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?
If you mean the target being the beehive
and not the guidestar, the target never went behind behind the tree, the
guidestar did.
Still, it doesnt make any sense to me that
the hotspot would increase on a shorter exposure.
When using the E200 with the same lens at
f/4 for 8 mins, I would get a nice illuminated center, but when I cut
down to 7 mins at the same site, the illuminated center was mostly gone
and the image was scanable...incredibly short exposure.
How can you guys go for umteen minutes
before stopping the exposure?
Are my skies really that
bad?!?
Now with the shorter of the
exposures,(23mins. vs. 30) using the H-a with the TP, it would seem to
me that there should have been less of a hotspot.
Now I dont even know where to begin...just
doesnt make sense.
My site is fairly dark...around 5.5-6.2 mag
depending on the night.
With the H-a, that shouldnt of really
mattered right?
Stopping the lens down will not effect 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.
Ya...I'll try that...this is killin
me!
Now thery'll be clouds for the rest of the
month.
Brian