ISO heat

Gwendal

Mu-43 Veteran
Joined
Jun 6, 2010
Messages
300
Hi all - currently sorting shots from, er, July, and noticing that the noise is very variable - some shots with ISO 800 or even 1600 seem to have less than other shots with ISO 400 (I have an EP1 - and looking at unprocessed RAW files).
Other than the subject, kind of detail etc, I have read somewhere than sensors create more noise when heated, ie for the same scene and the exact same settings, I will have more noise with a camera that has taken several shots before, than with a camera that is taking its first shot.
Any experience with that, similar conclusions ? As an aside, any hints - things I can do to limit the noise at a given ISO ?
 

bilzmale

Mu-43 All-Pro
Joined
Mar 2, 2010
Messages
1,743
Location
Perth, Western Australia
You are correct - noise can be thought of as electrical interference - a bit like static on a radio tuned to a distant station. As the sensor heats up noise is increased and the length of the exposure affects this too. Astrophotography sometimes uses external cooling of the sensor because they take very long exposures.

Increasing the ISO amplifies the sensor electrical signal and increases the noise with it. Many cameras have 'built-in' noise reduction - some better than others - but they often work at the expense of loss of detail in the image. Noise reduction in post processing gives more user control and is my preference.

Some cameras have a setting for very long exposures (measured in seconds) that takes a second image with the 'shutter closed' so that only the noise from the sensor is recorded and then subtracted from the first image. This dark screen approach is typically found on higher end dslrs. It will double the length of time needed by the camera.
 

arpoador

Mu-43 Regular
Joined
Jan 19, 2010
Messages
173
Location
san francisco ca usa & rio de janeiro br
....

Some cameras have a setting for very long exposures (measured in seconds) that takes a second image with the 'shutter closed' so that only the noise from the sensor is recorded and then subtracted from the first image. This dark screen approach is typically found on higher end dslrs. It will double the length of time needed by the camera.
See - another reason I want a programmable camera with a published API. I would -love- to have that feature in my lower end µ4/3.
 

xyzzy

Mu-43 Regular
Joined
Sep 15, 2010
Messages
27
Location
Sankt Gallen, Switzerland
Some cameras have a setting for very long exposures (measured in seconds) that takes a second image with the 'shutter closed' so that only the noise from the sensor is recorded and then subtracted from the first image. This dark screen approach is typically found on higher end dslrs. It will double the length of time needed by the camera.
Hm. Seeing that the "roise reduct" option (as opposed to noise filter) on the Olympus Pen series lengthens the total time to take a picture by a factor 2, I suspect that this is what the camera does. It does not say so in explicitly in the manual though.

Marcus
 

Streetshooter

Administrator Emeritus
Joined
Dec 15, 2009
Messages
5,138
Location
Phila, Pa USA
Bill,
Very nice explanation. May I ask a question. Does this heat factor only effect the camera while recording or also just being on?
 

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