Nex7 inferior auto focus in low light.

Discussion in 'Mirrorless Digital Cameras' started by frank_skomial, Dec 23, 2012.

  1. I was trying to take a picture of a Christmas tree with decorating lights on, in a dark room, mostly lighted by a large screen TV (that the picture brightness varies as the TV goes).
    The Nex7 with Sony SEL 50mm 1.8 lens could not do proper auto focus, in about 8 out of 10 pictures.
    The Nxx7 with Sony SEL 18-200 full size 67mm filter lens performed good auto focus in about 6 out of 10 pictures.
    Nikon D700 and D300S, and D200, taking the same picture, performed 100 % perfect focus instant auto focus without any hesitation.
    Surprisingly the bright 50/1.8 Sony lens auto focus was very poor. The bright lens was suppose to be better suitable for low light condition, but it could not do auto focus, practically at all.
    The picture attached below shows how NEX7 with SEL 50/1.8 lens locks up focus and refuses to do it right. It was necessary to refocus on something bright, e.g. TV, and the focus resumed working, otherwise the locked focus allowed taking the funny picture, then next picture possibly would have a better chance to focus, but really 8 out of 10 were back into this focus lock.
    I wonder if the new focus improvement in the NEX5R and NEX6 would provide better auto focus ?
    00b9tL-509721584.jpg
     
  2. The same picture auto focused by a Nikon DSLR looks like the one below:
    00b9tM-509721684.jpg
     
  3. Looks like the Nex7 was in a creative mode :) There will always be circumstances where autofocus does not function but remember that in the days of manual focus it was not easy to focus correctly also. Even sophistocated systems, be it of a DSLR or of a MILC camera have their limits. You just encountered one with the NEX7.
     
  4. Yes, every camera has limitations, but comparing NEX7 to any of Nikon DSLR mentioned that I tried in the same place, ...there is no contest.
    I posted this mainly to counter-weight posts about demise of DSLR and inevitable victory of mirrorless cameras. Some day this will happen, but not now, perhaps closer to the end of current decade.
    Some try to build a PRO system around NEX, and some already are dumping DSLR in favor of mirrorless. Perhaps they should think twice, or many times...
     
  5. Your not the first person to run into this specific problem, and I've seen similar posts before. It appears to be related to CDAF, particularly with large aperture lenses. I've had occasional problems with Olympus Pens with Christmas lights and fast lenses, but not my OM-D.
    I suspect that it's due to the way CDAF determines focus. The lens is driven through the point of highest contrast and back to the high contrast point. Since these lights point sources, with large aperture lenses, they go from large soft edged disks when out of focus to tiny points when in focus. When in focus they may be too small for the AF to focus on.
     
  6. Doesn't the NEX 7 have manual focus with peaking for this sort of situation?
     
  7. "Doesn't the NEX 7 have manual focus with peaking for this sort of situation?" - yes it does the focus peaking and image magnification to adjust the focus exactly - but this is beyond the point.

    However, in this case the focus peaking perhaps would be as much confused as the auto focus, since they use the same focusing system, so, I would not trust the focus peaking that much in difficult lighting conditions and use image magnification instead. Though final decision is from photographer.
    Also turning the lights On in the dark room eliminated the problem.
    You pay $$$$ for Auto focus camera and lens and do not expect this, especially in contrast when Nikon's did well.
     
  8. The picture attached below shows how NEX7 with SEL 50/1.8 lens locks up focus and refuses to do it right. It was necessary to refocus on something bright,​
    Contrast AF is known to be worst in dim light situations than dslr's phase AF. This is nothing new. One ought to refocus on something brighter with the same focus distance, if the camera can't focus, either with a mirrorless or dslr...
    I wonder if the new focus improvement in the NEX5R and NEX6 would provide better auto focus ?​
    Most likely no, if it's anything like the Nikon 1 system. The 1 system utilize their phase based AF in bright light only. They revert back to contrast based in dimmer light situations. Logically, you figure that it would be the opposite, right? No...
    I posted this mainly to counter-weight posts about demise of DSLR and inevitable victory of mirrorless cameras. Some day this will happen, but not now, perhaps closer to the end of current decade.​
    Dslr and mirrorless camers both have their limitations. AF in dim light is one of mirrorless, at least for now. DSLRs will never go completely away, much like middle format or film. I saw some looking at dslrs at the local Best Buy. These are also the very same people that would use liveview mode every shot on their dslrs:) Liveview AF in dslrs are (much) worst than mirrorless, no?
     
  9. I don't like the user problems I am reading about regarding focusing on the Sony and Fuji cameras. I can't help thinking that they launch their cameras too soon, and long before proper quality control has been executed on the models. The problems are left to the consumers to deal with. Photos of a life time can be lost if the camera refuses to focus. They have to do better than this. These quality issues are the main reason why I haven't switched brand yet. It doesn't matter how good the IQ is if the cameras are not working properly.
     
  10. Ann, limitations are quite different from "(cameras are) not working properly." Small sensors and larger sensors both have their limitations. And limitations can be good, they help us create, among other things...
     
  11. I am suprised by your experience becuase my Panasonic G3 with 14-140 lens performed as usual in similar low light conditions ... snapping into focus and I had a huge job trying to find an area of 'no contrast' to stop it working quickly and efficiently .... so for all its larger and piontlessly large sensor the NEX has its limitations. Else the problem is with DSLR lenses it uses :)
    Stick to Nikon and enjoy your Chritmas :)
    Sub standard Contrast Detection in dim light is one of the hory old tales of yore and from my experience, having heard and believed the tales, to my delight is completely unfounded with the right camera. Apparently better than Phase Detection in some situations.
     
  12. One must realise that Panasonic is a leader of the field with their G and GH models.
    Note it is Christmas Time and the freindly trolls are out :)
     
  13. Leslie, there are limitations and there are quality control issues. There is a significant difference between the two. I have limitations in my D300, but I have never had any quality problems with it. If the problem is in the way the focus system works, then there is a limitation. If you are getting several firmware upgrades right after the camera has been released, then there is quality control issues that should have been dealt with before the release. Don't you agree with that?
     
  14. Maybe the Sony is so smart that it decided the first sample was the more artistically desirable. :)
     
  15. Okey, now I want one too :)
     
  16. If the problem is in the way the focus system works, then there is a limitation.​
    There, Ann, it is how contrast based AF works. Firmwares do not improve the over all AF speed. It may, however, improve communication between camera and lens thereby improving some lens' speed slightly. Over all, the AF speed is mainly driven by the hardware. That said, hardware/tech advances, of course.
    PS. M. Chang:)
     
  17. Frank, Ann, others:
    Mirrorless cameras all focus much worse in low light. This isn't just a contrast-detection issue; it is because the cameras determine focus essentially by sampling from a processed image. This means that if you're in low light, even if you're using a flash, the camera is most likely trying to determine contrast, distance, etc. based on an image that was "shot" at very high ISO.
    By comparison, a traditional SLR has autofocus sensors that receive light photons directly, which means that edges, contrast, and phase detection are all much more accurate.
    Does that make sense? Basically, the current design of all mirrorless cameras - aside from Sony's, using the phase detection adapter - means that it's ability to autofocus in low light is tied directly to high ISO performance. If next year a company comes out with a mirrorless that can record images at 6400 ISO with absolutely no noise, I can assure you that camera will also autofocus well in low light. But since the NEX-7 is very noisy at high ISOs (and this is from a n NEX-7 worshipper), this means that the camera cannot autofocus well in low light either.
    The reason your 50mm lens has better AF is because, regardless of the aperture used to take the photo, the camera is able to use a brighter aperture to focus, meaning that the NEX actually sees less noise when focusing with the 50mm lens.
     
  18. I was just looking at the phase detection adapter. You would have to use the Alpha-mount lenses to get phase detection. It provides phase detection autofocusing with tracking, predictive control, and AF micro adjustment for all AF-capable Alpha-mount lenses, but cannot be used with a teleconverter.
     
  19. That's not a broken camera, it's just that contrast detection AF performs worse in low light than phase detection AF. Add to that, the Nikons in the comparison all have pretty high end AF systems.
    Sony is actually getting better at this. They have a new sensor design that puts phase-detect AF sensor points on the image sensor - this is in the 5R and the 6.
     
  20. If you look at the DPReview's conclusion in the Fujifilm X-Pro1 review, you can see that both autofocus and manual focus performance has been adressed in firmware update 2.0. Maybe there are things that could be improved on the NEX7 AF performance as well. I don't know.
     
  21. There are systemic issues with Fuji AF performance, that Sony simply does not have. Fuji AF is still significantly slower than Sony's. The firmware 2.0 update made the AF useable for most people.
    The AF issue here is specific to a particular subject, and not general to low light AF problems with CDAF. NOT having a problem with the 14-140 lens is typical, because is it a 4 - 5.6 lens.
    However, in this case the focus peaking perhaps would be as much confused as the auto focus, since they use the same focusing system, so, I would not trust the focus peaking
    Really? AF requires that the camera makes "decisions". Focus Peaking is only signal processing. Try it next time. Your grasp of technical subjects is historically tenuous at best.
     
  22. The focus peaking light turns On, when the camera thinks it has the best focus. Of cource user's action is required to follow.
    If auto focus is confused by staying at odd place, then perhaps the focus peaking light could possibly turn on in the state of confusion of the camera foocusing system, as it is not an independent system that would have own smarts. Both auto focus, and the focus peaking operate on the same signal that camera provides.
    Nice to see that I make a "tenuous history" here. This means a lot when spoken from someone who never makes mistake, and never admits to one.
     
  23. Zack Zoll ... you can repeat the old story about CD being inferior to PD as much as you like but the fact remains that you are living in the past and even people like dpreview commented on the 14-140 lens favourably in comparison with the DSLRs which of course normally have PD.
    I can tell no difference between my PD camera and my CD camera ... that is the current state of the art ... Canon and Panasonic respectively. I am sure both are superior to the other in some situations but for general photography in bright or low light there is no difference.
    If you want to quote split seconds which are only really of interest to the tech geeks go for it ... but in practical situations .....
     
  24. JC, you can put whatever words into my mouth that you like, and you're welcome to argue against a stance that I didn't take. But if you'll reread my previous post, you'll see that I made absolutely no value judgments about the AF systems, and even made it a point to mention that I LOVE the camera that we're talking about, which has a fairly poor AF system.
    All I said was that mirrorless cameras (both CD and PD, but mostly CD) focus worse in low light because there is less contrast to be measured, and details are blurred because of the higher ISO. Sure the Panasonic does pretty okay ... but since Panasonic does't have a traditional SLR using phase detection to compare it to, that doesn't go very far in proving that CD is any better or worse in low light, does it?
    Also, not every "old story" is untrue, and that sort of line sends up a red flag that says that you're not really familiar with that on which you speak. The fact that you clearly didn't read, or didn't understand, my post doesn't help any.
    Bruce, Frank ... focus peaking is basically worthless in low light, or when there is low contrast. It works with older manual lenses that don't have any contacts, so I can tell you that there is no 'focusing system' used. What it does is highlight edges based on edge contrast and sharpness. If you're photographing a low-contrast scene, or if your ISO is jacked up, the sensor won't be able to see enough contrast to trigger the peaking, even if you have the option turned all the way up.
    It also IS NOT the same as focus confirmation, as it will turn on when subjects are nearly in focus, while a focus confirmation lamp only lights when subjects are actually in focus. Focus confirmation "knows" when you are in focus, while focus peaking sees a certain amount of contrast and edge sharpness, and assumes that you must be in focus. It's still extremely useful, but only accurate if you're zoomed in, or shooting with a reasonable depth of field.
    But again, since 'accurate focus confirmation' is a feature really only found on cameras with phase detection sensors, we can't be sure of any of that. For all I know it may be a contrast/phase issue, or it may simply be that focus peaking is ported over from video cameras, where the resolution was lower and it wasn't nearly as noticeable if the picture was slightly out of focus.
     
  25. "they launch their cameras too soon, and long before proper quality control has been executed" Ann O.
    Ridiculous, no camera is perfect; what's "New & improved" can eventually become "Old & Cruddy".
    It's all about "Give & Take" - After-all, the big Nikon couldn't effectively affix and focus lenses made as far back as the 1930's etc. Sony did allow for the ability to override & manual focus, you're not left staring at a blurry tree.
    Now, I feel that my attitude is of the 1/2 Full variety:
    Along with over 100 truly fine cameras, I actually own an NEX-7 and this camera is the one I use the most !
    It's a "stunning" piece of technology that gives me joy & a sense of appreciation every time I pick it up...
     
  26. I am glad that Panasonic have the sense to not make a old fashioned DSLR, a make-over from the 1950's, but concentrate of 'the' digital camera, bridge and M4/3. I have older cameras which are not good with their CD AF in low light but I know with my Panasonic G3 and 14-140 lens I had a very hard job, despite the G's very small focusing area to stop it snapping into focus the way it does in bright light when working is poor light, night time street scene at 11pm. Street lights on just one side of the road and focusing on dark foliage on the opposite side of the road. I could barely see changes in tone but the camera could ..... I was frankly suprised becuase I believed CD could not work well in such situations .. but delighted it worked as normal. In my experience with my gear CD equals PD these days in good or poor light.
    I could well, and I know I have, gaps in my knowledge despite having owned or used just about every type of camera made in the past sixty years or so ... I am a user not a technician, though in my early days I was that way inclined.
     
  27. Are you sure the lens is a good copy? I've been using the 50 on my NEX5R with good results - but not as good as with the Zeiss 24.
     

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