View Full Version : Depth of Field markings on old M lenses with new M8 camera
If I use an older Leica M lens on the new M8 with a 1.33 crop factor, are the depth of field markings on the lens still correct?
Thanks,
Ira
Yes, they are still valid. It will just crop the picture a bit for you.
/Håkan
My experience with my Canon 20D (1.6x crop factor) is that my 50mm Takumar gets the same DOF as on my friend's 5D ( we checked very carefully with bowling pins at various distances along an alley--he owns a bowling alley) even though on the 20D the fov is actually more like an 80mm. So in short I still use the DOF markings on each lens and find them the same as they were on my Pentax film camera. In practice though I usually choose the markings for one stop wider than I'm actually shooting, because it tightens the tolerances up in case I need to crop.
I find it useful on the 20D for many shots that the lens I use for a 50mm angle has the extended DOF of a 35mm lens (which in fact is what it is), but when using the 50mm as an 80mm sometimes I'm frustrated by that longer DOF because more of the background is recognizable than I'd like.
Like Jaap once said, DOF is in the eye of the beholder :)
It depends on enlargement and viewing distance. If you enlarge to the
same print size the DOF will change.
In practice different lenses have different DOF scales, compare for instance
a Jupiter 3 to a fast older Leica or Canon lens.
Similar to what is said above, I usually use at least one less stop for DOF estimation which
puts me on the conservative side, even with Russian lenses.
Roland.
I am really thinking about this in terms of using the DOF scale on the lens for setting a hyperfocal distance at a particular F-stop for the purpose of obviating focusing, something I believe is commonly done with rangefinders. Are the lens markings reliable for that when the lens is on an M8?
Regards,
Ira
It is not generally known that it is easier to judge DOF in a RF viewfinder than in a SLR :eek: :eek:
With a SLR one pushes the preview button and everything goes black, removing all information about DOF and all else.
A rangefinder shows double contours in the RF patch and the distance between these contours is an exact indication of the relevant DOF. It needs some trial and error and practice but once one has mastered this it is nearly intuitive.
The Leica M3 and M2 used to have markings in the RF patch, the small one indicating f 16, the big one f 5.6 at 50 mm.
Just for Ira ;) I will repeat my DOF comparison chart:
All values at 3m distance:
135-2.8
08 cm film
06 cm M8
05 cm RD1
90-2.0
13 cm film
10 cm M8
09 cm RD1
90-2.8
18 cm film
14 cm M8
12 cm RD1
75 - 1.4
13 cm film
10 cm M8
9 cm RD1
75-2.0
27 cm film
20 cm M8
18 cm RD1
50-1.0
21 cm film
16 cm M8
14 cm RD1
50 -1.4
30 cm film
23 cm M8
20 cm RD1
50-2.0
43 cm film
33 cm M8
28 cm RD1
35-1.4
62 cm film
48 cm M8
41 CM RD1
35-2.0
89 cm film
60 cm M8
59 cm RD1
24-2.8
326 mm film
227 mm M8
192 mm RD1
I used DofMaster, calculated M8 at a COC of 0.023 mm, the RD1 at 0.020 mm and the film at 0.030 mm.Those are the accepted average values for those formats.
Btw. thanks for the quote, Roland :) I DID apologize for the remark :D
If I use an older Leica M lens on the new M8 with a 1.33 crop factor, are the depth of field markings on the lens still correct?
No, they aren't.
Read this:
http://www.bobatkins.com/photography/technical/digitaldof.html
J. Borger
10-10-2006, 19:59
This is all nice mathematics ....... but for all practicle purposes just use the current dof-markings as guidelines and your pictures will turn out fine 99,9% of the cases.
For dof .. yes it is different from full frame but you will addapt .... if you want to blow a background out of focus for instance... by lens/ aperture use and your distance to the subject ... this goes also automatic after a short period of use....
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.
DOF is a subjective measure based on circle of confusion, so laws of physics (aside from cognitive properties of human brain, which are statistical) do not play decisive role here.
sebastel
10-11-2006, 04:58
just my observation, made with 21mm elmarit on RD-1.
setting to hyperfocal distance using the DOF marks on the distance scale works, but only if you use the DOF marks for 2 aperture values smaller than actually used.
example:
actual aperture F/8
set the infinite scale mark to the DOF field mark for F/4 will result in sharp rendering of far away objects (more than 50 meters).
sharpness evaluated at 100% on my computer screen, so the 2 aperture values difference may be more than actually necessary for smaller sizes.
insofar, i can back by experience tha values jaapv has given. looks reasonable to me.
regards,
sebastian
Size certainly does matter...circle of confusion is a dimension that enlarges with print size.
FYI, Standard DOF marks are calculated to work at 8x10 print size. I got this from a technical guy at Canon when I asked him about the mode setting they used to have on the Pro SLRs that would automatically set aperture to keep two objects at different distances in focus.
and by the way, if you assume that viewing distance increases with print size, then size doesn't matter - because standing further away shrinks the apparent circle of confusion.
If you have ever made small and large copies of a print the relationship between size and focus becomes very obvious....
FYI, Standard DOF marks are calculated to work at 8x10 print size.
Old Zeiss lenses (and derivative Soviet designs) had DOF marks to provide satisfactory 13x18cm prints.
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.
You should look at it this way:
I once said DOF is in the eye of the beholder and though it sounds facetious, that is the essential point. As photographers we start our attempt at understanding at the wrong end, at the lens, making for no end of confusion.
Start at the human eye, which is not able to distinguish between two seperate points if they are too close together.That is all DOF is. As soon as that happens we perceive an unsharp photograph as sharp.
So,when we walk the chain backwards:
1. It depends on the viewing distance. Close up, you'll see more detail and less DOF
2. It depends on the size of the print, the enlargment: Smaller, points closer together, more DOF
3. It depends on the film or sensor format. Smaller sensor, more enlargement on the print, shallower DOF
4. It depends on the lens. A tele enlarges more, points further from one another, shallower DOF
5. It depends on the subject distance. Closer up, points more apart, shallower DOF.
6. It depends on aperture. Smaller aperture=smaller point with better separation=more DOF
So there you are: Sensor size matters according to point 3.
Of course, Mango, so everybody has to strike his own balance. But this subject distance is automatically considered in the COC, so that can be kept as a constant. As it is the difference in DOF between M8 and film is equivalent to less than one stop on the same lens. So it is rather theoretical anyway. The quality of the eyes of the viewer is the decisive factor on the other side.
3. It depends on the film or sensor format. Smaller sensor, more enlargement on the print, shallower DOF
I took my wife's tiny-sensor Canon S80 with 76-degree FOV lens, my APS-C sensor 20D with 76-degree FOV lens, and my friend's full-frame 5D with 76-degree (28mm) lens to his bowling alley with pins placed down the alley, and we shot the same shot with all 3 focused on the same pin and set to the widest common aperture. We made 8x12 prints of all 3 shots. The S80 (smallest sensor) had the obviously deepest DOF, the 5D (largest sensor) the obviously shallowest DOF, and the 20D in the middle somewhere. So in practical photography (the only place I care about the issue) the smaller sensor, deeper the DOF.
Perhaps your assertion is correct if the actual rather than the effective focal length (FOV) is the constant, but I can't really see the value of that.
Like Jaap once said, DOF is in the eye of the beholder :)
It depends on enlargement and viewing distance. If you enlarge to the
same print size the DOF will change.
In practice different lenses have different DOF scales, compare for instance
a Jupiter 3 to a fast older Leica or Canon lens.
Similar to what is said above, I usually use at least one less stop for DOF estimation which
puts me on the conservative side, even with Russian lenses.
Roland.
I R Stoopiid. How does changing the print size change the depth of field. I mean, once the image is recorded there is no resolving anything that is not already there.... Right? Maybe I'm just having problems wrapping my brain around that concept.
Gabriel M.A.
10-11-2006, 06:53
Technically, the DOF markings are already too conservative for modern emulsions. the perceived DOF is narrower when using film with very fine grain, and some even recommend that you should carry over the markings one stop (i.e., the DOF for f/4 is really for f/2, etc.) when examining large prints.
Given camera shake, the DOF markings are still rather useful.
But to many, I may be blowing smoke. Grab a bottle of Scotch and a book on optics for photography; it's a long road.
I took my wife's tiny-sensor Canon S80 with 76-degree FOV lens, my APS-C sensor 20D with 76-degree FOV lens, and my friend's full-frame 5D with 76-degree (28mm) lens to his bowling alley with pins placed down the alley, and we shot the same shot with all 3 focused on the same pin and set to the widest common aperture. We made 8x12 prints of all 3 shots. The S80 (smallest sensor) had the obviously deepest DOF, the 5D (largest sensor) the obviously shallowest DOF, and the 20D in the middle somewhere. So in practical photography (the only place I care about the issue) the smaller sensor, deeper the DOF.
Perhaps your assertion is correct if the actual rather than the effective focal length (FOV) is the constant, but I can't really see the value of that.
You changed two parameters, sensor size and focal length. The relationship is not linear.
DOF is NOT related to resolution - the ability to distingush between two points. DOF is related to the circle of confusion - the size of each point. When the circle appears too large, the human visual system thinks it is out of focus. Since the DOF scales are calulated based on a 35mm frame, they will not be "correct" for the smaller sensor. Whether they are accurate enough depends on the photographer as DOF is a subjective number based on viewing a standard size print at a relative viewing distance. DOF is always in relation to the human visual system and is not an absolute physical property.
The interesting thing that no one has talked about is as the sensor size decreases, the affects of diffraction increase. So a minimum aperture that is acceptable with a 35mm frame, may be too small for the smaller format. While small apertures increase the DOF, they also increase diffraction (the size of the Airy disk) which could mean the difference between a sharp looking image and one that looks soft.
Technically, the DOF markings are already too conservative for modern emulsions. the perceived DOF is narrower when using film with very fine grain, and some even recommend that you should carry over the markings one stop (i.e., the DOF for f/4 is really for f/2, etc.) when examining large prints.
Film resolution has nothing to do with depth of field. It is simply the size of the circle of confusion even if the circle of confusion is larger than what the film can resolve.
DOF is NOT related to resolution - the ability to distingush between two points. DOF is related to the circle of confusion - the size of each point. When the circle appears too large, the human visual system thinks it is out of focus. Since the DOF scales are calulated based on a 35mm frame, they will not be "correct" for the smaller sensor. Whether they are accurate enough depends on the photographer as DOF is a subjective number based on viewing a standard size print at a relative viewing distance. DOF is always in relation to the human visual system and is not an absolute physical property.
It is related to the resolution of the human eye, whether one or two photosites in the eye are excited. Nothing else. Your brain translates that to in or out of focus. If a car approaches you from a long distance in the dark you see one lightspot that suddenly transforms into two headlights. That is the resolution limit of your eye and you could say the car has reached the limit of DOF. Oviously large structures will hit more sites. The eye is remarkebly like a sensor in that way.
they are talking about shooting a ruler, for instance. As you enlarge a print of a photo of the ruler, there will be edges that looked fine at 3x5 that now are clearly blurred(!) at 8x10.
But one could say as you increase the magnification of the loupe, DOF shrinks, for the same reason. In the case of a crop sensor in a digital camera, you are cutting out the center of a 50mm lens image, for example, and blowing it up so the depth of field with that lens will actually be smaller than it would on a 35mm film camera (image magnified, so edges will appear less sharp).
If you consider the depth of field markings on a lens to be relative to some standard, say film negative on 8x10 prints, then the DOF never changes. As your usage deviates from the standard, you have to expect the DOF markings lose some of their meaning.
***
apparently i type slow - the post i was replying to is lost somewhere up there.
I R Stoopiid. How does changing the print size change the depth of field. I mean, once the image is recorded there is no resolving anything that is not already there.... Right? Maybe I'm just having problems wrapping my brain around that concept.
Does my avatar look sharp? Enlarge it in photoshop by 400%. Does it still look sharp? The resolution of the image has not changed, but it is really fuzzy when big.
Now look at a picture on the wall. At a large distance, the entire picture may look sharp. Walk up to it. When you get closer the background my separate from the subject. The closer you get, the more you will notice the difference of the object at the plane of focus and the background.
Think of a picture as a collection of circles. As an example, imagine the circle at the plane of focus is 1mm; just outside that plane, the circles are 2mm; and far from that plane in the background, the circles are 3mm. Your visual system has an angluar resolution in that at a certain angle a circle will be so small it will look like a dot. Let us say at 9m, a 3mm circle looks like a dot. The image will look completely sharp. If I move to 6m, the 2mm circle looks like a dot, but the 3mm circle will be big eough where it is bigger than a point and so the background looks soft, but the area around the subject appears sharp. Move to 3m from the print and now only the 1mm circle looks sharp so only the object at the plane of focus looks sharp and everything else looks fuzzy. The 3mm circles look really fuzzy and the picture appears to now have a narrow DOF. (At 9m, it had a large DOF.)
That is it.
It is related to the resolution of the human eye, whether one or two photosites in the eye are excited. Nothing else. Your brain translates that to in or out of focus. If a car approaches you from a long distance in the dark you see one lightspot that suddenly transforms into two headlights. That is the resolution limit of your eye and you could say the car has reached the limit of DOF. Oviously large structures will hit more sites. The eye is remarkebly like a sensor in that way.
It is related to the ANGULAR resolution of the eye, not the RESOLVING POWER of the eye. It is simply if the eye sees a circle of confusion as a disk or a point.
Gabriel M.A.
10-11-2006, 07:26
Film resolution has nothing to do with depth of field. It is simply the size of the circle of confusion even if the circle of confusion is larger than what the film can resolve.
You are correct, film resolution has nothing to do with DOF. The ability to resolve beyond the circle of confusion and printing large, upon examination, seems to make a difference.
If you want to start a little argument on Hooewe's on first and Watt's on second we can go down that path.
We are saying the same thing. Both depend on the "pixel" density of the eye. Of course that translates into a resolving angle, but that is already one step further.
We are saying the same thing. Both depend on the "pixel" density of the eye. Of course that translates into a resolving angle, but that is already one step further.
Well, we are talking about the same thing, but then again we are not. Here again, it is not a "pixel" density problem, but it is whether you see a disk (blur) or a point. (Your eye is always moving and rod and cone size (pixel pitch) is not what determines what you can see.) I know it sounds crazy, but the ability to resolve something and the perception of sharpness is not the same. So we agree on principle, but not on mechanics.
You changed two parameters, sensor size and focal length. The relationship is not linear.
I changed the sensor size because that's what we're talking about, different sensor size! I changed the focal length in order to keep the FOV constant. I needed the FOV constant because that actually has an application in practical use of these cameras for actually taking pictures. Keeping the focal length constant and only changing the sensor size might make a nice physics experiment but has little or no relevance to which sensor-size will give greater or lesser DOF for a given composition. That's what I think most people would be concerned with if they are actually shooting pictures. You've got a scene in front of you with a specific composition, requiring a particular FOV. That will require different focal length lenses depending on the sensor size. The smallest sensor will require the shortest focal length, and the DOF will be greatest.
Most people will be using the lenses they already have on th M8, Ben, not 7.5 mm focal length or similar....
Yes, but if they are taking pictures not studying physics they will be comparing the DOF based on the composition not the focal length. Someone will compare the same shot taken with his M7 and his M8, same size print and find that the M8 shot has more DOF ...because to get that same shot with the M8 he had to use a shorter focal length lens. How the DOF of a 50mm lens compares from one sensor to another is really not relevant to actual photography since using a 50mm on 2 different sized sensors won't give you the same shot. Capiche?
anselwannab
10-11-2006, 08:13
I always thought "Circle of Confusion" would be a good name for a band. CoC for short.
Rock On!
I'd like to see a plot with distance on the x axis, circle of confusion on the y and I assume bell shaped(?) type curves for different F-stops. That way you could know that some CoC is needed for a certian sensor size and enlargement.
I assume if the x were fashioned correctly, you could just slide it back and forth and get the curves for any distance. Plus you could get an idea of how close you were getting to OOF.
An idea, I don't claim that it is a good one.
Mark
Yes, but if they are taking pictures not studying physics they will be comparing the DOF based on the composition not the focal length. Someone will compare the same shot taken with his M7 and his M8, same size print and find that the M8 shot has more DOF ...because to get that same shot with the M8 he had to use a shorter focal length lens. How the DOF of a 50mm lens compares from one sensor to another is really not relevant to actual photography since using a 50mm on 2 different sized sensors won't give you the same shot. Capiche?
No, Ben , I do not capiche, for three reasons:
1. If the theory behind DOF is not understood one gets reactions like it is a law of physics, or it does not change, or it is a property of the lens etc. See this thread
2. The difference in DOF between film and the M8 is just over 1/2 a stop, so hardly relevant and it is not very illuminating to compare film to minisensors with the attendant focal lengths.
3. RD1 users report this to be a total non-issue.
Well, we are talking about the same thing, but then again we are not. Here again, it is not a "pixel" density problem, but it is whether you see a disk (blur) or a point. (Your eye is always moving and rod and cone size (pixel pitch) is not what determines what you can see.) I know it sounds crazy, but the ability to resolve something and the perception of sharpness is not the same. So we agree on principle, but not on mechanics.
So if I had Delirium Tremens I would have more DOF? :D:D
I don't know how the RD-1 people consider it a non-issue because that's a 1.5x and on my 1.6x 20D there's a very perceptible difference in DOF for shots of equal FOV compared to full frame. The same shot I use an 80mm lens for on a 5D, I must use a 50mm lens on my 20D and I get clearly, obviously and significantly more DOF (same size final printl). If there's only a half a stop difference between full frame and the 1.33x M8 I'll be a very happy camper...that would be terrific.
I'm sure we'll both be happy:):) It is about 2/3 of a stop, actually.(on the same lens, though)
I'm sure we'll both be happy:):) It is about 2/3 of a stop, actually.(on the same lens, though)
The shot I'd use a 50mm for on the M8 would require only a (closest approximation) 65mm on an M6, not an 80mm as it would on a 20D, so I'd expect less of a DOF difference. In some cases, like most outdoor photography, the slightly expanded DOF will probably be more an asset than a liability. Only with portraiture will it be a hindrance and fortunately it's easy to blur a background in Photoshop whereas sharpening it would probably require compositing 2 images.
Consider this as well: It may not always be necessary to move down in focal length for the same FOV. The use of a chimping screen will enable users to compose more tightly with confidence for many subjects. I don't know about others, but I often find I've left a "security margin" around my shots, resulting in a mild crop for the final composition.
Who was it who said "If they give you lemons, make lemonade" ? :D
The difference between a 35 on a M8 and a 50 on a film M will be a couple of inches at best. I don't think the markings on the lens are acurate enough to see it now.
IMHO they can't be because Leica doesn't know what I find acceptably sharp at what enlargement.
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.
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
10-11-2006, 19:36
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.
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.
10-11-2006, 20:11
I. Donough's on Third...
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.
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.
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
10-12-2006, 18:54
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
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.
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
10-12-2006, 20:17
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.)
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
10-12-2006, 22:59
I suggest you read a very good article (it was cited here before) on the Bob Atkins web site (http://www.bobatkins.com/photography/technical/digitaldof.html) 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).
http://www.bobatkins.com/photography/technical/digitaldof/10Ddof.jpg
I suggest you read a very good article (it was cited here before) on the Bob Atkins web site (http://www.bobatkins.com/photography/technical/digitaldof.html) 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).
http://www.bobatkins.com/photography/technical/digitaldof/10Ddof.jpg
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.
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
10-13-2006, 06:12
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:
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