Depth of Field markings on old M lenses with new M8 camera

[thurows]

I think everyone asking about depth of field is concerned because of the characteristics of teleconvertors. Since the crop factor is a result of the imaga area shrinking and not an optical device being put in front of the lens, depth of field is not altered.

 

[Finder]

I think everyone asking about depth of field is concerned because of the characteristics of teleconvertors. Since the crop factor is a result of the imaga area shrinking and not an optical device being put in front of the lens, depth of field is not altered.

So you are saying a full-frame 8x10 print from a 4x5 negative taken with a 55mm Grandagon will appear to have the same DOF as a full-frame 8x10 print from a 35mm negative taken with a 55mm Macro Nikkor? Sorry, but that is not the case. The larger format will have a greater DOF given equal focal lengths. However, given equal field of view, the smaller format has the greater DOF.

For the same reason larger formats can use a smaller minimum aperture, they also have a larger limit for the circle of confusion. DOF is always calculated in relation to the maximum size of the circle of confusion that appears as a point. DOF scales are not transferable between formats.

 

[Matthias]

in-depth info

in-depth info

some more in-depth information from wikipedia (no pun intended..)

cheers,
-mj


Depth of field versus format size

As the equations above show, depth of field is related to the circle of confusion criterion, which is typically chosen as a fraction, such as 1/1000 or 1/1500, of the image format size. Larger imaging devices (such as 8×10 cameras) can tolerate a larger circle of confusion, while smaller imaging devices such as point-and-shoot digital cameras need a smaller circle of confusion. For the same field of view and f-number, DOF is, to a first approximation, inversely proportional to the format size. Strictly speaking, this relationship is true only when the subject distance is large in comparison with the focal length and small in comparison with the hyperfocal distance, for both formats, but it nonetheless is generally useful for comparing results obtained from different formats.
At a given f-number and field of view, a smaller camera has greater DOF than a larger camera. The depth of field on an 8×10 camera using a normal lens at f/22 is one half that on a 4×5 with a normal lens at f/22. Similarly, a 35 mm camera with a normal lens at f/8 has the same depth of field as a 6×7 cm camera with a normal lens at f/16. This can be an advantage or disadvantage, depending on the desired effect. For the same amount of foreground and background blur, a small-format camera requires a smaller f-number than a large-format camera. Many point-and-shoot digital cameras cannot provide a very shallow DOF. For example, a point-and-shoot digital camera with a 1/1.8? sensor (7.18 mm × 5.32 mm) at a normal focal length and f/2.8 has the same DOF as a 35 mm camera with a normal lens at f/13.
In many cases, the DOF is fixed by the requirements of the desired image. For a given DOF and field of view, the required f-number is proportional to the format size. For example, if a 35 mm camera required f/11, a 4×5 camera would require f/45 to give the same DOF. For the same ISO speed, the exposure time on the 4×5 would be sixteen times as long; if the 35 camera required 1/250 second, the 4×5 camera would require 1/15 second. In windy conditions, the exposure time with the larger camera might allow motion blur.
For cameras of different formats to achieve the same depth of field when shooting from the same position, with focal lengths that capture the same field of view, it is necessary to use the same absolute aperture diameter with each, not the same f-number. Consider formats that differ approximately by factors of two: 35 mm, 6×7 cm, 4×5 inch, 8×10 inch. For a chosen camera position and field of view, to keep the same depth of field, double the f-number each time you step up to the next film size. For example: f/5.6 on 35 mm, f/11 on 6×7, f/22 on 4×5, f/45 on 8×10. This doubling is not exact but is a very good rule of thumb. Also adjust exposure, ISO speed, or both by two stops (factor of four) each time: 1/60, 1/15, 1/4, 1 sec.
In some cases, movements (tilt or swing) can be used with view cameras to better fit the DOF to the scene, and achieve the required sharpness at a smaller f-number. A few small-format cameras can employ the same principle by using tilt/shift lenses.

 

[Finder]

mj, don't cloud the issue with facts.

For others, I want to point out that the essay assumes equal fields of view (which is more logical) rather than equal focal lengths (which is under discussion).

 

[Gabriel M.A.]

I. Donough's on Third...

 

[gdewitt]

For others, I want to point out that the essay assumes equal fields of view (which is more logical) rather than equal focal lengths (which is under discussion).

I would hasten to point out, though, that equal focal lengths is much more apropos to the topic of this thread, which is about using the DOF marks on a lens.

 

[Ben Z]

Granted that, and so a 35mm is used in place of a 50mm and the image is thus cropped and enlarged, diminishing the DOF. Then, the concensus would be what, use the next-wider-aperture DOF markings when shooting on an M8? (Or, for those of us already using 1 wider stop, going to 2 wider stops?). That sounds doable.

 

[thurows]

So you are saying a full-frame 8x10 print from a 4x5 negative taken with a 55mm Grandagon will appear to have the same DOF as a full-frame 8x10 print from a 35mm negative taken with a 55mm Macro Nikkor? Sorry, but that is not the case. The larger format will have a greater DOF given equal focal lengths. However, given equal field of view, the smaller format has the greater DOF.
.

No I'm saying the physical charecteristics of the lens have not changed. If you crop a 35mm photo taken with x lens the same area with in the photo is still in focus, the photo has not magicly blurred because it all of the sudden thinks it was shot with a longer lens.

All you're doing is cropping when using a digital camera.:bang:

 

[richard_l]

I think we are forgetting what DOF is. It is usually understood to be relative to an 8"x10" print viewed at an 'appropriate' distance. The situation with a digital sensor having a crop factor greater than 1 is the same as with a 35mm film negative which is cropped down to the same size as the digital sensor. The cropped 35mm image will have to be enlarged more than the full 35mm image in order to make an 8"x10" print. Enlarging more will also increase the fuzziness of out of focus areas, and thus will increase the extent of out of focus areas and thereby decrease the range of acceptable focus. Therefore, by cropping the negative and then enlarging to 8"x10", you, in effect, lose DOF. The quantitative analysis of this from the DOF formulas is easier than trying to explain it.

Anyhow, the basic properties of the lens does not change just because it is using a smaller sensor. It is the enlargement to a gallery-viewable 8"x10" image that causes the change in the effective DOF. Okay?

Richard

 

[Finder]

No I'm saying the physical charecteristics of the lens have not changed. If you crop a 35mm photo taken with x lens the same area with in the photo is still in focus, the photo has not magicly blurred because it all of the sudden thinks it was shot with a longer lens.

All you're doing is cropping when using a digital camera.:bang:

I thought you were saying DOF would not change because the optics were the same regardless of the format size. That statement is false because display size does count. DOF is not an absolute quality like resolution. It is relative.

What is in focus and what appears sharp is not the same thing. Sharpness is not an absolute quality, focus is. DOF is about what we percieive as sharp. Focus is about two conjugate planes on each side of an otical system. These planes have no depth. Unfortunately, "focus" has a common meaning as "sharp," and can lead to confusion. Sharpness is alway in relation to the human visual sytem.

Given a constant focal length, DOF increases as format size increases.

 

[thurows]

Depth-of-field is the two points between which an image is in sharp focus. Your focal length is a constatnt, your aperture is a constant, your depth of field is engraved into the lens because it is a constant for that lens.

Homework. Take two pictures, one with a 35mm and any lens, take the other with a digital camera with the same lens. Now crop the 35mm shot to the same ratio as the digital file and both images have the same depth of field. OK. That's all you're doing is cropping the frame.

 

[richard_l]

Depth-of-field is the two points between which an image is in sharp focus.

That is incorrect. It is the range of distances in which a blowup of the image is apparently sharp. If a lens is focussed at 10 ft, only things exactly 10 ft from camera along the lens axis are in perfect focus. (There will, in fact, be a plane of perfect focus, which may or not be a flat plane.) Anything closer to or farther away from the camera than 10 ft will be out of focus. However, things which are not exactly 10 ft away may appear to be in focus because our eyesight is not perfect. What appears to be in focus will, of course, depend on the degree of enlargement of the image, which is traditionally taken to be 8"x10". The range of distances which appear to be in focus is the DOF. The notion of apparent sharpness is the basis of the idea of DOF. (It can be quantified by the circle of confusion, but that need not be of concern for a rudimentary understanding of the DOF concept.)

 

[Topdog1]

Now I think I've joined the CoC (circle of confusion)

Now I think I've joined the CoC (circle of confusion)

I saw a thread posted somewhere, could have been here or another site, declaring DOF was a non-issue with respect to the sensor size of the M8. From the welter of responses and perspectives expressed I'd say it is very much an issue - at least a confusion. Perhaps someone from Leica would care to do a definitive write-up on this issue - I say Leica since that would seem to make it from an authoritative source. Of course, the answer has as much to do with the M8 as with any other digital camera that has a crop factor with respect to its sensor. For the Leica this would also seem to have an impact on the bokeh that different lenses have, since this is a function of circles of confusion as well.

Regards,
Ira

 

[petermcwerner]

I suggest you read a very good article (it was cited here before) on the Bob Atkins web site While it does not alter the theory and much has already been said here by other posters, his explanation seems very clear to me for a practical photographer rather than a physicist or mathematician.

His conclusion:

The circle of confusion value for the 10D is reduced by a factor of 1.6x and what this means in terms of DOF scales is that you need to use the markings for about 1 1/3 stops wider aperture in order to estimate the DOF.

The below image shows (in red) the DOF for the same lens at f/16 on a digital camera that does not have a FF sensor (in his example an EOS 10D).

 

[jaapv]

I suggest you read a very good article (it was cited here before) on the Bob Atkins web site While it does not alter the theory and much has already been said here by other posters, his explanation seems very clear to me for a practical photographer rather than a physicist or mathematician.

His conclusion:

The below image shows (in red) the DOF for the same lens at f/16 on a digital camera that does not have a FF sensor (in his example an EOS 10D).

This is correct and illuminating. However the 10D has a 1.6 crop (making for the 1.6 difference on your illustration)and the M8 a 1.3 crop The difference between stops in DOF is a factor 1.4, so the difference on the M8 is about 2/3 of a stop. Not over 1 1/2 like shown on this photograph. I may add, that because of the different pictorial rendering of sensor vs. film, the impression of DOF on the 10D is more like just 1 stop difference., so the Leica M8 will exhibit just 1/2 a stop difference. That, in terms of photographic impact, is negligible in most cases.

 

[Finder]

Depth-of-field is the two points between which an image is in sharp focus.

Define "sharp focus." What is the criteria for "sharpness?"

Your focal length is a constatnt, your aperture is a constant, your depth of field is engraved into the lens because it is a constant for that lens.

And that format.

Homework. Take two pictures, one with a 35mm and any lens, take the other with a digital camera with the same lens. Now crop the 35mm shot to the same ratio as the digital file and both images have the same depth of field. OK. That's all you're doing is cropping the frame.

Well, if I crop the 35mm to the same size as the digital format, it would be the same as the digital format. DOF is dependant on format and so two formats of the same size have the same DOF.

When you crop an image, DOF decreases because the circle of confusion is based on display size of the full frame and the cropped area would be magnified more to fit that area and the circles of confusion are magnified along with it. But the conversation is about images from different size formats.

 

[greggebhardt]

Let's not stretch the laws of physics again. DOF for a lens will stay FIXED. If you stand with a cropped OR a FF camera at a certain distance from the target, the DOF is same, that is, what;s IN focus and OUT of focus will not change.

Enlarging will NOT change DOF.

I do not think it is exactly the same

Different Circle of Confusion!:bang: