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The procedure is simple and relatively fast.
In your case you would need to correct the metal back distance of your reducer and get it to 71.5mm. Make sure you allow for the thickness of the filters correctly. If they are 3mm you add 1mm (1/3rd) to your overall spacing.
1. Take focus image of an area of stars and focus the image (perhaps just focus the centre stars)
2. Examine all 4 corners and sides. Are they all in focus, tight looking and round? An in focus image looks a certain way. I am sure you know what it looks like. It has a tight look for want of a better word. I have learned to recognise that exact point but software that uses graphs is what I normally use (the old CCDsoft).
3. Let's say the top right corner has bloated stars perhaps a bit elongated as well but the other 3 corners are tight looking.
4. Determine the orientation of the image to your physical camera.
Standing behind your scope's camera the image displayed on your computer is reversed up and down and left and right. So top left in the image is bottom right on your camera looking at it from behind.
I loosen my camera where it attaches to the filter wheel (you will need some point where you can insert the packer then retighten or invest in a tllt adapter - Teleskop Services has serveral and Gerd Neuman has a nice one but expensive).
It will require a thinner packer than you might imagine. Try a thin one like .18mm.
Tighten up, refocuc and take another focus image. I use 2x2 binning to speed it up plus the faster download speed. But once you have it finish on 1x1 for maximum accuracy.
Is it better or worse or the same? It should be better. Check the other 3 corners. Sometimes you pack it the whole side as the whole side is off.
So repeat and get the packing right until its good on all 4 corners after refocusing.
If you find you have a lot of packing in one corner, start again, you went off the rails. Its usually only a smallish packer with these large sensors.
Once you got it right make a night using Windows notebook and save it on your computer so you know next time if you remove the camera or swap cameras. I tape the packer to my Proline so it stays in place even if I swap it out to another scope.
Tilt is not necessarily in the sensor, although that would be a source. It can be not quite square adapters, dovetail adapters for example can lock in slightly off the groove.
Flex is a different issue and if its flex then that would require stronger everything and tightening the focuser up etc. Flex seems to be more of an issue for Newts etc not refractors which are easy to handle.
Greg.
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