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09-16-2010, 09:42 AM   #1
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Distance Settings for focusing

can someone please explain the best way to choose a distance setting to focus on, especially for shooting @infinity? i just don't seem to get sharp results from front to back/left to right.
just out of curiosity, if i focus on a tree 50 meters away @ f/22, and in the view finder the objects closer don't appear in focus, will the exposure still show them in focus because of the aperture setting? i just don't know what to focus on for large depth of fields...
thanks

09-16-2010, 09:47 AM   #2
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here is the same question...using exactly the same example i was asking about. only written better.
Help: preset focus via distance settings. - The Photo Forum - Photography Discussion Forum
09-16-2010, 10:10 AM   #3
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I am reading the same book that the link mentions and what the book states is that if you are shooting at F22 the focus distance will depend on what focal length you are using, but the general rule of thumb is that the shorter the focal length the shorter distance you want to focus. For example if you at shooting at 12mm then focus on something that is about 2-3 feet away, shooting at 18mm focus about 5 feet away, at 28mm focus about 7-8 feet away.

I actually just read that section last night and have not been able to test it yet but from what I hear, that book gives great advice.
09-16-2010, 10:36 AM   #4
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i just read that too which is why i'm asking. the book mentions 5 times in that chapter about a "i pre set the focus via the dof scale"
what is he talking about?

09-16-2010, 11:57 AM   #5
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Found this link and it explains it perfectly but if your lens does not have this DOF scale then the book suggest to focus at the distances I gave in the earlier post (I did just read though that the author advised his students to use a 1/3 rule, to focus 1/3 of the way to the subject when shooting at F22).
Steve's Zone - Depth Of Field Explained
09-16-2010, 11:59 AM   #6
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QuoteOriginally posted by Deiberson Quote
i just read that too which is why i'm asking. the book mentions 5 times in that chapter about a "i pre set the focus via the dof scale"
what is he talking about?
on many lenses there is a scale above or below the focus distance scale, with pairs of lines corresponding to different apertures. The pairs will move out from the focus point in increasing numbers (i.e. smaller apertures)

If you are at F8 for example, everything at a distance between the two lines marked 8 should be acceptablyu in focus.

Now, let's extend that to a landscape shot.

If you are at F8 and you put the infinity focus mark at 8, then everything from infinity down to the next mark with an 8 will be in focus.

On a 50mm lens that means everything from 5 meters to infinity, with perfect focus at about 10 meters
09-16-2010, 06:34 PM   #7
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The viewfinder won't show you what will be in focus at f/22 unless you do a DOF preview - and in that case, it will probably be too dark to tell.

The idea that you literally get infinite DOF at f/22 is fantasy. It's still the case that only one plane is *perfectly* in focus. Everything else is just varying degrees of less well in focus, and depending on how closely you examine the picture, any given part of the image might be close enough to being in focus to work for you.

As for where to focus, I'm sure that book must explain that you typically focus somewhere around a third of the way into the zone you wish to have in focus, but it's all just guesswork and approximation, really. Take a shot, see for yourself how your like, then if you decie you want more in focus, stop down, and if decide you want the focus zone closer or further away, change your focus accordingly. Trial and error - that's all it takes to build the experience to not need to take so many practice shots in the future.

Last edited by Marc Sabatella; 09-17-2010 at 03:10 PM.
09-17-2010, 08:59 AM   #8
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mark,
as far as technique goes, if i'm going to use the thirds rule, should i focus on something @ 1/3 the distance and then recompose the shot, or should i keep the camera pointed in the direction that i intend to take the exposure and focus until something 1/3 of the way comes into focus? i know this is an easy techique to grab but i'm just wondering what others do specifially when composing the shot

09-17-2010, 10:26 AM   #9
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QuoteOriginally posted by Deiberson Quote
mark,
as far as technique goes, if i'm going to use the thirds rule, should i focus on something @ 1/3 the distance and then recompose the shot, or should i keep the camera pointed in the direction that i intend to take the exposure and focus until something 1/3 of the way comes into focus? i know this is an easy techique to grab but i'm just wondering what others do specifially when composing the shot
Maybe I an a bit out of turn here but I will put my $0.02 at this question.

You have multiple focusing sensors in the camera, manually pick one that puts it at the 1/3 point and let the AF do the job for you, then you don't need to recompose at all.

otherwise, focus. lock the focus and recompose, as you suggest.'

Either one will get to the same result.

Just for information, the rule of thirds is based upon the optics, and for distant objects, the DOF is a range 1/3 in front, and 2/3 behind th eplane of focus
09-17-2010, 07:21 PM   #10
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All this must be quite confusing to beginners. I have a very simple technique that works well for scenic shots. First of all, I like to have some foreground object to show depth. This may be a person, a tree, a big rock or whatever. I want that foregound object in focus, but I also want as much of background in focus as well. I always use manual focus when shooting scenic shots, because I want to control this "hyperfocal distance," which is what we're actually talking about.
With the composition set (camera on tripod), I turn the focus ring all the way to infinity (actually past it), then slowly turn it back until the foreground object just comes into focus.
How far you set up behind that foreground subject, and how much of that background will be in focus, depends as much on the focal length as it does on DOF. With my 15mm, I can have the foreground object in focus, all the way to infinity, with the object just a few feet from the lens. With my 100mm, I can't get the same results unless my foreground object is about 20 yards away.
Simply pick a foreground object and put it at the front edge of your hyperfocal distance. If the resulting shot doesn't give you enough infinity difinition, back up a bit, still keeping the foreground object in the lower portion of the composition.
By the way, rarely do I go above f-14 for such shots. I have some of the best lenses Pentax makes, but not one of them will be clear at infinity at f-22 because of diffraction.

Last edited by Ron Kruger; 09-17-2010 at 07:29 PM. Reason: Adding Info
09-18-2010, 01:46 AM   #11
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I am watching this thread with great interest as i too have not figured out about the DOF thingy for all this time, despite all the help the Gurus here try to teach my stubborn brain.
09-22-2010, 08:45 AM   #12
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QuoteOriginally posted by Deiberson Quote
if i focus on a tree 50 meters away @ f/22, and in the view finder the objects closer don't appear in focus, will the exposure still show them in focus because of the aperture setting?
When you look through the viewfinder to compose, the lens is wide open, so you are seeing the DOF you'd get at the widest aperture setting. When you take the picture, the aperture stops down to f/22.

If your camera has a DOF-preview button, you can stop the aperture down and see the affect in the viewfinder prior to taking a picture.
09-23-2010, 12:30 PM   #13
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QuoteOriginally posted by raider Quote
I am watching this thread with great interest as i too have not figured out about the DOF thingy for all this time, despite all the help the Gurus here try to teach my stubborn brain.
the problem is that we are trying, sometimes successfully sometimes not, to give answers to one specific question with one or two sentances, on the assumption that everyone has some fundamental understanding of photographic principles.

Unfortunately,. In many cases, I find we are explaining things to people that have never ever read a book on photography that explains in simple terms the scientific principles behind photography. Specifically, optics, and light and how cameras work. They also many times have not read the manual that came with the camera either, although I will admit that manuals are not necessairly the best peices of literary work out there.

At some point there is no substitute for reading a good book on the principles of photography.
09-24-2010, 07:08 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
At some point there is no substitute for reading a good book on the principles of photography.
any personal suggestions? i've only read the peterson's exposure book. looking on something that explains metering a little more along with dof w/ excersises
09-24-2010, 07:40 AM   #15
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QuoteOriginally posted by Deiberson Quote
any personal suggestions? i've only read the peterson's exposure book. looking on something that explains metering a little more along with dof w/ excersises
That's a tough one, the books I have are all done in the late 70's and early 80's when I started.

I have been looking for a more up to date book, and find most books in teh bookstore cover enough about hyperfocal distance, depth of field scales, lighting, metering and cmposition to make a good reference.

You should spend a little time in a stoor, and pick several topics randomly that you feel you need to have better information on, and check several books out to see which one best suites your need, Don;t just look at the contents, but perhaps try reading one area of interest in each and see which author writes in a style you can understand.
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