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Archive 2017 · Focus hunting

  
 
HarvM
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p.1 #1 · p.1 #1 · Focus hunting


When the focus "hunts" from close to far and back again is this the lens or the camera doing the hunting.

I'm using a Nikon d5100 and the Nikon 70-300 lens

Thanks



May 31, 2017 at 12:16 PM
jbouchard
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p.1 #2 · p.1 #2 · Focus hunting


The combo. The AF sensors are in the body, the focus motor in the lens. I think the software logic is largely in the body.

Look for a high contrast edge or something where it can focus. It won't focus on a flat painted wall, but catch the end of a window, and it will lock in on that quickly.



May 31, 2017 at 12:20 PM
Photozack81
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p.1 #3 · p.1 #3 · Focus hunting


It's a combination of factors. Some lenses are more prone to this than others. Lighting conditions can be a factor, but the focusing is all controlled by the camera. If the AF sensor in the camera isn't happy with what it sees, it will keep trying until it thinks it has focus.

Depending on which 70-300 you have, the lens could be an issue. I'd be more suspicious of the lighting conditions at the time of the focus hunting problem.

Also, if you're trying to focus on something with little contrast it can cause problems.

The AF sensor could also have some dirt or something on it. It happens, and it isn't cleaned by the normal camera sensor cleaning routine.

To rule out the lens, you can autofocus in live view. If that works, you know the lens is OK, and your attention should be directed more towards the AF sensor and lighting conditions and such.



May 31, 2017 at 12:23 PM
CanadaMark
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p.1 #4 · p.1 #4 · Focus hunting


It's mostly the camera and also very likely several factors with regard to shooting conditions. You can read a more detailed explanation here which may help:

https://www.fredmiranda.com/forum/topic/1371924/0#lastmessage

Hunting typically will be caused by either a confused AF system, not enough light, or not enough contrast on the AF target.



May 31, 2017 at 12:24 PM
jyo1
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p.1 #5 · p.1 #5 · Focus hunting


You need to have some detail to focus on---bland, one color surfaces with no detail to lock on are the hardest---a D5100 is considered kinda old in the current days and the 70-300 (non VR) is also kinda of older equip…


Jun 02, 2017 at 12:29 AM
HarvM
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p.1 #6 · p.1 #6 · Focus hunting


Thank you all for your responses. it's good to have such resources to call on.

HCM



Jun 15, 2017 at 06:05 AM
Alan321
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p.1 #7 · p.1 #7 · Focus hunting


In the first instance, hunting starts when the camera cannot detect focus well enough to know what adjustment is required of the lens. It's not just out of focus, it's too far out of focus - regardless of lighting or subject. So then it instructs the lens to head one way or the other in the expectation that it will see enough contrast to latch onto the correct focus.

Unfortunately, particularly in poor light or with a lens that has a small maximum aperture (too little light getting through) or with a lens that has a huge maximum aperture (no DOF and everything can be a uniform blur), it often isn't clever enough to tell the lens how fast to change focus. I've often seen focus come and go in the viewfinder while the camera has missed it. In those situations, if I manually move the focus close to where it should be then the camera sometimes makes a good decision on exactly where to focus, but sometimes it is just too dark for the AF system to work at all.



Jun 18, 2017 at 12:32 PM
saaber1
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p.1 #8 · p.1 #8 · Focus hunting


If you are talking about the Nikon 70-300 VR original version, that lens hunts a lot. I used it for a long time and if it doesn't lock on immediately it likes to rack all the way out, then rack all the way in, then try to find focus again. I recently rented the Nikon 200-500 and I found it's focus behavior to be very similar when shooting a subject with a busy background or trying to pick out a bird among a lot of branches (using d750). The 200-500 didn't hunt at all when the subject was isolated/non-busy background.


Jun 19, 2017 at 06:14 PM
HarvM
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p.1 #9 · p.1 #9 · Focus hunting


My 70-300 VR was purchased Sept 2007, does this make it the original version?

I know birds in branches are particularly tough. I am amazed at how well the lenses do the job.

Harv



Jun 19, 2017 at 07:18 PM
runamuck
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p.1 #10 · p.1 #10 · Focus hunting


Very tough. I have a pair of shots where the 70-300 and D300 focused on a slender weed. The next shot it focused on the deer several feet behind the weed.


Jun 19, 2017 at 09:51 PM
saaber1
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p.1 #11 · p.1 #11 · Focus hunting


HarvM wrote:
My 70-300 VR was purchased Sept 2007, does this make it the original version?

I know birds in branches are particularly tough. I am amazed at how well the lenses do the job.

Harv


Harv, yes that's the original version. A very capable lens in bright light, especially when shot at less than 300mm. But it does like to hunt a lot and is very slow to rack back and forth relative to other lenses. Imo the "hunting" seems normal until u use a lens like the 70-200 vrII. All of a sudden it is like bang! Instant focus lock! in most any background/situation. Obviously the 70-200 is much more expensive so I'm not trying to compare the two that way.

I have found the longer zooms and primes vary by lens as to how well they lock on to a subject, how fast they lock on, and how they behave when missing focus. It's a little like the lenses have different personalities. Some lenses like the 70-300 vr (original version) and 200-500 "recover" after missing focus by sort of throwing up their hands and saying "I don't know what to do so I'll just rack back and forth hoping something good will happen". Other lenses "recover" by saying, "I missed focus but this is pretty close so I'll just stop there". The latter of those two is much better behavior because u can instantly refocus and not have to wait for the lens to rack back and forth. Plus the initial missed focus is pretty close and a quick press of the AF-ON button get you perfect focus.

Also related to re-acquiring focus, if your camera has the ability to do "AF-ON" (often called back button focusing) that will make a world of difference in getting better initial target acquisition and in re-acquiring target. I don't know your cameras af system but if it allows you to use Af-On (camera focuses only when you press the focus button), af-c mode (continuos focus), single point focus (or dynamic 9) that setup will help a lot.

I would also note that many recent sigma and tamron lenses allow u to change their af behavior (as well as vr behavior and other things) via their dock/tap in console. For Nikon, if u are using a Nikon 300 2.8 or any of the longer exotic primes there is no need to change the af behavior anyway because they have "instant lock" amazing focus already.



Jun 20, 2017 at 09:43 AM
HarvM
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p.1 #12 · p.1 #12 · Focus hunting


Thanks, I have a Sigma 150-600 that I use for bird photography, but I haven't availed myself of the options using a dock. I'll have to look into those features.

Harv



Jun 20, 2017 at 04:30 PM
elkhornsun
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p.1 #13 · p.1 #13 · Focus hunting


A lens like the 70-300mm f/5.6 is going to provide at most the light from the f/5.6 aperture and that handicaps the camera's autofocus sensors. By way of comparison a 70-200mm f/2.8 lens is at f/2.8 when the camera is focusing and it provides 4 times as much light to the autofocus sensors.


Jun 20, 2017 at 09:31 PM





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