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Old Jun 20, 2009, 2:59 AM   #1
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Default Why This Noise ?

Why do I sometimes get this sort of noise in my shots ?
It happens with more than one lens, this shot was taken with a manual lens at f11, I can't remember what speed, iso 100 and pef raw.This shot has only been resized and saved as a jpeg.

I have put up with it for a while, it doesn't happen that often, but Murphy's Law it happened today when I finally get a shot of Dad, who never wants his photo taken, very frustrating. Any Clues why ?

Rodney
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Old Jun 20, 2009, 5:07 AM   #2
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Hi Rodney,
Not much to go on I'm afraid ... pic shows no EXIF data, so no clues there. ... Jack.
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Old Jun 20, 2009, 5:44 AM   #3
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Quote:
Originally Posted by jachol View Post
Hi Rodney,
Not much to go on I'm afraid ... pic shows no EXIF data, so no clues there. ... Jack.

Here is a smaller resize with the exif
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Old Jun 20, 2009, 6:43 AM   #4
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Manual Exposure at f/11, ISO 100 and 1/4 second, huh? No flash?

My guess is that it was *very* underexposed, and you brightened it (or your raw converter did using an auto algorithm) during raw conversion. When you do that, you increase noise levels significantly, just as if you'd used a much higher ISO speed to begin with.

In typical home lighting (usually around EV 5), you'd need a shutter speed of around 4 seconds at ISO 100 with the aperture at f/11 for a properly exposed image.

Since that one is at 1/4 second (much faster than you'd need for a properly exposed image at ISO 100 and f/11 in most home lighting), my guess is that it was probably very underexposed (drastically increasing noise levels when the image was brightened enough to see any detail).
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Old Jun 20, 2009, 6:48 AM   #5
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Hi Rodney, some peple have had issues with vertical noise banding, but more likely the clues are that you used F11 and ISO 100? So severe underexposure would be the likely cause. Do you have your camera setup to show histogram immediately after a photo is taken? A quick glance at the LCD screen to check the image plus histogram is a good check that your exposure settings are correct.
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Old Jun 20, 2009, 10:14 AM   #6
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The only times I see this type of noise pattern is where I've "pushed" a really underexposed shot. That's why I was surprised you said you just changed to jpg without other processing. Keep forgetting that programs can do things like this automatically, like Jim pointed out.

One of the things that took me a while to notice is that the camera doesn't use auto ISO when you use M mode, it will always us the lowest of the auto setting (since I leave the camera set to 100-1600, it goes to 100). I often will use manual lenses (or manual settings) in low, tricky light and often get surprised by the shutter speeds. I've learned to always check and adjust my ISO under these conditions.
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Old Jun 20, 2009, 5:29 PM   #7
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Well I do feel a little silly, Raw Therapee had done some 'auto' adjustments.
However even with everything set to 'neutral' I still think there is to much noise, maybe I'm being too fussy ?

I took the shot with my K20D and my new second hand Pentax 50mm F1.7 hand held at 1/4 sec, F11 or possibly f8 and iso 100.

So here is the shot again with no other adjustments from the original PEF except resizing and jpeg saving .

To me it looks the same as a pef or jpeg, too much noise.

Rodney
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Old Jun 20, 2009, 5:38 PM   #8
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Rodney,

I've had a simliar problem that I never found a reason for. My post was at http://forums.steves-digicams.com/pe...nge-image.html

And, periodically I've had a shot come out with the lines and noise, then the next shot same settings exactly of same thing came out fine.

Will be watching.

Patty
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Old Jun 20, 2009, 7:59 PM   #9
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Hey Rod,
I don't know what others may think but, I kinda like the shot the way it turned out.
Looks like an old grainy film shot from years gone by.

like the others said, you just didn't have enough ambient light for the settings used, I don't think its the fault of the camera or lens.
BTW, I think your dad is very photogenic! he looks very profound.
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Old Jun 20, 2009, 9:00 PM   #10
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Quote:
Originally Posted by nhmom View Post
Rodney,

I've had a simliar problem that I never found a reason for. My post was at http://forums.steves-digicams.com/pe...nge-image.html

And, periodically I've had a shot come out with the lines and noise, then the next shot same settings exactly of same thing came out fine.

Will be watching.

Patty
Thanks for your support Patty, hopefully we will wont get to many of these noisy shots.

Rodney.
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