1
Jan
2013

X-series AF performance: AF-L button focus method

AF-L Button

Back again!

Alexander from fujifilm-x-opinions linked me to the ongoing discussion in this forum (click here). He wrote:

“It seems that some people have better AF performance in manual mode using the AF-L button on the X-Pro1 than using the normal AF-S and half-pressing the shutter. I have tried to test this and here are my findings:

I do have the impression, that AF using the AF-L button in manual mode and AF-S are not the same (using the same size of AF focus field). I cannot yet say that one or the other is faster, but in the test I did I saw that the 35mm lens in AF-S mode sometimes went all the way to a very short distance and starting to search for the focus point from there (resulting in a high pitched sound). When I used manual mode and AF-L I did not observe the same behaviour. This was the same on the X-Pro1 as well as the X-E1.”

P.S.: He also posted the 4th part of his Trinity Comparison. This time Alexander compared the OVF’s of the X-100 and X-PRO1… no difference? Wrong. Read his test results here!

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  • http://vam.nu vam

    The AF-L method seems also less accurrate.

  • http://fb.me/akzphoto Andy

    I really wish they would add a compressed raw option. 26Mb seems a bit unwieldy, coming from my 14 bit lossless compressed D3s files. :) Yes, I want it all. =D

  • John

    I stopped using AF-S a few days in. AF-L button with manual focus is significantly more accurate and faster to grab a focus.

  • kuishinbou

    Is the camera’s AF really that bad? I have tried it a number of times in several stores, as I am considering buying one, and I did not have any problems with it. The AF with the 60mm was a little too slow for my liking, but I did have any problems with the 35mm or the 18mm. Perhaps the AF is terrible in low light ~ I am not sure, as I have never tried it in those conditions. However, in descent light, it seems fine to me.

    I took several photos around the store, including some portrait shots, and I have never seen sharper images SOOC ~ the sharpness with the 35mm SOOC blows that of my Canon 35mm f/1.4L away, which is largely due to the Fuji having no low-pass filter. Thus, the AF accuracy, though a little slower than my DSLRs, seems to be spot on.

    If the AF is really that bad, I will be very disappointed, as I am tired of using a DSLR. And, the Fuji X Series cameras are the only mirrorless cameras that I would consider getting at the moment, as the image quality appears to be fantastic and comparable to that of a full frame camera, though with a one-stop disadvantage in depth of field control; and, I love the manual controls…

  • edvarda

    Can fully confirm this strange behavior with the X-E1 + 35mm 1.4 combo. I did some test series under low light conditions selecting the same auto focus frame size that is used in the manual mode.

    Taking pictures of the same object the X-E1 in AF-S mode fails to focus accurately mostly while it works perfectly using the AF-L button in manual mode. Only 1 out of 5 shots taken in AF-S mode are comparable sharp than the ones taken in manual mode – they were all razor sharp! I didn’t notice any focus speed differences between both modes. In AF-S mode the focus seemed to lock quite fast but it was not accurate.

    I cannot judge if this has been introduced with the latest FW update as I own the camera + lens since 2 weeks only.

    • Chad

      Can’t duplicate this. In fact I am seeing no difference in AF speed when focusing on low contrast subjects (a white leather chair cushion).

      In fact the manual method is slower due to the extra step of reframing the frame lines for distance with a half shutter press. If you aren’t taking this step you are shooting a blind composition.

      • Antonio G

        Are you sure that in manual focus mode the half shutter press will reframe the frame lines again?

        I guess that the only effect of half press will be to fix exposure, if you are not using manual mode for it as well (meaning, you’re using A or S semi auto modes) and you “said” the camera (via menu) to use shutter only for that.

        At the end, using AF-L in manual mode is just the same as using it in AF-S mode. The idea to use AF-L in manual mode is only to let the camera use autofocus and afterwards to make fine adjustments using the lens ring.

        If it takes longer or not depends on the photographer and the kind of photography. Maybe if you move the focus point around within the viewfinder, instead of just focusing using the central area, will take you longer.

        One of the benefits of using range focusing mode in manual mode is that you don’t need to refocus when your subject stays in the appropriate range, and this is the reason why so many street photographers use it (namely with real manual rangefinder cameras).

        • Chad

          Yes, I am sure. Just tested again. In Manual mode, using AF-L button does one thing only – capture focus similar to what AF-S would do EXCEPT it does not change the frame lines, that is an extra step, accomplished by a half shutter press.

          So whatever perceived AF speed gains people think AF-L gives them (and I have seen none) are negated when you add the extra time needed to reframe with the half shutter.

          So that leaves us with the assertion that somehow AF-L in manual mode is more accurate than AF-S. Haven’t found that to be true either.

          Best,
          Chad

        • Chad

          Are we using the same camera? ;)

          You said: At the end, using AF-L in manual mode is just the same as using it in AF-S mode. The idea to use AF-L in manual mode is only to let the camera use autofocus and afterwards to make fine adjustments using the lens ring.

          Not true here. Using AF-L in AF-S does just what it says it does – lock the AF so you can recompose without changing focus. It does NOT attempt to AF like it does in manual mode.

          • Antonio G

            You’re right Chad, my mistake.
            As you say AF-L in AF-S mode just seems to lock focus. I checked the menu entries and there is no way to prevent shutter button to AF.
            TThe confusion comes from the possibilities offered by my full frame DSLR that already allows it and because I do use the Fuji in manual focus mode via the AF-L button and eventual micro adjustments with the ring.
            As a matter of fact it only adjusts the frame when pressuring the shutter button half way. For me it is not a bad thing because time reasons but because this way one of the advantages of using range focusing and the OVF to anticipate the image’s framing is partially compromised as you only know where the lines are at the moment you press the shutter, and this happens even if you use also manual exposure.
            This and the precision of focus range indication bar should be considered by Fujifilm for future firmware updates.

  • Chad

    Just tested on X-Pro and 35mm.

    No difference in focus speed but AF-L (manual) ends up being slower since the camera takes an additional step of re-framing the frame lines when you press half shutter (which you will need to in order to properly compose). In AF-S mode the reframing happens in concert with the AF confirm.

    Also, no difference between the two modes in terms of low contrast AF scenarios.

    I think there is a combination of wishful thinking and improper AF composition technique going on here.

  • Edmond

    I called Fuji HQ Japan and reported the back focus issue in AF-S mode. They confirmed that AF-L method in MF mode is more accurate than AF-S mode. Fuji Japan is developing new firmware to correct this issue.

    • edvarda

      I did my shots ( X-E1 + 35mm lens at f1.4) in lowlight of a bookshelf focusing on some glossy white books (with fine black lettering). For sure not an easy job but the camera managed it in the manual mode all the time while it failed in AF-S mode. I repeated this exercise this morning in daylight. Same results: no difference in focus speed between the two modes but the AF-S shots were just not 100 % sharp. So the camera seems to struggle especially with low contrast, glossy objects – but only in AF-S mode!

      I did also some test shots of other objects (lowlight and daylight) where there was absolutely no difference between the AF-S/manual mode. Neither in terms of focus speed nor in the resulting pictures (all were sharp).

      I couldn’t reproduce this with the 18-55 mm lens (at 35 mm and f 3.6). But maybe the larger DOF compensated the differences.

      • Antonio G

        Are you using “Multi” or “Area” when you select AF-S via the shutter button half pressing?

        And, when switch to “manual focus” and press AF-L do you change your settings and leave the shutter button just to measure exposure and trigger or you leave it just to change to AF-S and half press to autofocus?

        Did you try to set you camera in a way that AF-L is the only button to focus it and switch from AF-S to Manual using the focusing mode selector and “Area” focus? If so, do you see any difference?

      • Chad

        Edvarda,

        I cannot duplicate what you are seeing. Just a couple comments and suggestions.

        When you do your test, make sure you are in EVF mode (to ensure you are absolutely focusing on the same spot). Even better, use a tripod.

        The Fuji Contrast Detection system differs from others in that it excels at recognizing vertical lines as opposed to horizontal. A bookshelf has lots of vertical lines so make sure the AF spot is completely clear of any contrast or vertical lines. A plain white wall is a good torture test.

        Best,
        Chad

      • Edmond

        That’s what I reported to Fuji. Fuji told me that they need at least one month for new firmware to correct this issue.

    • edvarda

      Thanks to all of you for your answers. After many many test shots I am really sure now that my 35 mm lens struggles with a back focus issue in AF-S mode. If you try to focus on “challenging” low contrast objects it gets more pronounced while AF-L in manual mode is still capable to focus accurately.

      I doubt if this is a general problem since only a few people can duplicate this (see also
      http://www.fujix-forum.com/index.php?/topic/6752-afl-button-focus-method/ )

      Edmond,
      thanks for the good news from the Fuji HQ. Did they tell you if it is an issue of the camera FW or if only some lenses are affected? Before sending the 35mm lens to the Fuji service I will wait for some more weeks until the next FW update is available and hopefully fixes the issue. By then I will work in manual mode and mainly enjoy the incredible 18-55 lens.

      • Edmond

        I remember that before 2.01 update AF-S didn’t have a problem. Fuji told me they found the reason of the back focus and it can be fix with new firmware. Unfortunately If you bring your camera to Fuji service right now, Fuji cannot help you even they may deny the issue because Fuji Japan didn’t provide any comment about the back focus to local Fuji service. That was the why I reported the problem to Fuji Japan directly.

  • http://www.sagi-k.com Sagi

    With my XE1, I use both the AF-L and the AF-S methods to focus and at least with the 18mm lens I see no difference in focus speed or accuracy.