by ʇolɐǝz ǝɥʇ qoq

Submit your Photo
Hall of Fame

Please participate in Meta
and help us grow.

Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Take this lens I have for example, it has red values on the distance scale (not sure what do you call it exactly) next to the focus ring. What does these values mean?

share|improve this question
up vote 12 down vote accepted


If the markings show aperture values, those are hyperfocal-distance markings. It lets you know where the hyperfocal distance is at each full F-stop.

For example, one of the lines has a 16 in red next to it. That will let you set the focus to the hyperfocal distance at F/16.

If you do not know what the Hyperfocal-distance is you can read this short article. It even has a calculator to calculate the distance for you.

If the markings show focal-lengths, those are infrared focusing lines. They are used to adjust your focus for infrared photography.

share|improve this answer
Hmmm where exactly did you find the 16? I'm only looking at 28, 35, 50, 70, 135. – jon2512chua Jan 11 '11 at 15:55
Sorry, I could not read the numbers (too small) off the lens you linked to, so I looked at one of my lenses which is obviously not the same model. Looking another picture of the lens you sent, I realize this one is marked by focal-length on aperture. I will edit my answer to explain both cases. – Itai Jan 11 '11 at 16:10
Ok got it now. Thanks for explaining both cases, and also about hyperfocal-distance. – jon2512chua Jan 11 '11 at 16:22

IIRC, these are the focal length marks for IR (infrared) photography, but I can be terribly wrong...

EDIT: to be more precise, I think these lines mark the infinity focus for the different focal length (28-135) for IR photography.

share|improve this answer

That seems to be a DOF-marker for the different focal lengths, like there used to be markers for the aperture. The longer the focal length, the shallower the DOF. Edit: (make that "the shallower the relative DOF becomes" (due to magnification, thx ysap)).

Take, there you can see that it is "28,", "35", "50", "70" and "135".

Edit: Jukka Suomela actually read the article (and did not only look for a clearer picture, like me) and pointed out that Ken mentions them as infrared focus markers. That clearly makes a bit more sense.

share|improve this answer
are you shure about "The longer the focal length, the shallower the DOF"? I think the DoF gets larger the farther away your subject is (think Macro photography). Maybe you mean that the "relative/apparent" DoF is shallower? – ysap Jan 11 '11 at 15:37
@ysap- You are confusing focal-length and focus distance. DOF gets smaller at shorter focus distances AND it gets smaller at longer focal-lengths (and vice-versa). So Leonidas is correct. – Itai Jan 11 '11 at 16:12
The article in your link actually mentions that they are infrared focus indices (see also, e.g.,…), not DOF markers. – Jukka Suomela Jan 11 '11 at 16:17
@Itai - then it seems like I really have to refresh my memory regarding DoF relationships. I still find it hard to accept that it gets shallower with increasing FL, but for now I'll take your word for that ;-) – ysap Jan 11 '11 at 16:34
@ysap: Looking over the equations, I think you are right pointing out my mistake. Total DOF stays the same at fixed magnification of subject, but relative DOF (relative to distance) shrinks. I mostly ignore magnification, making relative DOF the important factor. – Leonidas Jan 12 '11 at 3:05

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.