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04-02-2011, 07:49 AM   #1
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Sensitivity starting from ISO 200 why not 100?

I am wondering why the ISO setting starts with ISO 200 instead of ISO 100 which is normally seen with cameras (I am new to dslr).
Is there any specific reasons for this?

thanks in advance

04-02-2011, 07:55 AM   #2
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Yes because that is the native ISO of the sensor. Base ISO is that ISO at which the signal from the pixels is unboosted (so boost = 0dB) and the image of a properly exposed grey card meets certain criteria of noise and brightness. The more efficient a sensor is, the higher its base ISO will be. Also, at base ISO, the sensor will have the widest dynamic range possible (that's the theory, although I don't see it in DxO Mark DR vs ISO graphs). The higher the base ISO, the less you need to boost the pixel signals to reach higher ISOs. A boost of 3dB is (theoretically) equal to one stop, so to boost the K-5 4 stops above its base ISO, or 12dB, would take it to ISO 3200. If Sony develops a sensor with a 400 base ISO, boosting 12dB would take you to ISO 6400, but the image would look as good as the K-5's ISO 3200 (assuming equal image processing techniques).

With film, lower ISO meant finer grain, which provided greater resolution at the expense of longer exposure times. With digital sensors, maximum resolution is determined by the number of pixels combined with the characteristics of the AA filter and the quality of the demosaicing software. Colour saturation is determined by the number of photons captured and how efficiently they're "translated" into zeroes and ones, while colour fidelity is a combination of the RGB filters and the quality of the algorithms that demosaic and determine white balance.

A lower ISO will not give you a shaper image or finer grain as in film days. The only advantage of a lower ISO would be for slow shutter speed shots such as a waterfall etc. These can be achieved with ND filters to slow the camera down a lot more than going from ISO 200 to ISO 100 or ISO 50.

In short, to get the high ISO properties everyone wants, the base ISO at 200 will allow making ISO 3200 or 6400 much cleaner.

Last edited by Peter Zack; 04-02-2011 at 08:02 AM.
04-02-2011, 10:29 AM   #3
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Thanks for the explanation,had been wondering about it myself.For someone who had did most color work at iso of 25 to 400 with film these modern dslr are more amazing to me than others who have only shot digital.Just got a new k-x to replace a Panasonic fz 15 which don't do good above iso 200.
Jake
04-02-2011, 10:50 AM   #4
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So in theory the ISO200 provides better quality than ISO100? :-)

04-02-2011, 11:10 AM   #5
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Original Poster
Thanks Peter, that was a wonderful explanation. I was sometimes thinking that base ISO 200 means that my camera is still a basic as it can't do at ISO 100 and made me to think ISO 100 would have been better with low noise. But your explanation was good.

Cheers
04-02-2011, 11:45 AM   #6
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Hello there!

Although taking my first steps into the digital world having bought recently my first dslr (pentax k-r) i will share something i've learned while reading the forums here (and i hope i'm not making any mistake here).

related to the K-R but i think we can say this regarding any DSLR. It's true that 200 is base iso but i assume it's because at that particular sensitivity (and higher, ofc) the sensor can achieve the best dinamic range.

I remember seeing a few photos here on the site (will link the thread when i get home), where in terms of noise (at pixel peeping levels) the photo shot at iso100 was slightly better than the one shot with iso 200. So, in certain conditions, with plenty of light, you might want iso 100.

Something else i, for one, don't quite understand.. How is it that with a lower sensitivity and no camera post-processing aplied (HDR, Highlight correct etc) it seems you get more detail with a lower iso than with the higher value at this level (100 - 200 iso)

Quote from the k-r review here on this forum: "
ISO 100, however, does seem to pull out just slightly more detail in the shadowed areas comparet to ISO 200."
04-02-2011, 12:39 PM   #7
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QuoteOriginally posted by Brydzo Quote
So in theory the ISO200 provides better quality than ISO100? :-)
Not really. All it means that if the base ISO is 200, less boost (gain) is required to get a cleaner image at a higher setting like ISO 3200. So in other words lets say camera A has a sensor that has a base ISO of 100, we take a shot at ISO 1600. Then camera B has a base ISO of 200 and we take the identical shot at 3200. If everything else was equal, the noise in each shot should be similar. The camera with a base ISO of 100 would produce a much noisier image at 3200.
04-02-2011, 12:48 PM   #8
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QuoteOriginally posted by Penumbra Quote
Something else i, for one, don't quite understand.. How is it that with a lower sensitivity and no camera post-processing aplied (HDR, Highlight correct etc) it seems you get more detail with a lower iso than with the higher value at this level (100 - 200 iso)

Quote from the k-r review here on this forum: "
ISO 100, however, does seem to pull out just slightly more detail in the shadowed areas comparet to ISO 200."
I honestly don't think that's actually happening. I think the shooter who is reviewing the camera thinks there's more detail only because they feel it should have more. If the camera's base ISO is 200, that is the optimum setting on the sensor.

The one camera we are sure of is the K-5. That's because Nikon uses the same sensor in their D7000 and with a Nikon, the lowest setting is ISO 200 and they have an over ride setting (Lo.5 and Lo1.0) that takes the camera to ISO 100. So they are showing us that the base is 200 and the setting for the best possible dynamic range, colour and noise.

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