Jon Isaacs loaned me one of his ST80's a few months ago to test out the effects of the 495 Longpass filter on CA. With my Vixen 140NA there is considerable CA and the longpass filter eliminates the violet fringing. Weather has been lousy and tonight was actually the first night with excellent skies for which I could test it out on the Moon.
I used the ST80 with a 2x Barlow and a 5.5mm Meade UWA which gives 145x. The CA without the filter was not bad, but there was some loss of sharpness and contrast evident without the filter. The 495 Longpass is just as effective with the ST80 as with the Vixen140. Purple fringing is eliminated and contrast is improved noticeably. Lunar features were sharper and cleaner with the filter than without.
There was one crater near the terminator which had a smaller crater on the rim. I did not notice this small crater until I added the Longpass filter. Then I was able to remove the filter and spot the crater, but it lost some sharpness when the filter was removed.
That said, the ST80 had much less CA than the Vixen 140. So the relative effects are not as dramatic even though the final result is the same. I think from this experience that the 495 Longpass is a excellent for a large aperture achromat, but you might get away with just a #8 light yellow with a ST80.
A final note - the moon wad quite spectacular using a 32mm Brandon and 2x Barlow (25x) with the ST80.
Edited by russell23, 08 August 2014 - 10:53 PM.