Depth of field

R

Roger Hicks

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This seems to be a perpetual source of confusion and dispute, and I can't see why. By definition, it's the zone either side of the focused point that is acceptably sharp. We all define 'acceptable' in our own ways, which should in itself be a clue, and obviously, 'acceptability' varies with subject matter, composition, enlargement size and viewing distance. Also, there are trivial differences (as between M8 and M9) and major differences (as between a mobile 'phone and an 8x10 inch camera).

Why, then, are there so many absolutists around, trying to reduce the whole question to mathematical formulae, good for all formats and all time? The d-o-f guidelines on lenses are just that: guidelines, based on stated or unstated assumptions. Thus, for most Leica lenses I tend to use the next smallest aperture, e.g. if I am shooting at f/8 and want to check the d-o-f, I use the f/5.6 markings. What do you do?

Ceers,

R.
 
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with the SMC Takumar 28mm 3.5 I just line up the orange marked distance and the orange marked f8 with orange diamond on the dof scale... adjust the shutter speed and fire away... no thinking at all...

Casey
 
Basically, I do not use the depth of field marks. Their exact position on the lens is determined by "a mythical viewer observing a mythical image enlarged to a specific size only known by the person deciding where the DOF lines should be set on the lens."

It based on perception. Perception of anything but the image I am about to make.
 
depth-of-field scales are nice guide-lines for me that I sometimes use to roughly estimate what could be in focus and what not. Everything else about it is to scientific for me
 
When I used ancient folding Voigtlanders with no rangefinders they all had DOF scales engraved on the lens. Very useful when distances were estimated.
My Rolleiflex has a neat moving scale showing DOF on the left hand side of the camera, my Nikon pre-AI lenses have a DOF scale engraved on them as do my modern Cosina Voigtlander lenses. I'm less inclined to use the scales when I have a rangefinder to verify but if in doubt I do.
If I had unmarked lenses I'd use the rule of thumb that says "one third in front of the focused distance to two thirds behind".
 
I only use the DOF guides as a rough indication of what will be acceptably sharp when I'm shooting from the hip. I set the distance at 100x the focal length (e.g. 5m for a 50mm lens and 2.5m for a 25) and the aperture at f8-f11. I look at the scale and know how much I can deviate from the set distance..

For landscapes, I use infinity focusing and set the aperture to f11-f16.. everything else follows. I don't worry about the DOF guides, because even if you shoot near/far stuf, you can't even get anything relevant comfortably in the frame that's outside the DOF.

Finally, when I'm shooting where exact focus counts, I just use three apertures: f2, f5.6 and f16; shallow, medium and deep DOF. I don't use the DOF guides.
 
I used to have the cv 25mm (old version, no rf-coupling) and for landscapes I always aligned the infinity mark with the aperture I used. It worked all the time. Perfect.
 
Leigh Youdale said:
When I used ancient folding Voigtlanders with no rangefinders they all had DOF scales engraved on the lens. Very useful when distances were estimated.
My Rolleiflex has a neat moving scale showing DOF on the left hand side of the camera, my Nikon pre-AI lenses have a DOF scale engraved on them as do my modern Cosina Voigtlander lenses. I'm less inclined to use the scales when I have a rangefinder to verify but if in doubt I do.
If I had unmarked lenses I'd use the rule of thumb that says "one third in front of the focused distance to two thirds behind".
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My VAGs don't have DOF markings, but then I guess it is figured they don't need it. You are correct on the 1/3 in front and 2/3 behind according to all I have read. I don't think I have ever seen a lens marked that way. They are always equal distance on either side of the middle mark.

I have use the lens markings on many occasions. I tend to try to be conservative, knowing they are approximations only. I have used them on both RF and SLR.
 
In the past times I was obsessed by the (subject) "out of focus" issue and I was used to close as much as possible the diaphragm to get as much DOF as possible...now I try to get a shallow DOF just because is more pleasant...but I never mind at the DOF scale on the barrell...maybe I'm wrong...maybe...

 
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Dear Lorenzo,

'As much as possible' is perfectly correct.

It's only when you begin a sentence wth "Much as..." that it shouldn't be "As much as..."

Thanks for everyone's stories. There's more to this than I thought...

Cheers,

R.
 
I must be peculiar, I seem to use the DOF scales more often than not to check something is out of focus not in, in order to reduce it’s importance in negative space or isolate the subject
 
Roger Hicks said:
This seems to be a perpetual source of confusion and dispute, and I can't see why.
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When calculating DoF, four things can be taken into account:

- angle of view
- sensor size
- focal length
- print size

The problem is, when comparing different systems, you must decide which of those elements are "normalized" so that they're equivalent across the systems. For conventional DoF calculations, two things are normalized:

- angle of view
- print size

I think the main problem is that people don't agree that those two things are the invariants in DoF calculations. They think that other things should be considered as constants.

However, in a practical sense, using angle of view and print size never leads to absurd conclusions. For example, say that we assume that focal length is the constant. Then as soon as someone pulls out their cellphone (FL = 4 mm) then you have to also search for a 4mm lens for your Hasselblad, which is absurd.
 
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Not sure what all the fuss is about. If I am shooting predominantly landscape/architecture I set the lens the maximum aperture that I can up to f/8 -- if with the available light I can get more than f/8 technically, then I increase the shutter speed instead.

So then I maximise the DOF with the infinity mark just beyond the f/8 mark on the lens and then shoot all day, just making sure the lens hasn't been knocked. That way I get the most detail I can on the ISO 100 films I tend to shoot.

Anything else which requires people in foucs, well I pretty much just focus on them and shoot, I don't pre-focus, miss too many shots that way, and I don't shoot from the hip either (unless with my TLR which dangles down to about that far on me!)

As for which aperture to use, well I just use my head and work out what kind of shot I want and recall previous shots that worked and their aperture in my head and go from there. Generally speaking if I am doing street photos for 35mm I'll shoot at f/2.8, 50mm f/4 and 100mm f/5.6 or f/8.

Vicky
 
DOF is also affected by how sharp the lens is, in the plane of focus. If shooting with an ASPH or other very sharp lens, I will stop down one more stop than the scale calls for; but not so far that diffraction will work against me. With most of my lenses, I just trust the DOF scale.

At times when I can't stop down enough, I might just focus on the most important area, and let the rest be a little soft. Chances are, they won't be all that soft, and I will get away with it.
 
When I got my first "adjustable" camera, my Signet 50, I just went balls out to nail the distance as closely as I could to the actual distance of the main subect, set a comfortable speed, and the stop followed.

It had a linked stop and speed mechanism, but I mostly ignored that.

More recently, I shot the same way with a Leica Standard, and it still works.

Most recently, using the CV lenses that are not linked, I was surprised that sometimes I was a bit off with the M8, and now I use Roger's -- "use the next stop down" method. I was getting acceptably sharp images with the 12mm, but not as sharp as I thought, so am paying a bit more attention in what I set.

The indicated DOF was so great I was getting sloppy, but it is a long way back from AF in my Contaxes.

I am not sure of all the math involved on using DOF scales on the M8, but I am sure I was not getting what I was looking for, so one stop "safety" is it now, and when someone explains the math to me, it will be a footnote.

In another direction, These days I am much more interested in the quality of the out of focus areas that compliment the main subject, so it becomes more involved than just getting the subject sharp.


I know I am getting old when I think beginners should start with two cameras, one that does everything for them, and one that they have to set everything, well, perhaps three, one that cannot be set.

I did distance estimation and measurement exercises with my classes, and it is surprising to all involved. We began with cubits, and ended up determining how much it would cost to fill the hallway with soda.

I had a lot of practice in my early days with the Kodak, but that was feet I believe.


Regards, John
 
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It seems to reflect the times. I'm playing with an Isolette-Speedex, which was considered serious hobbyist camera in its day and it doesn't have any focusing aids at all. It was accepted to use DoF as your sole means of focusing in the early '50s.

It has to do with the modern fixation with metric measurement.

In the '50s, image quality was measured bluntly in furlongs, hogsheads, and firkins. Then the British accepted the precision of an old French measurement system, and look what happened.

- Charlie
 
Rob-F said:
DOF is also affected by how sharp the lens is, in the plane of focus. If shooting with an ASPH or other very sharp lens, I will stop down one more stop than the scale calls for; but not so far that diffraction will work against me. With most of my lenses, I just trust the DOF scale.

At times when I can't stop down enough, I might just focus on the most important area, and let the rest be a little soft. Chances are, they won't be all that soft, and I will get away with it.
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Dear Rob,

VERY true. 'Soft' lenses effectively have more d-o-f.

Cheers,

R.
 
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