Lens hunting

[botty1963]

I recently purchased my first macro lens, and noticed that it 'hunts' a lot more than any of my other lenses. I use it in manual a lot of the time so no issue, but when I have it set to auto-focus it seems to struggle find focus a lot; it can be close up of further away, so no particular pattern.

Due to the very low DOF on macro lenses, is it a common issue?

[Stagecoach]

Which lens and on what camera are you using it Steve? I ask because others may have experience with the same combination.

I generally use manual focus/camera movement with my macro but also find AF does work well without hunting if I'm on a good target.

[Dave Humphries]

Hi Steve,

I would also ask whether your technique is perhaps contributing.
Are you using a single focus point?
Which one, when?
Are you keeping the camera's aim stable when focusing? (difficult when so close if hand holding)

e.g. some people (perhaps not you) expect AF to work when pointed at a plain featureless wall just because (say), it is in good light - afterall, the wall is plain to see, right there in front of them.

However, if we appreciate that most DSLR AF systems will work better (i.e. lock quicker) when the selected single focus is placed on an area that contains a contrasty edge, that helps. It may even matter which direction the edge is aligned, especially if not using the centre focus point.

Selecting a single focus point may remove 'indecision' (in the electronics) if the scene contains edges at different distances and if the subject is moving, camera not steady or wind blowing (say), a flower.


All that said; my Nikon 105mm macro lens is more likely to focus hunt than my other lenses, this can be exacerbated if I don't remember to use the little switch on the lens barrel to limit the focus range to the distance that the subject is in - because otherwise it will take ages going from one end to the other and back again each time it fails to lock on.

As Grahame has asked, we need to know more details to be more specific in advice. Perhaps even post an example image of a scene it struggled with.

HTH, Dave

[dem]

Are you trying to focus close to the minimum focus distance? If the lens hunts for some time and then gives up focusing, you might be too close to the subject. Also, are there any focus limiter switches on your lens?

[rpcrowe]

Most macro lenses that I have worked with have a focus limiter. This limits the range in which the lens has to focus and therefore limits the focus hunting.

However, my 90mm f/2.8 AF/SP Tamron Macro does tend to hunt. Perhaps I notice that because the auto focus is a lot slower and noisier than my Canon lenses, most of which are equipped with USM focusing capability...

OTOH, as previously mentioned; using the macro lens in manual focus (which is how I focus most macro images) negates the problems with focus hunting...

[Manfred M]

Steve - I'm not a macro photographer, so I am no expert here, but all the folks I know personally who do macro work focus manually, rather than relying on autofocus.

Over and above the focus lock issue you are describing, they have told me that this is the only way that they can guarantee that the the focus is where they want it to be.

[Geoff F]

Yes I agree with Manfred. There are many similar focus targets with the shallow depth from a macro lens so the camera doesn't know which one to choose. Manual focus and on a tripod is the only reliable way. I even manually focus on those few occasions when I shoot handheld.

AF is often unreliable when going from a close distance to a target further away. Sometimes I have to aim at a definite easy to recognise nearby area with sharp edges to give the camera a better idea of the intended subject then move to the required area.

Bird photographers often have similar problems when a camera prefers to focus on a sharp edged bit of the background instead of a soft edged bird.

Even worse when I'm using AI Servo option.

[Saorsa]

Working close your DOF means that the lens will be going in and out of focus quite a lot with any movement at all. Even breathing if you are handholding.

VR or IS can also contribute

In many cases, the AF system is looking at a larger area than perhaps you want it to. An insects eye for example is curved and it is quite possible for one part to be in focus and another out.

Manual focus is really the way to go when you are up close.

[botty1963]

Hi all, thanks for the replies. I have a Canon 7D and it's the Canon 60mm macro lens. Most of time I use manual and currently trying the 'set the focus and move in' method, the issue isn't just when using close up, but even using it as a general lens. For example, I had taken a close up which was ok, then just took some general none close up shots in and around the garden which prompted this post. I had noticed it before, but I used one of my other lenses as a test on the same shots from the same distance and they didn't hunt; the camera as set to automatic AF selection.

[DanK]

it can be close up of further away, so no particular pattern.

This rules out depth of field as a cause. A macro lens has the same depth of field at non-macro distances as any other lens with the same focal length and aperture. I have often used my 100mm macro as a short telephoto, and it functions just fine.

I suspect the main culprit is simply the enormous focusing range of macro lenses. That's why the focus limiting switch is so useful. If your lens doesn't have one, try this: if you are shooting something distance, pre-focus the lens at a distance that is not greatly different and see how fast the lens focuses.

[Stagecoach]

the camera as set to automatic AF selection.

Are you using a 'Single AF Point' ?

[Shadowman]

I have a short focal length macro lens (40mm) and I do have similar problems. It does have the focus limit switch that was mentioned by Dem and this seems to help with objects that I have to get very close to.

[rpcrowe]

I don't know about the Canon 60mm macro lens but my 90mm f/2.8 AF/SP Macro lens is fine for macro work (which I do manually) but is a PITA to auto focus for non-macro work like portraiture of humans... Granted, my model is one generation earlier than the present Di Macro offered by Tamron. That MAY be part of the problem. But, since I don't use the Tamron for anything except close-up and macro shooting, the slowness of non-macro focusing doesn't bother me...

I have lately been using my 100-400mm f/4.5-5.6L IS II lens for closeup shooting...

[Stagecoach]

I suspect the main culprit is simply the enormous focusing range of macro lenses

On my main macro lens there is a 270 degree rotation of the focus barrel (near to far focus adjustment) compared to way less on other standard modern lenses I have. This greater mechanical movement has to be dealt with by the motor so its likely that macro lenses are going to have a slower response time, hence more susceptible to missed/moving targets.

[GrahamS]

Steve, the Canon 60mm f2.8 EF-S macro USM is known to focus "slowly." If there is the slightest camera movement or subject movement while it is trying to achieve focus, it will hunt. This behavior is a common characteristic of this lens. A steady hand and pre-focussing manually will help. I owned the same combination, so I'm not guessing here.

[DanK]

Steve,

I missed your second post, where you noted the specific equipment. I have the same equipment, but I hadn't used that lens in a while, so I tried it out. I think your problem is just two things.

For my test, I used a single AF point (to avoid the risk of the camera switching between points) and a moderately distant object, the edge of a door perhaps 25 feet away (to take the thin DOF at macro distances out of the mix). I focused repeatedly, each time moving the initial setting on the lens to a shorter distance, hence farther out of focus.

Here's what I found.

The first thing is what Graham pointed out: the AF on this lens is slow. That doesn't make it hunt, but it makes it more annoying when it does hunt.

If the initial focusing distance on the lens is reasonably similar to the correct distance (in my trials, always closer), it focuses fine, but slowly.

If the initial focusing distance was far too close, so the image was very blurred and the camera couldn't find a point of contrast, AF always moved inwards first, which in my tests meant that it hunted--but only once. Once it started moving out, it locked on.

Underlying this is the huge focusing range of the lens. If the focusing range is more limited, you are less likely to encounter a situation where the camera can't do anything but guess which way to move. that's why many lenses, including at least one of Canon's more expensive macro lenses, have focus limiting switches.

Dan