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12-30-2011, 03:10 AM   #1
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Is there a down side to switching on expanded sensitivity

I turned on the 'expanded sensitivity' on my K-x within 2 weeks of buying the K-x, so I could get ISO 100...
As such I rarely (if ever) use ISO 200 and tend to skip straight to 400 when required...

I guess my questions are: Why does one need to 'expand sensitivity' in the first place? AND Why does the camera not come set up at its most sensitive?

Is there a downside to using this feature?

12-30-2011, 05:08 AM   #2
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Not really, it's just there because the manufacturer thinks that lower isos might force too slow shutter speeds, and higher isos might introduce too much noise.
12-30-2011, 07:22 AM   #3
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if its really bright n sunny outside then use ISO 100 other than that stick to the default 200 for faster shutter speeds (affects image sharpness). w/ the k-x (well i should say w/ most DSLR's now) your eyes wont even be able to differentiate between ISO 100 and 200. even between 100 and 400.
12-30-2011, 03:08 PM   #4
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My guess is that ISO 100 is not available by default because the K-x sensor's native sensitivity is ISO 200. In addition to this, if you turn on the extended dynamic range features, ISO 100 will no longer be available anyway.

That being said, there is nothing wrong with using ISO 100 on the K-x, as can be seen in dxomark test results too.

12-31-2011, 04:04 AM   #5
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QuoteOriginally posted by Laurentiu Cristofor Quote
My guess is that ISO 100 is not available by default because the K-x sensor's native sensitivity is ISO 200. In addition to this, if you turn on the extended dynamic range features, ISO 100 will no longer be available anyway.

That being said, there is nothing wrong with using ISO 100 on the K-x, as can be seen in dxomark test results too.
According DPreview it's closer to ISO400, the K20D and the K7 was at ISO200.
It's probably because the ISO range of the sensor is limited to that range, so ISO100 is gained by software adjustments, but that's just speculation from my side.
12-31-2011, 01:27 PM   #6
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QuoteOriginally posted by Anvh Quote
According DPreview it's closer to ISO400, the K20D and the K7 was at ISO200.
Can you rephrase this? It's missing some words to make a complete phrase. Are you trying to say that the K-x at 400 is as good as the other cameras at 200?

QuoteOriginally posted by Anvh Quote
It's probably because the ISO range of the sensor is limited to that range, so ISO100 is gained by software adjustments, but that's just speculation from my side.
Yes, but while ISO 100 is gained by software adjustments, it does seem to provide all the expected advantages: more DR, less noise, etc.
01-03-2012, 09:05 AM   #7
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That's the first time I've heard ISO 400. Previously when this has been discussed, 125 was claimed for the K-x native ISO.

The downside of using ISO 100 would be reduced dynamic range. They need to monkey around to fake it, so it is a special mode, and using ISO 200 and a faster shutter speed (or a 1-stop ND filter) might give better results.

The difference either way is pretty marginal, though. Enabling ISO 100 might yield less noise, but the benefit of that is marginal too (noise isn't an issue at ISO 200).
01-03-2012, 10:04 AM   #8
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QuoteOriginally posted by Laurentiu Cristofor Quote
Can you rephrase this? It's missing some words to make a complete phrase. Are you trying to say that the K-x at 400 is as good as the other cameras at 200?
Was about Base or native ISO off the sensor, it's a little lower then ISO400 though.
Base ISO of the K20D and K7 seemed to be ISO200 or just under that but the base ISO of the Kx was higher then that.
I thought it was DPreview but can't find it any more, might very well be another review.


QuoteOriginally posted by Laurentiu Cristofor Quote
Yes, but while ISO 100 is gained by software adjustments, it does seem to provide all the expected advantages: more DR, less noise, etc.
I was not saying it was not good ^^

01-03-2012, 04:11 PM   #9
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Could someone explain what's meant by 'Native' or 'Base ISO'?

I'm going to turn of the 'expanded sensitivity' unless I need to go really 'lowlight' and just shoot at 200 ISO then... Someone let me know if this is a bad idea...
01-03-2012, 07:46 PM   #10
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QuoteOriginally posted by DaveHolmes Quote
Could someone explain what's meant by 'Native' or 'Base ISO'?
There seems to be a lot of argument about this on the web, but I think people use it to mean the ISO at which there is a minimum amount of amplification and no 'tricks' are played to get a lower effective ISO.

My take on this subject, after doing a little bit of web research, is that you should use whatever ISO is available to maximize the amount of light hitting the sensor. On my recently sold K-x, I had expanded sensitivity on all the time and used ISO 100 the most. When I wanted a certain shutter speed and/or Av, then I would use iso/filters/whatever to get my exposure right.

QuoteOriginally posted by Anvh Quote
I thought it was DPreview
Found something on p17 of the test. It indicates peak measured dynamic range at 400, but it appears from the numbers that the actual peak is between 200 and 400. The DXOMark graph shows iso 100 having the best SNR, etc. This may have more to do with the light than the sensor.

QuoteOriginally posted by DaveHolmes Quote
Someone let me know if this is a bad idea
I don't think it matters all that much in practice. My theory is that Pentax has it off so that expanded dynamic range will work like Laurentiu Cristofor pointed out.
01-04-2012, 01:42 AM   #11
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My guess would be that ISO100 will result in a reduced dynamic range - specifically that you'll run the risk of washed-out highlights. I think if there's any risk of suffering from this on any particular shot, you'd be better off staying with ISO200.
01-04-2012, 03:41 AM   #12
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QuoteOriginally posted by drugal Quote
Found something on p17 of the test. It indicates peak measured dynamic range at 400, but it appears from the numbers that the actual peak is between 200 and 400. The DXOMark graph shows iso 100 having the best SNR, etc. This may have more to do with the light than the sensor.
Thanks that was it indeed, i had read over it.
I concluded from that that the peak was closer to ISO400 than ISO200.

We need to learn more how they measure things i think...
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