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04-21-2012, 12:42 AM   #1
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How to use the distance scale on lens.

Hi all. Can anyone tell me how to use the distance scale on my Pentax DA 16-50mm lens. I have been reading about hyperfocal distance for landscape photography. But I dont understand how this distance scale works as it doesnt seem to be affected by the apeture setting or the focal length. It just moves in relation to the focus ring no matter what apeture or focal range.

04-21-2012, 01:04 AM   #2
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The distance scale is used in MF mode typically. Importantly you need to ensure that you set your lens in automatic aperture (A mode on the aperture ring of the lens). (Edit: I do not have the DA16-50mm and hence my comment is more general.)

I use regularly the distance scale to pre-focus my MF lenses (eg VL58mm, CZ85mm) and it is very useful IMHO. Then in your camera, you set the aperture, shutter speed, .. depending upon your camera mode and settings.

Hope that the comment will help.

Last edited by hcc; 04-21-2012 at 01:53 AM.
04-21-2012, 01:13 AM   #3
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QuoteOriginally posted by jpeldrid Quote
I have been reading about hyperfocal distance for landscape photography.
The DA*16-50 lacks a Depth of Field scale, so you cannot use it for calculating hyperfocal distance.
04-21-2012, 02:31 AM   #4
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QuoteOriginally posted by selar Quote
The DA*16-50 lacks a Depth of Field scale, so you cannot use it for calculating hyperfocal distance.
That's right. For a lens (like every DA) that lacks a DOF scale, you need to go to DOFMASTER and plug in the relevant numbers.

If you *had* a lens with a DOF scale, here's how it would work:

We use what's called zone focus; if one end of the zone extends to infinity, it's called hyperfocus. The distance we set the focus to for a desired DOF is the prefocus. I have never seen a DA-type lens (built to project an image on an APS-C frame) or any AF lens with a DOF scale. AFAIK only manual FF lenses seem to have those scales, and they're calibrated for a FF frame, not for APS-C.

We need to adjust their usage a bit for APS-C. I call it fudging the f-stops. For hyperfocus (DOF out to infinity) I fudge by about 1.3 f-stops, just to ensure that infinity IS acceptably sharp. For closer zone-focus I'll fudge by 1 f-stop but I'll consider the boundaries of the DOF zone a bit iffy.

Here's an example: I'll set my Tokina 21mm to f/11. For hyperfocus, I'll fudge by ~1.3 f-stops and set the infinity mark just inside the f/8 mark, say around f/7. I'll read the near DOF distance from just inside the other f/8 mark. I'll see that my prefocus is 2m and DOF extends from around 1m to infinity, for sure!

Another example: I'll set my Komura 35mm to f/16 and prefocus to 2m. (The Komura 35/2.5's marks are much easier to read than the little Takumar 35/3.5's!) I'll read the zone distances at the f/11 marks: 1.25m to 5m. I'll expect most everything within that zone to be acceptably sharp. This is good for closer work.

But you need old manual FF lenses to do on-lens DOF readings. Otherwise, use the DOFMASTER or something similar. Good luck!

04-21-2012, 04:23 AM   #5
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QuoteOriginally posted by RioRico Quote
But you need old manual FF lenses to do on-lens DOF readings
Not really, both the FA 31 and the FA 20 have DOF scales. I think my F and FA series lenses have the DOF scale, but am too lazy to pull them out to check. It seems that the DOF scale was lost in the transition to APS-C, possibly due to the unreliability of a DOF scale with the new format.

But you do have a point, the DOF scale lost most of its relevance in the transition to autofocus.
04-21-2012, 07:39 AM   #6
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QuoteOriginally posted by selar Quote
Not really, both the FA 31 and the FA 20 have DOF scales. I think my F and FA series lenses have the DOF scale, but am too lazy to pull them out to check.
OK, I'll admit that I have only one AF prime, the FA50-/1.4, which does NOT have a DOF scale. I didn't remember seeing scales on pix of other Pentax AF primes, so I hastily generalized. Such scales are definitely not on any AF zooms I've seen, and those on MF zooms are pretty useless. But DOF scales seem to exist mainly (mostly) on MF primes, the bigger and wider the better.

Will zone.focus|hyperfocus become a lost art? Our nice dSLRs should maybe have DOF ranges displayed in VF and screen. How much firmware upgrade would that take?
04-21-2012, 07:56 AM   #7
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QuoteOriginally posted by selar Quote
Not really, both the FA 31 and the FA 20 have DOF scales. I think my F and FA series lenses have the DOF scale, but am too lazy to pull them out to check. It seems that the DOF scale was lost in the transition to APS-C, possibly due to the unreliability of a DOF scale with the new format.

But you do have a point, the DOF scale lost most of its relevance in the transition to autofocus.
Ummmm...all of the lenses you mention are FF. It would be possible to add a DOF scale for APS-C, there is no issue of reliability related to sensor format per se. The primary issue would be that the focus throw on many (most...all?) of the DA lenses is pretty short and the scale would be too compressed to be of much use.

As for the relevance of a DOF scale in an AF world...what does AF have to do with it? You use the scale when other focus systems (viewfinder or AF or whatever) are not useful for the subject of shooting mode. Take setting the hyperfocal for instance. Setting up this way (fixed aperture, fixed focus point) essentially configures the camera as a simple point & shoot. It is useful for street shooting where the task is to simply frame and capture. AF is pretty much useless because you may well lose the shot before focus locks and manual focus has much the same issue.

Here are a few bullet points to help the OP and others on their journey:
  • DOF scales are intended for the target format the lens was designed for
  • DOF itself is an illusive concept and even in the best case, the scales only give "acceptable" focus over the indicated range
  • Some lenses have them and some don't
  • Unless you are working with a camera with no focus system and/or no means to visually check DOF, the scale's usefulness is limited


Steve

Last edited by stevebrot; 04-21-2012 at 10:11 AM.
04-21-2012, 08:28 AM   #8
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QuoteOriginally posted by selar Quote
Not really, both the FA 31 and the FA 20 have DOF scales. I think my F and FA series lenses have the DOF scale, but am too lazy to pull them out to check. It seems that the DOF scale was lost in the transition to APS-C, possibly due to the unreliability of a DOF scale with the new format.

But you do have a point, the DOF scale lost most of its relevance in the transition to autofocus.
DOF field scales on lenses were made based on acceptable circles of confusion and the thread pitch of the focusing ring. They are no longer useful on many modern AF lenses that have extremely steep focusing. The scale would be compressed so close together that it is useless. And I suspect if they made a AF lens with a pitch to support a DOF scale you would not be happy with the AF speed.


Last edited by tuco; 04-21-2012 at 08:35 AM.
04-21-2012, 09:31 AM   #9
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QuoteOriginally posted by tuco Quote
And I suspect if they made a AF lens with a pitch to support a DOF scale you would not be happy with the AF speed.
...you mean something like my Sigma 50/2.8 EX DG Macro?

I should have made that a

The Sigma macro has a VERY long focus throw and it does have a focus scale...with one index...at f/32...with marks immediately to either side of the focus mark...



...focus scales being quite meaningless for a lens with a huge focus range. The marks on the lens are fantasy. Oh, and I might add that the AF performance of the Sigma is pretty good for normal shooting, but only barely acceptable in the macro range.

In addition to the Sigma, I do have two other AF lenses with focus scales. Both are Pentax product and one is a current offering and both have quite usable focus throw for manual focus and both have decent AF performance as well:
  • Pentax-FA 35/2
  • Pentax-FA 77/1.8 Limited
I believe that most, if not all of the FA series have scales.

Steve

Last edited by stevebrot; 04-21-2012 at 09:57 AM.
04-21-2012, 09:54 AM   #10
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QuoteOriginally posted by stevebrot Quote
DOF itself is an illusive concept and even in the best case, the scales only give "acceptable" focus over the indicated range
I should have added that the scales on many lenses are incredibly optimistic. The DOF app on my phone, calculates the hyperfocal at 34.3' (10.5m) for 35mm film at f/8 with a 50mm lens. My Jupiter-8 50/2 (based on the Zeiss Sonnar 50/2) indicates the hyperfocal at 26' (8m). The differences may be attributed to different notions of "acceptable" sharpness with the calculator opting for a stricter standard.

In practice, it may be easiest to simply do a little testing before heading into the field and taping an index mark on the lens barrel indicating your optimal focus point for your intended subjects.


Steve
04-21-2012, 10:34 AM   #11
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QuoteOriginally posted by RioRico Quote
That's right. For a lens (like every DA) that lacks a DOF scale

Pentax Super Wide Angle SMCP-DA 14mm f/2.8 Autofocus Lens 21510

Here's one out of three; although it's easy for most people to overllok these items.
04-21-2012, 08:17 PM   #12
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I'm doubtful about the usefulness of distance markings in general on some lenses. Live view means you can check the accuracy of focusing very easily, and on at least two of my M-series lenses the distances as indicated on the lens markings are off - by a couple of mm of lens rotation at least. This can be critical.
04-21-2012, 10:36 PM   #13
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QuoteOriginally posted by timo Quote
I'm doubtful about the usefulness of distance markings in general on some lenses. Live view means you can check the accuracy of focusing very easily, and on at least two of my M-series lenses the distances as indicated on the lens markings are off - by a couple of mm of lens rotation at least. This can be critical.
Marks on fairly small and/or short-focus-throw and/or long lenses are indeed useless. I mentioned earlier that I can use the marks on my big W-Komura 35/2.5 but not the tiny SuperTak 35/3.5. If the throw is less than 180 degrees, or the lens is longer than 60mm, you can pretty much forget it -- they're a joke. I can use such zone-focus only on a few select lenses.
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