Telephoto Lens Range Limiter - why only a close range limiter?

[garymak]

This question is open to anyone with a good, logical opinion or better, knowledge of the inner workings of Canon's corporate mind (such that it might be...)

Question: Telephoto Lens Range Limiter - why is there only a close distance limiter and not a long distance limiter???

On most of the zoom lenses I have (and EF or RF doesn't matter) there is a "range limiter" switch on the lens to speed up the autofocus mechanism for acquisition of targets far away.  The switch allows the AF to "skip past" objects within a close range (- for example, 3m in the case of the RD 100-500mm L, or 12m in the case of the 600mm ƒ11 -) supposedly to make for faster focusing and acquisition of the target and not be "distracted" by objects in the foreground.  Reasonable concept.

However, in my experience using these (and other) lenses, the acquisition of the target is often WITHIN these ranges and the inability to limit the AF from trying to find something between here and infinity and back when the subject is in close range inhibits the ability for faster focusing and acquisition of the target.  Often, for moving targets and/or small targets, the opportunity is lost because the AF can't, to use a phrase, find the end of its nose on its own face with both hands... AF, regardless of settings for "animals" regardless of the various "tracking sensitivity" modes, tends to grab the biggest things it can find first.  Those are usually large background objects, not smaller foreground objects.  It's also not very good at fast-moving targets, again, regardless of any of the "tracking sensitivity" settings.

Therefore, a paired limiter, say, of LESS THAN OR EQUAL TO whatever the long distance limiter is would seem to be a logical - and necessary - pairing and extremely practical .  Add the usual "off" switch to give you the full AF range, and you've got quite a useful set of tools.

As it is, the thinking seems to be that "the only thing that you'd ever want to shoot is far away anyway."

In shooting birds, for example, the inability to limit the AF range to the foreground to acquire the target that you know is going to appear quickly in the foreground results in lots of blurred shots of the subject with fine images of the neighbors' houses, and trees and telephone poles...

So, unless I'm missing something, I'd be curious if anyone has an explanation as to why there isn't a long-distance limiter on these lenses...

[garymak]

Can't quite say I follow you...  Are you saying that, even without a manual switch on lenses, there is an option I can set to limit the range of the AF focus so when I push the shutter button the AF will just hunt WITHIN a prescribed shorter-distance range and not blast off hunting to infinity?  I don't follow exactly what you meant, but I don't think you were implying that.  I've never heard of such a thing, only manual switches...  Thanks for any clarification...

[kvbarkley]

Look at the focus scale on this lens:

Note that the rotation required to get from 10 ft to infinity is less than the rotation to get from 1.5 to 2 feet. By locking out the close distances you reduce the amount of rotation to focus for a large range of distance. For example, in this lens, if you would limit the focus to 3 feet, you would knock off about half of the rotation required.

[garymak]

Right.  Gotcha. That's just manual focus though.  That's what we did in film days with manual lenses (which had DOF markings as well.) Or today, with manual focus settings on AF lenses (which are most of them.)

 One can manual pre-set the distance and hope the subject falls into that range, or, preset the distance and then start fiddling with the focus as soon as one can react when the subject pops into the general range and try to fine-tune it...

However, I am referring to using an auto-focus mechanism to limit the "seek focus" range so as to make the autofocus mechanism quicker and more responsive so it doesn't have to go from minimum to infinity all the time and then usually miss the objects up close.  Most lenses have a short-distance limited that will cause the AF to start from mid-range to infinity.  And "Peter" and "Wadizzle" mentioned a couple of lenses that have that function.  None of the lenses I use have had that and I've personally never seen it (so that was news to me) and I was wondering why it then isn't standard on lenses where there is a distance limiting switch, why not have both far and near limiting switches....?

[ebiggs1]

Manufacturers decide on what features they want to spend R&D on. They decide if that investment is worth the return or is a significant benefit to the consumer. In some lens the AF is fast enough that the extra cost would not be worth the additional final price. All manufacturers want to keep prices as low as possible.

[p4pictures]

The focus limit is a switch on certain lenses. Generally you will find these limit switches on telephoto and some macro lenses. 

[garymak]

Hmmm, that explains the internal mechanics of how a lens works.  Thank you.  But you are missing the point of limiting the focus-hunting range to shorter distances.  "...then avoiding the lots of steps at the closer distances makes the lens respond faster over a longer working range."  Yes that's true.  But we are not talking about long-range focusing, rather, short-range focusing.  EQUALLY, avoiding the auto-focus hunting at a longer range and concentrating the focus on a shorter range will not only make the lens respond faster over the shorter range, but also eliminate it unnecessarily locking on a subject in the background beyond the foreground, as it often the case, and missing the close-in shot altogether.

So, there are TWO reasons to want to limit the focus-range to a shorter range, and one of the big reasons is avoiding locking on to a subject way far off when the desired subject in in close.  All the mechanics of how many increments it takes to focus short vs long range is irrelevant.  If you can eliminate a certain range and leave only a subset of the full range for the lens to work with, it will be faster than hunting all over the full range.  That's just logical - and that's also just math.  A sub-set is by definition, less than the full set.   

So, again, I'm making a case for a long-range limiting switch as equally important to a short-range limiting switch. 

[Waddizzle]

“ So, again, I'm making a case for a long-range limiting switch as equally important to a short-range limiting switch. “

I am afraid that you are entirely missing the point.  You appear to be arguing that this feature should be mandatory on every lens on the market.  They don’t, and they won’t.

Some lenses do have that feature and some do not.  The lenses that do tend to be more costly than lenses that don’t.  My apoligies if your lenses do not have a feature that you desire.

[garymak]

I absolutely did not make any statement on it should be mandatory.  Not sure where you drew that conclusion from, so let me clarify: if there's a single switch with short-range limiter position and "off" position on a lens, why not have a long-range limiter position as well. I already made the case for the need. And if a lens doesn't have the switch at all, well, then it doesn't have a switch at all. I did not suggest putting one on where no switch exists.  And as far as the cost, the incremental cost of adding a long-range limiter is practically nothing, as all the mechanical components are in place already, costs covered.  It would merely be switching on a software algorithm, so you can't argue that there's any "increase in physical cost" and in terms of s/w development costs, minor.  

This discussion was initiated concerning why if there's a short-range limiter on lenses they don't include a long-range limiter.  Not sure how/why the discussion veered sharply off.  It was an intellectual discussion on the logic of not including them, since it isn't logical based on cost or lack of usefulness.  No need to apologize. 

At this point, having not read any valid on-point logic about why they should not been included, I've got my answer then and there's no point in continuing to discuss this, so I'll bring it to a close.  Thank you all for your thoughts.