Focus to Infinity

[justThorne]

I wonder often why that focus to infinity gets less attention than it does.


For example, if I'm out shooting grand cityscapes with my 50mm, I just AF onto a distant target, switch to MF, and then don't worry about focus anymore! In my experience, this has made cityscape/towering architecture shooting much simpler, because I can frame right away, rather than focus-then-recompose. (There are other advantages too.)


So does my own example provide some explanation? Would this strategy be useless with zoom lenses? (I only shoot with three primes.)


But I'm always surprised that the "distance to infinity" never comes up in lens reviews (especially for primes?). It seems to me like a very useful variable to know about a lens. I read a poster (over at FredMiranda, I think?) exult that he does street photography by just locking his 24mm on infinity (because it's so near on such a wide lens). Again, he could quit worrying about focus and just "frame on the first try" (and sometimes shoot without even looking through his viewfinder!) And this opened a huge door in my mind at the time.


So, first, is there something crazy wrong with this strategy (when circumstances suit it)? (I do carefully reset each lens when I pull it out of my bag and mount it again.)


Second, is there some reason that this "stat" never comes up in lens reviews? Does distance to infinity change on zoom lenses at different distances? Or do all lenses of the same length reach infinity at the same distance? If not, then surely this is an important stat?!?


I've learned a ton from reading (and experimenting) over the years - I'm none of a newbie anymore - but this subject seems only vanishingly mentioned. I'd like to write an essay on the subject soon, but I'm leery of trusting all my assumptions with so little exposure to anyone else's. ; )

[Tom Alicoate]

Thissounds likean interesting way to shoot. Is this the same thing as a hyperfocal distance? You can use a DOF calculator to to find it. Depending on the focal length, fstop and sensor size you can manipulate it to be closer or further away. I use a tripod for my landscapes and have been using liveview to guarantee sharp focus on what I want to see clearest. But, thats a whole different type of shooting than what you are talking about.


Tom

[justThorne]

Is this the same thing as a hyperfocal distance?

Quite the opposite! Focus to infinity captures everything behind the infinity distance with the same clarity (i.e., as if everything out there is on the same plane), and then degrades focus according to our depth-of-field as subjects fall short of that distance. (So it's like any traditional DOF, except in only one direction: toward us, but not further away from us.)


Hyperfocal distance intends to take advantage of the same phenomena, by bringing the focal plane closer, so that "all that infinity" at the rear is still within acceptable clarity, but more of the overall image appears in focus. (So there's "normal" DOF falloff closer than the focal plane, and minimally evident DOF behind the focal plane.)


So I say "quite the opposite!" because one requires calculations of one sort or the other, but the other requires no more than autofocus on a distant target, and then flipping the MF switch!


Often (especially with normal or shorter lenses), many people (seems to me) are probably worrying about hyperfocal distance when it'sunnecessary. If one isn't worrying about the ground in their composition (i.e., more or less "shooting UP") at tall buildings, mountain sides, sunsets or cloud formations, "focus to infinity" should entirely do the job.


Unless I'm missing something that I haven't found in my experience, which is why I've started this thread. (I've been meaning to write Bryan an email about this for months.)

[David Selby]

Hyperfocal distance has its time and place, its appropriate when you have near and far subject matter that you want similarly resolved with detail and sharpness.





Focusing at infinity is inefficient in that it wastes the depth of field behind infinity focus point. if the subject matter you care about is only very far away, then yes it makes sense. focusing at infinity has some leeway built into it so its never extremely accurate. however using live view and what not will obviously help.


I'm not really sure why someone would want to just walk around and not even look through their camera, focusing doesnt' take very long so why not try to be more efficient? If you're trying to save effort than I suppose to some that would be easier to them.


its inefficient to focus at infinity if you care about near and far ground subject matter, focusing at infinity and dropping aperture causes longer shutter speeds and exposure times, and introduces diffraction.

[justThorne]

Hyperfocal distance has its time and place, its appropriate when you have near and far subject matter that you want similarly resolved with detail and sharpness.

No doubt! (I do understand why landscape photographers shooting at hillsides are using it, among numerous other contexts.)



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I'm not really sure why someone would want to just walk around and not even look through their camera, focusing doesnt' take very long so why not try to be more efficient?

<div>Well, this guy was doing street photography, so a) he could "shoot from the hip" when he didn't want to broadcast that he was taking a picture, and b) he could pull up his camera, frame, and fire faster if the focus was already resolved. He was talking about the 24mm f/2.8, which reaches infinity at only ten or twelve feet. </div>
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Focusing at infinity is inefficient in that it wastes the depth of field behind infinity focus point. if the subject matter you care about is only very far away, then yes it makes sense. focusing at infinity has some leeway built into it so its never extremely accurate.

My 24mm f/2.8 is certainly extremely accurate at infinity - stunningly so, actually. My 100mm Macro might be less accurate, compared to its specialty. My 50 f/1.4 might definitely be less accurate - I'm not sure but years of experience with (three of) them make me feel infinity is its weak flank (though I'm actually talking about its AF performance, rather than the glass itself).


But I'm confused about "wastes the depth of field behind infinity focus point." Do you mean (to sometimes regret) that "it's all one big flat plane out there"? Yeah, lack of focal differentiation at a distance (from shorter lenses) would sometimes be frustrating, but my point here is to talk about the opposite times in which it wouldn't be.


And my biggest point, as I said, is to wonder why this is all discussed so rarely.



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[David Selby]

My 24mm f/2.8 is certainly extremely accurate at infinity - stunningly so, actually. My 100mm Macro might be less accurate, compared to its specialty. My 50 f/1.4 might definitely be less accurate - I'm not sure but years of experience with (three of) them make me feel infinity is its weak flank (though I'm actually talking about its AF performance, rather than the glass itself).


But I'm confused about "wastes the depth of field behind infinity focus point." Do you mean (to sometimes regret) that "it's all one big flat plane out there"? Yeah, lack of focal differentiation at a distance (from shorter lenses) would sometimes be frustrating, but my point here is to talk about the opposite times in which it wouldn't be.


And my biggest point, as I said, is to wonder why this is all discussed so rarely.

Thanks for the response! I think it is discussed fairly frequently actually, at least I have seen it discussed on various forums.


What i meant by wasting depth of field behind infinity focus point is... when you focus, the place you have focused is the sharpest area of a photo. You have a front DOF and Rear DOF that surrounds that focal plane like an oval inner tube. That tube is longer/shorter depending on aperture. If you focus at "infinity" you have an entire area of rear depth of field that is not used at all, it encompases no subject matter because you already put the focus point at the farthest subject. So up close subject matter (if there is any) is not resolved as well as it could have been. But like I said its only really a negative if you didn't want that "infinity" subject matter to be most focused.


Also what I was referring to is the fact that the manufacturer builds the infinity mark on the lens, but there is often times an ability to focus beyond that mark due to extra leniency provided by the manufacturer.