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PDAF on the EM1, interesting development!

Discussion in 'Olympus Cameras' started by atarijedi, Jan 31, 2016.

  1. atarijedi

    atarijedi Mu-43 Regular

    61
    Dec 13, 2015
    Greetings folks,

    Over in the thread titled "Is EM-1 focusing better than EM5-II?", I posted a picture showing the PDAF bounding box which appears on the EM-1 when you use Seq-H + SAF or CAF (non-tracking). I only recently learned about how the PDAF works and how it shows you it is working. I'll post the image again here at the end of this comment.

    I had only ever tested PDAF with M43 lenses, because I was lead to believe it would only work with M43 lenses and older 4/3 lenses, but I don't own any 4/3 lenses.

    However, curiosity got the best of me and I just tested it with my Metabones 0.71x SB and Sigma 150-600mm C, and that bounding box also appeared, I realize I had seen it before, but I didn't know what it meant. In fact, it seems that only PDAF mode is enabled, thus no CDAF, just like when using an older 4/3 lens. And this is in all shooting modes: Single, Seq-L, and Seq-H. On top of that, you can choose different AF patterns for the PDAF (small spot, spot, 3x3, and all).

    Very interesting!

    p.s. If anyone wants, I can post a picture of the PDAF grid when my Sigma is mounted?

    6hQYA4R.
     
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  2. yendikeno

    yendikeno Mu-43 Regular

    128
    Sep 5, 2015
    Interesting - I'll have to try it with my E-M1. Thanks for sharing.
     
  3. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    Errr - I must be missing something here. The Sigma lens is a PDAF lens so this makes sense. This does not show it is working (well it does) but it really shows the limited area of the PDAF grid.

    Rather than the full 81 point grid for CDAF.
     
    Last edited: Feb 1, 2016
  4. atarijedi

    atarijedi Mu-43 Regular

    61
    Dec 13, 2015
    Lenses aren't PDAF or CDAF. The camera is, and it could have just as easily only used CDAF, like the EM5/10 series, to do autofocusing with the lens. The picture shows that with M43 lenses, SeqH + SAF/CAF, it will use PDAF. The same PDAF border appears when using the Sigma+SB combination, and on top of that, there is no CDAF at all.
     
  5. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    Actually they are. The motors and software in PDAF lenses are different than CDAF lenses. That does not mean you can't use CDAF on a lens designed for PDAF (other than the potential for motor damage), but it will be very slow and potentially won't be able to focus accurately.

    From Wikipedia:

    Contrast detection places different constraints on lens design when compared with phase detection. While phase detection requires the lens to move its focus point quickly and directly to a new position, contrast detection autofocus instead employs lenses which can quickly sweep through the focal range, stopping precisely at the point where maximum contrast is detected. This means that lenses designed for phase detection often perform poorly on camera bodies which use contrast detection.
     
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  6. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Agreed. As an example, at The Complete Micro 4/3 Lens List you can scroll down to the 4/3 section and see that there were PDAF lenses, and 'CDAF Optimized' lenses, which could handle PDAF+CDAF.
    Using a non-CDAF optimized lens on a non-PDAF mu-43 body will give very poor AF results.

    Barry
     
    • Agree Agree x 1
  7. atarijedi

    atarijedi Mu-43 Regular

    61
    Dec 13, 2015
    Wow, didn't know that. I stand corrected.
     
  8. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    That was so true with my Sigma 150mm macro lens. It was so disappointing I couldn't use AF on the E-M5 (with CD-AF) because it would almost consistently be out of focus with it, but it works great on the E-M1 with PD-AF.
     
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  9. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    I had the same issue with the 50-200, it was consistently out of focus with the E-M5, not by much but at longer distances the results were quite disappointing.
     
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  10. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    Atarijedi is right in that they aren't one or the other. They're both. Just like how mirrorless cameras aren't SAF or CAF, they are both -- even though some models are better at one type than the other. Same for lenses. :)
     
  11. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    The E-M1 uses a combination of CD-AF and PD-AF with Metabones smart adapters, it will use PD-AF to get close to the correct focus and then do a minor adjustment with CD-AF (backwards/forwards, quickly) for precise final focus (an SLR generally only does the first part, however they use cross type sensors so it's also more accurate and doesn't need the contrast check).

    One of the limitations with this implementation is that autofocus will be disabled for video on the E-M1 with these adapters.
     
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  12. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    Actually the firmware and the stepper motor design is quite different, this is more than optimization. But sure they are both lenses with motor and software, and DSLR and MILCs both have a sensor and an eyepiece :drinks:.
     
  13. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    This is interesting - do you have a link for this? The A7ii adapter let's you choose between PDAF and CDAF with Canon lenses and the general conclusion is PDAF is superior. I am not aware that the Oly body will even do PDAF->CDAF with a PDAF lens. There was some discussion of this in this this thread - PDAF and m43 lenses on the EM1 - putting a controversy to rest
     
  14. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    I don't have a link sorry, the E-M1 is the only body that behaves in that way as it's the only body which currently has PD-AF. Because it's not marketable I highly doubt there's any citable source for it either, it was a compromise of sorts... given the technology available putting cross type PD sensors would have degraded the performance to a noticeable degree (the current sensors are measurable but not noticeable in normal use) whereas using CD-AF for the final check was something which the camera was already built around. It won't do this using C-AF (C-AF also does not work with metabones adapters).

    Regardless, the E-M1 really is first generation - I would expect newer cameras to outperform it (remember that you're also using third party lenses for a completely different system for said test).

    I also can't comment on Sony bodies as I'm not familiar with how they operate however I would suggest that the benefits of CD-AF are only achieved when the lens has low enough sprung mass (the weight moved by the focusing motor), with the heavy focusing elements like those seen in older Canon designs there's no real surprise that PD-AF is faster. Given a newer design (generally ones marked STM) I would expect that CD-AF would be far more accurate and approaching the same speed (once waiting on the lens to move is less of a factor in total time you can sacrifice a tiny amount of speed for a huge gain in accuracy) assuming optimal camera performance (when camera speed is limited PD-AF will pull ahead on speed as it requires less processing power).
     
  15. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    I didn't have the 50-200 SWD lens while I was using the E30 but always wanted one except it didn't have the attraction when I only had an E-M5 (just with CD-AF), however about a year ago I decided to buy a used one (from Japan) being much cheaper than getting the Pro 40-150 & MC14 & I find it very nice on the E-M1 (with HLD-7 to help with hold as well as battery life) since it uses PD-AF, but the only drawback with the E-M1's PD-AF is it only having horizontally aligned PD-AF pixels & sometimes I find a 90 degree tilt might be needed to lock focus on certain subjects, which requires some quick thinking (if I do think of it) if a bird or something else is only in sight for a fleeting moment with that sometimes being the only way to get the AF to lock (going to MF just takes longer). Using that lens also means I get to use the EC14 (I already owned) sometimes too.
     
    Last edited: Feb 2, 2016
  16. Carbonman

    Carbonman Mu-43 All-Pro

    Jul 10, 2014
    Vancouver BC
    Graham
    I noticed that I get the PDAF frame when shooting HDR as well. It doesn't seem to be active during focus stacking.
     
  17. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    I wish the E-M1 had that option with Live View 4/3's optimised lenses such as the ZD14-54 II because there are times that CD-AF works much better (on the E-M5) than with the PD-AF on the E-M1.
     
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