Pentax 645D 100iso vs 200iso

[larkis]

Has anyone tested which iso gives more dynamic range besides dxomark ? The Pentax 645D ships with a lowest iso setting of 200iso but one can enable 100iso in the settings. I have heard that shooting at an lower iso than the sensor native iso limits dynamic range, but that is not what the DXOmark test results show. Does anyone have more insight into this ?

[ErikKaffehr]

Hi,

Download "rawdigger" and expose to the right and check out your histograms. Longest exposure always gives best dynamic range and I don't think there have been a camera ever that reduced dynamic range by increasing exposure. Lowering ISO may lead to overexposure, that is the reason to check histograms with a real tool like Rawdigger. Rawconverters don't show real histograms.

Best regards
Erik

Has anyone tested which iso gives more dynamic range besides dxomark ? The Pentax 645D ships with a lowest iso setting of 200iso but one can enable 100iso in the settings. I have heard that shooting at an lower iso than the sensor native iso limits dynamic range, but that is not what the DXOmark test results show. Does anyone have more insight into this ?

[Bart_van_der_Wolf]

Has anyone tested which iso gives more dynamic range besides dxomark ? The Pentax 645D ships with a lowest iso setting of 200iso but one can enable 100iso in the settings. I have heard that shooting at an lower iso than the sensor native iso limits dynamic range, but that is not what the DXOmark test results show. Does anyone have more insight into this ?

Hi,

I once did a quick test of read noise and clipping level with RawDigger, and I arrived at the following summary:

ISO    approx. DynamicRange
 100    log(16062 / 6.2) / log(2) = 11.3 stops
 200    log(16062 / 10) / log(2) = 10.6 stops
 400    log(16062 / 20) / log(2) = 9.6 stops
 800    log(16062 / 40) / log(2) = 8.6 stops

I didn't have an ISO 1600 set of images to compare, and I had to use some of the masked sensels to get what may be assumed to be proper unclipped read-noise levels.

My measurements come close, as usual, to the DxOmark measurements (for screen DR). DxOmark measurements can usually be seen as reliable.
 
This all suggests that there is indeed more Dynamic range to be had when enabling and using ISO 100.

Cheers,
Bart

[Lacunapratum]

Very informative test, Bart, and valuable question, larkis.  Thanks, both. 

[Vladimirovich]

Rawconverters don't show real histograms.

some don't, some do... RPP for example does show (if you select a certain output mode and WB = UniWB)

[leeonmaui]

Aloha,

I always shoot my 645D at 100 and get stellar results.
I am very careful with metering though, as good as the metering system is you can blow highlights in changing light, but I bracket almost everything anyway.

I use 100 primarily to get a cleaned image for big prints, seems to work pretty well.
There is tons of room to open the files up as long as they are clean, so native DR should not really be that big an issue!

That might be a better test;
shoot at 100 and 200 then open them up as far as you can and still get a solid clean image...