Focus problem

hartz

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I have a D5100 and use an 18-105 as my walk-about lens. I've had this camera for about 4 years and recently went through the 9999-photos count.

Suddenly a few days ago I noticed that 99% of my photos were soft, badly so. After taking a deep breath I did a few tests.

1. All photos taken with the 18-105 are affected equally, but only when the zoom is between 18 and 35.
2. Beyond the 35mm mark the focus appears to be fine.
3. Photos taken with my 70-300mm lens appears to be fine.

This suggested to me that it is the lens rather than the camera. OK, it is a cheap lens (as lenses go), and I bought it second hand about 3.5 years ago. Being a bit of an adventure seeker, when on the mountain the camera and lenses tend to sometimes get bumped a bit, so I accept that this was due to happen sooner or later.

But to make sure I dug my 18-55 backup lens out of the drawer.
4. All photos taken with the 18-55 with zoom set anywhere between 18-35mm are soft.
5. All photos taken at zoom settings above 35 appears suddenly fine.

Focus tests beyond 35mm with either lens appears to be spot-on.

I have made many test shots, tripod-mounted, high shutter speed and low ISO, with a variety of F-stop values, and all tests appears to indicate that the problem exists only between 18-35mm, with either lens.

Two different lenses are affected on the exact same range of zoom values. The 70-300 lens is unaffected but doesn't cover the "affected" / suspicious 18-35 mm zoom range. I'm hoping to try my lenses on a friend's camera later today, but would like to ask: have anybody encountered something like this before? Any advice/suggestions? Would seeing my test shots mean anything, if so I will upload some.
 
This is interesting, I don't I ever seen this before. Typically focus problems are lens issues only and nothing to do with the body. But you obviously did the tests to prove otherwise. You should share some of those images. When did the test, did you use a focus chart?

Also did you find older pictures you've taken with that lens at those focal lengths and compare to the ones you've taken now and see if there is any difference? Maybe its been the same, you just never noticed until now?

Another thing you could try is to clean the contacts on the body and check to see if there is a firmware update.
 
Those are good suggestions. I'm going to look through my photos, even to find out how long ago this started!

I tried with a Friend's Tamron 18-270 lens and had the same issue! I also tried my lenses on his body but I was in a hurry and his ISO was set to auto so the comparison is difficult, but it does look like his camera focuses fairly well at all zoom values, all of which suggests that it is the body.

I'm going to go try to talk to a technician at the local Nikon repair center tomorrow, if they will let me, and hear what his opinion is.

I've been wishing for a D7x00 just to get that bigger Viewfinder ... so maybe now is the time for a good second hand D7000. Which is weather sealed. And can focus with older AF-type lenses. And takes to memory cards. And and and!!! But the viewfinder is the thing I want.
 
Any chance you'll be in Cape Town this week?
 
at first I thought you were in Florida. now I'm guessing South Africa.
But I'd say not a chance to either to be there.
 
I'm relieved cause I'm too broke to buy it anyways.
 
Check the rear element of the lens, and make sure it is not smudged!!! If it is immaculately clean, then you've likely got a lens problem. Short focal length lenses have very limited depth of focus (not to be confused with depth of field) at the film plane, and if the lens takes a drop, impact, or knock, and becomes out of specification, at the short focal lengths, the images will be rubbish.

If there is any consolation to this, it is that the 18-105mm lenses are plentiful and relatively inexpensive, and are not worth sinking much money into repair-wise, so there's no need for a big repair bill on this. This is a better situation than say, a $2,499 70-200/2.8 lens that has been dropped onto concrete, and now needs $649 in parts and labor...know what I mean????
 
Derrel what you say makes complete sense to me, except that I have the same problem with a friend's Tamron (18-270) and with my backup 18-55mm lens. All of them refuse to focus from 18-35 mm and suddenly from that point onward become fine!?
 
I uploaded 4 photos, all at F5.6, ISO 100.
18-105mm lens, wider than 35 mm
18-105mm lens, beyond 35 mm (sharp)
18-55mm lens, wider than 35 mm
18-55mm lens, beyond 35 mm (sharp)
Focus Tests Flickr - Photo Sharing
 
How weird! I would set the camera to 15 or 30 seconds shutter speed, and remove the lens, trip the shutter, and let the mirror swing up; then, with a flashlight, look down into the bottom of the mirrorbox, and see if there's something blocking the AF sensors, which are located on the "floor" of the box area. Something being most likely, a garment fiber or hair.
 
Derrel, I can see the focus sensors, but not well enough to see if there is something. But your suggestion made me think if there is something, it might not block all the sensors. So I tested by taking photos, each time using a different sensor selected for the photo. One photo, taken using the far right focal point, came out sharp.
 
Derrel, I can see the focus sensors, but not well enough to see if there is something. But your suggestion made me think if there is something, it might not block all the sensors. So I tested by taking photos, each time using a different sensor selected for the photo. One photo, taken using the far right focal point, came out sharp.

Good thought you had on cross-checking, and you might be correct. Here is an article that might help with the focus sensor issue...I once had this problem with my D70--turns out there was a teeny-tiny sweater fiber!!! blocking the AF sensor!Autofocus troubleshooting by Thom Hogan
 

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