Nikon 35mm 1.8g lens

Why does this lens have issues with Auto-Focus

Why do think it has AF issues? I had one and had no problems with it.

Well, sometimes mine works ok, other times not, tell me Why? Am I the issue or the lens is malfunctioning?

I've never had an issue with autofocus with this lens either and I use it almost exclusively when I'm taking photos. Perhaps you could give some more info as to the types of problems you are having?

Can you give more information as to when AF does not work for you, what camera you use it on, the AF settings of that camera, if there are filters on the lens etc? Without more info, it's near impossible to say a sensible thing about the cause of the issue you encounter.

Good responses are more likely with detailed information for a basis. Shot in the dark -- Have you cleaned the contacts?

One has to understand how the AF works. On my Nikon DSLRs, it is optical, not IR or ultrasonic.

• If you put the AF sensor on a solid colored shirt or a blank wall, there is no contrast for the AF to focus on.
   
  
• You have to put the AF on something that has contrast. Like where the shirt collar and neck is, a patterned shirt, a poster on the wall, etc.
  
• If there is something between you and the subject, such as the bars on a bird cage, the AF will focus on the "something" between you and the subject. In this situation, you have to switch to manual focus.
  

My assumption:

 

Your focus issues are "most likely" occurring at a wide-opening aperture (e.g. f1.8.) This is due to the focus circuitry "hunting" to find good focus within a shallow depth of field. This effect is even more pronounced with larger aperture lenses such as f1.4 and f1.2, when they, too, are being used at their widest openings.

 

The shallower the depth of field, the more difficulty the focus circuit has in deciding "where is the best focus in this image." The camera eventually decides to focus on "something" within that shallow depth of field, and often this focal point is NOT what the photographer wants.

 

I get around this annoyance by "usually" using my cameras (I"m 95% a film guy and 5% a digital guy) in the manual mode and focusing my shots manually.

 

At smaller aperture openings, for example f8, f11, etc., the depth of field increases much. So at smaller apertures, your auto-focus will have more in focus and thus the camera can focus more easily and quickly, with more of your photo in focus. With the smaller apertures (and resultant greater depth of field,) the camera does not have to "hunt" so much to find / recognize a suitable focus that it is "happy" with.

It would help a lot to determine whether the problem is failure to find a focus spot, or failure to operate at all. If the auto focus is actually not working, then a suspect would be the camera, or the contacts between lens and camera, which might need cleaning.

 

If the problem is that the lens is failing to settle on a focus spot, the first thing I'd check is that the camera's AF setting is correct. Start by making sure that it is set for something other than Auto Area focus, which does not always choose the focus point you want.. On a stationary subject, set it to single servo AF, and make sure that the focus point is where you want it to be. What options are available will depend on the camera, but all AF cameras have single servo single point AF, and that's a good place to start determining whether there's a problem with the equipment. If you shoot a stationary object in single servo single point mode, it should be sharp and consistent. If not, I'd suspect a problem.

 

Since we are presuming a digital camera, there is no good reason not to take lots of test pictures. Make sure you try it in various configurations, ways, times, and distances,, as the more you can narrow down when and where the problem occurs, the easier it is to figure out.

 

By the way, I think that Keith S is not quite right on how AF works, at least in viewfinder mode. It is true that if you're shooting at a smaller aperture things will appear to be focused better, but in viewfinder mode, viewing and focusing are done with the lens wide open. Your chosen aperture is not actuated until you open the shutter. At least some cameras will carry an aperture setting over into Live View, but in the viewfinder you always look and focus, through the lens wide open, and your aperture setting should not have any effect on how the camera focuses.

By the way, I think that Keith S is not quite right on how AF works, at least in viewfinder mode. It is true that if you're shooting at a smaller aperture things will appear to be focused better, but in viewfinder mode, viewing and focusing are done with the lens wide open.

 

I will fully admit that the only auto focus Nikon I own is an F4, and my only DSLR(a Canon Rebel XS) is a used about 80% of the time on a tripod in live view mode with me manually focusing with the computer screen.

 

With that said, on both the F4 and the Rebel the AF module doesn't seem to care where the aperture is set when it's focusing. I also only have "screwdriver" AF lenses for the F4. Low end and early AF systems tend to "hunt" in low light even when you put an AF point directly on a high contrast area(i.e. I'll often use a white door frame against a darker wall when testing/playing with AF), but focusing is done wide open and I doubt that the AF module pays attention to the aperture you're going to use to take the shot since that could change between the time you focus and when you actually take the shot.

 

The only time the aperture is going to come into play is, again, if you're in low light and using a slower lens. Even though the camera is focusing with the lens wide open, it still has less light falling on the focus CCDs to work with. That would not be an issue with a 35mm 1.8. In fact, going to my limited selection of zoom lenses, I find that my F4 focuses faster and more decisively in lower light situations with a 50mm 1.8 than it does with a slower zoom. I do have one zoom that beats it in bright light since it's geared much faster, but the 50mm wins in marginal conditions.

 

BTW, I'm eying an F100 in a local shop that most likely will be coming home with me sometime soon, so I'll be interested to see how a somewhat more modern AF system does. I'd jump on a D750 at the current low price if I had a spare $1500.

If you have an issue with autofocus look into settings.

Are both your lens and camera set to "autofocus" instead of "manual focus"? That camera/lens combo should auto focus without any problems. Most likely, it is a settings issue. Also, make sure the lens is fully locked in place. Remove the lens and re mount it making sure it clicks into place.

FWIW, since my post above I now have a couple of new(ish) digital bodies as well as the lens in question.

 

With my D2X and the 35mm 1.8, AF is fast and sure provided that there is enough contrast for the selected sensor to pick up. Heck, the lens is fast on all my AF cameras that are capable of focusing it, although of course with film and FX cameras you get a bit of vignetting.