E-M5 Firmware update... V 2.0 today..

Started Jan 29, 2014 | Discussions thread
Thomas Niemann Veteran Member • Posts: 4,354
Re: Incorrect Explanation

texinwien wrote:

Thomas Niemann wrote:

texinwien wrote:

duartix wrote:

texinwien wrote:

Thomas Niemann wrote:

Two new features were included in the firmware update: ISO 100 and small focus points.

ISO 100. In the ISO menu you'll notice ISO 100 is marked as LOW and ISO 200 is Recommended. This indicates that ISO 100 is actually ISO 200 over-exposed by one stop. For example, if the ISO 200 exposure was 1/100 @ f/4, and you shot it at 1/50 instead, you would be over-exposing by one stop. And 1/50 @ f/4 would be the proper exposure for ISO 100. The result would be highlight clipping and less dynamic range because ISO 200 is the optimal ISO for the sensor. As a benefit, shadows would receive more exposure and, consequently, less noise.

As I have noted elsewhere in this thread, this explanation is incorrect. It is incorrect for the E-M1 and the E-P5, and will with practical certainty also be incorrect for the E-M5.

ISO 200 on the E-M5 (and all of the other Olympus m43 cameras with this Sony sensor) is actually ISO ~100 underexposed. The new LOW settings will be like ISO 100 exposed correctly.

Are you talking about this? http://www.dxomark.com/Cameras/Olympus/OM-D-E-M1#tabs-2

That is correct. As you can see from that graph, the sensor saturation ISO is close to 100 when the camera is set to ISO 100. It's even closer than that on the E-M5.

Then you also mean that ISO400 is also ISO ~200 underexposed and that ISO800 is ISO ~1600 underexposed, and so on...

That is correct, and exactly how the cameras are calibrated to work. They 'underexpose' by one stop, by design, at every ISO (except for LOW / 100) in order to preserve highlights. It's been known and talked about in detail since shortly after the E-M5 was released.

We were talking nominal ISO here, that's why it gets confusing. But if this is your reason, then it's nothing but a JPEG trick.

Whether you want to call it a JPEG 'trick' or not is your call. I'm interested in the effects on RAW, which are, basically, none at all. No (or very minor) loss of DR for RAW shooters, so anyone saying LOW will result in reduced DR is incorrect.

Interesting articles on this topic are here and here.

Both of those articles contain a number of incorrect and misleading statements. They've been discussed in detail here, almost exactly a year ago. I originally defended them as flawed primers on their respective subjects when they were first shared on this board, but subsequently had to admit that they are indefensible and likely do more harm than good.

Nonetheless, I am talking exactly about the difference between sensor ISO and camera ISO. The fact that the E-M5 has a sensor ISO 107 at camera ISO 200 means Olympus can (and did) add a Low / ~100 Camera ISO that has a sensor ISO of 107 without really sacrificing DR.

Note that ISO 12232:2006 includes the Recommended Exposure Index that allows manufacturers to specify an ISO value that produces well-exposed images. I wonder why Olympus would recommend ISO 200 when, per your comment, ISO 100 would be better as an increase in exposure would yield less noise.

Can you link to tests that have been done to verify that no highlight clipping takes place when  switching from ISO 200 to ISO 100 and increasing exposure?

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