Re: Focus vs temperature Graph Request
- DaveH wrote:
> Holy cow...Serious bunch here !There are electric focusers that monitor the temperature of the OTA, and
> I am going to love it ...
> Listen I thought there was all kinds of software that could reset/evaluate focus..
> Not that I am that high end...I take test shots and ran a cable to the house..
> So would that not be the way to go...setting up a periodic automated refocus...or was I dreaming ??
automatically adjust themselves according to calibration curves that you
create ahead of time.
Another way to maintain good focus is to use automation software such as
ACP or CCDAutoPilot that can be configured to periodically invoke a
focusing program such as FocusMax to refocus the telescope.
I believe that imaging programs such as CCDSoft and Maxim also have the
ability to automatically focus, but I haven't used these features for
Automated focusing is not as trivial as it sounds. To achieve good
focus, FocusMax or other software needs a suitable star, which might not
be available in your camera's FOV for the target you're currently
imaging. Consequently, the automation software or the focusing software
must use a star catalog to identify a suitable star, slew the telescope
to it, center it on the chip, perform the focusing operation, then slew
back to your target and center it, all unattended.
The choice is yours. If you don't mind staying up all night or getting
up in the wee hours, it's perfectly reasonable to interrupt the imaging
process and focus the telescope yourself. I did exactly this for several
years. I set an alarm clock for just before my target was to transit,
then got up and walked out to the observatory to perform the meridian
flip on my German equatorial mount. Following this, I refocused,
centered the target and resumed imaging. Then I went back to bed. With
remote-control software on the observatory PC, I was able to do this
from inside the house -- much more comfortable than going outside in
15°F winter nights.
Currently, though, I'm using ACP automation software, and this makes
imaging soooo much more productive and enjoyable. Aside from the
automatic periodic focusing, ACP's big benefit to me is its ability to
accurately center by target on the chip. This alone saves me 5-10
minutes at the beginning of imaging session, and another 5-10 minutes
after the meridian flip.
Montpelier, VA USA
Thanks for that info...
I am one of the "set the alarm clock" crowd..and probably will be for some time..Doing it from inside is my only comfort.
I avoid/fear complexity(and more software !)
You have some very good results on your site.
We are neighbors,(atmospherically),I am in Ottawa.
- You're on the right path. I've always had more luck with refocusing than temperature compensation. Just use FocusMax along with an automation program like CCDCommander, CCDAutopilot, or ACP. All three programs will let the software pick a star and go off and do a focus run, although I admit I prefer CCDC in this regard...as I can pick the focus star on my own, when I want it to happen.
Direct from Boston - brilliant diamonds in pea soup
Also check out the astro_narrowbandYahoo group!
From: DaveH <davehalliday51@...>
Sent: Fri, March 12, 2010 9:48:09 PM
Subject: [ccd-newastro] Re: Focus vs temperature Graph Request
Holy cow...Serious bunch here !
I am going to love it ...
Listen I thought there was all kinds of software that could reset/evaluate focus..
Not that I am that high end...I take test shots and ran a cable to the house..
So would that not be the way to go...setting up a periodic automated refocus...or was I dreaming ??
--- In firstname.lastname@example.org, "Rick" <rickwiggins@...> wrote:
> Hi Don,
> Since the data desired is how the scope foucus tracks with ambient temperature, you should take the ambient temperature as you pointed out. One thing to consider here is what you are trying to achieve. If you are imaging and you know what the outside temperature gradient will be, you could measure the outside temperature vs. focus behavior. Of course there will be lag and variation, but if you are gauging on outside temp, then measure that. I measure and track the temp in my dome and outside and I have a pretty good feel for how both will change and track over the night for given conditions.
> If you want to know what the scope does at various temps (i.e. how much the focus varies over temp), then you should measure the scope. As you point out, the scope has different materials in different thicknesses, so it will not track uniformly. In the lab, we instrument with many sensors to understand each area independently and learn the interrelationships over temp and temp rate change.
> I think the most important thing for us is the measurement that you suggested as that is probably the temp that most people measure and track.
> I will be interested in your results.
> Thanks, Rick
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