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  1. #11
    Senior Member
    guillermo_arp's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    Quote Originally Posted by LouCioccio View Post
    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
    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.


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  2. #12
    Senior Member
    FredKingston's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    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...

  3. #13
    Senior Member
    guillermo_arp's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    Quote Originally Posted by FredKingston View Post
    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...
    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.

  4. #14
    Senior Member
    FredKingston's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    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...

  5. #15
    Senior Member
    Horoscope Fish's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    @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
    ~ Paul
    ....
    ....
    Primary Kit :: D850, Tamron 70-200mm f/2.8 G2, Tamron 24-70mm f/2.8 G2, Sigma 135mm f/1.8 Art, Sigma 50mm f/1.4 Art,
    Godox Flashes & Triggers, Manfrotto X055PROB, 3-Legged Thing Airhed II... All Stuffed into a Manfrotto Pro Backpack 50
    ....
    ....
    ● ▬▬▬▬▬▬▬ ๑۩۩๑ ▬▬▬▬▬▬▬ ●

  6. #16
    Senior Member
    guillermo_arp's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    D7100 Inconsistent autofocus. Backfocus / front-focus
    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 :-(

  7. #17
    Senior Member
    Bikerbrent's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    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.
    Brent: Poway, CA
    D7200, D200, F100
    Tokina 12-24mm
    Nikon 18-200mm
    Tokina 28-70mm f2.6-2.8
    Nikon 80-200mm f2.8
    Sigma 150-600mm
    Nikon 50 AF f1.8
    Tokina 100mm f2.8 Macro
    Nikon SB800

  8. #18
    Staff
    Super Mod
    hark's Avatar

    Re: D7100 Inconsistent autofocus. Backfocus / front-focus

    Quote Originally Posted by guillermo_arp View Post
    On Short distances, it seems to autofocus just fine, but with a weird looking bokeh at 1.4
    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.
    Last edited by hark; 04-18-2018 at 12:43 PM.
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