How Far is Infinity?

Discussion in 'Canon EOS' started by travismcgee, Aug 3, 2010.

  1. 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!
     
  2. How wet is wet?
     
  3. How high is up?
     
  4. Infinity is just as far as two infinities.
     
  5. A good zen question to ponder when you're set up and waiting for the light to change.
    Maybe it's all just varying degrees of infinity?
     
  6. you need a DOF calculator thingy, to see where the CoC is acceptably sharp at the closest distance, when focus is set to infinity
     
  7. 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.
    The answer depends on the lens and on the f/stop the lens is set to. What I am talking about is "hyperfocal distance" (link).
    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.
    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.
     
  8. 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?
     
  9. ...what if something is beyond infinity? Will it still be in focus?​
    Yes, but you can't see it because it would take forever for the light to reach you.
     
  10. ...ad infinitum?
     
  11. How far is infinity, this is a question that only Buzz Lightyear can answer.
     
  12. Infinity = 100 feet and beyond.
     
  13. Infinity = 100 feet and beyond.

    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!
     
  14. 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?
     
  15. 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.
     
  16. 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.
     
  17. 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.
     
  18. 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.
     
  19. Photographically, infinity starts at the hyperfocal distance.
     
  20. 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.
    BTW, a lot of long lenses focus beyond infinity. Though they usually don't actually focus beyond infinity, under some conditions they do. Though it's infinity, not beyond infinity when they do. Got that?
     
  21. 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?

    Not to be flippant, but why wouldn't you? I don't shoot portraits, so it would never occur to me not to use the sharpest aperture possible.
     
  22. 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.
     
  23. "If you are not sitting on the knees of your model, you are damn too far"
    It's not me to blame for saying that, it's Robert Capa
    Paul
     
  24. 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.)
     
  25. As a mathematician, infinity is a funny concept. In my area of mathematics, any value above 3 is equivalent to infinity.

    What branch of math is that? Are you a computer guy working in base 2?
     
  26. Ooops! didn't see it is already posted :((
    I've read somewhere that The point of interest is considered to be at infinite distance when its distance from the focal plane is 200 times the focal length of the lens(in cm.). So, 'infinity' varies with the focal length of the lens used.

    FOCAL LENGTH INFINITY(FEET) INFINITY(METER)
    20mm 13 4
    24mm 16 5
    35mm 23 7
    50mm 33 10
    100mm 66 20
    200mm 131 40
    300mm 197 60
    400mm 262 80
    500mm 328 100
    1000mm 656 200
    etc.
     
  27. Infinity is sort of like trying to figure out the speed of dark (as the speed of light is a known value,) the sudden lack of light should equal the speed of dark, no?
    Take your camera and go out to take a few more images...
     
  28. 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.​
    unfortunately, the calculations on lenses, and indeed in the iphone app, are well outdated for current digicam sensors, film, and modern optics. there still is a hyperfocal distance, it's just not going to be where the scale/chart says it is. a combination of infinity focus, and the the aperture that yields the best compromise between contrast, diffraction, and sharpness will usually give the best results. and that aperture will change with the focal length, ie the wider the lens, the larger the f/stop.
     
  29. The only problem with the 200xFL rule of thumb is it doesn't work. Depth of field, therefore hyperfocal distance, varies with aperture.
    It also varies with format; in the calculations for hyperfocal distance the Circle of Confusion is larger with larger formats. The degree of enlargement, on a practical level, will also make a difference. Even discounting those points, the fact remains that the aperture will have the greatest single effect on the hyperfocal distance of any given focal length.
    What Alan Bryant said is right. What Bob said is also right, in that the infinity setting for any given aperture extends from the infinity mark on the lens to the mark on the lens (if there is one) corresponding to the hyperfocal distance. In another sense, infinity starts with the near limit of DoF.
    Go to http://www.DOFmaster.com for a depth of field and hyperfocal distance calculator, plus HD and DoF charts for many different focal lengths, apertures and formats.
    For example, with 24x36mm format the hyperfocal distance for a 50mm f/1.2 lens:
    @ f/1.2= 230.1 feet, with Dof at that subject distance ranging from 115 feet to infinity.
    @ f/1.4=193.5 feet, with Dof at that subject distance ranging from 96.7 feet to infinity.
    @ f/16= 17.3 feet, with Dof at that subject distance ranging from 8.64 feet to infinity.
     
  30. Dave, it's not necessary to do portraiture to use an aperture other than the sharpest one.
    I consider control of depth of field to be one of the most important tools I have. I will accept less than optimal resolution sometimes to get maximum DoF, or even to minimize flare ghosts if there is a bright light source in the frame. With long focal lengths or macro, sometimes I need all the DoF I can get to get the picture I'm after. For that matter, I have used my 17mm at f/16 on my 35mm cameras many times, to get extreme near/far definition, even though absolute quality is lowered by doing so.
    Sometimes instead I'll want to use a wide aperture to isolate the subject, to get a look I'm after, or to blur a distracting background and/or foreground.
    If you always use the same aperture with a lens, you're never going to discover the full range of possibilities for different images of your subjects.
     
  31. I thought for a while that it is very far...
     
  32. How far is infinity?
    When this thread has run its course, print it out, and lay the pages end to end. Place your camera at one end of the string of pages. The other end will be infinity. ;-)
    I like Ed V's answer the best -- true, amusing, and thought provoking.
     
  33. I think we've solved this one. Let's move on to decide how many angels fit on the head of a pin. And what focal length lens should you use to get them all in the picture.
     
  34. Charles Schultz has already established that the answer to the angels/pin question is "Eight if they're skinny, four if they're fat". And the proper lens for capturing them is the MP-E 65mm.
     
  35. Dave, it's not necessary to do portraiture to use an aperture other than the sharpest one. I consider control of depth of field to be one of the most important tools I have.

    No argument here, Jeff, but the initial condition was a flat plane or all subjects so far away the lens will focus at infinity, so DOF is a non-issue, in which case the sharpest aperture is appropriate, unless you're trying for an intentional fuzzy look, I suppose, but there are probably better ways to achieve that than with diffraction.
     
  36. I can almost hear Buzz Lightyear now...
     
  37. For Dave:
    My area of study was numerical solutions of dual singluar integral equations, with an application focus of fracture mechanics.
     
  38. The lenght for this thread to go on. Pretty far I guess...
     
  39. Dave-
    OK, understood. Thought you meant in a broader sense.
    BTW, I think it's best to be conservative with the hyperfocal distance. I don't really trust the lens markings to be dead accurate, if they are even there, and the coarseness of the focusing screen tends to make it difficult to determine DoF with absolute accuracy. At the hyperfocal limit the DoF is on its way out of being in acceptable focus so it becomes critical not to exceed it.
    Which brings up an important point. DoF as a term defines a range of acceptable focus. While a general standard exists by which acceptable DoF is defined, an individual's own standards for acceptable might be different. As mentioned earlier, degree of enlargement makes a big difference to what looks acceptably sharp, too.
     
  40. How far is infinity?
    ... right up to the moon - and back!
     
  41. 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.)​
    Thank you. I knew is was some multiple of the focal length, but I'd forgotten the value. And yes, it actually is important to know. Say you to set the infinity stops on a camera like a crown or speed graphic. You need a target at the infinity distance for the lens you're using. Focus on the ground glass and set the infinity stops accordingly. Another thing to notice is that the image of a target placed at 200 times the focal length of any lens will be exactly the same size on the ground glass, film plane, sensor plane, whatever. Easy to do when you have the right know how.
     
  42. Are we talking a different concept? I mean, I know from experience that 200 times focal length for an object distance does not necessarily result in an object which is in adequate focus. The 200xFL rule does not even address aperture. So what is the concept behind the rule? I have to figure at this point that it refers to something other than what it seems to refer to.
     
  43. This is ancient "rule" was for LF lenses; often the fastest say F4.5 as Tessar; and often just F5.6 or F6.3.
     
  44. Six
     
  45. There seem to be an infinite amount of answers to this question
     
  46. Thanks, Kelly. So if Kelly is right, what relevance does the 200xFL rule have to Canon EOS lenses?
     
  47. Sorry, I just have to add another tongue-in-cheek value: If I am not mistaken, the edge of the universe is now thought to be 13.7 billion light years away. At least at that point, the speed at which objects are receding very nearly approaches the speed of light. (I'm sure someone here has more knowledge in this area than I do, though.)
     
  48. Maybe it's best to ask Buzz Lightyear. He's been there.
     
  49. How deep is the ocean? How high is the sky? I. Berlin
     

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