From: "Tim" <tjp314@pacbell.net>
Date: November 23, 2005 6:12:22 PM MST
To: Astro_IIDC@yahoogroups.com
Subject: On focusing (was Re: Resolution vs. sensitivity)
Steve:
The display sharpness (or something like that) option in Astro IIDC does a pretty good job.
I fiddle with my focus until the number is maximum most of the time (it goes up and down
depending on the instantaneous seeing). Another way to do it, which I haven't used in a
long time (mainly with the ToUcam and Registax, in the "old days") is to take short 100-
frame videos, stack and process the results from a few focus positions and compare the
results. This works really well if the seeing is consistent, but if it changes much it might
not.
-Tim.
--- In Astro_IIDC@yahoogroups.com, "Steve Bryson" <stevebeam@y...> wrote:
Hi Again - Alan wrote
--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:
--- snip ---
If focusing is a drag at 640 x 480
you need to improve the focuser
Focus control is not really an issue: I have a JMI motorized NGF-DX2 w/ digital readout -
That cost some $600 alone so I hope I don't have to improve it more :)
But Alan's comment raises an issue I've been wondering about: In even the best seeing
I've
seen in the last month, at best the image goes in and out of focus. I try to set the focus
to
maximize the time the image is in focus. I shift focus a little bit, watch it (in Astro IIDC)
for a few seconds, shift the focus and watch again. The motor control and digital
readout
earn their keep here 'cause I can go back to the what I recall to be the focus value and
verify it.
But this is all very qualitative and I'm not sure I'm getting best focus. A time graph of
the
sharpness measure could be a real help here. Do any of you have a better technique?
Unfortunately I can't focus on a nearby star since I have to remove my barlow (which
breaks focus) to find new objects.
Thanks
Steve
http://homepage.mac.com/stevepur/astrophotos.htm