Tilt - Anything to worry about ?

[AlistairW]

Hello,

So I downloaded CCD Inspector and simply added in a 10 minute FIT file that I took of the Veil on a Atik 383l on a WOGT81 with 0.8 FR/FF. However I have read that the Inspector works better if pointed at a star field; that said though, I am not sure if there is need for concern or not. I guess Tilt is likely to be sag in the drawtube (?) - but I am not sure whether I should be looking at tweaking backfocus or not.

Any thought on what these figures mean for me ?

Thanks

Alistair

 

 

 

[sloz1664]

I don't think you have any worries regarding tilt. Those figures are near as dammit spot on. You can check your flat field using the 3d image but if your stars are nice and round at the corners of your image you have nothing to trouble you.

Steve

[swag72]

We can spend many an hour as imagers looking at statistics and diagrams and guide graphs telling us (or so we think) about how good / bad our imaging system is. In my opinion the proof is in the pudding. What do your subs look like? I think that if you go looking for problems you *will* find them and that in turn leads to a kind of obsessive paranoia. Look at the subs and if you are happy with them don't look any further. You could spend a lifetime looking at issues that don't manifest themselves in any noticeable way in your images.

Well that's my thoughts and ones that have probably given me a little sanity over time

[alan4908]

5 hours ago, AlistairW said:

Hello,

So I downloaded CCD Inspector and simply added in a 10 minute FIT file that I took of the Veil on a Atik 383l on a WOGT81 with 0.8 FR/FF. However I have read that the Inspector works better if pointed at a star field; that said though, I am not sure if there is need for concern or not. I guess Tilt is likely to be sag in the drawtube (?) - but I am not sure whether I should be looking at tweaking backfocus or not.

Any thought on what these figures mean for me ?

Thanks

Alistair

Hi Alistair

Firstly, in order to get the most accurate figures from CCDinspector you need get it to examine the calibrated but unstreached FITS data. You'll also get more accurate figures if you ask CCD inspector to average over several subs.  You can also end up with very misleading information if you attempt to examine post processed images, since non linear stretches and convention to other image formats distorts the data. 

Anyway, assuming you're examining valid data then this then these figures are telling you that your system appears to be slightly off optimum.  For my particular system, I was experiencing slightly worse figures  than yourself - in my case my subs had slightly elongated stars at the edges of the field which was due to my Moonlite focuser not being accurately adjusted. So, after the acquisition of a laser colliminator, checking that the collimator was collimated and adjusting the Moonlite I was able to get my tilt down to about 6%, curvature 15% and collimation of about 1pixel.  The result is that I am now happy with my subs. Before doing anything you need to look at your subs - if you are happy with them then I would suggest you don't make any adjustments to your system.   

Alan

[AlistairW]

Thanks for the advice Alan ?

[AlistairW]

Sorry - should have said thanks to all :-)