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Focus changes in MF with certain lenses when half pressing shutter button

Nielk Mike
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p.1 #1 · p.1 #1 · Focus changes in MF with certain lenses when half pressing shutter button

It appears to me that this is worth a seperate topic, as in the 14mm lens thread it gets somewhat sidelined.

On my X-E3, X-T2 and X-Pro3, the 27f2.8 WR, the 14f2.8, Sigma 18-50 and the (so to a lesser extend) the 18-55 show a strange behavior:

The camera (and in the case of the 14mm: The lens) is set to MF. Setting the focus distance manually to certain focus steps and then half pressing the shutter button activates the focus motor, the barrel moves and the focus distance indicator moves, too. The resulting distance is then no longer what I have set manually.

Below are three short videos that show this behavior with the 14mm and theX-Pro3, the 27mm and the X-E3, and the Sigma 18-50 on the X-T2. Setting Shutter AF to "off" doesn't help.

27/X-E3: https://www.amazon.de/photos/share/2ie4Dc46TIN9prtYPE2hkkblaXPyYQYcShuK3o1wYGJ
14 X-Pro3: https://www.amazon.de/photos/share/zbrzLoPmsN15sdlmyNROFCvPDpoTQIl6Kp0gtL16f9i
Sigma 18-50 X-T2: https://www.amazon.de/photos/share/3X0MJSYusEXfHbimjhhmY4pbsLjysNVlycekamnndkW

Fortunately, none of my other lenses (Classic Primes 16/23/35/50 and the 90f2( show this behavior. Half pressing the shutter seems to send an electric impulse to the focus system. Not always, only at some focus steps, though.

Can someone explain that behavior?

Aug 24, 2024 at 01:53 PM

jcw1982
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p.1 #2 · p.1 #2 · Focus changes in MF with certain lenses when half pressing shutter button

What is your assessment?

Aug 24, 2024 at 02:11 PM

Nielk Mike
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p.1 #3 · p.1 #3 · Focus changes in MF with certain lenses when half pressing shutter button

Just don't know. There seems to be some kind of impulse that activates focus. But only with certain lenses. I can only speak for use with three models (X-E3, X-T2 and X-Pro3). Now, the X-Pro3 wih the latest firmware is relatively recent.

Does the behavior impact photography? Well, it can. It just bothers me that when I try to set focus acurately, the camera changes that setting on its own. I might sell the 27 and 14 because of this.

Aug 24, 2024 at 02:23 PM

bobby350z
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p.1 #4 · p.1 #4 · Focus changes in MF with certain lenses when half pressing shutter button

Is the focussing disabled from the shutter button?

Aug 24, 2024 at 03:21 PM

Nielk Mike
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p.1 #5 · p.1 #5 · Focus changes in MF with certain lenses when half pressing shutter button

Yes, but Shutter AF "On" or "Of" makes no difference.

Aug 25, 2024 at 12:46 AM

Nielk Mike
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p.1 #6 · p.1 #6 · Focus changes in MF with certain lenses when half pressing shutter button

Found this on dpreview - and there is more: https://www.dpreview.com/forums/thread/4544897

Will sell the lenses that are affected unless I can find, or someone points me to, a work around.

Aug 25, 2024 at 04:59 AM

Nielk Mike
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p.1 #7 · p.1 #7 · Focus changes in MF with certain lenses when half pressing shutter button

There is, in fact, a setting that can serve as a work around. Not ideal - but at least it keeps the lens from changing focus. Set the camera to AF + MF. Focus in AF-S mode and use the focus ring to adjust focus. Then press all the way.

Aug 25, 2024 at 08:09 AM

Nielk Mike
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p.1 #8 · p.1 #8 · Focus changes in MF with certain lenses when half pressing shutter button

Let's continue the discussion here. It certainly seems as if the camera with certain leses either has a feedback loop even in MF to assure the "correct" setting of the focus element. Since the focus happens in steps, it could be that teh manual focus puts the focus element "inbetween" "proper" focus steps.

Aug 29, 2024 at 01:20 PM

Geoff D F
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p.1 #9 · p.1 #9 · Focus changes in MF with certain lenses when half pressing shutter button

So I further tested my 14mm f2.8 on the X-E2S last night using multiple different settings and at multiple different focus distances and still can't replicate the result. I can definitely hear the aperture blades moving and what sounds like the focus motor moving, but it may be a motor that moves the aperture blades. Interestingly there is no sound at all when the lens set to f2.8, so the noise is entirely consistent with something to do with the aperture.

I tested the focus in magnified view and can't see the slightest change.

Curiously something about my settings turns the focus scale off in manual focus mode.

Aug 29, 2024 at 07:23 PM

Nielk Mike
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p.1 #10 · p.1 #10 · Focus changes in MF with certain lenses when half pressing shutter button

The sound of the aperture blades moving is very distinct from the sound of the AF motor engaging. Tried again this morning with the X-E3 and teh 14mm, aperture wide open. The Distance indicator moves and I can hear the focus motor (made another video clip to document the behavior). My Distance Scale always shows (unless I disable it in the Display Settings, or if I use Large Indicator mode.

Manual focus with the 14mm is pretty jumpy, anyway. Tunring the focus ring slightly often results in the lens moving the focus element more than one step at a time.

Try setting the focus point to different positions between the 2m and the 5m mark on the distance scale. Half press the shutter button and hold it a second.

Of course there is always the possibility that my 14mm lens (which I bought used) is defective. And if I would only observe this behavior with the 14mm lens, it would probably be the case. Same for camera bodies: If had only seen this with one boda, it could well be that that body is defective. But I am currently seeing this with four lenses on three different bodies. What are the chances that all of them are defective? And then there are lenses (the Classic Primes and the 90) who do not show that behavior at all!

It seems that it is the older design of the lenses (which doesn't explain the Sigma 18-50 behavior).

It is an anyoing behavior as it can impact the precision of manual focus, and like the AF-S inconsistencies, it happens not on a regular basis but intermittently. Takes away the confidence I have in these lenses. There is a way to keep the focus from moving which is to set the camera to AF+MF in the AF settings. But I am still considering selling the lenses.

Aug 30, 2024 at 12:54 AM

alundeb
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p.1 #11 · p.1 #11 · Focus changes in MF with certain lenses when half pressing shutter button

The reason that the focus system is even engaged in MF, is that the lenses are focus by wire also in MF.
The camera needs to respond to certain conditions, updating the focus. It seems that this happens when the shutter is half pressed, at least under some circumstances.

As I said in the other thread, some lens designs are more sensitive to manufacturing tolerances and "noise" in the focus loop, that being either the sensor or the actuator.

Regarding the MF "sensor", there are two possible designs for the MF ring. It can either detect motion and the camera "remembers" the position, or it can detect the absolute position.

I don't own any X mount camera or lens, but it seems that at least the 14 mm has an absolute focus scale on the lens, meaning that the sensor has to read the exact position of the ring. This design approach is more prone to noise and sensor inaccuracy than reading movement and modifying the "position" in software.

Since many are not able to reproduce movement by the camera in MF, I stand by my hypothesis that this is a manufacturing tolerances problem. It might be difficult to get a lens deemed "defective", but I would certainly investigate the lens copy variation approach if I was into the system.

Aug 30, 2024 at 01:11 AM

Geoff D F
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p.1 #12 · p.1 #12 · Focus changes in MF with certain lenses when half pressing shutter button

Nielk Mike wrote:
The sound of the aperture blades moving is very distinct from the sound of the AF motor engaging. Tried again this morning with the X-E3 and teh 14mm, aperture wide open. The Distance indicator moves and I can hear the focus motor (made another video clip to document the behavior). My Distance Scale always shows (unless I disable it in the Display Settings, or if I use Large Indicator mode.

Manual focus with the 14mm is pretty jumpy, anyway. Tunring the focus ring slightly often results in the lens moving the focus element more than one step at a time....Show more →

All I can do is assure you that there is no noise at all coming from my lens when the aperture is set to wide open.

Aug 30, 2024 at 01:21 AM

Nielk Mike
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p.1 #13 · p.1 #13 · Focus changes in MF with certain lenses when half pressing shutter button

Have no reason to doubt your findings. Most of the time my lenses don't do a sound or move, too. It is only at some positions that the AF-motor engages and can be heard, and the barrel of the 27mm moves (as does the distance scale). The AF on the 27 is particularly noise - so the sound is hard to ignore.

Question is: Is it the camera or the lens that is causing this behavior? My guess is that it are the lenses as there are some that do not show this at all, and some (older sedsigns) which do. Why does the Sigma 18-50 show this, too? It is a relatively new lens. Could it be that Sigma reverse engineered the older Fuji AF technology? The Sigma 18-50 is also prone to the AF-S inconsistencies/focus beyond infinity.

Knowing about the uncommanded focus movement in MF and the AF-inconsistecies helps me to avoid them and to reduce frustration from images that are not in critical focus.

While I am aware that many will never notice the issues (cause they use OOC JPEGs and don't do post, crop, or pixel peep), for those who do notice or wonder about images that are not critically sharp, a discussion like this can be very helpful.

Aug 30, 2024 at 03:00 AM

Nielk Mike
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p.1 #14 · p.1 #14 · Focus changes in MF with certain lenses when half pressing shutter button

Looking into this a bit more with the 27mm WR and the X-E3, it seems as if the movement of the focus motor and the lens barrel does not impact the focus position in the end. Looking that the barrel, I can see a short back and forth movement that is similar to the focus movement in contrast detect mode. Start and end position of barrel appear to be the same, however.

This is good news. The behavior is strange, though (as in MF there should be no electrical impulse to the focus motor from the shutter button, in particular if "AF Focus" is set to off). Using "AF+MF" is still the best way to focus manually without uncommanded movement.

Aug 30, 2024 at 03:49 AM

Makten
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p.1 #15 · p.1 #15 · Focus changes in MF with certain lenses when half pressing shutter button

It's the same on the GFX 50S II. The lens "refocuses" for no reason at all, when in manual mode and half-pressing the shutter. I think it's only happening with the lenses that don't have linear motors (mainly GF55, 80).
The same lenses also move focus when you go from shooting to viewing images, or into the menu. Stupid programming.

Aug 30, 2024 at 04:33 AM

Nielk Mike
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p.1 #16 · p.1 #16 · Focus changes in MF with certain lenses when half pressing shutter button

Makten wrote:
It's the same on the GFX 50S II. The lens "refocuses" for no reason at all, when in manual mode and half-pressing the shutter. I think it's only happening with the lenses that don't have linear motors (mainly GF55, 80).
The same lenses also move focus when you go from shooting to viewing images, or into the menu. Stupid programming.

Thank you for sharing. That would explain why the Sigma 18-50 shows the same behavior: It also sports a stepping motor for AF as far as I know. But: The Classic Primes also use stepper motores, make no sound at all, and AF doesn't move uncommanded.

Aug 30, 2024 at 05:07 AM

alundeb
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p.1 #17 · p.1 #17 · Focus changes in MF with certain lenses when half pressing shutter button

When a focus-by-wire lens with an absolute scale on the focus ring is not mounted on a camera, moving the focus ring does not move the lens focus.
When the lens is mounted back on the camera, the camera is in MF mode, and you press the shutter button, what do you expect to happen?

Do you expect the photo to be taken at a random focus distance not matching the lens ring, or do you expect the camera to engage the focus "uncommanded" to focus on the selected distance?

Aug 30, 2024 at 06:26 AM

Nielk Mike
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p.1 #18 · p.1 #18 · Focus changes in MF with certain lenses when half pressing shutter button

alundeb wrote:
When a focus-by-wire lens with an absolute scale on the focus ring is not mounted on a camera, moving the focus ring does not move the lens focus.
When the lens is mounted back on the camera, the camera is in MF mode, and you press the shutter button, what do you expect to happen?

Do you expect the photo to be taken at a random focus distance not matching the lens ring, or do you expect the camera to engage the focus "uncommanded" to focus on the selected distance?

Interesting thought. So I set the 27 on the X-E3 to 1.5m in MF, then took the lens off, moved the focus ring, and put the lens back on (all with the camera switched on). The result was a move of the focus element. When I took the lens off, but didn't move the focus ring while it was off, the focus element did not move upon putting the lens back on.

Tried the same procedure with the 35f2. It behaves the same. When the focus ring of the lens is moved from the selected distance when not on the body, the camera resets teh distance when it is being re-mounted.

However: While both lenses react in the same way, only the 27mm lens moves uncommanded when the shutter is half pressed. The 23f2 (as all other Classic Primes) doesn't.

Aug 30, 2024 at 06:38 AM

alundeb
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p.1 #19 · p.1 #19 · Focus changes in MF with certain lenses when half pressing shutter button

Hopefully you got an answer to one question, how is it even possible that the focus moves when half-pressing the shutter button in MF.
With focus by wire, it has to be designed to do that if necessary.

Sep 06, 2024 at 04:30 AM

Nielk Mike
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p.1 #20 · p.1 #20 · Focus changes in MF with certain lenses when half pressing shutter button

alundeb wrote:
Hopefully you got an answer to one question, how is it even possible that the focus moves when half-pressing the shutter button in MF.
With focus by wire, it has to be designed to do that if necessary.

Son is focus by wire - and doesn't do it. The 16f2.8, 23f2, 35f2, 50f2 and the 90f2 don't do it. So why with certain lenses?

Sep 06, 2024 at 04:43 AM

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