travismcgee Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
daniel flather Posted August 3, 2010 Share Posted August 3, 2010 <p>How wet is wet?</p> Link to comment Share on other sites More sharing options...
railphotog Posted August 3, 2010 Share Posted August 3, 2010 <p>How high is up?</p> Link to comment Share on other sites More sharing options...
luis_g Posted August 3, 2010 Share Posted August 3, 2010 <p>Infinity is just as far as two infinities.</p> Link to comment Share on other sites More sharing options...
frank_dzambic Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
toddr Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
JDMvW Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
wayne_campbell Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
ed_v. Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
tom_harvey3 Posted August 3, 2010 Share Posted August 3, 2010 <p>...ad infinitum?</p> Link to comment Share on other sites More sharing options...
bob_rodman Posted August 3, 2010 Share Posted August 3, 2010 <p>How far is infinity, this is a question that only Buzz Lightyear can answer.</p> Link to comment Share on other sites More sharing options...
tom_cheshire Posted August 3, 2010 Share Posted August 3, 2010 <p>Infinity = 100 feet and beyond. </p> Link to comment Share on other sites More sharing options...
travismcgee Posted August 3, 2010 Author Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
david_henderson Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
paul_wheatland Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
steve_dunn2 Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
charles_clark1 Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
alan_bryant1 Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
bobatkins Posted August 3, 2010 Share Posted August 3, 2010 <p>Photographically, infinity starts at the hyperfocal distance.</p> Link to comment Share on other sites More sharing options...
jeff_livacich Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
travismcgee Posted August 3, 2010 Author Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
michael_p.1 Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
polka Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
thomas_lozinski Posted August 3, 2010 Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
travismcgee Posted August 3, 2010 Author Share Posted August 3, 2010 <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> Link to comment Share on other sites More sharing options...
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