Spot metering question - Fuji middle gray?

Started Mar 20, 2017 | Questions thread
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allineedislight Regular Member • Posts: 415
Spot metering question - Fuji middle gray?

Probably this has been discussed many times, but I couldn't find a definite answer.

What is the middle gray that the meter in Fuji cameras are calibrated to? It seems that it is 21% gray, not 18% or 12-13% (at least on my X100).

If I spot meter my gray card in auto mode with no exposure correction (and custom white balance based on gray card), and measure the RGB values in the resulting OOC JPG (sRGB color space) they gray card is rendered with a value around 127. In other words, there is a peak corresponding to the gray patch right in the middle of the histogram. Now, an RGB value of 127 in sRGB color space corresponds to 21% reflectance (see e.g the calculator , line 1 vs line 3 )

On the other hand, if I measure the light with a Sekonic incident light meter, set the camera to manual mode with settings obtained by the Sekonic, then the gray card has a RGB value in the JPG of 118, which shows that the exposure is pretty much perfect (since 118 RGB in sRGB color space corresponds to 18% reflectance, and my gray card has 18% reflectance).

Thus, to get the correct exposure I have to spot meter the gray card in auto mode and apply -1/3 EV negative exposure correction.

Do all Fuji's camera meters calibrate middle gray to 21% reflectance? Or is this unique to the X100?

I am bringing this up because a lot of literature on spot metering assumes that the camera meter is either calibrated to 18% middle gray (so no exposure compensation is needed when spot metering a 18% gray card) or to 13% middle gray (so +1/3 EV positive exposure compensation is required).

I am particular curious to learn about the behaviour of newer Fuji models (esp. X100F)!

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Sigma DP2 Fujifilm FinePix X100
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Fujifilm FinePix X100
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