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03-25-2010, 08:08 AM   #1
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Auto iso - k10d

Is anybody able to describe the algorithm or the methodology used by Pentax (K10D) to determine that, during AUTO ISO operation, the ISO needs to be bumped up and by how much?

Obviously, at some particular point in its decision making it will determine that correct exposure is not achievable and it will decide to bump up the ISO to a particular level. I'm interested in trying to anticipate what the camera will do.

03-25-2010, 08:38 AM   #2
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From memory (my k10 days are one year old now), it roughly stuck to the 1/(1.5*focal length) rule (with FA/DA lenses).

With manual lenses, the limit was 1/100, whatever focal length you entered...
03-25-2010, 10:19 AM   #3
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QuoteOriginally posted by dlacouture Quote
From memory (my k10 days are one year old now), it roughly stuck to the 1/(1.5*focal length) rule (with FA/DA lenses).

With manual lenses, the limit was 1/100, whatever focal length you entered...
I do miss this rule with Canon 5D2, stupid thing keeps it 1/0.8*Focal Length.
Major pain in the *ss.
03-25-2010, 11:39 AM   #4
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QuoteOriginally posted by dlacouture Quote
From memory (my k10 days are one year old now), it roughly stuck to the 1/(1.5*focal length) rule (with FA/DA lenses).

With manual lenses, the limit was 1/100, whatever focal length you entered...
Thanks for responding.......

If I understand this correctly then you mean that if the shutter speed drops below 150 (for a 100mm lens) then the AUTO ISO increments until the 150 target is reached?

03-25-2010, 01:22 PM   #5
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Well, that's it...
03-25-2010, 01:42 PM   #6
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Yep! Unforunately this simple change is not working for old lenses that don't have A contacts. It just goes to an arbitrary 1/125 or something... see my firmware complaint thread!
03-25-2010, 02:58 PM   #7
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QuoteOriginally posted by Eruditass Quote
Yep! Unforunately this simple change is not working for old lenses that don't have A contacts. It just goes to an arbitrary 1/125 or something... see my firmware complaint thread!
I have not seen your firmware complaint thread, but there's nothing to complain about in regards to the firmware. Our cameras require stop down metering for full manual lenses, it's nothing firmware can fix.

The camera can't calculate when there are things it does not know. If I told you A x S x I = 25, can you tell me what A, S, and I MUST be?
03-25-2010, 04:30 PM   #8
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I always found it almost always wanted to shoot at the highest ISO no matter what.


Last edited by omega leader; 03-25-2010 at 04:39 PM. Reason: Still can't spell
03-25-2010, 04:41 PM   #9
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QuoteOriginally posted by AVANT Quote
Our cameras require stop down metering for full manual lenses, it's nothing firmware can fix.
Well, that's not true... m42 lenses do not require it, so the camera can meter in real time... As it knows the focal length for the SR, it would have been a simple thing to use it for auto-iso also...
03-25-2010, 05:14 PM   #10
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QuoteOriginally posted by dlacouture Quote
Well, that's not true... m42 lenses do not require it, so the camera can meter in real time... As it knows the focal length for the SR, it would have been a simple thing to use it for auto-iso also...
That's a moot point isn't it? As the K line dSLRs were never promoted to be M42 compatible, they are only K mount compatible. We just MAKE them fit with adapters.

While the ability would be nice, I don't see why Pentax would/should incorporate a feature into their firmware for an application that they never designed to support.
03-25-2010, 05:32 PM   #11
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It depends on operating mode, but I have found that Auto ISO seems to attempt to make the exposude by moving ISO up first, then shifting either shutter or aperture (depending Tv or Av mode) to then make the exposure.

Omega leader is correct, it will max out ISO first.

not sure the line it follows in Av mode, in terms of 1/focal length. or 1/(1.5 x focal lenght) but all pentax cameras seem to follow the same method
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