@ Manual shooters: focusing while halfway pressing shutter?

Dear contributors

Very interesting discussion. Many thanks to all of you! Trying to summarize the current status. But a continuation of the discussion is welcome! E. g., I am curious how the X-T4 behaves.

Context

This thread is about focusing w/ manual lenses with the viewfinder magnification on.

(Magnification is achieved through the 'focus check' function. This function can be assigned to a button; in my case, it is pressing the rear command dial.)

Motivation

Imagine you shoot a portrait with a fast manual lens. DoF is fairly small. You want to nail the eye and then shoot immediately. Any delay or loss of control is undesired in such a situation. Having to fully press the shutter all the way down is, at least for me, also undesired (reasons: higher risk of camera shake; feels like it takes more time than releasing just from half pressed shutter button). You want to be fast and precise.

Thus, ideally...

• ...I'd keep the viewfinder magnification & MF assist & viewfinder brightness of the magnified section when half pressing the shutter and can release the shutter w/o time delay.
• ...I can select in the camera menu whether the viewfinder magnification remains in place for the next shot or whether the viewfinder returns to the full image. The former option would enable 'burst' like portrait shoots.

Behavior of the X-T20

This is my camera model from where I started this discussion.

Mode: AF-M + viewfinder magnification + MF assist

• Half pressing shutter: viewfinder magnification disappears (i.e., you see the full image). At the same time, the MF assist disappears, too. From this position, there is no shutter lag.
• Fully pressing shutter all the way down w/o stopping at half pressed: significant shutter lag, about 1/3 second (estimated).

Mode: AF-S + viewfinder magnification

• Half pressing shutter: viewfinder magnification remains. From this position, no shutter lag. I have to press the focus check (in my case the rear command dial) before each and every shot because the frame magnification returns to normal after each photo. Disadvantages: (i) brightness of the magnified viewfinder section may change (depending on lighting situation of the subject - section can become darker and thus harder to see; and (ii) there is no MF assist available w/ AF-S. Overall, this is now my preferred mode for focusing w/ manual lenses with viewfinder magnification on. Though not ideal, in most situations, I prefer this over the AF-M + half press alternative, reason being that I do not lose control of the focus (viewfinder magnification remains).
• Fully pressing shutter all the way down w/o stopping at half pressed: significant shutter lag.

Note. Change of release/focus priority settings do not change the X-T20’s behavior.

Behavior of the X-T2

• Similar behavior.
• But: less or occasional or no shutter lag in AF-M mode as compared to X-T20.
• Hypothesis: reason is a faster processor than that of the X-T20.

See exemplary posts

• https://www.dpreview.com/forums/post/63929091
• https://www.dpreview.com/forums/post/63929143
• https://www.dpreview.com/forums/post/63929209

Behavior of the X-T3

• Similar behavior.
• But: no shutter lag except from one situation: fully pressing shutter all the way down w/o stopping at half pressed in AF-S mode with magnification on.
• Hypothesis: reason is a faster processor than that of the X-T2.

See post: https://www.dpreview.com/forums/post/63929233

BR,

Martin