Do you know what can cause this?

[andydg]

I have a particular lens, manuf. I won't mention, that confuses me with its behavior. For instance with the lens wide open and I take a shot of a static object the image is properly exposed. (Using aperture priority) Then stopping the lens down one stop the image is again properly exposed, but the overall lighting of the image changes. Also looking at the histogram, it shifts to the left a bit. IOW between the two f-stops I see a small lighting difference and the histogram always moves ever so slightly between the two different exposures. I've stopped the lens down further and the difference between those exposures is nil, the histogram does not move side to side.
Being an electronic type lens with firmware, would this be considered a software issue or related to hardware?

 

[Finder]

Digital camera have difficulty in determining correct exposures at large aperture around f/2 or so. This is because the light cone intersects the sensor at a significantly large angle. You may notice some cameras in P exposure mode will not or rarely use the largest possible aperture on fast lenses.

 

[antiquark]

Also, vignetting increases with a wider aperture, which would alter the hisogram.

 

[Finder]

Also, vignetting increases with a wider aperture, which would alter the hisogram.

But if that were the case, wouldn't the histogram shift to the right when stopped down rather than the left as the OP described?

 

[ampguy]

interesting

interesting

What happens when you shoot an evenly lit wall wide open, then 1 and 2 stops down?

Does your AE shutter speed indicator double, every time you stop down by 1 stop?

I have a particular lens, manuf. I won't mention, that confuses me with its behavior. For instance with the lens wide open and I take a shot of a static object the image is properly exposed. (Using aperture priority) Then stopping the lens down one stop the image is again properly exposed, but the overall lighting of the image changes. Also looking at the histogram, it shifts to the left a bit. IOW between the two f-stops I see a small lighting difference and the histogram always moves ever so slightly between the two different exposures. I've stopped the lens down further and the difference between those exposures is nil, the histogram does not move side to side.
Being an electronic type lens with firmware, would this be considered a software issue or related to hardware?

 

[andydg]

yes it does

yes it does

The shutter speed does double with each full stop change. This is with full pattern metering.

Regarding the histogram shift, I may have gotten it wrong in my previous explanation. At wide open it shifts right from the next stop, not left as I had mentioned. Not by much though, just a tad.

What happens when you shoot an evenly lit wall wide open, then 1 and 2 stops down?

Does your AE shutter speed indicator double, every time you stop down by 1 stop?

 

[andydg]

thank you for the comments

thank you for the comments

I appreciate the feedback. My mind is at ease that the lens behavior is normal and I shouldn't think too much of it.🙂