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