From: "Steve Bryson" <stevebeam@yahoo.com>

Date: November 23, 2005 4:06:23 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: On focusing (was Re: Resolution vs. sensitivity)

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