AF on M43's vs SLRs

Discussion in 'Digital and Video Cameras' started by Syringer, Feb 3, 2013.

  1. Syringer

    Syringer Lifer

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    I'm getting confused to the differences between contrast/phase autofocus. What are the pros/cons to each, and is there a "better" one? Do SONY's SLT cameras have a different system?
     
  2. PixelSquish

    PixelSquish Golden Member

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    i don't quite get it myself. i will say the oly om-d contrast AF is impressive to me. i was a 40D shooter for awhile and i find the oly better. of course i don't shoot action stuff - i am a focus and recompose shooter. but this article seems pretty good on explaining stuff although it seems it was written a bit before the more recent impressive contrast AF systems came out:

    http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works
     
  3. randomrogue

    randomrogue Diamond Member

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    The thing that the Sony's have that's different is since they use a digital viewfinder you can literally have it show you were the image is in focus by highlighting the area with little yellow dots. So if you increase the aperture you'll see how it expands your focal plane.

    Here's the problem though. In real use I found that at low apertures it was merely a guide. Shooting at say F1.4 it would never be in focus correctly if I used the yellow dots. It would be close but not close enough. So a Sony camera without AF fine tuning pretty much renders this feature useless. You'll want a A77 or a A99 I think since those have AF fine tune. The A65 doesn't have it.
     
  4. cantholdanymore

    cantholdanymore Senior member

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    Very basic: m43 and other EVF cameras use contrast focus that works great most of the time but not so good with moving object since it can't tell if the subject is moving towards or away from the camera. D/SLR with OVF use phase focus that works great most of the time and it is faster, it can also tell the direction of the subject so it is better for action. The sony has a EVF but uses phase focus, the same as the nikon V1 (I think)
     
    #4 cantholdanymore, Feb 3, 2013
    Last edited: Feb 3, 2013
  5. Throckmorton

    Throckmorton Lifer

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    What do you mean by direction of the subject?
     
  6. cantholdanymore

    cantholdanymore Senior member

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    It knows if the subject is moving closer or away from the camera
     
  7. iGas

    iGas Diamond Member

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    http://en.wikipedia.org/wiki/Autofocus

    Phase detection (PD) is achieved by dividing the incoming light into pairs of images and comparing them.

    Contrast detection autofocus is achieved by measuring contrast within a sensor field, through the lens. In this method, AF does not involve actual distance measurement at all and is generally slower than phase detection systems, especially when operating under dim light. Furthermore, as the autofocus system does not calculate whether the subject is in front focus or back focus, focus tracking is not feasible.
     
  8. Midwayman

    Midwayman Diamond Member

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    Its more than that from what I understand. It knows which direction out of focus a subject is so it can drive the lens the right direction the first time instead of guessing and having to reverse half the time.

    If you're getting a camera with interchangeable lenses I would make a real effort to get one with phase detect.
     
  9. blastingcap

    blastingcap Diamond Member

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    Dont believe everything you read, esp on wiki. Ive heard of new techniques in cdaf that may help speed things up, but even today with existing cameras like the latest m43 cams, cdaf is faster and more accurate for single shots even of moving things. Cdaf can also track moving things contrary to wiki... Just not as well as pdaf, especially for things moving quickly toward or away. But to say cdaf cant do it at all is blatantly wrong.
     
  10. cantholdanymore

    cantholdanymore Senior member

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    Not necessary. My Olympus OM-D focus great and fast but it may not be the best camera to take to the Superbowl
     
  11. Syborg1211

    Syborg1211 Diamond Member

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    I think the takeaway from this is that there isn't an easy way to measure autofocus performance. You basically have to go off people's observations. I was just recently trying to tell a friend a reason to get an SLR over a mirrorless is faster autofocus, but I failed to find any definitive proof on the internet stating so. I ended up telling him to go test out each camera and see if he noticed a difference.

    It's funny reading reviews of the exact same camera and having one reviewer say the camera focuses fast as lightning and another reviewer commenting how slow and inconsistent it is.

    I remember reading one lens review where they purposely turned the focus ring to the maximum and measured how long it took to focus, but that doesn't simulate real world conditions that well. I also don't remember if the results were even that useful.
     
  12. blastingcap

    blastingcap Diamond Member

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    Whatever you may have heard about CDAF is likely out of date. The new breed of MFT cameras in particularly have very quick AF. Even of moving objects. Where they falter is when you are trying to take a burst of shots in a row of a small, fast-moving object, especially if it is moving toward/away from you. PDAF is still better for that.
     
  13. JohnnyRebel

    JohnnyRebel Senior member

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    The OM-D is a very tempting camera, especially considering the excellent prime lenses that are now available (12mm, 45mm, 75mm). Steve Huff has some good reviews and examples, including using the OM-D in a gym for sports shots. I'm really tempted...
     
    #13 JohnnyRebel, Feb 5, 2013
    Last edited: Feb 5, 2013
  14. iGas

    iGas Diamond Member

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    The general consensus is that CDAF can be more accurate than PDAF, and PDAF is quicker at focusing hence still is use for tracking moving subject.

    http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html

    Autofocus: phase detection

    Applet: Nora Willett
    Text: Marc Levoy
    Technical assistance: Andrew Adams​

    "The ability to move directly to the in-focus position makes phase detection a fast autofocus method, faster at least than contrast detection. Unfortunately, this method can only be used when the reflex mirror is down. Thus, in Live preview mode (called "Live View" on Canon cameras), in which the mirror is flipped up, the camera cannot use phase detection. In this mode the camera either offers no autofocusing at all or it offers only contrast detection, which we consider in the next applet."


    Please provide links to articles that suggests CDAF is faster than PDAF.
     
  15. blastingcap

    blastingcap Diamond Member

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    The latest M43 cameras have faster CDAF than similarly-priced DSLRs. The top of the line DSRs might be a little faster but they also cost much more, making it apples to oranges.

    Complicating matters is that it depends on the lens used--some lenses are faster than others.

    Example: Pany G5 beating out the T3i and D5100 (kit lens vs kit lens) in single-point full AF, though to be fair, the T3i did beat the G5 in full-area AF... though frankly when you need every scrap of AF speed you're most likely in single-point center AF mode anyway so I would argue that is the more important metric:

    http://www.imaging-resource.com/PRODS/T3I/T3IA6.HTM
    http://www.imaging-resource.com/PRODS/D5100/D5100A6.HTM
    http://www.imaging-resource.com/PRODS/panasonic-g5/panasonic-g5A6.HTM

    "The Panasonic G5's contrast-detect autofocus is quick, faster than most consumer SLRs."

    CDAF got a bad rap because up until recently it was slower, but Oly/Pany spent a lot of resources to get it up to speed, pun intended. CDAF still trails in burst mode AF-C mode of course, as I previously noted.

    Note that the G5's full AF single point center is actually slightly faster than even the mighty (and FAR more expensive) D800: http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800A6.HTM
     
    #15 blastingcap, Feb 5, 2013
    Last edited: Feb 5, 2013
  16. iGas

    iGas Diamond Member

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    Cherries picking much aren't we.

    They are apple to orange comparisons, as in crop frames vs. micro four third (different lens size, weight, torque, motors).

    Second of all they are different lenses and are making by different manufactures, hence focusing speeds are going to be different.

    Thirdly, the DMC-G5 shutter lag in manual focus mode and prefocus mode destroyed the Canikon in your example. Suggesting that the shutter time is not a focus related one, but could be due to mirror speed and electronic/mechanical working of the shutter.
     
  17. blastingcap

    blastingcap Diamond Member

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    Smaller lenses are easier to shift around quickly, true, and the numbers might favor M43 on that account, but given that M43 is a competitor to APS-C/DX DSLRs and can give equal or better image quality than Canon crop DSLRs and near-Nikon/Sony/Pentax crop DSLR results, the comparison is still valid from a consumer point of view. And I already mentioned that lenses impact things much, that's why I said kit vs kit. As for your shutter lag in manual focus... that wasn't the number I was looking at. In fact I didn't mention those numbers at all. If you look at the times in the AF tests it's kind of obvious that the G5 is quite speedy. I just quoted Imaging Resource as saying that the G5's AF speed actually beats many consumer DSLRs. If you have a problem with the way Imaging Resource does their tests take it up with them. And by the way in case you think I was cherrypicking the G5, the E-M5 is slower than the G5 but still goes toe to toe with the D5100, for example, and the E-M5's kit lens is even lamer than the Nikon kit lens so if anything the E-M5 got handicapped in that comparison. (The GH3 numbers are not out so I had to use the G5 as Pany's latest M43 camera that has performance stats at Imaging Resource.)
     
    #17 blastingcap, Feb 6, 2013
    Last edited: Feb 6, 2013
  18. JohnnyRebel

    JohnnyRebel Senior member

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    It is exciting to have some real players in the game pushing innovation and price. This is a win-win for everyone. There is nothing inherent to the design of a DSLR to make it a superior camera. I would expect high-end mirrorless to compete very well against low-end DSLRs.
     
  19. blastingcap

    blastingcap Diamond Member

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    Eh, D5100 isn't exactly low-end. If you prefer to compare cameras of similar price, E-M5 doesn't look too bad at all compared to the D7000: http://www.imaging-resource.com/PRODS/D7000/D7000A6.HTM No data yet for D5200 performance unfortunately.

    And G5 is lower-end than E-M5 in terms of price and features, yet beats all three of those cameras.

    But everything's a tradeoff and Nikon has some great glass available for the F-mount, even more so than the M43 mount, plus PDAF is much better for tracking moving things in burst mode, and EVFs still haven't caught up to OVFs (especially in burst mode), among many other advantages of DSLRs.

    Right now my plan is to stick with my RX100 and wait patiently for the Nikon D7200 and if that isn't enough of an upgrade over the D5200 then I'll get the D5200 instead.
     
  20. iGas

    iGas Diamond Member

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    Canon EOS Rebel T3i Performance

    Shutter Response (Lag Time) Full Autofocus
    Single-point AF
    Optical Viewfinder

    0.283 second​
    Time from fully pressing shutter button to image capture. (All AF timing measured with Sigma 70mm f/2.8 Macro lens.)
    Full Autofocus
    Auto Selection AF
    Optical Viewfinder

    0.160 second​
    Time from fully pressing shutter button to image capture.
    Full Autofocus
    Auto Selection AF
    TTL flash enabled
    Optical Viewfinder
    0.260 second​
    Time to capture while forcing flash to fire. Metering pulses from flash often slow shutter response.​
    Prefocused
    Optical Viewfinder

    0.087 second
    Time to capture, after half-pressing and holding shutter button.
    Continuous AF
    Optical Viewfinder
    0.129 second​
    This mode usually shows no speed increase with our static subject; we have no way to measure performance with moving subjects.​
    Manual Focus
    Optical Viewfinder
    0.114 second
    For most cameras, shutter lag is less in manual focus than autofocus, but usually not as fast as when the camera is "prefocused". ​
    Live View
    Full Autofocus
    Live View
    "Quick Mode"
    (Phase Detect)
    1.176 seconds​
    Time from fully pressing shutter button to image capture. This is phase-detect autofocus, the camera drops the mirror to focus, then raises it to grab the shot. ​
    Full Autofocus
    Live View
    "Live Mode"
    (Contrast Detect)
    0.826 second​
    Time from fully pressing shutter button to image capture. This is contrast-detect autofocus, the camera reads Live View data from the image sensor to determine focus.​
    Prefocused
    Live View
    0.084 second​
    Time to capture, after half-pressing and holding shutter button..​


    Panasonic G5 Performance


    Shutter Response (Lag Time)
    Full Autofocus,
    Single-area AF mode
    0.194 second​
    Time from fully pressing shutter button to image capture, with the lens already at the proper focal distance setting. (All AF timing done with the Panasonic 14-42mm X PZ kit lens at approximately 25mm.)
    Full Autofocus,
    Multi-area AF mode
    0.191 second​
    Time from fully pressing shutter button to image capture, with the lens already at the proper focal distance setting.​
    Full Autofocus,
    Single-area AF mode,
    Flash enabled
    0.471 second​
    Time from fully pressing shutter button to image capture, with the lens already at the proper focal distance setting, auto flash enabled.​
    Continuous AF
    0.188 second​
    This mode usually shows no speed increase with our static subject; we have no way to measure performance with moving subjects.​
    Manual Focus
    0.079 second
    For most cameras, shutter lag is less in manual focus than autofocus, but usually not as fast as when the camera is "prefocused".​
    Prefocused
    0.063 second
    Time to capture, after half-pressing and holding shutter button.


    1. Third party lens tend to be slower than OEM lenses, and macro lens is known to be slower than most lenses.

    2. Manual focus and Prefocused shutter lag shows that the electronic and mechanical working of the camera affect the overall performance of the camera between shutter depression and released.

    3. The Table indicated that the test is a Shutter Lag Time test and is not an autofocus test between PDAF vs. CDAF.
     
    #20 iGas, Feb 6, 2013
    Last edited: Feb 6, 2013
  21. blastingcap

    blastingcap Diamond Member

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    This is an exact quote from ir: "The Panasonic G5's contrast-detect autofocus is quick, faster than most consumer SLRs." And the g5 beat the d5100 and d7000 as well. Look at more dslr perf reviews if you wish.

    P.S. Subjectively the G5 has been noticed by some to be quite fast:

    http://soundimageplus.blogspot.com/2012/09/panasonic-g5-review-continued.html
    "Secondly, the G5 is the quietest and fastest m4/3 camera I've ever used. In fact its probably the quietest and fastest camera of any kind I've ever used."

    And the G5 isn't even the fastest M43 camera; the GH3 for instance with its 240Hz sampling is reputed to be faster: http://www.eoshd.com/content/9022/panasonic-gh3-hands-on-report

    "AF is incredibly quick, we’re talking phase-detect beating, Nikon D3 beating in terms of speed and accuracy in stills mode."

    I think it is safe to say that the most recent M43 cameras are competitive with DSLRs of similar price range, when it comes to single-shot autofocus speeds. Bursts of shots of moving objects are the main weakness of M43 and for that PDAF is still preferred.
     
    #21 blastingcap, Feb 6, 2013
    Last edited: Feb 6, 2013