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07-13-2011, 11:43 AM   #1
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What is the ring with red diamond

Just to help me point out as an example, please see the image of lens here<br />
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I know the first ring is for aperture setting (on the left) and on extreme right is the distance setting, what is the ring in center for - the one with the red diamond. Please can somebody explain as I am soon receiving a copy of this lens.<br />
<br />
And anything that I may have to know from your point if you have used this particular lens already. This will become my first manual lens so any knowledge sharing on this lens and in general the M series will be of much help for me, thanks in advance<br />
<br />
thanks


Last edited by sany; 08-15-2011 at 07:41 AM.
07-13-2011, 11:53 AM   #2
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That's a depth of field scale. They're common on manual focus lenses.

The markings indicate the range of what will be in focus at the given aperture setting (the numbers attached to the lines to the left and right of the red diamond).

You line up the lines with the ft. / m. markings above that and it tells you how deep your depth of field is. So for instance, in that photo with the way the focus is set, at f/22 everything from just over 10 feet to just under 40 feet would be in focus, while at f/8 everything from just over 13 feet to just under 20 feet would be in focus.

edit: though I believe the DoF is different on APS-C than it is on film.
07-13-2011, 11:59 AM   #3
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QuoteOriginally posted by deadwolfbones Quote
. . .

edit: though I believe the DoF is different on APS-C than it is on film.
This is correct for a lens made for film and used on aps-c in that the lens will have more depth of field on the APS-c than 135 film at an equivalent fov. For Pentax sensors, this is about 1.5x. (the same for Nikon and Sony, 1.6 for canon and 1.7 for Sigma) Just the opposite would be true for the DA 70mm Ltd used on a film body.

Last edited by Blue; 07-15-2011 at 08:34 AM.
07-13-2011, 12:08 PM   #4
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so literally that feature will not be useful for me since the dofield reading will not be right on my dslr

07-13-2011, 12:25 PM - 1 Like   #5
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QuoteOriginally posted by sany Quote
so literally that feature will not be useful for me since the dofield reading will not be right on my dslr
You can still use it. I even don't bother with conversion when I am using digital unless I am trying for shallow dof because I know if I have adequate dof for film, I have it covered on my digital aps-c bodies. Other wise just use the 1.5x conversion factor on the focus distance.

Edit: There is a section in the hyperfocal section of this article.

http://www.cjcom.net/articles/hyperfoc.htm

Last edited by Blue; 07-13-2011 at 01:00 PM.
07-14-2011, 10:05 PM   #6
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No, and this is important: it works the other way. When you put a lens intended for a 35mm camera on an APS-C camera, the DOF will be shallower than that indicated by its DOF scale, and you must allow for this.

In theory, you should be using the scale for 1 stop less than your actual aperture, BUT in practice you'll find you should be at least 2 stops less (so, for example, use the DOF scale for f5.6 if your lens is set to f11).
07-15-2011, 06:46 AM   #7
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QuoteOriginally posted by m42man Quote
No, and this is important: it works the other way. When you put a lens intended for a 35mm camera on an APS-C camera, the DOF will be shallower than that indicated by its DOF scale, and you must allow for this.

In theory, you should be using the scale for 1 stop less than your actual aperture, BUT in practice you'll find you should be at least 2 stops less (so, for example, use the DOF scale for f5.6 if your lens is set to f11).
That doesn't sound right...
07-15-2011, 06:56 AM   #8
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QuoteOriginally posted by deadwolfbones Quote
That doesn't sound right...
It may not sound right to you, neverthless it is right. To produce the same sized final image from APS C, you will need to enlarge by approximately 1.5x. This represents a fraction over one stop on your effective aperture for DOF purposes. ie, F/8 will have a DOF roughly equal to that at F/5.6 on 35mm (all other factors being equal)

07-15-2011, 07:34 AM - 1 Like   #9
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I have used a little over one stop difference for correction. When setting aperture to F8 = setting scale to 5.6 or just a little closer to 4
07-15-2011, 07:40 AM   #10
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QuoteOriginally posted by m42man Quote
No, and this is important: it works the other way. When you put a lens intended for a 35mm camera on an APS-C camera, the DOF will be shallower than that indicated by its DOF scale, and you must allow for this.

In theory, you should be using the scale for 1 stop less than your actual aperture, BUT in practice you'll find you should be at least 2 stops less (so, for example, use the DOF scale for f5.6 if your lens is set to f11).
What are you saying no to? It can still be useful. Go back and re-read my post. I didn't say to multiply the dof by 1.5, I said the focus distance. The dof markings on the lenses are estimates anyway. The marks can still be used for hyper focusing with the 1.5x.

However, on an aps-c sensor, an equivalent field of view will have more dof than the equivalent on 135. For example on film, the dof for the fa 77 focused on a person at 15 feet @f16 has a dof 17.5' whereas the A 50mm at the same distance aperture will have 26'. However, the hyperfocal distance for the A 50 @ f16 is 17.3 on film and 25.8 on the Pentax aps-c.

Edit:

DOF for the A 50 focusing on a person at 15' @f16 will have 7' in front 99' behind the subject, 105.8 total, 8' near and 114' far.
DOF for the A 50 focusing on a person at 15' f16 will have 5.5' in front and 20.6' behind a total of 26.1' with 9.5' near and 35.6 far.

Last edited by Blue; 07-15-2011 at 09:46 AM.
07-15-2011, 07:41 AM   #11
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QuoteOriginally posted by MSM Quote
I have used a little over one stop difference for correction. When setting aperture to F8 = setting scale to 5.6 or just a little closer to 4
That is about right for Pentax.
07-15-2011, 08:48 AM - 1 Like   #12
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I have noticed that when this issue comes up, people will argue both sides. Someone has to be right but I have never decided who it is. I think it doesn't matter, for these reasons:

How accurately can you estimate distances? This is the key to the whole system. If you are terrible at distance estimation, forget using the scales.

OK, you are great at it. Now pick up any lens with a depth of field scale. I have an example here, M50/1.7:



The scales that you'll apply your distance estimate to aren't very detailed, and this scale is actually usable.

Some lenses are just not going to have usable scales. Set my K300/4 at 35 feet. Even at f32, the scale says my DOF is from about 32 to 40 feet. I'm not going to use f32, and I can't estimate distances well enough to use any wider aperture.

IMO the technique is an approximation, and you will never find a situation where the format used makes enough of a difference in that guess.
07-15-2011, 08:57 AM   #13
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QuoteOriginally posted by MSM Quote
I have used a little over one stop difference for correction. When setting aperture to F8 = setting scale to 5.6 or just a little closer to 4
This is my approach also, and it works just fine. So if I want DOF to infinity and I set the aperture to f/8, I set the focus ring so that infinity is just inside the f/5.6 mark.
07-15-2011, 09:51 AM   #14
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QuoteOriginally posted by Just1MoreDave Quote
I have noticed that when this issue comes up, people will argue both sides. Someone has to be right but I have never decided who it is. I think it doesn't matter, for these reasons:

How accurately can you estimate distances? This is the key to the whole system. If you are terrible at distance estimation, forget using the scales.

OK, you are great at it. Now pick up any lens with a depth of field scale. I have an example here, M50/1.7:



The scales that you'll apply your distance estimate to aren't very detailed, and this scale is actually usable.

Some lenses are just not going to have usable scales. Set my K300/4 at 35 feet. Even at f32, the scale says my DOF is from about 32 to 40 feet. I'm not going to use f32, and I can't estimate distances well enough to use any wider aperture.

IMO the technique is an approximation, and you will never find a situation where the format used makes enough of a difference in that guess.
That is a pretty good assessment and explaination.
07-15-2011, 02:20 PM   #15
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QuoteOriginally posted by RioRico Quote
This is my approach also, and it works just fine. So if I want DOF to infinity and I set the aperture to f/8, I set the focus ring so that infinity is just inside the f/5.6 mark.
Exactly. You said it better than me. :- )
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