Fuji vs Sony ISO

Started May 26, 2019 | Discussions thread
Doug Pardee
Doug Pardee Veteran Member • Posts: 9,876
Re: Here we go again

madhav56 wrote:

Knew that base ISOs are different and also the overstating of ISO by Mfgrs...................

Being picky on terminology: nobody's "overstating" ISO.

Fujifilm, Olympus, Panasonic, and Pentax use classic ISO behavior that dates back to the beginning of ASA film ratings. In simple metering modes like Spot, or when used with a handheld meter, they reproduce an 18% gray card as 18% gray in the JPEG (as close as possible).

Canon, Nikon, and Sony have chosen to go with a new ISO rating system for the digital age. Compared with classic ISO, they're understating the ISO number by about one stop. The result is that in simple metering modes like Spot, or when used with a handheld meter, they reproduce an 18% gray card as somewhere around 35% gray in the JPEG.

For multi-zone metering (Evaluative, Matrix, Multi, ESP, etc.), there's no functional difference: all cameras from all brands will reproduce that 18% gray card at maybe 35% gray. The only difference is what ISO number you see. At a given exposure (shutter speed and aperture), the Fuji will have a higher ISO number than a Sony with the same sensor, but the resulting capture will be pretty much the same with the same noise level. Unfortunately, people like to whine about the ISO numbers being different. Canon, Nikon, and Sony sell the most cameras, and might makes right, so clearly Fujifilm must be wrong. Which is why the Canadian speed limits are wrong.

The functional difference is in simple metering modes, especially Spot metering, or when using a handheld meter. There, you'll see a difference in the capture. The 35% gray rendering of an 18% gray target by Canon (etc.) is the same as with multi-zone metering. The 18% gray rendering by Fuji (etc.) is different from multi-zone metering on the very same camera.

The increased exposure necessary to achieve the 35% gray on a Canon (etc.) camera obviously reduces the overall noise levels. Old timers (like me) will point out that's obviously overexposed, but I can also see that people overwhelmingly like their color photos "overexposed." In fact, that "new ISO" (REI) scale that Canon (etc.) are using requires the cameras to produce JPEG images that people consider to be pleasingly exposed.

Recall from above that on all brands, even Fuji, multi-zone metering will produce that 35% gray "overexposure" because, again, it's what people like. [When I say "35% gray" or whatever, that's always a rough approximation. Remember that exposure can only be controlled in 1/3 stop increments, and besides, there's no numerical standard for what constitutes a pleasing exposure.]

In short: for simple metering modes or with a handheld meter, the classic SOS ISO gives "accurately exposed," and the new REI ISO gives "pleasingly overexposed with less noise." With multi-zone metering, you always get "pleasingly overexposed with less noise," but the ISO numbers are different between the two systems. Most importantly (in my opinion): cameras using classic SOS ISO (Fuji, etc.) will give a reduced exposure with the simple metering modes like Spot when compared with Multi metering.

It's certainly arguable that maybe it's time for Fuji, Oly, Panny, and Pentax to let go of the classic ISO ratings and catch up with the times. You don't see people complaining that their Canikony cameras aren't reproducing an 18% gray card at 18% gray when spot-metering or when using hand-held meters. It seems that nobody cares, where "nobody" means almost literally nobody. Virtually everybody likes, and is comfortable with, the new ISO system.

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