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09-17-2009, 11:27 PM   #16
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QuoteOriginally posted by jct us101 Quote
No, every camera has a base ISO of 200. 100 is a digitally downgraded version of 200.
Not true. Depends on the sensor.

09-17-2009, 11:39 PM   #17
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I'm pretty sure that it's true.
09-17-2009, 11:59 PM   #18
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QuoteOriginally posted by jct us101 Quote
I'm pretty sure that it's true.
Sorry, but I'm completely sure that it's not. It depends on the sensor design. The K10D/K200D sensor, the Sony ICX493AQA, is a good example; it is the same sensor used by the Nikon D80 and Sony Alpha 100, and you can confirm on any number of web sites with reviews of these cameras that it indeed has a base ISO of 100. Google it.
09-18-2009, 12:00 AM   #19
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Yes, but that just means that they have already extended the range for you.

09-18-2009, 12:10 AM   #20
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QuoteOriginally posted by jct us101 Quote
Yes, but that just means that they have already extended the range for you.
I'm not sure what you mean? It means that the unamplified signal from the sensor is equivalent to ISO 100, and that's quite simply all it means. So, by example:

The Pentax K10D has a base ISO of 100.
The Nikon D90 has a base ISO of 200 yet goes down to 100 -- this is done with firmware and is not true ISO 100.
The Pentax K100D Super has a base ISO of 200 and does not even attempt to go down to 100. ISO 200 is true ISO 200 and the base ISO.
Some other cameras (I seem to recall some Canons) have a base ISO of 100 and go down to 50 through firmware. This is not true ISO 50.

Different cameras choose to push or pull the maximum and minimum sensitivities of the sensor in order to extend the range downwards or upwards, but this doesn't change the fact that different sensors have different base ISOs. All other things being equal, which they in reality are not, it is my understanding that base ISO is a function of physical photosite size, which explains why 6MP sensors frequently have a base ISO of 200, and higher resolution sensors are often 100.

Last edited by Erik; 09-18-2009 at 12:15 AM.
09-18-2009, 12:11 AM   #21
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The mathematical formula for ISO only allows 200 to be a true base.
09-18-2009, 12:16 AM   #22
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QuoteOriginally posted by jct us101 Quote
The mathematical formula for ISO only allows 200 to be a true base.
That's cool.
09-18-2009, 12:25 AM   #23
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QuoteOriginally posted by jct us101 Quote
No, every camera has a base ISO of 200. 100 is a digitally downgraded version of 200.
You don't know what you're talking about.

Most of the Optios start at ISO 64, which I also think is their base ISO.
The Hasselblad cameras have base ISO 50, in fact they only have ISO 50 - all higher ISOs are just pushed (explanation here: DxOMark review for the Hasselblad H3DII-39)

09-18-2009, 12:26 AM   #24
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I'm pretty sure I do but I always welcome unwarranted condensation from people on this forum.
09-18-2009, 05:53 AM   #25
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jct us101: This paper from Kodak explains base ISO and gives two examples.

See also these formulas from the Wikipedia article on film speed
09-18-2009, 06:12 AM   #26
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QuoteOriginally posted by jct us101 Quote
I'm pretty sure I do but I always welcome unwarranted condensation from people on this forum.
I think that it might be because you are only making statements where you're not providing reference material of how you ascertained your information. If you're saying ISO 200 is the base, show proof. I want to see the mathematical formula that calculates ISO 200 to be the true base. Just because you "say so" doesn't mean its true. You need to show proof.
09-18-2009, 06:16 AM   #27
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QuoteOriginally posted by jct us101 Quote
Yes, but that just means that they have already extended the range for you.
Wrong, no manufacturer will expand the range "for you", it would mean ISO100 is noisier than ISO200. Manufacturers are not *that* stupid.
09-18-2009, 07:58 AM   #28
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QuoteOriginally posted by jct us101 Quote
I'm pretty sure I do but I always welcome unwarranted condensation from people on this forum.
It may have something to do with your own behavior ever considered that? It may be that you're too fast to exhibe to the rest of us a thin brain and a thick ego.
At least one or 2 of the people your so eager to contradict with just because "you know so" are working professional in this field. Are you one too or you just *know things*?

BTW, you are so evidently wrong about this matter but I feel that no outside input will sway you.

Radu
09-18-2009, 09:07 AM   #29
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I think you mean "condescension" not "condensation"... I don't mean to poke fun at anyone but I'm sure even you can get a little chuckle at your typo there

I have no mathematical "proof" but my Canon 1DmkIII has ISO 100-3200. It also has "L" and "H" which represent ISO 50 and ISO 6400. It would make no sense for this camera to have a base ISO of 200... then identify only ISO 50 as the "pushed" setting. It seems to me if that was the case they would have ISO200 and then L1 and L2. The term Canon uses for the "L" and "H" settings are "ISO Speed Expansion"

Anyway... I can't imagine anyone having a real vested interest in the outcome of this discussion but I have to say there seems to be no logic in a manufacturer acknowledging some range expansion on a sensor and not others... particularily if all cameras are constrained by the same mathematical formula.
09-18-2009, 09:37 AM   #30
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Let me see if I understand it correctly. OP started with Kx pics...........and now we are talking about what?

I have a cool Kx pic people...it is a pic of the camera and not a pic taken by the camera. So what.......let us enjoy it
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