Quote:
Originally Posted by Shiraz
At 0.5 degrees fofv with an 8 inch aperture, AO will not help with seeing, even if you can find a really bright guide star.
The main lunar image in the link shows the problem http://www.footootjes.nl/Astrophotog...hy_Seeing.html - the turbulence induced displacements on the left hand side of the image are not in any way synchronised with those on the right hand side. Even within the main craters, the central peaks seem to be moving independently of the motion of the crater walls. If, instead of the moon, you had a guide star in the left hand part of the field and a target in the right hand bit, an AO tracking the guide star will regularly see it moving in a different direction to the motion of the target - an AO correction in the wrong direction will result in worse effective target motion than with no correction at all. The "isokinetic patch" for this set of turbulence (the region over which points are moving in synch), is smaller than one of the lunar craters shown. With typical conditions it will only be one or two arc minutes with your scope and AO simply cannot help with seeing if the guide star and target are separated by much more than this - in fact AO is likely to increase the star sizes due to seeing - they will probably be round, but bigger. |
Hi Ray,
I can understand your logic.
How does it explain the pictures on SBIG's page?
https://www.sbig.com/products/adaptive-optics/ao-x/
The star size is smaller.
Also an ONAG only passes 5% of the light to the guide camera.