Jeff S
Well-known
On the relationship of DOF to focal length, just look at the pictures in the Luminous Landscape article I linked in my last post (you did read it , right?). If you can't follow that, I obviously can't offer more 'proof' on that issue.
As for DOF scales on lenses, here's an interesting discussion from the LUF...http://www.l-camera-forum.com/leica...934-accuracy-depth-field-scale-lenses-m8.html See especially the comments from Lars Berquist and Sean Reid, two guys who know more than I, and who base their conclusions on real picture taking, not theories. (We at least agree that real tests trump therories.)
In particular, Sean even notes that two lenses of the same focal length don't even necessarily show the same DOF...let alone what the scales show.
Most pros have learned to at least halve the apertures indicated on lens DOF scales (say f4 rather than f8) to accommodate larger modern print sizes as well as digital versus film issues. But, even then, as Sean points out, there are tons of other variables involved. Anyone who relies on a scale, or on a set formula, either is not very discerning, or else doesn't understand the factors involved.
Jeff
Finder
Veteran
So the Luminous Landscape article is changing two factors at the same time. It is a very sloppy article and sloppy thinking to come to the conclusion that DoF is unrelated to focal length. Especially since the test shows the DoF changing in each picture.
First, a "theory" in science is a hypothosis supported by evidence. A "theory" is not an opinion. The link to the forum is simply showing opinion. Can Sean offer proof of his assertions and can he show the underlying reasons for the difference in DoF?
Who are these "professsionals"? I happen to be a professional. Show me the scales on Horseman SW612 actually are not accurate even though I think they are. Mind you I mostly print 4ft prints and rarely go above a 6ft print, although I did help produce several 12 ft prints this spring.
And here is something for you to think about--DoF in a print will be the same when the viewing distance is kept proportional to the print size. I would say your "experts" don't know what they are doing. They certainly don't understand depth of field.
The OP wants to know what to do with his 135 lens depth of field scales when using it on a smaller sensor. I have shown him a method to adjust for that. I see no evidence that DoF has changed where my advice is wrong.
Rob-F
Likes Leicas
not only is it metaphysical, it is completely irrational
I wonder how many folks got this subtle play on words!
jaapv
RFF Sponsoring Member.
This is DOF confusion thread # 14 since I joined this forum... Guys use the search function and remember DOF is an optical illusion anyway, caused by the imperfection of the human eye. When I take a photograph I always try to place the plane of focus where I want it and assume DOF = 0. Gives me plenty of reserve, irrespective of the size of the final print....
ampguy
Veteran
probably no one but you
probably no one but you
The other folks are too busy re-hashing internet babble, as opposed to getting out and and spending an few hours of time to test what I've proposed earlier.
probably no one but you
The other folks are too busy re-hashing internet babble, as opposed to getting out and and spending an few hours of time to test what I've proposed earlier.
ampguy
Veteran
yup
yup
As digital users, going beyond f4 is silly anyways because of diffraction. The problem is most Leica users have slow shutter speeds of 1K and will get more flare if they use ND filters, so if you don't want to go to digital, you should go to Bessa film cameras or ZI/Hexar RF, etc.
Leica should be issuing their lenses with an a la carte option of wide open only, and focus fixed on infinity.
yup
As digital users, going beyond f4 is silly anyways because of diffraction. The problem is most Leica users have slow shutter speeds of 1K and will get more flare if they use ND filters, so if you don't want to go to digital, you should go to Bessa film cameras or ZI/Hexar RF, etc.
Leica should be issuing their lenses with an a la carte option of wide open only, and focus fixed on infinity.
This is DOF confusion thread # 14 since I joined this forum... Guys use the search function and remember DOF is an optical illusion anyway, caused by the imperfection of the human eye. When I take a photograph I always try to place the plane of focus where I want it and assume DOF = 0. Gives me plenty of reserve, irrespective of the size of the final print....
peterm1
Veteran
DOF is controlled by the lens not the sensor. To be more precise its the size of the aperture in use. Remember that f stops measure the amount of light hitting the film plane / sensor. And the size of the aperture varies depending on a range of factors. - Longer lenses other things being equal must have a physically larger aperture at (say) f8 than a shorter lens to have the correct amount of light hitting the film plane when using f8. This means less depth of field as the larger the "hole" the smaller the DOF. For a similar reason DOF tends to vary with camera format - large format cameras have larger lenses which are further from the film plane (with larger physical aperture sizes) and so narrowed DOF than equivalent 35mm format cameras. At the other end of the scale a small sensor digital camera will have more DOF at each f stop if it is designed to use physically smaller lenses. But as you are using a standard 35mm format lens on your camera DOF should be the same.
Finder
Veteran
Done the test and you are wrong.
Jaques H
-
I totally don't understand this.
1K = 1/1000 ? I thought that was a fast shutter speed not slow.
jaapv
RFF Sponsoring Member.
Umm - All very well, but when taking the same image with the lens appropriate to the sensor/film format the DOF will shrink as the size of the sensor/film gets larger. And that is what counts in real life. All the rest is theoretical smokeblowing.
Whether the lens is designed for a larger format i.e. with a larger coverage is irrelevant. It is the angle of view that the particular format uses that counts. Otherwise a shift lens would have a different DOF from a standard lens of the same focal length when used on an identical camera.
JoeV
Thin Air, Bright Sun
Actually, these DOF threads are interesting. There are lots of pre-conditions built into manual focus lens' DOF scales, which we can all-too-easy take for granted. One thing that's obvious is these scales were originally intended for use with 135-format camera bodies. When we adapt them to other camera formats (M8 or u4/3 for instance) we have to understand the underlying assumptions all over again.
As many have already stated, DOF, is related to magnification ratio. But if you're comparing images using the same lens from two different format bodies (135 vs M8 for instance), are you comparing final images of equal size? Because if you are, then you've already violated one assumption, which is magnification ratio. The smaller camera format would be given a higher magnification ratio in comparison to the larger format, if final image size were kept constant between both formats under examination.
Another assumption is about one's testing criteria: are you comparing equal subject distances between both formats, or equal angles of view? Because the results will vary depending on your preconditions.
The Circle of Confusion factor in the DOF formula also need to be understood, as these depend on magnification ratio. If you're using the same COC factor between two different camera formats in your comparisons, you may have also violated the preconditions to a valid test, since different sensor sizes may yield different magnification ratios, depending on your final image size. If you maintain a constant COC factor and magnification ratio, then your final image sizes being compared will be of different sizes between the formats under comparison.
Remember, DOF is all about changes in focus that produce no visible change in resolution to the human observer, based on a standard print size, enlarged from the in-camera image at a specific magnification ratio, being viewed at a specific distance. So you ALWAYS have to take into account magnification ratio.
How all of this applies to viewing digital images at specific distances on computer monitors of various sizes, that's another discussion entirely.
~Joe
PS: When we speak of "magnification ratio" in reference to DOF, it is the ratio of size between the in-camera image and the enlarged, final (i.e. printed) image, which is the standard for defining DOF. We're not talking about the ratio of size between the subject and the in-camera image projected by the lens to the film/sensor.
As many have already stated, DOF, is related to magnification ratio. But if you're comparing images using the same lens from two different format bodies (135 vs M8 for instance), are you comparing final images of equal size? Because if you are, then you've already violated one assumption, which is magnification ratio. The smaller camera format would be given a higher magnification ratio in comparison to the larger format, if final image size were kept constant between both formats under examination.
Another assumption is about one's testing criteria: are you comparing equal subject distances between both formats, or equal angles of view? Because the results will vary depending on your preconditions.
The Circle of Confusion factor in the DOF formula also need to be understood, as these depend on magnification ratio. If you're using the same COC factor between two different camera formats in your comparisons, you may have also violated the preconditions to a valid test, since different sensor sizes may yield different magnification ratios, depending on your final image size. If you maintain a constant COC factor and magnification ratio, then your final image sizes being compared will be of different sizes between the formats under comparison.
Remember, DOF is all about changes in focus that produce no visible change in resolution to the human observer, based on a standard print size, enlarged from the in-camera image at a specific magnification ratio, being viewed at a specific distance. So you ALWAYS have to take into account magnification ratio.
How all of this applies to viewing digital images at specific distances on computer monitors of various sizes, that's another discussion entirely.
~Joe
PS: When we speak of "magnification ratio" in reference to DOF, it is the ratio of size between the in-camera image and the enlarged, final (i.e. printed) image, which is the standard for defining DOF. We're not talking about the ratio of size between the subject and the in-camera image projected by the lens to the film/sensor.
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ampguy
Veteran
Peter - here's an alternate explanation
Peter - here's an alternate explanation
from the cambridgeincolour site, on why fl may not matter, as the larger physical opening is offset by the divergence created by the distance to focal plane:
On their DOF page, they do mention the ratios of front/rear DOF shifting rearwards with longer fl's.
"
Technical Note:
Since the physical size of the lens aperture is larger for telephoto lenses (f/22 is a larger aperture at 200 mm than at 50 mm), why doesn't the size of the airy disk vary with focal length? This is because the distance to the focal plane also increases with focal length, and so the airy disk diverges more over this greater distance. As a result, the two effects of physical aperture size and focal length cancel out. Therefore the size of the airy disk only depends on the f-stop, which describes both focal length and aperture size. The term used to universally describe the lens opening is the "numerical aperture" (inverse of twice the f-stop). There is some variation between lenses though, but this is mostly due more to the different design and distance between the focal plane and "entrance pupil."
"
Peter - here's an alternate explanation
from the cambridgeincolour site, on why fl may not matter, as the larger physical opening is offset by the divergence created by the distance to focal plane:
On their DOF page, they do mention the ratios of front/rear DOF shifting rearwards with longer fl's.
"
Technical Note:
Since the physical size of the lens aperture is larger for telephoto lenses (f/22 is a larger aperture at 200 mm than at 50 mm), why doesn't the size of the airy disk vary with focal length? This is because the distance to the focal plane also increases with focal length, and so the airy disk diverges more over this greater distance. As a result, the two effects of physical aperture size and focal length cancel out. Therefore the size of the airy disk only depends on the f-stop, which describes both focal length and aperture size. The term used to universally describe the lens opening is the "numerical aperture" (inverse of twice the f-stop). There is some variation between lenses though, but this is mostly due more to the different design and distance between the focal plane and "entrance pupil."
"
Finder
Veteran
Joe, very well put, except I take issue with that.
Simply stated, you cannot know how someone will frame something or at what distance you will shoot from. You can't assume that with the loss of angle of view, the photographer would try to use the lens the same way as with the same field of view on the larger format. I know angle of view changes how I use a lens. There is not much I can do to get further away from a sunset.
So what can be said about DoF that is not going to have arbitrary uses such as framing is important. So I use a cv 12mm on my E-P1. I know the depth of field scales are compensated by two stops--I use f/5.6 scales when shooting at f/11. I don't need to know anything else to use it. Framing, angle of view, object distance are irrelevant.
Finder
Veteran
Roland, nicely put, but I am getting the feeling of Deja vu all over again. :bang:
Why are we the only ones with examples? :angel:
:bang:Why are we the only ones with examples? :angel:
ferider
Veteran
Yeah, sorry, I just thought a pretty girl and booze might help.
Finder
Veteran
It certainly would! But I will content myself with your photos.
ampguy
Veteran
OK, I'd like some input here for my testing. I'm delaying my planned viewing of "It's Complicated" to another night. I have my tripod setup and cleared off the table, but only have about 3-4m to work with and getting f8 at hyperfocal is going to require me to use a wide lens, is 21 OK with everyone?
Also, I don't have an MP, only an M6, hope that's OK. Any preferences for film type, subject distances?
Also, I don't have an MP, only an M6, hope that's OK. Any preferences for film type, subject distances?
I can’t see a difference.
ferider
Veteran
Look at the background and the size of the oof "blur" circles (behind her left ear).
Keith
The best camera is one that still works!
It's no wonder this place struggles to attract actual photographers ... and the ones that do land here get bored pretty quickly and soon make a hasty exit.
Bloody scientists!
(tongue in cheek)
Bloody scientists!
(tongue in cheek)