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03-14-2014, 02:58 PM   #1
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Hyperfocal Distance/Focusing Question

Quick question on something I've been trying to wrap my head around. I have my DA15 Limited attached to my K-5 99% of the time I use it and I'm primarily shooting landscapes/scenery and i typically let the autofocus do it's thing, usually on something very far in the distant (mountains, sunset, whatever). A lot of times though, I will look at the focus ring and it won't be at infinite but before it. What I'm wondering is why that is, and is there a difference if I just quick shift it to infinite? If I'm shooting landscapes should I just keep my camera in manual and always have it on infinite? What is the difference? Typically I will stop down to f/8-11 so I haven't really noticed any focus issues but I'm a little confused.

03-14-2014, 03:02 PM - 1 Like   #2
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Many lenses go past infinity due to variations in the actual location of infinity focus. It's best to stick with what the camera picks.

Having said that, if you let your camera focus to infinity and then set the camera to manual focus, you should be able to leave the focusing ring alone and let the hyperfocal distance do its thing

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03-14-2014, 03:14 PM   #3
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I know what you mean about some lenses going past infinite and I've read about people just cranking the focus all the way to one end and having problems, but on the DA15 it stops precisely on the infinite mark. I don't get it though, is there a difference? Using the hyperfocal chart on my lens, as long as I'm not focusing on anything 1.5 feet or closer then it really shouldnt matter, no? I'm just confused about the concept with landscape photography. Infinite should produce a focused shot everytime regardless, right?
03-14-2014, 04:43 PM   #4
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Hperfocal depends on aperture and size of COF

Basically at 22.5mm equivalent, your hyper focal distance changes depending upon aperture.

Here is a basic table for your lens (assumes you want infinity in focus for a "normal" Circle of Confusion):

22.5mm @ f/2.8 = 22.7ft
22.5mm @ f/4.0 = 29.4ft
22.5mm @ f/5.6 = 20.8ft
22.5mm @ f/8.0 = 14.7ft
22.5mm @ f/11 = 10.4ft
22.5mm@ f/16 = 7.4ft

also note: that the image will be noticeably sharper at the given focal length and that infinity would have the same overall sharpness independent of focus point

03-14-2014, 09:02 PM   #5
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actually not sure what you meant about infinity sharpness. But to clarify (I hope): the sharpest infinity setting is to focus on infinity. At a hyperfocal distance of (about) 10 ft at f/11 and FL=22.5 mm--the sharpest plane is at 10 feet. But 5 ft. to infinity will be in acceptable focus for the circle of confusion you (MJ...1956) used.

BTW the hyperfocal distances given are not the standard ones (the one given is for a more stringent criteria, and thus a larger print and/or looking more closely. The standard one at 10 ft hyperfocal disatnce and f/11 (for 1.5 crop dslr--e.g., Pentax dslr)) is at (about) FL=28mm--so your criterion is for something like a 13"x19" print at normal viewing distance..

Last edited by dms; 03-14-2014 at 09:08 PM.
03-15-2014, 09:56 AM   #6
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this is the issue with hyperfocal distance -- even though the range of acceptable COF (circle of confusion) is from say, 10ft to infinity, the absolute sharpest focus will always be (as you say) where you focus (NOTE: when stopped down beyond the diffraction limit, e.g. f/8 for most DX cameras, this may not necessarily hold true). Of course, if you focus at infinity then yes, infinity will always be the sharpest, but you will also have reduced the range of acceptable COF greatly -- this is fine if all you have in the image are some distant mountains, however, this is probably not so fine for most landscape photos which generally include foreground subject matter. In other words, at a minimum always focus a little before infinity you will get greater range of COF and still keep infinity sharp enough. That being said, other than astrophotography, it is rare that an image is best focused at infinity.

Michael
03-15-2014, 01:06 PM   #7
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QuoteOriginally posted by MJSfoto1956 Quote
Basically at 22.5mm equivalent, your hyper focal distance changes depending upon aperture.

Here is a basic table for your lens (assumes you want infinity in focus for a "normal" Circle of Confusion):

22.5mm @ f/2.8 = 22.7ft
22.5mm @ f/4.0 = 29.4ft
22.5mm @ f/5.6 = 20.8ft
22.5mm @ f/8.0 = 14.7ft
22.5mm @ f/11 = 10.4ft
22.5mm@ f/16 = 7.4ft

also note: that the image will be noticeably sharper at the given focal length and that infinity would have the same overall sharpness independent of focus point
Why would you not go by the distance scale on the lens itself? I thought the crop factor had nothing to do with DOF.
Also could you define for me the term "Circle of Confusion." I've not encountered this before. Thanks.

Last edited by sundr; 03-15-2014 at 01:27 PM.
03-15-2014, 01:19 PM   #8
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QuoteOriginally posted by sundr Quote
The crop factor has nothing to do with DOF.
Who said anything about crop factor?
But you are correct: the distance scale on the Limited lenses will actually reveal the hyperfocal distance you will get at each aperture setting.

Michael

03-15-2014, 03:42 PM   #9
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QuoteOriginally posted by MJSfoto1956 Quote
Who said anything about crop factor?
But you are correct: the distance scale on the Limited lenses will actually reveal the hyperfocal distance you will get at each aperture setting.

Michael
The table you gave is based on15mm x 1.5 crop factor (22.5). It's different from the scale on the lens, hence my confusion. Speaking of which...what is "circle of confusion?"

Last edited by sundr; 03-16-2014 at 12:23 PM.
03-15-2014, 04:39 PM   #10
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QuoteOriginally posted by sundr Quote
Speaking of which...what is "circle of confusion?"
Google and the Wikipedia are our friends. I am not sure that Michael used the term appropriately in his comments, though he did use a VERY important word. That word is the term "acceptable". The circle of confusion is the diameter of the intersection of the out-of-focus optical cone with the focal plane. Maximum diameter of CoC is that number that will still yield an acceptably sharp image to the person viewing the photo at a reasonable viewing distance for a given final image size. It is that maximum that is used for calculation of DOF. Acceptable maximum CoC varies by the frame size of the capture media (say APS-C vs. 35mm FF vs. 4x5 film and so on) assuming that final image size and viewing distance are held constant. Oh, and one more thing, average visual acuity of the person viewing is assumed.

I can not emphasize too strongly that DOF is a measure of adequacy and is not absolute. In addition, it is relative to size and viewing distance. Stand too close or pixel peep and DOF disappears.


Steve

Last edited by stevebrot; 03-15-2014 at 04:45 PM.
03-15-2014, 05:16 PM   #11
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here is a link describing Hyperfocal distance and Circle of Confusion: Hyperfocal distance - Wikipedia, the free encyclopedia

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03-15-2014, 06:03 PM   #12
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Thank you both for the clarification. I do often use Google and Wikipedia, I just forgot this time. I'm a little foggy after a long stretch of 12 hr night shifts:-)
03-15-2014, 07:12 PM   #13
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Two points about hyperfocal distance and the DOF values.

I. It does depend on the crop factor--if you like the DOF results you get w/ (for example) 35mm film, and use the same lens on a 1.5 crop sensor, you should use the DOF marking for 1 stop more open--assuming you are printing, and printing the same size--because w/ 1.5 crop factor the magnification in the print is larger (by 1.5) and thus sharpness or lack of will be more apparent.

So using a full frame lens on a pentax dslr (1.5 cropped sensor) start by using the DOF markings for the lens 1 stop more open. e.g., taking at f/11, use the DOF markings for f/8

II. Also, while the basis of the DOF/hyperfocal values may not coincide w/ what you want--it provides a starting point, and you may find you would be happier using the values for 1 or 2 stops more open, or 1 stop closed down. Once you make that observation you continue to use the concept--except modified. It still is a practical/useful method--you just modify it to do what you want.

It would be a mistake IMO to not use it because the circle of confusion is not the one you want--or you have no idea what that is. And if the lens has the DOF markings--it sure beats a computer/tables/or whatever in speed and convenience. (For my wider angle zoom lenses I write the hyperfocal distances vs aperture and FL, as a table on the lens hood.)
03-16-2014, 12:10 AM   #14
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WHOA, lots of technical information in here. A lot more than i expected. I think I'm twice as confused as before now, lol....
03-16-2014, 12:30 PM   #15
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QuoteOriginally posted by menappi Quote
WHOA, lots of technical information in here. A lot more than i expected. I think I'm twice as confused as before now, lol....
I know, right?:-D
Just when I think I have a concept figured out, someone comes in and adds a whole new layer of complexity. One of the things I like about photography, always something new to learn:-)
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