Author Topic: Lunar imaging question  (Read 1510 times)

Davids

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Lunar imaging question
« on: April 26, 2017, 02:22:39 PM »
Hi All,

I picked up an ASI130MM camera recently to use for the eclipse in August.  I figured I might as well practice on the moon also.  My question regards exposure time vs. gain and how to avoid washing out the brightest features.  I got this shot that turned out ok, but Copernicus and Aristarchus are over exposed and the other images I have during the same session that aren't just don't have the same detail (I know it could be seeing). 

I'm using a C8 (note to self, get a Crayford focuser), AutoStakkert for Stacking, and Registax 6 for wavelet processing.

Any suggestions are very welcome.

Cheers,

Dave

John Pierce

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Re: Lunar imaging question
« Reply #1 on: April 26, 2017, 02:40:12 PM »
using a regular (DSLR) camera, I've based my lunar exposures on daylight. good old 'sunny 16' rule,   shutter speed == ISO at f/16.    f/10 (your C8) is about 1 stop faster than f/11, so if you're using ISO 100 equivalent, then try 1/200th.

Davids

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Re: Lunar imaging question
« Reply #2 on: April 26, 2017, 03:03:24 PM »
I'm using Firecapture for camera control and it only gives me a gain control number from 1 to 100 and exposure times in milliseconds.  Based on your recommendation of 1/200th, that works out to an exposure of 300 milliseconds.

The shot I posted was done with a gain of 38 (38%) and exposure time of 4.125 milli seconds.  So it looks like to duplicate what you are talking about, I should drop the gain to about 4 and increase the exposure time to about 300 mSec.

I'll give that a try.  I'm glad I didn't wait to get this camera...the learning curve has been a bit steep for me.

Cheers,

Dave

John Pierce

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Re: Lunar imaging question
« Reply #3 on: April 26, 2017, 03:08:49 PM »
1/200th is 5 milliseconds (1/200 = 0.005)

of course, I have no idea how to correlate your "gain" setting to ISO.

Davids

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Re: Lunar imaging question
« Reply #4 on: April 26, 2017, 03:14:37 PM »
Oops, got to stop using alternative math.  I wasn't far off your exposure time then.  I guess I'll just have to play with gain versus exposure some more.  I could try a neutral density filter also, I have one that I use for visual observing, maybe that will help.

Dave

John Pierce

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Re: Lunar imaging question
« Reply #5 on: April 26, 2017, 03:18:47 PM »
I'd just adjust one factor, the gain, at least until you run into some sort of limitation....   lowering gain shouldn't increase noise, which is your biggest enemy.

oldfrankland

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Re: Lunar imaging question
« Reply #6 on: May 23, 2017, 06:18:54 PM »
Hi All,

I picked up an ASI130MM camera recently to use for the eclipse in August.  I figured I might as well practice on the moon also.  My question regards exposure time vs. gain and how to avoid washing out the brightest features.  I got this shot that turned out ok, but Copernicus and Aristarchus are over exposed and the other images I have during the same session that aren't just don't have the same detail (I know it could be seeing). 

I'm using a C8 (note to self, get a Crayford focuser), AutoStakkert for Stacking, and Registax 6 for wavelet processing.

Any suggestions are very welcome.

Cheers,

Dave

Dave, I'm using a ZWO 120MM and Imaging Source DMK21 and DMK41 monochrome cameras.  I typically keep gain to a minimum, increase contrast a little with camera gamma, the rest is adjusting shutter speed using histogram and judging live view on the monitor.  There really are no 'silver bullet' exposure combinations.  As in all areas of astrophotography, the more you do, the more you refine and improve your imaging techniques.

This image is shot with the ZWO 120MM with zero gain.  The other side of the coin, as you no doubt noticed, is the post processing.  You look to be off to a really good start, but I might point out that capturing the solar corona during the eclipse may require a different approach.  Shoot lots and learn all you can about your camera and scope combination.



http://www.lafterhall.com/maurolycus_moretus_18dayold_jferreira_001.png
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html

Davids

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Re: Lunar imaging question
« Reply #7 on: June 01, 2017, 03:39:13 PM »
Hi Jim,

Thanks for the reply, it's definitely helped.  I tried a series of images with 0 gain and it turned out ok. 

I've also just discovered that with stacking, sometimes less is more.  Fewer, higher quality frames vs. more lower quality frames.  Makes sense, but then again I'm a slow learner :).  Now I have to go back through some old data that I thought was junk and see if I can get useful images.

Cheers,

Dave

oldfrankland

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Re: Lunar imaging question
« Reply #8 on: June 04, 2017, 11:20:22 AM »
A lot also depends on image scale.  Working at prime focus is far easier than adjusting exposure when using a 2x or 3x Barlow.  So much to try and learn.
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html

Davids

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Re: Lunar imaging question
« Reply #9 on: June 04, 2017, 04:01:23 PM »
An Autostakkert question for you.  Do you use the AP place grid button or do you place your own and how many is enough, or conversly to little.

Dave

oldfrankland

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Re: Lunar imaging question
« Reply #10 on: June 06, 2017, 12:00:11 PM »
Routinely I use the AP button, then place additional points to areas that the AP routine ignored.  Also, using the smallest point frames is not always the best approach, even with some planetary AVIs.  Lots of trial and error, but since it is post processing, you can do that at your leisure.
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html