EV+2or+3 shot not issing properly by night (A3000is) - General Discussion and Assistance - CHDK Forum
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EV+2or+3 shot not issing properly by night (A3000is)

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Offline vincedchart

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EV+2or+3 shot not issing properly by night (A3000is)
« on: 26 / January / 2012, 14:16:04 »
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Hi,

I have CHDK installed on my A3000 IS for a while now, that gives me auto-bracketing (bracketing in cont. mode, tv bracketing 2 2/3). Before I had this, I did manual bracketing by changing settings while shooting.

By this time and now, I have always the same issue when shooting EV+1, +2 or +3 pictures by night : pictures were, and are still blurred. or weird issues with the lights.

Look at 2 series of three images I did. EV- and EV=0 are OK but not EV+. Why?!



(But by day, it all works properly  ;))

PS: I disable flash
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Offline outslider

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Re: EV+2or+3 shot not issing properly by night (A3000is)
« Reply #1 on: 26 / January / 2012, 15:09:47 »
Do you have fixed focus? I mean manual focus. Maybe somehow camera can't refocus on some settings...

However for me the blur seems to be caused by move - are you using a tripod? Or it was hand-held? When you use bracketing at night camera might set long exposure to have light image, so it's very easy to get blurred photo.
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Offline Mr_Speedy

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Re: EV+2or+3 shot not issing properly by night (A3000is)
« Reply #2 on: 26 / January / 2012, 16:15:50 »
Shutter speed. Plain and simple.
Your middle exposures, and even your darkest exposures are not perfectly sharp (too slow shutter).

As far as I can see, you are not using a tripod because the frames are not identical.

Step 1:  Use a tripod. This will stop camera shake and all things that are stationary in the pictures should turn out fine. If you have no tripod, try step 2.

Step 2:  Raise the ISO (and open the aperture if its not wide open) to get faster shutter speeds. This also includes zoom. If you are zoomed in, the camera will have a smaller aperture (larger F number) and let less light in. Camera shake is worse when zoomed in. So zoom all the way out if you are not already.

Explanation:
This is why you are experiencing what you are seeing:
Cameras need to "catch" a certain amount of light for a correct exposure. When there is a lot of light (during the day), the camera can do this quickly. At night, where there is little light, the camera will take longer to catch the same amount of light.
Your first exposure is the "correct" exposure and catches a certain amount of light, which takes a certain amount of time.
Your +1 exposure is asking the camera to catch TWO TIMES as much light = shutter speed 2 times longer
Your +2 exposure is asking the camera to catch FOUR TIMES as much light = shutter speed 4 times longer
Your +3 exposure is asking the camera to catch EIGHT TIMES as much light = shutter speed 8 times longer

The same thing occurs with your -1 -2 or -3 exposures, only opposite. The shutter speed is 2, 4, or 8 times quicker. This is why the darkest frame will always have the fastest shutter speed, and the brightest frame will have the slowest shutter speed.

In my opinion, you can forget hand-held HDR at night. Shutter speeds are just going to be too slow.
« Last Edit: 26 / January / 2012, 16:19:14 by Mr_Speedy »
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