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Re: [OM] "Native" ISO of DSLR sensors

Subject: Re: [OM] "Native" ISO of DSLR sensors
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Fri, 01 May 2009 22:32:31 -0400
I can't answer the question specific to Oly but I can validate some of 
your comments by explaining how a Canon 5D works.  The 5D's native ISO 
is clearly ISO 100.  One can select any ISO level in 1/3 stop increments 
between ISO 100 and ISO 1600.  But the camera also offers ISO 50 and ISO 
3200.  But these values are not normally selectable unless you quite 
deliberately enter the custom function menu and select "ISO Expansion" 
to enable these "LO" and "HI" settings.  In fact, when you turn the ISO 
dial to it's lowest or highest setttings you don't see 50 or 3200.  You 
see "L" (for low) and "H" for high).  Also, there are no 1/3 stop 
increments between 50 and 100 or 1600 and 3200.

Although the manual clearly states that low = 50 and high = 3200 the 
special treatment of the boundary values tell me clearly that this is 
Canon's roundabout way of saying:  "Well, we've put them there if you 
really want to use them but we don't really recommend it because the 
quality doesn't really meet our standards."

3200 is clearly noisier than 1600.  There is presumably something lesser 
about 50 relative to 100 from having to throttle the signal but I don't 
know what it is.  I've only used it once when trying to work around some 
daylight fill flash problems.  It helped get the exposure but the shots 
were never used and I never examined them critically.

Chuck Norcutt

GMcGrath@xxxxxxx wrote:
> I apologize if this has been discussed before, but I missed it if it  was.
>  
> I read something to the effect that there is a "native" ISO to camera  
> sensors, and faster speeds are accomplished by turning up the gain. (I think 
> we  
> all know this.) The interesting part was that the item also stated that 
> some  camera manufacturers allow users to select lower ISOs, but they don't 
> give any  improvement in image quality over the native ISO. For instance, the 
> sensor's  native ISO might be 200, and selecting an ISO of 100 wouldn't give 
> you any  better results (other than selecting a slightly different shutter 
> speed or  aperture). Is this a valid concept? If so, does anyone know what 
> the native ISO  of the various Oly DSLRs is? I'm particularly interested in 
> the 510 and 520,  since I have one of each.
>  
> Thanks!
> Greg
> 
> 
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