D5500 Missing focus in low light with 35mm f/1.8 DX

Discussion in 'Nikon Cameras' started by Peeb, Jan 2, 2016.

  1. Peeb

    Peeb Semi-automatic Mediocrity Generator Supporting Member

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    Mounted on a D5500. Very sharp lens, generally, but in a large room at night (New Years party), I was trying to take pics without flash, assuming it should be no problem for this rig.

    When I downloaded today I was shocked at how many pics missed the focus- VERY soft on many occasions. Ideas:

    1) maybe aperture prioritize shooting so that DOF is larger to cover for small focus misses?
    2) maybe switch to sing'e-point focusing so that my margin of error is smaller?


     
  2. jaomul

    jaomul Been spending a lot of time on here!

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    What focus point were you using, what aperture. Do you have an af assist light. How dark was it (what settings gave you an ok exposure?)
     
  3. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    Can you provide some examples and EXIF?
    As you know it all comes down to 3 things.
    1 - appropriate shutter speed to stop motion, otherwise you get motion blur
    2 - appropriate DOF, otherwise DOF blur
    3 - ISO
    But for low light I'll add this
    4 - was you AF assist beam turned on

    in dim lighting though your AF sensor needs to get enough light to focus properly.
    The f/1.8 lens will provide Af at f/1.8 to provide the most light for the AF sensor, from what I understand.
    But it's still dependent upon contrast detection and under dim light it may not be enough.

    In addition to your in-camera AF assist beam you can also use one that is better in dimmer light.

    An AF assist beam from flashes/commanders can help with focusing in dim lighting if you don't want to add light. I had a Nikon SU-800 which helped in this, also in higher end flashes. In many triggers you can see the red light AF assist beam being used in low light too. This all helps the camera focus in low light without adding a flash and if you assist light isn't enough.
     
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  4. Peeb

    Peeb Semi-automatic Mediocrity Generator Supporting Member

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    I can't use the subject photos as examples as I don't have permission to use them but I'll create some more, complete with exif.
     
  5. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    found the article I read a long time ago about this ==> How to Make Autofocus Work in Extremely Low Light


    Additionally, this may help your understanding of the DSLR AF process ==> How Phase Detection Autofocus Works

    And AF focus points ==> Understanding Camera Autofocus

    In general I think of it as this - the Exposure (aperture, shutter, ISO) doesn't actually help the AF sensor. Light does (large aperture lens like your f/1.8), the number and quality of focus points and the assist beam or the red AF flash assist beams really help in super low light from all that I understand.
     
    Last edited: Jan 2, 2016
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  6. Peeb

    Peeb Semi-automatic Mediocrity Generator Supporting Member

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    EDIT: multiple images deleted- better example posted further down in this thread.

    Camera set to 'no flash' with me sitting stationary on the couch (selfie in TV). The focus distances seem all out-of-whack in the EXIF info. A 'focusing light' comes on. Focus set to single point to assure I hit only the intended target with the auto focus.
     
    Last edited: Jan 2, 2016
  7. jaomul

    jaomul Been spending a lot of time on here!

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    These examples are poor. You can't tell anything from them.

    The party shots, what was normal iso you ended up with, and did the af assist work, how many points af did you use there and where you near or far from targets, what aperture and ss was approx what you ended up with, what focus mode,
     
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  8. Dave442

    Dave442 Been spending a lot of time on here!

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    When I start to see any focus issues in low light conditions I first go to single point and the center focus point (I can just hit the center of the multi-selector and it goes there so I don't have to look). Then focus on the best lit areas at the distance I want. If I need more help I prefer the infrared beams from a flash in the hotshoe (I have the function button set so pushing it will let me have the flash on for focus assist, but not fire the flash).

    I don't like to use it, but the focus assist light works. At parties I often grab focus when a cellphone flash goes off.
     
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  9. Peeb

    Peeb Semi-automatic Mediocrity Generator Supporting Member

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    Fair enough. Here is a better sample. Batteries set at 45 degree angle to camera- focus system set to single focus point in middle of frame and the third (middle battery as the focal point). Meant to shoot wide open but the exif shows f/2.4, but close enough for this test.

    Focus is obviously biasing toward the back side of the battery progression. Is this what they call 'back focusing?'

    Sadly, this test confirms that the focus glitch isn't limited to low light situations- it just manifests due to the decreased DOF of shooting wide open.
     

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    Last edited: Jan 2, 2016
  10. jaomul

    jaomul Been spending a lot of time on here!

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    To be honest Peeb I'd like to try help because I've used the 35 in dark conditions a lot, but mostly I'm on my phone and can't open each link and search for exif. If you give me an example of exif from a shot that you took at the party there may be something obvious, also you can give the focus info and if you used your af assist. Sure your lens could be front or back focussed, but this front back focus thing seems to be blamed for a lot of issues more than ever before
     
  11. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    exif of the batteries
    Camera: Nikon D5500
    Lens: 35 mm f/1.8
    Exposure: Auto exposure, Not Defined, 1/60 sec, f/2.4, ISO 800

    extended

    create 2016-01-02T15:44:15+00:00
    sampling-factor 1x1,1x1,1x1
    ApertureValue 2526069/1000000
    ColorSpace 1
    ComponentsConfiguration 1, 2, 3, 0
    CompressedBitsPerPixel 4/1
    Compression 6
    Contrast 0
    ExifImageLength 4000
    ExifImageWidth 6000
    ExposureBiasValue 0/6
    ExposureTime 10/600
    FNumber 24/10
    FocalLength 350/10
    FocalLengthIn35mmFilm 52
    ImageLength 4000
    ImageWidth 6000
    ISOSpeedRatings 800
    Make NIKON CORPORATION
    MaxApertureValue 16/10
    MeteringMode 5
    Model NIKON D5500
    Orientation 1
    PhotometricInterpretation 2
    ResolutionUnit 2
    SamplesPerPixel 3
    Saturation 0
    SceneCaptureType 2
    SceneType 1
    SensingMethod 2
    Sharpness 0
    ShutterSpeedValue 5906891/1000000
    Software Adobe Photoshop Elements 14.0 (Windows)
    WhiteBalance 0
     
    Last edited: Jan 2, 2016
  12. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    Close focus of this lens is 1 foot / 1.3 meters. So you don't want to be closer than this otherwise it's going to seem to focus further away than it should.

    I see how the 2nd battery from the right is In focus and not the center battery.

    Does it seem to have these issues in bright light?
    Can you take a photo of a tape measure at an angle rather than batteries. The tape measure is continuous and if you select the 12 inch mark it will be more telling of any issues especially if you take in bright light and then to dim light.
     

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