x-t4 Despite all settings being manual, X-T4 insists on changing exposure.

[Shootinglight]

Can anyone explain this annoying phenomenon?

X-T4 with 18-55 kit lens.

Everything set to manual.

Only time the camera won't do this is if the aperture is set to 2.8 when at 18mm. Set like that, you will see the aperture change from 2.8 to 4 as it gets to 55mm, BUT no exposure stepping issue as seen here in this vid.

[Florian]

This is standard behaviour for many zoom lenses: when you zoom in, the minimum possible aperture increases. This is a physical limitation of the lens' construction, that's why it says F2.8-4.0 and not F2.8 in the product name.

Edited April 22, 2022 by Florian
typo

[Shootinglight]

4 hours ago, Florian said:

This is standard behaviour for many zoom lenses: when you zoom in, the minimum possible aperture increases. This is a physical limitation of the lens' construction, that's why it says F2.8-4.0 and not F2.8 in the product name.

I am well aware.

Ironically, the only time this doesn't happen is when the the aperture is set to 2.8 at 18mm and you then zoom in. Indeed the aperture does change to f4 but with no obvious change in exposure.

As a side note, this is also happening when taking stills. I have taken a set of photos with fully manual settings and they all vary in exposure despite all the data (as seem in Lightroom) being exactly the same. Not good.

[jerryy]

Quote

 

There are several things going on, the 18-55mm lens is not a constant aperture lens, so even with all others settings being manual, the metering is affected by the focal length. Even with spot metering being used, you have an area of 18/2.8 vs 55/4.0 for the meter to use. This happens across cameras built by every manufacturer.

You can switch to using constant aperture lenses so that the effect is not as noticeable or use “cinematic” lenses with T-Stops instead of F-Stops to make sure the light transmission is steady regardless of the zoom setting. It is more expensive, but that is the way a lot of people go to solve the issue.

edit:

p.s. Before you ask, I have never gotten a good understandable answer as to why metering should affect the exposure when the shutter speed, f-stop and ISO are all manually set.

Edited April 22, 2022 by jerryy