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01-04-2013, 12:32 PM   #1
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Help with lens markings

I have just bought a Pentax A 50mm 1.4 and it is my first "manual" lens. Can anyone explain what the markings mean?

Here is a pic as an example: https://www.pentaxforums.com/lensreviews/data/28/smc_Pentax-A_50mm_F1_7.jpg

Obviously I have the aperture set to A. However, what do the other markings mean? So taking the pic above as an example, what are those markings supposed to tell me? Is it something about what the "in focus" range would be for the different possible aperture setting? Eg in above is it saying that if my aperture was set to 16 then everything from around 1.5 to 3m away would be in focus?

Hope that question makes sense...

01-04-2013, 12:38 PM   #2
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That is correct. That is called the focus zone markings - at the selected aperture markings, all the distance between the two markings will be in focus. It is very helpful when determining the hyperfocal distance.
01-04-2013, 12:38 PM   #3
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The numbers on the ring with the A on it are the selectable aperture values. Above the aperture ring is the DOF scale which shows you what will be in focus at various aperture settings.

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01-04-2013, 12:44 PM   #4
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QuoteOriginally posted by thechumpen Quote
Eg in above is it saying that if my aperture was set to 16 then everything from around 1.5 to 3m away would be in focus?
That is correct and as noted is very helpful with hyperfocal distance and shooting landscapes. However, the markings were scaled for a full frame camera and I have seen it suggested several places that you discount them by at least one f-stop if you are using an APS-C camera. I have taken that on faith and it works but if someone has a good (simple) explanation of why you need to adjust for APS-C I would appreciate it.

01-04-2013, 01:03 PM   #5
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Great, thanks. Now, hyperfocal distance? I just looked that up on Wikipedia and it gives a few meanings I don't fully understand. Easy there an easy description of what that means and the practical implication that a simpleton like me can understand?
01-04-2013, 01:05 PM - 1 Like   #6
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Hyperfocal distance is where you set your aperture, set infinity to the marking on the right, and everything from the marking on the left to infinity will be in focus. It's very useful in shooting landscapes and in street shooting.
01-04-2013, 01:26 PM   #7
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Ok, that makes sense if you swap your left and rights over from your answer I think. So for example if I set my infinity symbol on the left hand 16 then it's saying everything from 8ft to infinity is in focus.

So next question is how do I do that on a newer lens with no markings? Eg if I wanted to use my 18-50 kit lens at 18mm for a landscape. How do I know what the hyperfocal distances are, or is that where you need to know the formulas or just memorise some rough rules?
01-04-2013, 01:29 PM   #8
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Memorize the general ones, or draw markings on your lens.

For example, the easiest rule I ever had was my Sigma 10-20mm, at F8, everything from 5ft to infinity was in focus.

01-04-2013, 01:37 PM   #9
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Thanks so much for your answers. What a great forum.
01-04-2013, 01:47 PM   #10
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Hyperfocal distance is one aspect of a broader concept, depth of field, which is often abbreviated as DOF. In addition to the scales on some lenses, and the use of calculators, you have the option of using the DOF preview function on your camera to directly view the effects of stopping down your lens. There is lots of info about DOF to be found on the Web and in books.
01-04-2013, 01:58 PM   #11
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Yes, DOF was one if the first things I stumbled on when my learning began a month or so ago and I have read up on it lots. Also currently reading Understanding Exposure by Bryan Peterson which is teaching me lots. I haven't tried DOF preview yet so will take a look at it, thanks.
01-04-2013, 04:11 PM   #12
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QuoteOriginally posted by jatrax Quote
That is correct and as noted is very helpful with hyperfocal distance and shooting landscapes. However, the markings were scaled for a full frame camera and I have seen it suggested several places that you discount them by at least one f-stop if you are using an APS-C camera. I have taken that on faith and it works but if someone has a good (simple) explanation of why you need to adjust for APS-C I would appreciate it.
I'm confused too. Smaller sensors have wider DOF, so I would think that the markings on a FF lens would be on the conservative side. On the other hand, the sensor crop of the image tends to magnify the image, so that would tend to magnify the OOF areas. Not sure why one factor would tend to outweigh the other.
01-04-2013, 04:26 PM   #13
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Most of what I understand came from reading various posts on this forum. For example read post #4 on this thread: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/183231-how-use...cale-lens.html Sadly RioRico does not seem to be with us any longer so I cannot ask him.

I wonder if the difference is only that when DOF scales were put on lenses, printed output was smaller and therefore the acceptable degree of focus was not as critical? With everyone looking at things 1:1 on big monitors maybe the scale is not as relevant anymore? Just thinking out loud. I would really like to understand how to better use those scales on my lenses with APS-C.
01-04-2013, 05:34 PM   #14
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QuoteOriginally posted by jatrax Quote
Most of what I understand came from reading various posts on this forum. For example read post #4 on this thread: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/183231-how-use...cale-lens.html Sadly RioRico does not seem to be with us any longer so I cannot ask him.

I wonder if the difference is only that when DOF scales were put on lenses, printed output was smaller and therefore the acceptable degree of focus was not as critical? With everyone looking at things 1:1 on big monitors maybe the scale is not as relevant anymore? Just thinking out loud. I would really like to understand how to better use those scales on my lenses with APS-C.
Sensor size does not affect DOF directly. A lens stopped down to a particular aperture will always produce the same DOF, no matter what size sensor is used.

There is a pretty good two-page discussion of DOF on the Canon Europe website: Canon Professional Network - Depth-of-field

The criteria used for DOF scales are somewhat arbitrary. Best approach is to determine through experimentation what you consider acceptable sharpness, and what apertures give you that sharpness at appropriate shooting distances. Compare your own results with the DOF scales on your lenses and develop a personal fudge factor if necessary.

For example, for FF I tend to close down one more stop than recommended by DOF scales. For APS-C, I use the scales as-is.

In this case I think it is much wiser to simply take a bunch of pictures at different apertures and focal lengths and draw your own conclusions than to agonize over theories.
01-05-2013, 02:07 AM   #15
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I've learned from all this that I appear to be using the wrong technique when taking landscape pictures. Taking my 18-50 kit I normally set it at small aperture and 18 zoom then autofocus on the horizon, or something far away in my scene. Sounds like what I should be doing us using manual focus to focus just a few feet ahead, or just autofocus on the ground in front me then recompose. Sound about right? Then I can trial and error a bit to see what focus distances give best results.
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