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Old 03-02-2011, 05:16 AM
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Problem with focusing

Hi All,

I hope someone can help me understand wot is happening,when I try to focus using inspect in maxim DL, last night started of on IC434 exposure 5 seconds opened up inspect and got FWHM = 0.00 to 1.75, Half Flux Dia = 0.00 to 1.5, then went to 30 seconds and got FWHM = 12.4 HFD = 18.8, 120 seconds, FWHM = 24.3 HFD = 28.7, this append without moving focus or tushing scope, all help very much appreciated.

peter

Last edited by p1taylor; 03-02-2011 at 09:50 AM.
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Old 03-02-2011, 07:07 AM
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lepton3 (Ivan)
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Don't know what is your scope or camera, but 5s and 30s(!) sound like very long exposures for such a bright target as Betelgeuse. Are you sure you aren't saturated?

When I look at the FWHM measurement from Artemis Capture, I find I need to have a reasonably dark background and be well away from saturation for it to make sense. This means reasonably faint targets. Maybe the same applies to Maxim?

-Ivan
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Old 03-02-2011, 07:38 AM
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Ivan I thought you focused on a star, I have to do it on some thing as I cannot see IC 434 on screen, scope RCX 10", camera SX H9C, will this help.

peter
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Old 03-02-2011, 09:54 AM
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I'd find a star in the vicinity or even in that field and draw a box around it with Maxim, but you will have the "check" the box that says "Mouse" or similar, so you just select a small area. Then use "Large Statistics" to get the readings. With something like the H9 I would be aiming for a 6th mag star I guess, but each scope/night/camera/person is different. 5 seconds, or more? No way. I use about one second usually.
Gary
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Old 03-02-2011, 06:16 PM
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Peter,

Yes, you are right you need to focus on a star, but with your scope and 5s on Betelgeuse I'm surprised if you see anything but glare!

I'd typically choose a star in the same field or nearby that gives me around 10,000 ADUs peak and focus on that. Also, if your camera/software lets you do a smaller subimage with quicker download times, that makes feedback quicker.

Good luck.

-Ivan

P.S. I just recently made myself a Carey mask, and it does make focusing easier than monitoring the FHWM value from the capture software.
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Old 04-02-2011, 09:52 AM
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Gary, Ivan,

No it wasn't on Betelgeuse it was a star in IC434, so do I need to pick a star not to britte draw a box round it and image at say 1 or leas seconds, then ignore if numbers go up in longer exposures.

peter
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Old 04-02-2011, 09:59 AM
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Peter,
not sure (still) what you are asking.
Shoot a one second shot with the guide camera. I like to use a star about 5th mag or so, but that is me, using a Lodestar, and a 50mm finder, so yours may be different. Contrary to what others have said I like the star to be pretty crisp to start with, so eyeball it first. Again, different to some, I like the count to be about 40,000, and if it gets to 65,000 then I find another.
Then draw a box around the star you want. You may have to check "sub-frame" or similar so that the box gets used, it is different I believe on the latest V5. Having the smaller box allows quicker downloads, and speeds the process up. I usually use "Display Large Statistics" as well, in the "Options" section of "Expose".
Focus using the readout you get, looking for the highest number(s).
Make sense?
Gary
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Old 04-02-2011, 10:27 AM
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Gary,
what I am after is focusing the RCX, not lodestar that is working OK in PHD, where do I find this count of 40,000 canot seam to find it in my Maxim 4.61.

peter
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Old 04-02-2011, 11:53 AM
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http://steve000.dyndns.org/images/as...s/IMG_5734.JPG

30 second of Betelgeuse. focus issues probably cause of the flare
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Old 04-02-2011, 06:10 PM
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Peter,
the Lodestar comment was unfortunate, as I can now see it threw all off the scent. Forget it.
The image your imaging camera produces is what you should be concerned with. The readout (and I forget the actual terminology) should be about 40,0000, but not peak out, saturated.
In your case, get the lowest FWHM you can. In Maxim it also reports the "value" of the star concerned, that should be as high as you can get, but again, not saturated (above 63000/65000).
Gary
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Old 04-02-2011, 06:15 PM
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This is getting interesting!

Steve000, not sure what the point of your image is. No offense intended, but in that image, it looks like Betelgeuse is saturated so I'd be surprised if you can get a reasonable FWHM reading.

Anyhow, Peter has clarified he's not trying to focus using Betelgeuse, but a fainter star, so OK on that score.

Peter, sounds like your question is specific to the Maxim software you are using. I use the Artemis software, so I can't give specific instruction, only general advice.

What works for me is to use a star that is below saturation (40000 counts is probably still OK) with a short (say 2s) exposure time, then adjust your focus so that FWHM is minimized. At that point, peak ADUs will be maximized.

So you need to work out what quantity your software is reporting, and optimize for that.

-Ivan
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Old 05-02-2011, 05:02 AM
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Hi Rally,

This may sound silly but where do I find ADU in Maxim DL 4.61 the only thing I can see is in Information^Aperture - are ether Intensity or Pixel is it one of these, thanks for all the info.

peter
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Old 07-02-2011, 12:46 PM
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Quote:
Originally Posted by lepton3 View Post
This is getting interesting!

Steve000, not sure what the point of your image is. No offense intended, but in that image, it looks like Betelgeuse is saturated so I'd be surprised if you can get a reasonable FWHM reading.

Anyhow, Peter has clarified he's not trying to focus using Betelgeuse, but a fainter star, so OK on that score.

Peter, sounds like your question is specific to the Maxim software you are using. I use the Artemis software, so I can't give specific instruction, only general advice.

What works for me is to use a star that is below saturation (40000 counts is probably still OK) with a short (say 2s) exposure time, then adjust your focus so that FWHM is minimized. At that point, peak ADUs will be maximized.

So you need to work out what quantity your software is reporting, and optimize for that.

-Ivan

My point of the image was to show a 30 second exposure how flared out the star looks. if his reading is all over the places this is probably why as i believe the software is designed for even light sources not over exposed flaring like my pic. thats all
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Old 07-02-2011, 09:20 PM
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Quote:
Originally Posted by steve000 View Post
My point of the image was to show a 30 second exposure how flared out the star looks. if his reading is all over the places this is probably why as i believe the software is designed for even light sources not over exposed flaring like my pic. thats all
Oh, I see. I wasn't sure, but thought maybe you were suggesting it was all ok. But now I understand you were showing just how over-bright it really was. Good illustration then.

-Ivan
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