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Full Moon Mosaic, 24 Oct (am)

brianb

By brianb
in Imaging - Lunar

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brianb

brianb

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Very bright Full Moon spoiled viewing. During the small hours cloud increased and I decided to counterattack:

Moon-101024-0350-FLTX1-mosaic-small.jpg

2010 Oct 24, 0350 UT. WO FLT 110, prime focus, no filter, Imaging Source DMK41 camera. 6 frame mosaic. This is a 50% resize; full size version here (pick "hi res image" from the zoom menu).

Transparency poor, fairly uniform high cloud. Seeing unstable with continuous slow undulations of large amplitude. Temperature 2C, wind NE force 3-4.

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Takahashi

Takahashi

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Lovely image Brian. You're using almost exactly the same hardware as I did recently, bar your DMK41 over my DMK21, but I totally overblew the light areas. Any tips as to how to avoid doing so? Is it purely a matter or calibrating exposure/gain on the brightest regions?

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brianb

brianb

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overblew the light areas. Any tips as to how to avoid doing so? Is it purely a matter or calibrating exposure/gain on the brightest regions?
Yes. I pointed at Aristarchus (the brightest part of the Moon, when not near the terminator) and adjusted gain/exposure to get the top end of the live histogram to about 90%. In fact I set minimum gain & still got 1/769 sec at f/7 prime focus ... using a low gain means I don't have to shoot a lot of frames to get a smooth result, the individual panes were 150 frames stacked from 500 frames shot. Terminator area lightened using the "shadows/highlights" tool in PS Elements. Same exposure & shadows/highlights settings for all the panes.
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old_eyes

old_eyes

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Yes. I pointed at Aristarchus (the brightest part of the Moon, when not near the terminator) and adjusted gain/exposure to get the top end of the live histogram to about 90%. In fact I set minimum gain & still got 1/769 sec at f/7 prime focus ... using a low gain means I don't have to shoot a lot of frames to get a smooth result, the individual panes were 150 frames stacked from 500 frames shot. Terminator area lightened using the "shadows/highlights" tool in PS Elements. Same exposure & shadows/highlights settings for all the panes.

Really nice image and good tip on using Aristarchus as a reference brightness. I am assuming you stacked in Registax. If so I am interested in how many reference points you used for the stacking, and how you selected the best 150 frames? when I have been using Registax, I can't really understand/see the difference with where you set the quality threshold.

old_eyes

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brianb

brianb

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I am assuming you stacked in Registax.

Avistack. Approx. 600 reference points per image (selected by the software). And you set the best n frames as a percentage in a slider ... 30% seems to work fairly well for me, for lunar images taken in reasonable seeing.

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brianb

brianb

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Prime focus is with the camera sensor where the objective lens focuses it. To get a smaller image you can use a focal reducer, a larger one with a barlow / powermate. There's no lens on the camera, and I don't use an eyepiece except when I want to look at something with my eyes rather than a camera.

In this case, the FLT 110 is acting as a 770mm focal length f/7 lens.

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nightfisher

nightfisher

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Prime focus is with the camera sensor where the objective lens focuses it. To get a smaller image you can use a focal reducer, a larger one with a barlow / powermate. There's no lens on the camera, and I don't use an eyepiece except when I want to look at something with my eyes rather than a camera.

In this case, the FLT 110 is acting as a 770mm focal length f/7 lens.

Many thanks brian, i am hoping to achieve some images like this using 120 refractor with a webcam mounted into barlow, will this be possible, sorry but im a total newbie to imaging

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Takahashi

Takahashi

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Yes. I pointed at Aristarchus (the brightest part of the Moon, when not near the terminator) and adjusted gain/exposure to get the top end of the live histogram to about 90%. In fact I set minimum gain & still got 1/769 sec at f/7 prime focus ... using a low gain means I don't have to shoot a lot of frames to get a smooth result, the individual panes were 150 frames stacked from 500 frames shot. Terminator area lightened using the "shadows/highlights" tool in PS Elements. Same exposure & shadows/highlights settings for all the panes.

Interesting. So, am I overdoing it with 2000 frames per video (at 60fps)?

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brianb

brianb

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am I overdoing it with 2000 frames per video

I can't see your video ... if the stacked result needs noise reduction then you either have the gain turned up too far or you need to stack more frames. If you need to stack more frames then you need to shoot more. If I was shooting at f/20 or f/30 the exposure would be longer, the gain would be higher (to help freeze the seeing) and I'd be shooting more frames ... with consequent increase in file sizes & processing times. It's all a compromise & you have to work out what works for you with your scope & camera, and the compensation you need when seeing is bad enough to be a nuisance.

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Takahashi

Takahashi

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I can't see your video ... if the stacked result needs noise reduction then you either have the gain turned up too far or you need to stack more frames. If you need to stack more frames then you need to shoot more. If I was shooting at f/20 or f/30 the exposure would be longer, the gain would be higher (to help freeze the seeing) and I'd be shooting more frames ... with consequent increase in file sizes & processing times. It's all a compromise & you have to work out what works for you with your scope & camera, and the compensation you need when seeing is bad enough to be a nuisance.

The gain was at its lowest setting, (whatever that is, I can't remember right now), I adjusted the exposure to compensate instead.

All I meant was, given "average" seeing, should it really be necessary for me to shoot so many frames, or would 500 to 1000 be enough of a selection for <whatever> stacker to work with? I suppose I should just test it and see, but the problem I have is time, or the lack thereof, and weather, and travel to site, all of which leave me with a very tight bracket in which to carry out any work, so testing stuff is very "expensive", in lost-observing/capturing terms.

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brianb

brianb

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testing stuff is very "expensive", in lost-observing/capturing terms.

The best advice I can give you is to stick to what you know works, then duplicate one shot with less frames & see if the quality holds up when you process it. If so drop your "standard" frame count & repeat next time you get a chance.

I find shooting 500 frames at minimum gain on the DMK21 / DMK41 to be enough, even if you need to start lifting the shadows.

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