I was using a 105mm f/2.5 and it was wide
open for both shots. My first shot was for 30 mins., but I forgot to set
the focus right.
The 2nd shot was focused right, but was cut
short at 23 mins, because my guidestar hid behind a tree...murphy missed
me(g).
My unfocused shot of 30 mins has the least
vignette, while my focused shot of 23 has the most.
About how far should I stop down? Will this
in any way effect my calibration mark and how it focuses?
Thanks,
Brian
I thought you were using a wider angle lens
than that. You should get pretty even illumination with an H-Alpha
on the 105mm f/2.5. I am now puzzled by the longer shot having less
vignetting. Perhaps this is related to your target going behind a
tree?
Stopping the lens down will not affect a
focus that has been recalibrated to H-Alpha focus.
Just for grins, try the shot again at f/4,
focus properly, and stay away from the trees <g>. I'll
bet you will find almost no vignetting at all and seriously sharp star
images. Good luck.