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

Peeb

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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?
 

jaomul

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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?)
 

astroNikon

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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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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.
 

astroNikon

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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.
 
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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.
 
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jaomul

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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,
 

Dave442

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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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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,
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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jaomul

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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
 

astroNikon

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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
 
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astroNikon

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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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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.
You don't need permission to post the photos for a non-commercial use.

AF is always done with the lens as wide open as it can be.
If the aperture is set to a smaller than max wide open aperture the lens stops down to the set aperture just before the shutter opens.

There is a limit to how little light it takes for the AF system to work properly. That limit for your camera is listed in the camera's specifications and is -1 EV.
 
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As astroNikon mentioned, if the closer three batteries are inside of the minimum focusing distance of the lens (called the MFD quite often), they will be OOF. You ran into a good learning experience at the New Year's Party...shooting a fluid event like a New Year's party in low light with a fast prime lens on a small, pentamirror viewfinder d-slr, all those things can easily result in out of focus shots when you get back to the computer. Low light makes it tricky to really see the viewfinder image, the smaller overall viewfinder image of the APS-C cameras, and the slightly less-crisp, less-contrasty image that a pentamirror camera has, plus the fluid nature of the shooting situation, all that is a really,really significant list of potential challenges! If the camera was in AF-C, for continuous focusing, the camera will allow the photographer to shoot a picture at ANY time, even if the focus is not yet achieved. Plus, a fluid situation...people moving around, shots not being set-up and managed, but grabbed as best as one can grab them, and then the potential for actual fluids, like beer,wine, and spirits...

This is the kind of scenario where the reject rate is likely to be VERY high, almost as a given unless you take some steps to maximize your chances for success by adjusting the camera to the absolute maximally optimal set of shooting parameters and custom functions. I think setting the camera up and switching from AF-C focusing to AF-S, single focus, with the AF assist system most definitely enabled, is a good start. Set the firing rate on the camera to Continuous High, and shoot 3 or 4 shots on every situation, maybe 6,7,8 shots on things you really,really want to capture, and be prepared to kill-file over half the images.

The one way to come back with a high keeper rate is to elevate the ISO level, so that you can use a small squirt of flash, not a full-capacitor dump of juice per shot, and shoot far fewer shots with flash, so you're not a total buzz-kill for everybody, at least until the get good and liquored up, then they'll be slurring things like, "Hey,hey,hey! Camera-man! Dake ourrrr pit-cherrrr! Dake ouuur pi-tcher!" and you can snap away more freely. But seriously...go AF-S, AF Assist set to ON, jack the ISO up to 800, so the flash is not overly obnoxious, and that will also allow you to drag the shutter a bit, use second curtain synch if your camera has that, and you could get a really,really high rate of in-focus shots. Buuuut, they will all be flash shots. So....

You might find that in crummy light, single-point AF is weak, and that enabling more AF points will help the camera "grab on to something" so you can get a focus lock. The problem in dim light, especially with only one AF area enabled, is that dim, flat, or low contrast subjects are TRICKY TARGETS for most AF systems. If you hit the flat patch of a person's cheek in dim light, chances are the focus will see-saw and hunt/hunt/hunt and not get a good lock! In AF-C mode, when you hit the button, the focus might or might not be locked on. In AF-S, with the focus assist beam enabled and a speedlight in the hot shoe, you automatically about quadruple the chances of getting a no-flash shot that will be in-focus. If you turn the speedlight on, and shoot all-flash you're going to go from 80 percent junker shots to maybe 10 percent junkers.
 
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Peeb

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As astroNikon mentioned, if the closer three batteries are inside of the minimum focusing distance of the lens (called the MFD quite often), they will be OOF. You ran into a good learning experience at the New Year's Party...shooting a fluid event like a New Year's party in low light with a fast prime lens on a small, pentamirror viewfinder d-slr, all those things can easily result in out of focus shots when you get back to the computer. Low light makes it tricky to really see the viewfinder image, the smaller overall viewfinder image of the APS-C cameras, and the slightly less-crisp, less-contrasty image that a pentamirror camera has, plus the fluid nature of the shooting situation, all that is a really,really significant list of potential challenges! If the camera was in AF-C, for continuous focusing, the camera will allow the photographer to shoot a picture at ANY time, even if the focus is not yet achieved. Plus, a fluid situation...people moving around, shots not being set-up and managed, but grabbed as best as one can grab them, and then the potential for actual fluids, like beer,wine, and spirits...

This is the kind of scenario where the reject rate is likely to be VERY high, almost as a given unless you take some steps to maximize your chances for success by adjusting the camera to the absolute maximally optimal set of shooting parameters and custom functions. I think setting the camera up and switching from AF-C focusing to AF-S, single focus, with the AF assist system most definitely enabled, is a good start. Set the firing rate on the camera to Continuous High, and shoot 3 or 4 shots on every situation, maybe 6,7,8 shots on things you really,really want to capture, and be prepared to kill-file over half the images.

The one way to come back with a high keeper rate is to elevate the ISO level, so that you can use a small squirt of flash, not a full-capacitor dump of juice per shot, and shoot far fewer shots with flash, so you're not a total buzz-kill for everybody, at least until the get good and liquored up, then they'll be slurring things like, "Hey,hey,hey! Camera-man! Dake ourrrr pit-cherrrr! Dake ouuur pi-tcher!" and you can snap away more freely. But seriously...go AF-S, AF Assist set to ON, jack the ISO up to 800, so the flash is not overly obnoxious, and that will also allow you to drag the shutter a bit, use second curtain synch if your camera has that, and you could get a really,really high rate of in-focus shots. Buuuut, they will all be flash shots. So....

You might find that in crummy light, single-point AF is weak, and that enabling more AF points will help the camera "grab on to something" so you can get a focus lock. The problem in dim light, especially with only one AF area enabled, is that dim, flat, or low contrast subjects are TRICKY TARGETS for most AF systems. If you hit the flat patch of a person's cheek in dim light, chances are the focus will see-saw and hunt/hunt/hunt and not get a good lock! In AF-C mode, when you hit the button, the focus might or might not be locked on. In AF-S, with the focus assist beam enabled and a speedlight in the hot shoe, you automatically about quadruple the chances of getting a no-flash shot that will be in-focus. If you turn the speedlight on, and shoot all-flash you're going to go from 80 percent junker shots to maybe 10 percent junkers.
All I have is the pop-up on my camera, but it definitely seems to help.

Took a pic of my headphones with and without flash. The flash version is on the left and is MUCH more clear.
combined.jpg
 

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