LCD preview changes when focusing in AF-C (part 2)

[majosm]

The previous thread on this (https://www.dpreview.com/forums/thread/4767008) went a little off topic, but I think the question was valid and it didn’t quite get a satisfactory answer. So I wanted to revisit it.

The user in the other thread reported seeing a change in previewed exposure on the LCD screen with their X-T5 when half-pressing the shutter in AF-C (but not AF-S). I remembered seeing something like this on my X-H2S, so I attempted to reproduce it. I was able to see behavior similar to what they reported:



Notice how the highlight blinkies are not visible before focusing, but appear during. Here is another demo with the highlight alert disabled:



To me this looks more like a change in highlight rolloff rather than a change to overall brightness/exposure. Not sure exactly what would cause this. For completeness, here is AF-S:



Notice how the preview doesn’t change upon focusing here.

As the user in the other thread reported, this only occurs on the LCD screen (and HDMI out, apparently), not the EVF. It also doesn’t affect the resulting image (as long as one doesn’t try to compensate by underexposing).

A few more observations/notes:

• Independent of metering mode
• Independent of Auto-ISO vs. manual
• Natural live view is off
• Preview Exp/WB in manual mode is set to Exp/WB
• Seemingly not lens specific (I tried 16-55, 23mm f/1.4, and 150-600)
• Happens with lens wide open or stopped down
• Happens with back button AF-On as well
• This is with the current X-H2S 7.00 firmware (it also happened with the previous version, and possibly earlier versions)

For myself personally this hasn’t been too much of an issue, but I mostly use the EVF for stills. For someone using the LCD primarily, I could see how this might lead them to chronically underexpose in order to correct for the perceived blown out highlights seen when focusing.

Anyone have any clues what could cause this? I’m assuming it’s not a fundamental part of the AF-C focusing machinery (otherwise it would be seen in both the LCD and EVF, not just the LCD). Happy to test other things if anyone wants me to. Mostly I just wanted to make this thread so that others can find it if they are seeing the same thing and wondering their camera is broken. Hopefully this is something Fuji can/will fix at some point.

 

[Erik Baumgartner]

I'm not sure what causes the occasional slight discrepancy between no-press and half-press blinkie response, but it varies a bit from lens to lens and has to do with how the AE locks (if the SHUTTER AE option is off, you won't likely see any blinky discrepancy with a half-press). My experience has been that the half-press blinky response closely matches what you'll see in the jpeg result and is probably the way to go, but you won't typically be clipping the highlights in the RAW file either way.

Note: the highlight clipping indication response is only valid within plus or minus 3 stops of exposure compensation, beyond that, the exposure must be locked with a half-press (SHUTTER AE on) or AEL engaged for a valid highlight clipping indication.