I just did some tests with my X100S
However from the pics of the LCD screen that OP provided it looks like the aperture parameter was already at its widest possible for that lens. That's because the aperture value in his preview image is colored red to show that it'd need to go wider for proper exposure but can't.
To me it simply looks like the camera can't match the desired exposure because ISO and SS are manually fixed while aperture is in auto mode but has already reached the physical limit of the lens. Yet the exposure preview shows what the image would have looked like if the desired exposure had been possible instead of showing what is actually possible and will be produced once the shot is taken.
The type in bold is definitely true with my camera
with Aperture priority and ISO and Shutter Speed fixed. That is, my camera's LCD display behaved exactly the same as the Original Poster's.
I'm a bit confused by what you mean here with "aperture priority". If the ISO and SS are also fixed then aren't you in full manual mode?
In
aperture priority mode OP's problem should only appear once the shutter speed would need to get slower than 1/30 sec (at chosen Maximum Sensitivity), or once the shutter speed would need to get faster than 1/32000 sec (at base ISO). These should be very extreme conditions and extremely rare in practice.
In
shutter speed priority mode the problem appears much sooner however, because the aperture range is much more limited than SS range so the camera doesn't have much available range to work in in low light. At the same time bigger SS range also allows you to set crazier demands with very fast SS. Unlike with aperture priority and Min. Shutter Speed setting the camera can't override the physically limit of your lens's widest aperture. But if you simply give the full ISO range to Auto ISO then that's practically the same as the camera overriding your Maximum Sensitivity setting and having a wider range to work in.
Thanks to you, phohod, I've learnt there are occasions when I need to activate Auto ISO rather than miss the shot or get an inferior shot.
That's what I've been recommending to OP as well. There's no reason not to use higher ISOs if the choice is between getting the shot or missing it, and it's better to get exposure right in camera. The fact that you also get correct exposure preview is a welcome side effect.
Having said that, I also see OP's complaint as valid. There's no good reason for the camera not to provide you with an option to always show exposure preview. Fujifilm's own marketing boasts about
WYSIWYG. The red warning symbols are bare minimum but it's very easy to miss them when there's a lot of action going on in front of your camera, whereas exposure preview is immediately obvious.
I don't want high ISO. I want it the lowest possible as higher than base ISO is useless to me.
You people don't get it what I'm trying to say. Read this post:
https://www.dpreview.com/forums/post/67211177
Here's a practical example why I set up the way I do.
S-priority so the camera reacts only to shutter changes.
Base ISO.
I shoot very slow paninng motorsport shots, sometimes as low as 1/13th. That makes the images very bright, so I don't want high ISO. It's unneccessary image degradation.
Being in S-priority if the image becomes way too bright the aperture goes to something like F4 or F5.6 or whatever to compensate.
However I do use variable ND filter to set the correct exposure and get as close to f2.8 as possible, otherwise I get a lot of dust showing up.
If the exposure is initially set correctly and there's a sudden overcast, the picture I see through the lcd/viewfinder doesn't change.
Histogram doesn't change.
So I'm led to believe everything is correctly exposed, unless I review the images on my PC or the camera (which is tiresome as sometimes there is a lot of weather changes and I don't have time to review photos every 1-2 minutes).
What's baffling is that this issue doesn't present itself in A or M modes. If the image is underexposed, it shows straight on the lcd/viewfinder without having to review the photos taken.
