Hi All, I was wondering how accurate does a primary mirror need to be for deep sky photography?
I'm thinking that for long exposures the accuracy of the optical surface just need to be good enough to achieve a resolution equal to that limited by the average seeing? (Well actually more like 1/3 of seeing, to get good sampling)
This would typically still be less stringent than 'diffraction limited' I suppose.
The reason I ask is because my primary mirror really needs a resurfacing, and local options here in NZ are limited especially when I also want a good protective overcoating. The cost of packing and shipping the mirror overseas, plus recoating, would most likely be higher than a new standard 10" mirror (for example one of the Bintel ones). And I would be without a mirror for a while too (oh the horror...
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My current mirror is just a no-name one that I bought 17 years ago as part of a kitset, with sonotube, cheap focuser etc. I have no idea of how good it is, but doubt it is anything special. But it does produce images that are fine for my purpose. As you may know I have taken images of various high resolution features over the years so the mirror definitely delivers. I'm just thinking that a cheap standard mirror would be just as good, or maybe even better? But I really have nothing to compare with as I have never owned another mirror.
So does anybody know if it really matters - is there perhaps a way to calculate the resolution expected from a mirror, given its properties such as strehl etc? In short, is a high end mirror really worth it for deep sky imaging?
Regards,
Rolf