D7100 Inconsistent autofocus. Backfocus / front-focus

I just got a new lens, a 24mm 1.8, went on a photo shoot indoors with natural light and I noticed that ALL my photos at 1.8 were out of focus. Tack sharp results in front of the subject.

So I made a few tests with a 50mm 1.4 AF-D. Camera on a solid tripod, shooting at a steady subject at 45° at 20" in front of the camera.

1. De-focus the lens manually all the way to infinity. Take a shot and check for focus on the LCD.
2. Same process, this time de-focusing the lens to its closest focus and take a shot.

ALL my shots were out of focus, the most annoying, its not consistent :miserable:. Trying to micro adjust its useless, sometimes it back focus a little, and sometimes a lot. Other times its front focus by a few milimeters, but at 1.4 and even at 1.8 with the 35mm DX its more than enough to make a picture useless.

Manual focusing works fine, spot on.
Live view focusing works fine as well.

Reset the camera to factory did nothing.

Is this an issue with the D7100?? I've seen a few threads that present similar issues with AF.

My D7100 has great AF with all lenses. I have fine tuned all my lenses on that camera.


Sent from my iPhone using Tapatalk

My D7100 is spot on with the more than a dozen AF lenses that I've had. 3rd party same as Nikon.

That is very weird, that for a particular lens only, that live view and phase detect focusing don't agree pretty closely. Can't imagine the failure mode here.

Does setting the focus mode to "focus" rather than "release" have any effect ?

I'm not sure what you did... You just gave a scenario for two different lenses... and your narrative didn't explain the problem except with one lens.

If you're expecting two different lenses to focus/adjust to the same specification, then your understanding is incorrect. Each lens will have its own data points with regard to where exactly it focuses... One lens may front-focus, and another may back-focus...

If you're having issues... rather than attempt to get mishmash between two lenses... do your testing with one lens, and report your results for that one lens only.

That is confusing, actually mentioned 3 different lenses...24, 35, and 50
If all three are flakey bad then the D7100 body has failed.

Are all your lenses with focus issues AF-D type lenses? When you manually focus, are you just eyeballing the focus or using the green dot in the viewfinder to verify focus? Do your AF-S lenses focus correctly? If the answers to these questions are yes then it would appear the D7100 "screw drive" focus motor may have an issue.

Says the 35 DX is also having focus problem, not screw drive it if is that particular lens.

I noticed the problems with the 24mm 1.8. I saw the photos and thought to myself... Crap.

1 first photo is the whole portrait (A shelter for women with mental issues in México)
2 Second photo is a crop of the face.. Out of focus
3 Third photo a crop of the hands.

My technique is as follows: 1. Frame the picture, 2. Manually Select the sensor closest to one of the eyes. 3. Auto Focus 4. Take the shot.

When I got home I made some tests using the 35mm 1.8 DX. Steady target, camera on tripod. I noticed focusing problems (sometimes it focused in front, sometimes in the back).

To confirm I switched to the 50mm. At 1.4 narrow depth of field can emphasize any focusing issues. So I made some more tests, same methodology as before, and results were very clear, AF is inconsistent.

I didn't test the 24mm 1.8 due to its larger depth of field.

I sent the camera, along with the 50mm for service. So I'll keep you posted.


QUESTION about micro-adjustment. Is it completely necessary? --- For example: Brand new lens. One gets the lens to focus perfectly with a micro adjustment of +4. In my mind, micro-adjustment should be used only when something is wrong. Maybe a busted/old lens or a camera with a faulty sensor. But it should not be something that needs to be performed with factory new equipment. That's what I believe but I might be wrong here.

How often do you micro-adjust your bodies / lenses?

FULL SIZE portrait, taken with the 24mm at 1.8, ISO at 640 (just some crop to reduce file size)



CROP of the face... soft, out of focus.



Crop of the hands, with a little bit of motion blur

Good info but you left out distance from camera to subject. If you know the distance use this online calculator enter you camera, lens and aperture. I would have bumped the shutter speed to twice if hand holding (to eliminate camera shake) and would have selected F/5.6 to F/8 to give me sharpness. If you have a pad or smart phone there some excellent DOF calculators out there that shows you ⅓ in front and ⅔ behind.
Wide open gives you a narrow DOF Subject distance 10 ft this is selecting 24mm lens at F/1.8
Depth of field
Near limit 8.42 ft
Far limit 12.3 ft
Total 3.88 ft

In front of subject 1.58 ft (41%)
Behind subject 2.3 ft (59%)
Remember if shooting wide open any movement by you from the plane of focus you'd have to refocus. Thats why wide open is hard to shoot and demands consistence and discipline.
Lou Cioccio

LouCioccio said:

Good info but you left out distance from camera to subject. If you know the distance use this online enter you camera, lens and aperture. I would have bumped the shutter speed to twice if hand holding (to eliminate camera shake) and would have selected F/5.6 to F/8 to give me sharpness. If you have a pad or smart phone there some excellent DOF calculators out there that shows you ⅓ in front and ⅔ behind.
Wide open gives you a narrow DOF Subject distance 10 ft this is selecting 24mm lens at F/1.8
Depth of field
Near limit 8.42 ft
Far limit 12.3 ft
Total 3.88 ft

In front of subject 1.58 ft (41%)
Behind subject 2.3 ft (59%)
Remember if shooting wide open any movement by you from the plane of focus you'd have to refocus. Thats why wide open is hard to shoot and demands consistence and discipline.
Lou Cioccio

Click to expand...

Thanks Lou!!

The subject must have been... maybe 6.5 ft away from me (give or take).

In this case her hands must have been 11" away from her face, probably a little bit more. That's a lot off from the plane of focus! I mean, I could have moved 1" backwards or forwards while taking the picture, which I know it can cause me to miss focus at 1.8. But in this case, the plane of focus is waaay off. Lens is brand new, this was its first time "on the field" by the way.

First... Let me explain micro or fine adjustment...

Cameras and lenses are made in factories. Quality control inspects to make sure the manufactured item is within a specific design tolerance. That tolerance as usually expressed as plus or minus X%.

Cameras are not mated with lenses and are made in a different factory.

So... let's us an example of a camera that meets the design spec but is +5%... It still meets the design tolerance of +-10% Now let's also assume your lens is +7%... It also is within tolerance...

Now when you add the +7 lens to the +5 body... the combination is no longer within tolerance...

neither component is broken... that's called cumulative tolerance error... The Fine or Micro adjustment lets the user adjust for that error...

The assumption is that the camera will be -1 and the lens +1 which would cancel out any error. Reality is, that's rarely the case.


Next issue I see in your images... you're shooting in low light, at 1/50th of a second... which is very slow, and you're also shooting with an aperture that appears to be wide Open... Most lesns, wide open, are very soft...

Here's a tip... Set your camera for single-point focus AF-S and turn on the Beep in the menus... now, when your camera achieves focus lock, the camera will beep to let you know that it has achieved focus.

Retest the camera and lens, but do it in bright light so that you can set the speed to 1/250 sec or faster, and close the aperture down to one or two stops off the f1.8 so you're not using softest lens setting...

FredKingston said:

Retest the camera and lens, but do it in bright light so that you can set the speed to 1/250 sec or faster, and close the aperture down to one or two stops off the f1.8 so you're not using softest lens setting...

Click to expand...

Thanks for explaining Microadjustment. It's very useful!

If I use an aperture of 5.6 (for example), how would I know if there is a focusing problem with the extended depth of field? In my case with this back/front focus problem, I know I could walkaround the issue by using a smaller aperture, but that means using a slower speed that could demand a tripod or something similar. That's precisely why I bought the 24mm 1.8 & 50mm 1.4: So I don't have to lug a tripod, which on my line of work its almost impossible.

By using a diagonal ruler and focusing on the mid-point... you can take test pictures and by looking at the in-focus and out-of-focus tick marks, you can determine whether that particular lens is front-focusing or back-focusing... There are dozens of YouTube videos that walk you thru this process... as well as commercial companies that sell/license various focusing systems/targets for the Nikon fine-tuning system.

There's a database in your camera to store the adjustments. Every lens needs to be tested and adjusted... the database in the camera keeps track of the adjustments for each lens and adjustment.

You can test/adjust the lens at the F1.8 but in actual use, just understand that most lenses are "soft" wide-open... It's just a fact of optics... unless you get into the really expensive art prime lenses...

You need to set up a ruler and target... taking pictures of your friend is not precise enough...

@guillermo_arp

Here's the method I use to adjust the auto-focus on my lenses; I adjusted a lens today using this technique. It's simple, costs nothing and is very effective. You use the widest aperture on your lens while doing the testing because it provides the shallowest depth of field.

How to Use the Auto-focus Fine Tune Feature

Me again, so I sent my camera to service, they told me this

1. My autofocus sensor was somehow damaged, they replaced it.

I sent the camera along with a 50mm 1.4 AF-D.

Now I have this weird problem:

- On Short distances, it seems to autofocus just fine, but with a weird looking bokeh at 1.4 (First picture - Left is closest - Subject is a roll of film at 1.5 feet -- RED is weird bokeh, blue circle is where I set my focus.) (ISO 100, 50mm at 1.4 /160). If this is not normal, then it has to be a problem with the lens.
- Beyond 3-4 feet the front focus problem seems to be about 23"
- Beyond 4 feet everything is out of focus no matter what I do.



This is sad :-(

The problem you see is called "Depth of Field". At 1.5 feet the depth of field atF1.4 is very small. Try shooting this same picture at F11 and your out of focus areas will disappear.

guillermo_arp said:

On Short distances, it seems to autofocus just fine, but with a weird looking bokeh at 1.4

Click to expand...

The bokeh you get comes from the lenses. Different lenses yield different looking bokeh. Bokeh basically is determined by the aperture blades themselves. For example, my Sigma 24-70mm f/2.8 lens is fantastic with the exception of the bokeh it yields when shot at wider f/stops. It has what is called onion ring bokeh. Instead of nice, creamy bokeh, it looks like varying circles. The bokeh is very different when compared to the Nikon 24-70mm f/2.8 lens. And not all lenses use the same number of blades. So there are a lot of differing factors in any one lens that contributes to bokeh.

And as Brent mentioned, you have a very shallow depth of field. Depth of field is shallowest when using the widest aperture and when shooting from the closest focusing distance. And the length of a lens also factors into bokeh.

Try a different lens and see how the bokeh compares to this image.

I just want to confirm this focus issue with the D7100. This week I upgraded from the D7000 to the D7100. As it turns out I got TWO different cameras from TWO different vendors by accident. SO Naturally the question is which one to keep and which to return?


My first instinct was to return the camera body with a much higher shutter count. But as it turns out, tests with the same lens (35mm 1.8 DX G) and the same focus settings showed one camera to be suffering from very bad focus issues! As noted both back and in front of the subject. But generally Backfocus was worse. At least now I know which camera to return. And also to note the auto focus in Live View is much better and consistent. This is a very odd thing and I wonder if the LV uses a different focus sensor?

When I was having issues with my 300mm f/4 PF not focusing properly in the distance, Jake @BackdoorHippie told me to switch to LiveView and focus that way because it focuses directly to the sensor. It definitely helps.

How in the world did you receive bodies from two different vendors? And what is the shutter count of the body you want to keep?