Autofocus Hunting

I think this is really a lens issue but since it's happening with my D7100 I'll post here. My 18-200 Nikon zoom recently started hunting during autofocus. I use BBF and normally have AFS-C and d21 set. It seems to focus then either hunt back and forth slightly around the correct focus point…even for stationary subjects like tree stumps. Alternatively…sometimes instead of hunting it zooms to minimum focus distance then back to approximately correct…then either hunts around that point or goes to minimum distance.

Neither my Sigma 10-20 or Sigma 50-500 exhibit the same symptoms; although the 50-500 did until I locked the mirror up and used a can of air to blast off the autofocus sensors. Mirror is clean, and I have sensor cleaning set for both startup and shutdown. The 18-200 exhibits the same symptoms when moved to my wife's D7000…leading me to think it's the lens and not the body.

I've tried selecting AF-S, AF-A and various other focus point selection options including single but that doesn't fix the issue.

I've cleaned the front and rear lens surfaces…as well as the UV filter it's always got on it…and even tried leaving the filter off in case that was it as it is a couple years old and is showing some minor scratching on the filter outside surface…but they're small enough that I wouldn't think they're any issue. Internally…at least as well as I can tell holding the lens up to the light…I don't see anything to cause a problem.

Is this a sign that there's something wrong with the lens…or does it just need a good internal cleaning at the shop…or possibly something else? Trying to figure out where to troubleshoot next. How about needing a professional cleaning on the body to get the autofocus sensors cleaned…as I said I blew any dust out but if there's something adhering to them it might not have gotten blown off and you really can't see down into the autofocus sensor well very well. Both cameras…along with lenses and other gear…are 5-6 years old and have traveled extensively to AK and the west where it's dusty…but there isn't any indication on photos of any dust buildup that I can see.

Thanks.
 
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cwgrizz

Senior Member
Challenge Team
Welcome to the forum. Are you saying that this lens/camera combination just started doing this, but didn't have the hunting issue previously? I really don't have a clue what to tell you, but I am sure there will be someone on here that will be able to help you along with the problem..
 

Ironwood

Senior Member
Welcome to the forum Neil.
Sounds like a lens issue to me. As it will be out of warranty you will have to weigh up the difference to repair or replace.
Do you have any repair shops nearby you could talk to ?
 
Brad…I'll look around for a shop but will have to wait a week or 10 days until we get to a "more than one horse" town…we live in our RV full time and travel and Port Angeles WA is pretty small.
 
Brent, thanks for the link…the contacts on both lens and body look fine but I haven't cleaned them so it can't hurt.
--added later
Nope…cleaned both lens and body contacts even though they both looked fine…no change in the symptoms.
 
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RocketCowboy

Senior Member
First, howdy and welcome to Nikonites!!!

I wouldn't think you need to lock up the mirror to clean the "autofocus" sensor ... wouldn't that be the camera sensor itself? Unless you're shooting in live view, autofocus happens before the mirror lifts to capture a shot???

Can you post a sample image where you were having problems with the 18-200 hunting? I don't think that lens is a terribly fast lens, could it just be poor lighting or low contrast in the scene making the camera work harder???
 

spb_stan

Senior Member
Acting the same on the D7000 and D7100 sure suggests a problem isolated to the lens. The lens contact suggestion cleaning is very unlikely to fix anything, the only "dirt" that would be able to be cleaned off is not dirt but oxide of the alloyed metal mixed with the gold plating. Alcohol would just make it oxidize faster. A deoxidizer chemical would be needed in the rare event that contacts were oxidized. If there was a contact problem the error message would display.

Periodically body/lens alone or combined just need adjustment for AF to remain consistent. Both my D7000 and D800 needed it and my 70-200 2.8 needed alignment suddenly each time. They get hard ridden, so I am amazed how stable they are, but once, during a paid event shot my D800 stopped focusing well on any longer focal lengths, say over 110mm but was ok at 70mm. That turned out to be a len calibration problem. Another event my 24-70 stopped focusing well on wider angles, worse on the D7000. Again minor adjustment done with 1 day turnaround. The lens was the one needing adjustment. Another time my D7000 became unreliable on any lens with 2.8 or slower with any lens and another quick alignment, this time to the D7000. It came back focusing more sure than even when it was new. It never seemed to have a problem after 140,000 frames but there was a sureness of the lock that I never saw before. It now locks without any hunting giving the impression it is more consistent than the D800 using the same lenses

So what you are describing sound familiar and it suggests the lens needing adjustment.
How do you like full time RV living? Sounds both like fun and a challenge. Good luck!
 
Thanks for the reply Charlie…yes, one does need to lock the mirror up to get to the autofocus sensors…they're on the bottom of the body underneath the mirror so locking it up is necessary to get access to them. I'm using BBF and the viewfinder…there's a little recessed area in front of the shutter and below/behind the lens that has the focus sensors in it.
Posting a sample image won't help much…as all the hunting is happening before shutter release during BBF via the AE-L button. True…it's not a terribly fast focusing lens but before the problem started it focused right in on the subject at the selected focus point…now it's hunting back and forth across the correct focal distance around that point. Not a poor lighting or contrast problem either…tried it in bright daylight with wide open aperture (as well as other apertures) and it's just not focusing on the selected point and stopping there any longer.
 
Maybe it's just a lens adjustment that's needed…I will get with a repair. shop and/or Nikon themselves and figure out how to get that done. It's worse on longer focal lengths…but part of that is probably because shorter ones are more forgiving of focus. Given that it's the same results with the lens on both bodies…and the normal performance with other lens on the 7100 it's probably just the lens that needs adjusting.

Living in the RV is great…we told our son and DIL that we just did the estate sale for them already. Been doing it since summer of 2012, traveled about 55,000 miles so far with the RV including all 48 of the lower 48 and Alaska along with 4 Canadian provinces. We have some "stuff" in storage but pretty much everything we "need" is with us at all times. It's a load of fun…seeing new stuff and places and sampling local brews wherever we go. Once you get used to living in a smaller area and for me…the lack of a completely equipped kitchen like I used to have although it's not like we're only eating beanies and weinies…I just don't have as many gadgets as I used to have…but then we're not really eating much different or lower tastiness so maybe I really didn't need all that stuff anyway.
I'll see if I can figure out how to get the lens adjusted…most likely will have to go back to Nikon so that means it won't happen until November when we complete the travel season are in North Fort Myers FL at our 6 months in the winter location.
 

spb_stan

Senior Member
The best decision I ever made was leasing out the house in NorCal, Marin county and moved with 2 suitcases to a city in a country I did not know the language,having no clue what I would do to support myself or where to live in 2001. I gave everything away, cars, property, everything except 1 house, and 1 car and a small storage unit filled with awards, old photos, some old electronic test equipment, not much was saved. Moving from a 14 room house to a 35 square meter apartment in a 1828 building in the heart of a large city was like freedom. I was never a city person but I had visited hundreds around the world but living simply, getting rid of TV and the cars. Was a great adventure and opened infinite possibilities. It is still fun every day low stress, very low cost of living. Now I have a larger apartment but also gained a live-in GF and a 12 yo Persian cat. Slowly over the years brought back any test gear that would fit in my suitcases so all the test gear now sit in an electronics lab in a spare bedroom. We operate a business together, do a lot of traveling and I got back into photography which is the best hobby for meeting people...particularly very attractive young women who love good photos;>)
My total living expense if out of the city or country for a month, the bills waiting for me when I return are less than $30. So costs are direct costs,food, concert tickets, opera, theater, dance clubs and dining out which we do 3-5 nights a week. Too busy having fun to even spend 1 minute watching TV or even listening to a stereo...I gave all those away because now I only prefer live music despite being in the recording industry for over 25 years. Life is a lot more fun out and about, with no bills, living simply. So I understand completely how and why you cut the extension cord. No one collected more stuff than I did, from boats cars, plane, houses...and never had time to enjoy them due to working to support them. Instead of a car here I have a great, cheap pubic transportation system, and a high speed subway across the street that allows me to get to any district of a city of 7million in 20 minutes or less, instead 1.5 hours by taxi or private surface car. Anywhere in the city for $0.65
Happy motoring!
 

RocketCowboy

Senior Member
Posting a sample image won't help much…

The sample image was just to get an idea of the lighting and exposure settings, to see if that can help provide clues as to why the lens is hunting. Your aperture setting doesn't matter as far as autofocus goes ... the camera will autofocus with the lens wide open, and only stops down to the selected aperture when the shutter is tripped.
 
Ah…I see.

It's pretty much universally hunting no matter the lighting conditions or selected exposure. Everything from birds out in bright sunlight to canyons to deep in the woods waterfalls. Shutter speeds from a second or more for the tripod mounted waterfall shots to 1/3200 for birds…aperture setting from wide open 3.5 to F29 for the waterfalls, and ISO setting from 100 to 1600. I've been futzing with it for 3 or 4 weeks now and haven't found any particular set of circumstances that isn't affected…although the low contrast/low light in the deep woods waterfall seem to be a bit worse for autofocus…but then that's really expected and I'm manually focusing then anyway. Here's a shot from today…tripod mounted at ISO 100, the 18-200 at 100mm or so, aperture at maximum I could get it and shutter speed of 0.8 seconds. I did try autofocus with a single point on the large rock right in the middle of the shot and it hunted about as much as it does these days…so manually focused on that point.

It actually focuses correctly on manual…but it's the hunting around instead of just locking in on the selected point that started recently.

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