Low-light focusing with the 50mm f/1.8G

Discussion in 'Nikon' started by cjk, Oct 27, 2014.

  1. cjk

    cjk

    Hi there,
    A few days ago I was shooting my kids' school Halloween disco party and had with me a D810, an SB-700, a Nikon 24-120 f/4 and a Nikon 50mm f/1.8G.
    I ended up taking most of the photos with the 24-120, which locked focus in almost total darkness or crazy lights. It would hunt a bit but would focus properly after 1-2 sec. I tried the 50mm f/1.8G and was very surprised to find it just wouldn't focus at all (almost). I think I managed to get 4-5 shots with it, while missing many many more. I took about 200 shots with the 24-120 in about 1h.
    Any other lens would you recommend for this kind of situation? In zooms I can only see the 24-70 f/2.8 -- which is not an option at this point... But about prime lenses? Any fast low-light focusers out there?
    Most of the shots were taken around 35mm...
     
  2. Hmm I have had no problems with my 50mm f/1.8 G focusing in low or crazy light. But if you like 35mm and want fast and sharp take a look at the Sigma 35mm f/1.4
     
  3. ShunCheung

    ShunCheung Administrator

    Being an f1.8, the 50mm/f1.8 AF-S should let more light onto the AF module so that I would think it should AF better than the 24-120mm/f4 AF-S VR under dim light. Generally speaking, my experience is that f2.8 zooms can AF better than f4 zooms indoors. Outdoors, when there is plenty of light, the difference in terms of AF speed and accuracy seems to be small.
    I also have those lenses and would give them a quick test when I get home.
     
  4. cjk

    cjk

    Shun:
    Thanks.
    That was my rationale too when I picked the 50mm to take with me alongside the 24-120 f/4, hence my surprise when it kept hunting while the f/4 zoom was focusing.
    The 24-70 f/2.8 would have been ideal: I tried it at 2 parties about a year ago and it was fast, precise and sharp, but that's not currently an option.
    Aside from this specific issue, I've had no issue whatsoever with my 50 f/1.8 (it's super sharp).
    Michael:
    Thanks for the recommendation. I might give it a try...
     
  5. I have both those lenses and have not had the problem with the 50 as you describe.
     
  6. There is an issue with wide aperture lenses showing some residual spherical aberration. SA reduces contrast and "spreads" the plane of focus. If the light is at such a marginal level that focusing is hit-or-miss, then I'm not really surprised that a lens with better open-aperture contrast is able to focus a bit more reliably.
    Just pointed my D800 + Tamron SP 28-75mm f/2.8 zoom at a dark corner of my room lit only by the light from my laptop screen. Focus was achieved somewhat erratically after some hunting. Swapped the zoom for my AF 50mm f/1.8 Nikkor and focus lock on the same area of the room was if anything slightly more difficult to get and definitely more inaccurate - with a tendency to front focus quite noticeably.
    In normal room lighting, i.e. at a level where you can comfortably and safely see to move around, there's no such difference between the lenses.
     
  7. Is it possible that the 50/1.8 was being used closer to wide open? Depending on how you had the camera set up, you might have actually been shooting at f/1.8, and had essentially no depth of field. If you where shooting in AF-S (not AF-C), and were dealing a bit with your own motion and moving subjects, that's all it takes to have marginally blurry results. Shooting at f/1.8 is very unforgiving that way.
     
  8. I might be wrong, but I think I've read that modern Nikon cameras really don't focus any better with lenses faster than f2.8, i.e. f2.8 is sort of a cut off for benefit.
    Kent in SD
     
  9. Depending on how you had the camera set up, you might have actually been shooting at f/1.8
    The setting of the aperture you want to use is not used by the camera when focussing, the camera effectuates the aperture just before the shot is taken.
    Here the 24-120 lens has more DOF at its widest aperture ( F 3.5) than the 50mm does ( not sure wether the D810 still sets aperture at F/2.8 max when autofocussing, earlier SLR's and DSLRs do) but in difficult situations more DOF helps the camera to acquire focus easier because it finds the focal point earlier than a lens that gives it minimal DOF wide open and hence no contrats at all within the DOF to work with. mm difficult to explain in english, hope this makes sence...
     
  10. I'd try and borrow another copy and see if it does exactly the same thing....if it does, it's a fault (feature) of the lens design, if it doesn't it's a fault with your lens!
    I don't know whether a dirty contact pin can produce such an effect?
     
  11. I've got both those lenses, on a D700 (which for all intents and purposes should be having more AF difficulties than a D8x0 in any circumstance). The 24-120 f/4 tends to have a bit more issues, unless the outer AF points are used, in which case the 50 f/1.8G usually has a lot of issues. On the central AF points (the cross-sensitive ones), the 50 is usually fine though. But overall, yes, I think the 24-120 feels more "planted" - it just does the job without much fuss.
    So maybe worth checking which AF points you were using, it could be related to those from the tiny bit of empirical evidence I've got.
     
  12. The 24-120 f/4 tends to have a bit more issues ... in low light. Forgot a piece of sentence there.
     
  13. ShunCheung

    ShunCheung Administrator

    Checked both of my 50mm/f1.8 AF-S and 24-120mm/f4 AF-S VR on the D800E, inside my home at 7am while it was still quite dark outside. I see no major issues with AF using the 50mm/f1.8 AF-S, with the center 15 cross-type AF points and the outside line-type AF points. In my case, AF speed with the 50mm is certainly no slower than that with the 24-120.
     
  14. cjk

    cjk

    Shun, thanks. I will check again my 50mm f/1.8. Maybe I did something wrong that evening.
     
  15. hi there
    i love low light and i am shooting alot in dim situations.
    stuff like this:
    [​IMG]
    https://500px.com/photo/64420261/pavementpizza-luxury-shops-and-life-in-between-by-norbert-wabnig?from=user
    this portrait was shot with the 50 1.8G on a d3 using autofocus.
    what camera are you using?
    the thing with autofocus in low light is, that you have to give it restrictions.
    turn off the 3d matrix and all that crap. on a d3, stick with 21 af points.
    turn off the autofocus from the shutter button and enable AF only by hitting the af-on
    button at the back of the camera.
    now with ur Af settings way back to basic you can look through the viewfidner and move along with your af point, make sure you got wrap around enabled, otherwise you will have to reframe after focusing which isnt a big deal either (i use af in the centerpoint for almost everything, i focus, i reframe i press the shutter, works really really fast if used to it).
    make sure to hold that focus ring.
    give the camera some lead by prefocusing roughly into the area of interest before you hit that af button. otherwise it will go crazy focusing from all they way to infinite to whatever your closest distance is..which, to be honest, is the most annoying thing that can happen.
    if you notice that the AF is starting to wander off, turn that ring, thats why you hold it in the first place. not tight, just lose so you can intervene quickly.
    what you might consider aswell, with 1.8 in lowlight is a depth of field chart...learn it until your head hurts..like me, or if you own a smartphone check this:
    http://www.dofmaster.com/dofjs.html
    this is important because 1.8 is very shallow.
    if people are moving about it is very helpful to guess their distance and quickly prefocus.
    there is alot ot learn but i hope i gave you some tips on how you can tackle your problem.
    it is all about practice, really
    do not get frustrated, hang in there!
    cheers
     
  16. one more thing
    high contrast situations do help
    for example:
    you go down a very dim and dark street but there is let's say for fun sake one light source in there.
    if you wanna take a shot there, it will be in the light.
    now lets say someone is walking towards that light and you wanna photograph the person passing through.
    focus not on the person, focus on something with edges in that lighting area that will be roughly on the hight as your subject will be and adjust autofocs as the subject draws nearer.
    udnerxpose for the background, at night i go from about -0.3 as standard (the nikon d3 has a not wanted expose to the right kind of metering, which is kinda cool but not at night) all the way down to -3.
    what i really recomment is go to concerts and photograph musicians..i did this ... A LOT..
    go on ten concerts, take as much photos as you can and you will never complain about ur fast 50 again :)
    but do not forget to udenrexpose and get shots for whitebalance too :)
    have fun
     

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