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Moon movie recording - decreased sensitivity

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Offline barret

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Moon movie recording - decreased sensitivity
« on: 27 / January / 2009, 08:54:02 »
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hello all, i have a problem:
as we all know, moon is quite bright body. when we take photos of it we set shutter speed to some relatively high value, like 1/100th of second. everything works fine. we take series of photos, and then stack it with registax to get more detail from photos.

but, if we try to do the same with movie, we can't because the moon is too bright, and camera automatically sets exposure. because everything around the moon is dark (we shoot at night), camera tries to compensate exposure, and result is over burn moon.

so my question is: can we make movie of moon with decreased brightness (or increased shutter speed)?

note for newbies: why stacking photos allows us to extract more detail from photos which are terrible? ;) air in atmosphere is in continuous movement causing image waving (which you can see while looking through hot air). computer programs like registax can compensate such waving, and thus reconstruct the original image of the moon, based on differences between each shot. so, the more pictures you take, the more detail can you get (although they are heavily hardware limited).
and why do i want to make a movie of (still) moon? because then i can get more frames per second (30/60fps) than in continuous burst mode (2-3 fps).

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Offline fe50

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Re: Moon movie recording - decreased sensitivity
« Reply #1 on: 31 / January / 2009, 07:48:06 »
so my question is: can we make movie of moon with decreased brightness (or increased shutter speed)?
AFAIK not with the current CHDK builds.
But - have you tried all the camera's 'standard' settings, e.g on most cameras you can set Ev compensation in video in a small range, this should help. It's the [+/-] key on most cameras (the same function as AELock), UP (ISO) key on some Ixus models...

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Offline barret

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Re: Moon movie recording - decreased sensitivity
« Reply #2 on: 01 / February / 2009, 09:34:44 »
thanks for your input.
yes, i have tried Ev compensation, but range of +-2 is too tiny for this kind of situation. i tried this with -2 Ev compensation but still, moon is overbright.

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Offline fudgey

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Re: Moon movie recording - decreased sensitivity
« Reply #3 on: 01 / February / 2009, 10:29:23 »
Even though you get higher frame rate in movie mode it's possible that a timelapse (well, burst mode really in your case as you said) may result in higher quality even if you manage to decrease exposure enough.

Not only because of the higher resolution, but also because bright areas cause ugly artifacts in LCD viewfinder image (and hence in recorded video), that may or may not become present in moon movies too.

For example if you'd shoot jpegs in a 2 fps (that's the fastest my a570is can do, when cropping to 1600x1200 jpeg without scaling) burst and stack 5 seconds worth images (the moon isn't very fast so a frame rate of 0.2 fps could be OK?), you'd have a stack (alignment required) of 10 good high resolution images from a burst, as opposed to a stack (alignment required) of 150 low resolution, potentially distorted mjpeg images from a 30 fps video.

But that's just a guess, can't for sure tell before someone tries it out. I think Ev compensation in video mode was discussed/developed in this thread: http://chdk.setepontos.com/index.php/topic,1075.msg9569.html#msg9569, I didn't read it through today, educate yourself. Maybe Tv could be brought even darker than the current limit (I vaguely remember that might cause flickering or some other trouble, the thread may or may not discuss this).

In the source code, look for strings ev_video and CAM_EV_IN_VIDEO, at least in core/ include/ and platform/generic/.


 

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