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Old 13-01-2009, 05:11 PM
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suma126 (Shane)
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slow camera

HI I have a olympus dslr camera when i take a 4 min picture it takes a another 4 min to process the picture does happen on all cameras
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Old 13-01-2009, 05:14 PM
Dennis
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Hi Shane

That sounds like you have “Noise Reduction” turned on?

When a modern DSLR takes an exposure of longer than a few seconds, it usually takes an equally long exposure “with the lens cap on” as it were.

This 2nd (automatic exposure) is an image of the “thermal noise” on the sensor which it then subtracts from your previous exposures, giving you a hopefully cleaner photo.

On some cameras, there is a Menu function to turn off this automatic “noise reduction” or “dark” frame.

Cheers

Dennis
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Old 13-01-2009, 05:16 PM
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Originally Posted by suma126 View Post
HI I have a olympus dslr camera when i take a 4 min picture it takes a another 4 min to process the picture does happen on all cameras
Hi,

I am not sure about the Olympus but on a Canon it is possible to turn noise reduction on. Then the camera will take a dark frame of exactly the same length as the previous light frame and combine the two to remove noise.

You should check your manual to see if noise reduction is turned on.

Cheers
Paul
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Old 13-01-2009, 05:38 PM
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Noise Reduction Is On But Dont I Need It On To Get A Better Picture
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Old 13-01-2009, 05:48 PM
Dennis
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Try some exposures of 1, 10, 30 and 60 seconds with NR turned on and off and compare the results. I suspect you will be easily ably to see the difference.

On my Canon 40D the default setting is that the camera will perform NR on exposures of longer than 1 second. This is a good indication that the designers of the camera perceive that noise may increase to become objectionable at exposures of longer than 1 second.

Cheers

Dennis
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Old 13-01-2009, 07:25 PM
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Hi Dennis.

Where do I find this default setting in the 40D?

I've checked in the menu and can only find a long exposure noise reduction option, but no default 1 second option.
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Old 13-01-2009, 07:48 PM
Dennis
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Hi Dennis.
Where do I find this default setting in the 40D?
I've checked in the menu and can only find a long exposure noise reduction option, but no default 1 second option.
Hi Matt

See attached screen print. It is Page 156 C.Fn II Image.
Setting 1: Auto

Cheers

Dennis
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Old 13-01-2009, 11:52 PM
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Ah....I see.

Mine is set to Off as default.

I haven't detected any real noise issues so far with exposures of up to 5-10 seconds.

I work mostly between 100 and 400ISO, though...

So it's probably best left Off for me until I try longer exposures.

Thanks, Dennis
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Old 14-01-2009, 04:55 AM
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iceman (Mike)
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Quote:
Originally Posted by suma126 View Post
Noise Reduction Is On But Dont I Need It On To Get A Better Picture
If you're doing a 4 minute exposure, noise reduction will definitely help.

It just means it takes twice as long to capture a single frame.

It also means you don't need to worry about darks. You do still need to worry about flats though.
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Old 14-01-2009, 11:31 AM
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Originally Posted by suma126 View Post
Noise Reduction Is On But Dont I Need It On To Get A Better Picture
Swings and roudabouts. If you turn off noise reduction you have to take darks. But unless you are imaging from a very dark site, you can get away with fewer darks than lights, so using darks will probably take less total time.
Geoff
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