Back focus incorrect?

[CraigD1986]

I have my ASI533MC Pro set at 55mm from my flattener on the 72ED, as recommended but I think the stars at the corners are all pointing towards the centre. Here is an individual sub. Does anyone have any experience of this and if so, how much more spacing should I be adding? And how?

TIA!

Light_NGC6992_120.0s_Bin1_20230824-215245_0005.fit

[symmetal]

Around 1mm more spacing I would suggest. The filters and the glass protect window will increase the required FF spacing distance by 1/3 of the total glass thickness which is about 1mm. 😉

Your bottom left stars are pretty good compared to the rest so their may be some tilt as well, but with the spacing increased to a more correct value this tilt may not be a problem.

Alan

[CraigD1986]

Thanks so much. I hope I have a 1mm spacer somewhere. If it didn’t come with the camera then I’ll have to buy one.

I recently bought a acre-in adapter from FLO, which reduced tilt a lot