How Far is Infinity?

<p>As you know, if the subject is a flat plane or so far away that the lens will focus at infinity, you should use your sharpest aperture. So how far away is infinity? A hundred yards? A half mile? Do you look at the barrel of your lens to see where it focused or do you have a rule of thumb? Thanks!</p>

<p>How wet is wet?</p>

<p>How high is up?</p>

<p>Infinity is just as far as two infinities.</p>

<p>A good zen question to ponder when you're set up and waiting for the light to change.</p>

<p>Maybe it's all just varying degrees of infinity?</p>

<p>you need a DOF calculator thingy, to see where the CoC is acceptably sharp at the closest distance, when focus is set to infinity</p>

<p>The more meaningful question in relation to lenses is not how "far" infinity is (that, not surprisingly, is infinity), but how "close" infinity on the lens is so that the image on the film/sensor plane is close enough to focus to fool the human eye.</p>

<p>The answer depends on the lens and on the f/stop the lens is set to. What I am talking about is "hyperfocal distance" (<a href="http://en.wikipedia.org/wiki/Hyperfocal_distance">link</a>).</p>

<p>On my Zeiss Tessar 50mm f/2.8 at f/2.8 everything from roughly 10 meters to infinity will be in focus (more or less). At f/16, the Tessar is in focus from less than 2 meters to infinity. Or to put it as you did, if the lens is set to infinity mark, then at f/2.8 depth of field will cover to 20 m or so, at f/16 to 3.5 m.</p>

<p>Older, prime lenses used to have markings showing all this, but these became difficult with zoom lens (hence all the curving lines on the barrel), and seem to have mostly and literally dropped off the scale with AF lenses.</p>

<p>Infinity is somewhere beyond 25-30 feet from the camera. A better question is what if something is beyond infinity? Will it still be in focus?</p>

<blockquote>

<p>...what if something is beyond infinity? Will it still be in focus?</p>

</blockquote>

<p>Yes, but you can't see it because it would take forever for the light to reach you.</p>

 

<p>...ad infinitum?</p>

<p>How far is infinity, this is a question that only Buzz Lightyear can answer.</p>

<p>Infinity = 100 feet and beyond. </p>

<p><em>Infinity = 100 feet and beyond.</em><br>

<em> </em><br>

That's what I was looking for -- a rule of thumb that says "All subjects in this image are more than 100 feet away, so this looks like a job for f/8." Many thanks!</p>

<p>I'm not sure why you think that you need to use the "sharpest aperture" when your subject is a long way away. Could you say? </p>

<p>I was always taught to check for infinity with ground glass at the film plane, using a loupe aim at an object like a sign or a sharply defined object that is at least 300 feet away.</p>

<p>How far away is acceptably close to infinity will depend to some degree on the focal length of the lens. A distance that is close enough to infinity for an ultrawide lens may not be for a supertele.</p>

<p>I have enjoyed this discussion a bunch. As a mathematician, infinity is a funny concept. In my area of mathematics, any value above 3 is equivalent to infinity.</p>

<p>It really depends on the focal length and aperture you're wanting to work with. For an extreme example, with the 1200mm f/5.6 on full frame, the hyperfocal distance (which seems to be more or less what you mean by "infinity") is over 5 miles away. I've shot with the 200mm f/2, and it has no difficulty blurring a background with subjects 40 feet away. On the other hand, with a 24mm at f/8, the hyperfocal distance is a mere 8 feet.</p>

<p>Photographically, infinity starts at the hyperfocal distance.</p>

<p>That answer right there- what Bob said. It is not correct that infinity is something like 100 ft from the camera, and if you look through my 500 or 1000mm lens on one of my 35mm cameras you'd know that's false. It depends, as has already been explained.<br /> BTW, a lot of long lenses focus beyond infinity. Though they usually don't actually <em><strong>focus</strong></em> beyond infinity, under some conditions they do. Though it's infinity, not beyond infinity when they do. Got that?</p>

<p><em>I'm not sure why you think that you need to use the "sharpest aperture" when your subject is a long way away. Could you say?</em><br>

<em> </em><br>

Not to be flippant<em>, </em>but why wouldn't you? I don't shoot portraits, so it would never occur to me not to use the sharpest aperture possible.</p>

<p>FWIW, I downloaded an app for my iPhone that is a DOF calculator. It adjust for various makes and models. It allows you to set lens, aperture, and distance and shows you the DOF. IT identifies hyper focal distance. Very easy to use. There are a number of such apps available.</p>

<p>"If you are not sitting on the knees of your model, you are damn too far"<br />It's not me to blame for saying that, it's Robert Capa</p>

<p>Paul</p>

<p>According to Steve Simmons in Using the View Camera, "An object is considered to be at an infinity position when its distance from the camera is 200 times the focal length of the lens." So for a 50mm lens that would be 10,000 mm or 10 meters (30 feet.)</p>

<p><em>As a mathematician, infinity is a funny concept. In my area of mathematics, any value above 3 is equivalent to infinity.</em><br>

<em> </em><br>

What branch of math is that? Are you a computer guy working in base 2?</p>