Rich1939 Loc: Pike County Penna.

Sorry, that should read; correct for you One man's goose is another man's gander.

Steve Perry Loc: Sylvania, Ohio

Thanks for the book purchase :)

I too have found that this sometimes happens with slower zooms, especially in dim light or tricky to focus situations. The PDAF system simply can't get enough differentiation from the incoming light do decide which way it needs to turn the lens - and it just sort of hangs. Most people will never experience it, but it does happen with the slower zooms in poor conditions - although I've on occasion had it happen with faster primes too (heck, try to focus on a white sheet of paper and every lens will try and then give up). If there's not enough contrast to focus, the lens may give it a go, hunting a little, and then just quite. Normally where you see the AF confirmation dot you'll get some flashing, indicating the lens can't achieve focus.

The trick is to try to point the AF sensor at a more contrasty area if possible (like an edge for instance). It can also help to manually focus the lens so the subject is "roughly" in focus, then let AF finish the job.

This can also happen more frequently if your AF sensors are "dirty" too. See this video for a demo on how to clean them:

https://backcountrygallery.com/solving-autofocus-problems-8-common-af-problems-and-solutions/

The cleaning technique is at 2.21, although it may be worth trying some of the other tips as well.

seeker613 Loc: Brooklyn, N.Y.

The type of settings you have for AF measurement might have something to do w/it. There is Avg/center weighted, spot & dynamic. I use BBAF & use dynamic virtually all the time. Then there is the focus grid - # of points of focus - my camera maxes at 51 but that's plenty for me, I did a # of karate exhibitions (fast changing / moving subjects ) & got great shots all in P mode, using dynamic & AF-C autofocus setting that Busch's book recommended (see next paragraph) for fast sport fotography- even b4 I used BBAF.

Mentioning this may book may be redundant, but when I saw the topic, & your description; I was already aware of potential issues having read David Busch's Guide to Nikon (fill in the model #) Photography.

His coverage of all the features & explanations are way better documented w/fotos, charts, etc., than the Nikon manual & goes into stuff like 3d party solutions for gear - everything fm best straps (3mentioned) to replacement plastic connector covers (if the rubber one Nikon provides is too clumsy to use or is lost)for flash & remote connectors. Also which other Nikon charger models will work w/batteries for your model (or was it the wall charger for the body, which should be used when transferring pix str-ight fm th: camera.

The chapter on Custom Menus is worth the price of the book, just to have ready reference to what the defaults are & what can & cannot be used when working w/settings that interact w/Main & Sub Command dials i.e. the Fn button & others.

Worst case scenario, it is about $25-30 & has clear descriptions & lots of added value - another case, go to a big brick & mortar foto store & look at the relevant material in-store b4 buying.

Check out if they have a book for your camera model number @ Cenage course materials - Cenage is the publisher. They have Bush on most popular DSLRs. I depended on this book very much for when I switched over fm an analog to a digital camera & still use it yrs later for reminders on the finer points like bracheying that I don't often use.

jr168

I had this issue with the Tamron 150-600 version 1. Steve’s explanation is spot on. A couple of things that help are to use single, 9 point, or group focus points. I also will play around with how long the focus lock is set for. If it hangs, try manually focusing the lens for a moment then retry af.

treadwl Loc: South Florida

I use BBAF all the time BUT---I use it in conjunction of Continuous servo. Thus the camera will continue to focus aslong as you hold the BBAF.

seeker613 Loc: Brooklyn, N.Y.

I was convinced at a seminar @ B&H w/Pro Photog Steve Simon & either check out his site, or look for something on YouTube… to be sure you have all pre-reqs of BBAF.

chasgroh Loc: Buena Park, CA

...if you shoot a *lot* of sports where its required to get shot volume you're shooting BBF. Before I changed over, my results were pretty much like yours. After I changed (and went through a learning curve, of course) my productivity increased exponentially, and I now use it for *everything*...every situation other than handing the camera to someone else to take a shot, lol. Another, less discussed, plus for the technique is that you're pushing forward, not down, to acquire focus...minor point, I know. Not searching for an argument here, just pointing out a "why"...

sathca Loc: Narragansett Rhode Island

Thanks for the reply Steve, With the help of the things I learned from your book that was my hunch too. It was puzzling though that after it hangs up no matter what I point it at it wouldn't focus. I don't think the sensors could be dirty since it just came back from Nikon, but I'll do it anyway. I want this resolved before osprey season! I'm also reading your wildlife book and as you say you have to go where the wildlife is. I've done that and I've missed too many potential "wall hangers"because of these slow lenses. So I'm shopping for a faster lens. Do you think an F/4 will change things dramatically or do I need to go to a 2.8? I'm thinking a used Nikon 200-400 f/4 or a Nikon 300 2.8

jeep_daddy Loc: Prescott AZ

If your lenses have a switch on the side that focuses from full focus range to partial focus range, try switching it. Sometimes lenses focus to one the close extreme when they lose focus on the subject and then can't reacquire focus again. But limiting the close focus distance might alleviate this problem.

tomcat

I encounter the same situation when using AF-C + focus priority sometimes. When I'm shooting soccer, it does not happen and the camera will track and continually refocus as the player moves. However, when I'm shooting birds or other subjects with lower contrast, is when it seems that happens and the focus tracking stops. I can track a bird on a tree branch, focusing on it's eye, and then all of a sudden, the focus tracking stops. I think that if the camera loses it's contrast-phase detection, then the tracking will stop. This is a similar situation to when you can't acquire focus on a soft baby skin when using AF-S---if the electronics can't detect enough contrast in your subject, then it can't lock focus. By the way, I do not use BFF, but instead use the shutter button for all AF-C tracking.

To test this idea for yourself, make certain that you lock on a subject and then just move to different subjects and see if the tracking continues. I'll bet that it does so long as you point at high contrast subjects. Then just move a little bit around the one subject and see if it stops tracking when you get to a low contrast area.

speters Loc: Grangeville/Idaho

Sounds like you have your BB button set to >focus OFF<, which a lot of folks like (for scenes were a lot of obsticles are getting in the way)! It's just the way you set it up!

IDguy Loc: Idaho

Probably not > f8. Most are only reliable to f5.6.

Do not confuse the f-stop you have set for the image with the wide open f-stop for the lens at it’s zoom setting. The camera uses wide open to focus and stops down the lens when taking the image.

Kristian Loc: Monrovia, CA

I don't use AF-C much, but on my D-810 there's a menu item called focus tracking with lock on which can be set to freeze the AF-C for up to 5 seconds, say if something gets between you and your subject. Could something like this be the culprit?

Pegasus Loc: Texas Gulf Coast

That's a reasonable question, but the OP did mention the issue does not happened with another faster lens.

tomcat

Thanks and that's an excellent suggestion. I had not thought about that being an issue. I use that feature quite a lot to keep referees and other players from interrupting my target tracking and I read from a couple of Nikon experts that you should reduce that setting down to a very low value of 1 or 2 because it can cause an issue with the camera responding very quickly when there is a need to refocus. I did not equate head and beak movements from a "semi-static" bird body as being the same as a running soccer player, but you know that the bird head movements on a static body should be the exact same as the whole body moving, very interesting hypothesis. I'll turn that feature off now until I actually need it and see if I continue to get that problem return.

Brilliant catch!!