement in it. Perhaps that accounted for the fact that last nights flats looked off centre, whereas this mornings look pretty central.

I would welcome your comments on this. Wonder

a) whether it really was as simple as not tightening the screw in reducer - I stopped screwing it tight as in the cold it was a pain to unscrew or

it's somethng else in my imsging setup that I haven't put on today, such as guider, cables etc.

c) whether this means that I can stop worrying about my optics needing aligning and that my camera sensor is square and lastly

d) I cancel that moonlite order as my focuser is fine!!

[jgs001]

I'm no expert, but they look good to me... If something in the train isn't tight, then you can get small amounts of flex and that will cause all sorts of issues. Therefore I'd be inclined to think it was the reducer causing it. I don't have screw fittings, but have now taken to, once I've got the connections finger tight, just given them a small (1/4-1/2 turn) tweak with either a screw driver or pliers. Not enough to cause compression damage, but enough to lock things down tightly. That resolved the off centre flats and oddly focused single edge iamges I was getting.

[Photosbykev]

There doesn't appear to be any change in the vignette pattern so that would suggest there isn't any mechanical movement in the optical path. The reducer should be screwed in until it is bottomed out, if you have problems removing it then a touch of grease on the thread might help.

[swag72]

Cheers both - My thoughts as well, vignette seems static.

So , tonight I'll try again withthe reducer screwed in nice and tight and have a look at the stars. If there's no elongation, then maybe I get myself a CCD instead with the money I'll save from not replacing the focuser!!!!

[Psychobilly]

It soemtimes helps if the bits are fitted together with the scope pointing vertically downwards as you tighten them up..

Billy...

[swag72]

Cheers for that tip Billy.