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Auto Focus: Accuracy of Optical Viewfinder compared to Mirrorless?

Discussion in 'Open Discussion' started by Ricoh, Aug 4, 2015.

  1. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    Anyone reading this running a DLSR alongside a mirrorless, or has experienced both worlds, I'd be obliged if you could advise w.r.t focussing accuracy and speed of focus.

    I'm finding missed opportunities in my street work due to inaccurate focus, and this is driving me nuts! I hear the bleep and have to assume the camera has hit the spot as the situation does not allow focus peaking, magnification or any of the focus assistance that comes with 4/3s; speed is of the essence.

    Looking on Flickr, nine times out of ten, images that are 'spot-on' in terms of focus are taken with a DSLR. That may be a bit of an exaggeration, I have to admit, but the balance does seem to swing in favour of the Canon 5D or similar. (Comparative weight is a different matter, so too is stealthiness.)

    Any views on this?
     
  2. wjiang

    wjiang Mu-43 Hall of Famer

    I'm surprised people put stuff up on Flickr that's not pretty much spot on in terms of focus... are you sure it isn't availability bias?
     
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  3. tyrphoto

    tyrphoto Mu-43 All-Pro

    May 25, 2014
    Seoul | NYC
    ㅇtㅈyㅅr
    I'm not sure what you're asking? Since you're using AF, I'm not sure why you would think it's an EVF vs OVF issue? Unless I'm misinterpreting what you're trying to say? Or are you trying to say that the focus point on an OVF is more accurately placed versus that of an EVF?

    From my perspective, I get about the same hit/miss ratio from my previous Canon 5D Mk.II versus any of my other cameras with the exception of fast tracking where the Canon was superior. Focus acquisition on any of the OMDs and your EP5 is quick enough that if I'm not positive that I got correct focus lock, I'll shoot again or sometimes even half press the shutter again if timing is critical.

    For street work, I tend to use the bigger green AF box versus using the the smaller green AF box for more static subjects.

    The one thing I wish Olympus would add, via firmware, is a DoF scale in the viewfinder and LCD when you switch to MF. My X100T does this, both in the EVF and OVF, and is quite useful since it allows me to shoot with zone focusing in addition to having back button AF in MF mode. Even my Ricoh GRD3 allows me to set a predetermined distance in the "snap focus" mode.
     
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  4. Zee

    Zee Mu-43 Top Veteran

    I bought an E-M1 and sold my 7D *because* of inconsistent focus on the DSLR. There will always be missed focus shots, but my keeper rate on the E-M1 is much higher vs the 7D, and I'm slowly kicking the "take two shots from every angle" habit I picked up while using the DSLR...

    Z...
     
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  5. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    @tyrphoto@tyrphoto, my question was about the accuracy of the OVF on a DSLR compared to the EVF (or rear screen) of a mirrorless, since I have no experience in using a DSLR with an optical finder.

    A lot of street photography is dynamic, little is static and certainly no second chance of shooting a second time if you miss. You either hit or not and walk on.

    Interesting to read your account of the 5D II compared to mirrorless. Perhaps I need to rent one and try it myself, rather than ask questions that are, after all, fairly subjective, given the user has a significant impact, eg correct or incorrect technique.

    I've tried back button focus, prefocusing on a static object before taking the shot, but find I need a small aperture to get the accuracy required, and end up losing subject isolation.
     
  6. tkbslc

    tkbslc Mu-43 Hall of Famer

    From a pure accuracy standpoint, mirrorless is definitely superior since it focuses right from the image and generally has a lot more flexibility in focus point placement. However, better DSLR cameras definitely can focus more quickly.

    Regarding the focus confirmation beep, that just means the camera focused on something. Whether or not you had the AF point on your intended target is another matter. You still should be choosing a specific AF area and placing that over your subject if you want to ensure it is in focus.
     
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  7. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    I do try to get the AF point on the target, well it's my intention at least. I'm using the smallest target available and quickly recompose having locked it with half press.

    So DSLRs focus quicker, not necessarily more accurately. I thought there was an advantage before starting the thread, but wasn't sure. Why are they quicker?
     
  8. gryphon1911

    gryphon1911 Mu-43 Hall of Famer

    Mar 13, 2014
    Central Ohio, USA
    Andrew
    The likelyhood of a DSLR missing focus because of miscalibration of the AF module is a going to be a lot higher than a mirrorless version.

    For those who do not know and in short:
    DSLRs - The AF module that communicate to the lens for AF is not on the same plane as the sensor. You can have 2 points of contention, the AF module and the lens miscalibration. For this reason, a lot of mid grade to higher end DSLRs provide the phase detect AF fine tuning. Depending on how out of alignment the AF module or lens might be, you may need to manually calibrate every lens or just specific ones.

    Mirrorless - even the ones with PDAF on the sensor still use the contrast AF to lock focus. The focus is done at the sensor plane, therefore, unless you are having an issue with a communication issue between camera and lens, when a mirrorless camera achieves focus, it is pretty spot on.

    Even give all the above, there are lots of other factors that might be causing an image to be out of focus on a mirrorless camera. Including but not, limited to the following:

    shutter lag
    release delay
    AF type(single servo versus continuous)
    release priority (Focus lock versus release priority)
    Are you prefocusing with S-AF and following the subject which could cause the subject to be out of the focus plane
    Are you using too wide an aperture with a shallow DOF?
    Is your focus point too large and is it grabbing something in the background that is more contrasty than your subject?
    Focus and recompose - you could be moving the focus plane. I stopped doing this long ago and select an appropriate focus point.
     
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  9. agentlossing

    agentlossing Mu-43 Hall of Famer

    Jun 26, 2013
    Andrew Lossing
    This is what I thought as well.
     
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  10. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    Thank you for the comprehensive explanation, that's cleared a number of point for me.

    I'm using S-AF and try to minimise aperture for subject isolation, but use what ever f number I feel is required (or more likely the f number set for the previous shot because I've forgotten to make a subsequent adjustment).
    Camera is set focus lock so won't release until focus is acquired (either my choice of target or the cameras).
    Focus point is set to the smallest available.
    People tend to move when they're out and about so I wonder if I should set to continuous AF. Downside to this it gives the camera opportunity to focus on something entirely different.

    Perhaps I should take up Landscape instead. ;)

    Edit: I do of course place the target point on the subject in the scene. Always have.
     
    Last edited: Aug 4, 2015
  11. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    Focus-recompose is a good way to get misfocused images if you're dealing with shallow depth-of-field. Unless the initial focus placement was in a perfect arc relative to the direction you're panning the camera to recompose, you'll end up with an altered focal plane. Even then, there's a chance you'll be dealing with field curvature. It's just not a superior focus method for total accuracy, and really only came about because SLRs with PDAF used to rely on very few focus points spread across the frame, so you needed to recompose. With contrast detect, you don't have to.

    My advice is to compose the image as you want to, then use single-autofocus with a small box and use the touch-screen to directly pick your point of focus exactly where you intend to shoot. If you use the touchscreen shutter release you'll probably get even better results, since it will release the shutter as soon as it's confirmed focus in the correct spot.

    Presumably your shutter speeds are also plenty high, as well.
     
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  12. tkbslc

    tkbslc Mu-43 Hall of Famer

    Yes. They are quicker because they use math and light waves to decide where to focus vs actually looking at the image and on the sensor. This is also why they can be less accurate. They can also only focus on specific AF hardware sensor points vs almost anywhere on the sensor like mirrorless.

    I shouldn't say DSLR, though, because really it is the phase-detect AF system that they use. Some mirrorless cameras have began incorporating that. For example, the Oly E-M1.

    I will also say the AF motor in the lens is 1/2 the speed equation for AF. That's true on any system. A mediocre lens with a weak and buzzy AF motor on the fastest focusing DSLR would be significantly slower than m4/3 with one of the nice new MSC AF motors.
     
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  13. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    Thank you both, Turbofrog and tkbslc, some good points by both of you.

    I'll try the touch-screen focus with release as suggested. In the past I've only used the touch screen for focus using the shutter button to complete the capture, but found it rather clumsy in use, it slowed me down and brought attention to myself. Next time I'm out I'll try as recommended.
     
  14. gryphon1911

    gryphon1911 Mu-43 Hall of Famer

    Mar 13, 2014
    Central Ohio, USA
    Andrew
    My personal opinion, given the cameras you have listed, C-AF will probably make the matter worse. The GX7 might be more like the GH4 if it has any kind of DFD focusing tech in it.

    I would (and do, when I shoot street with my EM5/EM5 Mk II/EM1) is move the AF point to where you want to focus using the rear DPad and then press the shutter all the way in one smooth motion. the S-AF should be plenty fast to get what you want. If you don't like doing that, I would use the EM5/EP5 back panel to touch focus and trigger the shutter.
    It's either that or use a zone focusing method and wait for the subject to come into the sweet spot.
     
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  15. tkbslc

    tkbslc Mu-43 Hall of Famer

    On your GX7 (maybe others, but I have a GX7) you can change AF to "focus priority", which means it won't take a shot unless it has confirmed focus. The other setting is shutter priority, which means it will try to focus as fast as it can, but that shutter is opening when you hit the button. The latter can be useful if you need critical timing, but you have to potential for more OOF shots if you are quick firing. The former ensures your focus is good on the AF point, but may sacrifice timing by a half second or very rarely not fire because focus is iffy.
     
  16. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    In my time with U43 I could possibly count the number of times I've shot using C-AF on one or possibly two fingers, only seriously using S-AF. I also have my cameras set to focus priority, and yes I have missed some excellent shots where the camera has refused to fire (the ones you miss are always the best, like the fish that got away!).
    I've also used zone focusing using legacy glass, but to achieve adequate DoF small apertures comes with a downside called diffraction, and it shows in the results.
    I've been eyeing-up the Nokton 17.5 which I believe would make a pretty good street lens, it's like old school with aperture, distance and depth of field scales, but I doubt it up my keeper rate.
     
  17. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    Check to see if there is at least something in the picture that is in focus more then your subject.
    If you cannot find anything it could be something else, like motion blur or shutter shock.
    It's not 100% reliable, because it could happen that there was nothing at all exactly in the focused zone, but it's worth to check.
    Does it happens with all lenses or only a few, like the 75?

    Regarding diffraction: you can get plenty of DoF with no diffraction problems. If you are referring to an old book/article on zone focusing they will be using the 35mm/full frame apertures. On m43 you have to use half that value. You can stop down to f8 with no problems, only the sharpest lenses will suffer a little.
     
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  18. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    I think a lot of it is that the decisive moment is just really darn hard to get, and a lot of it is operator skill rather than the camera. I'm pretty terrible at street photography, and too self-conscious to enjoy it, anyway, so my advice comes mostly from trying to photography elusive quick-moving critters.

    If most of the street photography keepers on Flickr are taken with 5D's and the like, it might just be indicative that the people shelling out for $3000 bodies and lenses may have a lot more skin in the game and the time to devote to it.
     
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  19. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    Here's an example of missed focus:

    20244639051_1669d0a393_b. Looks like 'Wet Wet Wet' are back by Steve Wales, on Flickr

    I wasn't aiming for the distant individuals, but the near subjects, trying to get the near polka dot umbrella in focus, but I was walking trying to keep up with them, pausing to take the shot. It could be said that the shot sort of works, but that's probably being kind.
     
  20. Ricoh

    Ricoh Mu-43 Top Veteran

    906
    Nov 2, 2013
    UK
    Steve
    It has to be said that there's something special about the likes of the 5D, something I just can't come anywhere close to no matter how hard I try.