Will this result in Vignetting ?

[AlistairW]

Hello,

I am introducing a tilt adjuster between my Atik383L+ and my Filterwheel (i.e Scope /FF/FR /Filterwheel /Tilt Adjuster /Backfocus Adapter / CCD). This means there will be a distance from CCD chip to Filter of around 38mm. Now normally the CCD screws in to the Filterwheel, so the distance between CCD Chip/Filter would be around 23mm.

My question is by introducing this extra distance between the CCD and Filter, should I expect significant Vignetting ? I should mention the Filters are 2" Baaders, and I will be taking flats so this might negate the Vignetting in processing.

Thanks

Alistair.

[alacant]

Hi. The tilt adjuster will introduce extra spacing between the ff and the camera sensor. It won't introduce vignetting but my guess is that you'd have elongated stars toward the edge of the frame as the ff would not then have the correct spacing. How about telescope/tilt adjuster/FF/FR /Filterwheel /Backfocus Adapter/camera?

[DaveS]

Why are you putting the spacing adaptor between the filter wheel and the CCD? You want to have the CCD as close to the filters as possible to reduce vignetting. Therefore:

Telescope > FR > Backfocus Spacer > Tilt Adjuster > Filter Wheel > Camera

[AlistairW]

Thanks for the replies,

@alacant - The backfocus distance will still be ok. I need 64.38mm, and I can get to with .12mm of that, so I am hoping star elongation will not be an issue.

@daves - Couple of reasons.

This article (towards bottom) http://www.365astronomy.com/T2-Camera-Tilting-Unit-from-Teleskop-Service.html - suggests that "especially if large bodies ccd camera are used, like Atik 383, rather than Starlight Xpress. My advice is to mount a T2 extensions, 10mm minum size, between the camera and the mechanism, to have a full access with the allen key". (Note: I am using a Atik 383).

and this article https://www.altairastro.com/altair-m48-camera-tilt-adjuster.html - suggests  " Camera > M48 Adapter > M48 Tilt Adjuster > Field Flattener > Focuser"

So partly I was following that advise, but agreed that it is better to have the camera nearer the filters, maybe I can rejig the order, but I was wondering if my original configuration would give Vignetting, given I am using 2" filters, and the backfocus is still correct ? Also partly it was how the male\female connections seemed best to work, without buying T2 invertors etc ...

Thanks

Alistair.

[AlistairW]

I think I can jig the arrangement to what has been suggested. But I guess the adjuster is being sold as a "Camera" tilt adjuster - hence why is should come after the CCD, - as it is correcting any tilt at the camera end. I can't see there being an issue with having it "earlier" in the train. Maybe I should do that - need to have a think. To be honest I will only be using it for fine tweaking as the tilt on my system is not huge, but I would like to have a go at correcting my corners on my subs.

Thanks

Alistair.

[Peter Drew]

I'm no AP expert by any means but why would anyone use a tilt adaptor for stellar imaging rather than addressing sag or mechanical issues instead. From posts I've read in the past I have the impression that imagers go to great lengths to keep the camera et al as square as possible. I am aware that solar imagers frequently use tilt adaptors to mitigate or eliminate Newton rings but this seems to me to be a different type of imaging.    

[AlistairW]

Hi Peter,

You are right of course. It's simply that I find that some of my corners on my subs have out of shape stars. So I wanted to see if a small tweak with a tilt adjuster would help. No idea if it will, just an experiment at this stage. Ultimately it might just become an elaborate T2 extender of course ...

Alistair.

[AlistairW]

(I guess another reason is that the chip on the CCD could be slightly tilted, and then there would be very little you could do to correct).