When a new camera model is introduced many photographers pour over its specifications looking for technical advancements. One aspect that draws a lot of attention is the range of ISO settings that are available.  Seeing ever-increasing native ISO-settings looks great. But, is your camera actually shooting RAW files at the ISO you set? The differences between manufacturer-stated ISO and measured ISO may surprise you.

Since I shoot with Nikon 1 cameras let start with an illustration using four different models: V1, V2, V3 and J5. These four models represent various generations of sensors used in the Nikon 1 product line. These sensors have increased in mega-pixels over time from 10.2, 14.2, 18.4 and 20.8.

Rather than compare all ISO ratings for these cameras, let’s look at manufacturer ratings of ISO-1600 and higher. Which models perform best in terms of actually operating closest to the manufacturer’s stated ISO? Using independent DxO testing we find that they stack up in this order: V2, V1, J5 and V3.

How much of a difference is there between the Nikon 1 V2 and V3 models? About 2/5 of a stop.

Here’s some details:
Manufacturer stated ISO-1600
V2 measured ISO-1236
V3 measured ISO-907
Manufacturer stated ISO-3200
V2 measured ISO-2416
V3 measured ISO-1750
Manufacturer stated ISO-6400
V2 measured ISO-4973
V3 measured ISO-3576
Manufacturer stated ISO12800
V2 not available
V3 measured ISO-7437

This means that to get the same exposure when shooting RAW files with my Nikon 1 V2 at a camera setting of ISO-1600, I would need to shoot the Nikon 1 V3 at about ISO-2250… this assumes identical shutter and aperture settings of course.

NOTE: The difference between the Nikon 1 V2 and the J5 is about 0.35 of a stop.

As a result, what could happen is that an owner of a Nikon 1 V3 or J5 could look at their files shot at ISO-3200 and feel their cameras have pretty decent low light performance. The reality is that their cameras were actually shooting RAW files at ISO-1750 and ISO-1853 respectively, not ISO-3200.

There are also differences with Nikon DSLR’s. Let’s look at the D7200, D750 and D810.
Manufacturer stated ISO-1600
Nikon D7200 ISO-1144
Nikon D750 ISO-1147
Nikon D810 ISO-1194
Manufacturer stated ISO-3200
Nikon D7200 ISO-2267
Nikon D750 ISO-2332
Nikon D810 ISO-2367
Manufacturer stated ISO-6400
Nikon D7200 ISO-4647
Nikon D750 ISO-4804
Nikon D810 ISO-4914
Manufacturer stated ISO-12800
Nikon D7200 ISO-8998
Nikon D750 ISO-9443
Nikon D810 ISO-9631
Manufacturer stated ISO-25600
Nikon D7200 ISO-17954
Nikon D750 ISO-19249
Nikon D810 ISO-19263

Is Nikon the only manufacturer that produces cameras where this discrepancy between manufacturer stated ISO and measured ISO when shooting RAW files exists? Let’s have a look at a few popular camera models from other manufacturers.

Here’s some details on the Canon EOS 760D and the Canon EOS 5DS.
Manufacturer stated ISO-1600
Canon EOS 760D measured ISO-1235
Canon EOS 5DS measured ISO-1126
Manufacturer stated ISO-3200
Canon EOS 760D measured ISO-2463
Canon EOS 5DS measured ISO-2201
Manufacturer stated ISO-6400
Canon EOS 760D measured ISO-4943
Canon EOS 5DS measured ISO-4480
Manufacturer stated ISO-12800
Canon EOS 760D measured ISO-10008
Canon EOS 5DS measured ISO-8723
Manufacturer stated ISO-25600
Canon EOS 760D measured ISO-18154
Canon EOS 5DS not available

Let’s investigate some M4/3 cameras. Here’s how the Olympus OM-D E-M5 Mark II and the Panasonic GH4 stack up.
Manufacturer stated ISO-1600
Olympus OM-D E-M5 Mark II measured ISO-770
Panasonic GH4 measured ISO-937
Manufacturer stated ISO-3200
Olympus OM-D E-M5 Mark EOS 760D measured ISO-1584
Panasonic GH4 measured ISO-1860
Manufacturer stated ISO-6400
Olympus OM-D E-M5 Mark II measured ISO-3223
Panasonic GH4 measured ISO-3835
Manufacturer stated ISO-12800
Olympus OM-D E-M5 Mark II measured ISO-6305
Panasonic GH4 measured ISO-7533
Manufacturer stated ISO-25600
Olympus OM-D E-M5 Mark II measured ISO-12339
Panasonic GH4 measured ISO-7533 (this is not a typo)

To round out our examples let’s toss in the Pentax K-3 II, and two models from Sony, the A6000 (A6300 was not tested by DxO at the time of this article) and A7R II.
Manufacturer stated ISO-1600
Pentax K-3 II ISO-1398
Sony A6000 ISO-1257
Sony A7R II ISO-1151
Manufacturer stated ISO-3200
Pentax K-3 II ISO-2821
Sony A6000 ISO-2510
Sony A7R II ISO-2293
Manufacturer stated ISO-6400
Pentax K-3 II ISO-5853
Sony A6000 ISO-5181
Sony A7R II ISO-4749
Manufacturer stated ISO-12800
Pentax K-3 II ISO-11717
Sony A6000 ISO-10260
Sony A7R II ISO-9173
Manufacturer stated ISO-25600
Pentax K-3 II ISO-22725
Sony A6000 ISO-20456
Sony A7R II ISO-18440

So, is all of this simply some technical mumbo-jumbo or does it have some practical application when using and/or buying camera gear?

Earlier this week I took delivery of a Nikon 1 J5. I went out today taking a few images in town, and I also visited Bird Kingdom. Being familiar with DxO test data I already knew that the J5’s sensor performs quite a bit differently than does the sensor in my V2 in terms of measured ISO of RAW files.

At Bird Kingdom I set both cameras to the identical settings in Manual mode, and used identical ISO settings. Throughout my visit while using these identical settings the Nikon 1 J5 consistently underexposed every single image that I took when compared to the Nikon 1 V2. I had to use a higher Auto-ISO setting with the J5 in order to get proper exposures. Obviously for photographers who use all manual settings and try to match exposures with different cameras this could be a factor.

Differences between manufacturer stated ISO and measured ISO with RAW files can also be important when comparing cameras from different manufacturers. For example, at ISO-1600 the Olympus OM-D EM-5 Mark II shoots RAW at a measured ISO of 770 compared to ISO-1236 with my Nikon 1 V2. That difference of 466 ISO is about 3/5 of a stop when going from ISO-800 to ISO-1600.

At a manufacturer setting of ISO-3200 the OMD EM-5 Mark II shoots RAW files at ISO-1584. If I’ve done the math correctly that means to get the same exposure of a RAW file when comparing a Nikon 1 V2 at a setting of ISO-1600 (i.e. measured ISO-1236) the OMD EM-5 Mark II would need to be set to about ISO-2500.

It is good to remember that these types of differences between manufacturer stated ISO and measured ISO will impact the exposure triangle used to capture an image. Low light performance of a sensor in terms of noise is a separate issue.

For more information on how DxO calculates measured ISO of RAW files you can use this link.

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