Overexposure with X100: my error in auto-ISO

[Richard G]

I was loving auto-ISO set for maximum 1600 and minimum shutter speed 1/60s. Everything worked. But yesterday I used manual ISO, moving it from 200 to 2500. After switching back to auto I did not realize that the camera would now try to keep the ISO as close to 2500 as possible. I wanted to photograph some clouds this afternoon and they were all blown. Then I remembered that 1/1000 is top speed at f2 and f2.8 and 1/2000 top speed for f4 And f5.6 with 1/4000 only available for f8 and above. The red 1000 was flashing in the viewfinder but I hadn't noticed it. I've now returned the manual ISO setting to 200 and my previously charmed existence seems to have returned. Read the manual I can hear someone saying. "This sort of thing has cropped up before, and it has always been due to human error."

 

[willie_901]

It turns out that the camera worked exactly as it was designed to work. Auto ISO on the X100 is great (I set mine to 200-1600 and just leave it there), but the problem is you have to understand exactly how it works or there will be surprises. If you never turn auto ISO off and if you set the minimum ISO (200) for each mode (AF-C, AF-S and MF) you will never have this problem. If you change ISO and don't turn Auto ISO off, you must remember exactly how auto ISO works.

With auto ISO invoked, I set the Fn button to select the ND filter. Whenever I'm outdoors, I switch ND on. This is the price you pay for the whisper quiet shutter.

 

[ampguy]

maybe I'm missing something, but why wouldn't it be a good thing if the auto iso moved closer towards 200 rather than staying at the higher range in this overexposed situation?

 

[willie_901]

ampguy

On the X100, when the minimum ISO is set to (and left at) 200 in AFC, AFS and MF modes, the camera will indeed use ISO 200 until shutter speed drops below the minimum speed specified during auto ISO set up. The ISO is increased until the minimum shutter speed gives proper exposure.

I beleive Richard G unintentionally set the minimum ISO to 2500 from 200. At the same time he did not notice the error message (red flashing shutter speed) in the finder. This is a common beginner error with the X100. I did this myself once.

The X100 implements auto ISO mode in the following way:

You set Auto ISO

You set the highest acceptable ISO

You set the minimum shutter speed.

The minimum ISO defaults to the current ISO setting. This means the minimum ISO will vary if the user changes the ISO parameter. So – if you change to ISO from 200 to 800, then the minimum ISO becomes 800.

 

[ampguy]

Hi Willie

Hi Willie

The manual on p. 83 states a bit different, in that the min ISO in auto ISO mode is fixed at 200. Only the max ISO can be user defined, along with slowest shutter speed.

So when on, and dark enough to exceed the EV of highest selected max auto iso and lowest selected shutter speed, it will fire, and underexpose.

I think the manual states their goal. I wonder if they actually got it right though 😉

Kind of like the Hexar AF's P mode where it will open the aperture wider (if it can), once the lowest set shutter speed is reached, but in the Hexar's A mode, it will just fire at the set A.

ampguy

On the X100, when the minimum ISO is set to (and left at) 200 in AFC, AFS and MF modes, the camera will indeed use ISO 200 until shutter speed drops below the minimum speed specified during auto ISO set up. The ISO is increased until the minimum shutter speed gives proper exposure.

I beleive Richard G unintentionally set the minimum ISO to 2500 from 200. At the same time he did not notice the error message (red flashing shutter speed) in the finder. This is a common beginner error with the X100. I did this myself once.

The X100 implements auto ISO mode in the following way:

You set Auto ISO

You set the highest acceptable ISO

You set the minimum shutter speed.

The minimum ISO defaults to the current ISO setting. This means the minimum ISO will vary if the user changes the ISO parameter. So – if you change to ISO from 200 to 800, then the minimum ISO becomes 800.

 

[Arjay]

I think the manual states their goal. I wonder if they actually got it right though 😉

In fact, the X100 manual is full of mistakes and omissions (I know that from practical experience).

The normal (Non Auto) ISO value indeed acts as minimum ISO value in Auto ISO mode, and we can only speculate why Fuji programmed it that way. One possible reason is to support the 200 & 400% DR settings, which effectively lower the ISO value used by 1 or 2 stops. Why Fuji did not design the firmware in such a way that those DR settings simply raise minimum ISO to a minimum of 400 or 800 ISO (and just forget about the previously selected Non-Auto setting) is beyond me... This just makes using the camera unnecessarily difficult.

Mind you though, the X100 still is one hell of a good camera ...