So why DO mfrs (e.g. Mamiya 7) fudge DOF markings on lenses?

I was reading some older posts about the Mamiya 7 (for example,

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=001rf7) and most

people here agree that Mamiya's DOF markings on the M7 lenses are

about 2 stops optimistic (i.e., users should set the camera to f22

when using the f11 markings).

 

My question is what advantage Mamiya (or anyone else) gains by doing

this. I can't picture buyers comparing two systems in a camera store

and going with the one that has more generous DOF markings on the

lenses. And after purchase, it seems that buyers would be happier with

the product if their photographs had more rather than less DOF than

they expected based on the lens markings.

 

Any explanation for this?

They think, M7 users enlarge to 5x7 most probably...

Most medium format camera manufacturers use a circle of confusion of about 60 microns as opposed to 30 microns for 35mm cameras. The reason is that the medium format needs less magnification to give a certain print size. This kind of logic also gives you a print that is no better than 35mm, so why pay for the bigger film? Use 30 microns for medium format and I think that you'll be happy with the results.

They just thinks that too many overrate their ability to handhold the camera steady. By encourage to use a larger aperture and faster shutterspeed, they increase the propability that at least something will appear sharp. My guess btw.

Zeiss used to to this on the Contax, compared to Leica DOF settings. Apparently it's determined by COC tolerance.

Does this only relate to lenses that came with the Mamiya 7, and not the 7II? The reason I ask is that I read the previous posts about the DOF scale before I purchased a Mamiya 7II. The first thing I did was compare the Mamiya DOF scale of the 80mm lens with the DOF scale of my Rolleiflex 2.8F 80mm lens. They match exactly, distance for distance, aperture for aperture. I may be getting this wrong, but does that mean Rollei also fudged the DOF scale of the 'flex all those years ago? I have never had a problem with it.

Steve, the M7 and M7II lenses (and DOF markings) are the same.

They do this because most photographer's technique is indeed so poor that they don't get the last bit out of a lens anyway.

The difference between the "in focus" parts and the "out of focus but still acceptable parts" (i.e. DoF) is then not that great, so when looking at the resulting prints or slides you won't notice the sharpness falling off as soon as strict DoF criteria would suggest. The scales printed on the lens reflect that.

 

So everybody still handholding (to name but one aspect) is to blame, not the manufacturer.

Steve, the largest acceptable COC is related to the diagonal of the negative, so if we assume that the M7 (56x69mm) has a too generous d.o.f scale, then the smaller Rolleiflex (56x56mm) should have a less generous d.o.f scale compared to the M7. Since it hasn´t, the Rolleiflex is even more fudged.

There is no fudging ; the COC (circle of confusion) varies by film size usually....Kodaks 1946 criteria vary:<BR><BR>8mm movie is 1/2000 inch<BR>16mm movie is 1/1000 inch<BR>The Kodak Ektra 35mm RF was 1/500 inch<BR>The old Kodak folder were 1/200 inch.<BR>Kodak Ektar Studio lenses are 2 arc minutes = F/1720 ; were F= focal lenght..<BR><BR>To make a scale; a COC must be choosen....<BR><BR>Professional Movie Camera lens tables give the DOF (Depth of Field) versus COC...ie there are several COC one can choose from; depending on the cinematographers plans.......<BR><BR>The DOF scale on my 50mm F1.4 SC Nikkor for the Nikon F is alot wider @ f5.6 than the 50 mm FL 16mm movie objective I own; The 50mm FL 8mm movie camera has even a tighter scale @F5.6....<BR><BR>there usually is no fudging; different camera formats, makers and people have different Criteria for what is sharp..This has been standard optical design criteria since probably the 1920's

Terry,

yes I know the lenses are the same, I meant maybe early ones made at the time the M7 was current had bad printing on them or something. I should have said. It was just a thought, I wasn't sure if the posts were generic 'M7' rather than specific.

Kelly, you are right strictly speeking, since there are no formal agreement on which COC should be choosen for a given film size. As I understand, The d.o.f scale on the M7 lenses are based on a larger COC than the rest of the current 6x7 models lenses of all manufactors. This deviation from a non formal standard has apperently fooled some users.

-- Bengt ;<BR><BR>Some of the 2nd tier 35mm rangefinders and SLR's will also sport slighty wider DOF scale markings; they used a slightly larger definition value for Circle of Confusion....<BR><BR>My first "discovery" of this was when I was using 35mm SLR lenses on 8mm and 16mm movie cameras....<BR><BR>I have a Nikon F to C mount adapter; and a C mount to D mount adapter.....The D mount is for my Beaulieu MR8 8mm Reflex camera with variable shutter and film speeds....The D mount to C mount adapter was purchased from Century precision optics in Hollywood.....; the only guy at the New York dealers who had heard of an adapter like this was Olden Camera.....They refered me to Century; the adapter was 12 buck 30 years ago...<BR><BR>Using the Nikkor 50mm F1.4 @f4 or F5.6 yielded fantastic results with the tiny Regular 8mm film; Kodachrome..........Because of the great magnification; the smaller 1/2000 inch COC must be used on 8mm...Thus when switching formats the DOF scales should be altered and made smaller.......Using the American Cinematograpers Manual is helpfull; it discusses the COC for different film formats....<BR><BR>As a goof we mounted my 400mm F6,3 Spiratone "girlwatcher" lens to the 8mm Beaulieu MR8 8mm camera...This was by using the T mount to Nikon F; Nikon F to C mount (16mm); and lastly the C mount to D mount......The rig had to had to be supported at both ends.....reflex focusing at F6.3 was poor...to get focus we would hunt for a specular highlight (round chrome hubcap) to focus upon......

For anybody interested still, there is an interactive DOF calculator at http://people.smu.edu/rmonagha/brondof.html Very easy to use, and guess what? Yes, it does seem to agree with the DOF scale on the 80mm Mamiya lens at least.

There seems to be a international standard in DOF scales, Zeiss explains this (http://www.zeiss.de/C12567A8003B0478?Open) in the Camera Lens News #1 on their website. The most important thing I learned from this is, that these on-lens DOF scales are not valid with good lenses and fine films today. A DOF caculator that let's YOU choose what COC you want, would be the way to go IMHO. I personally do as the poster does, e.g. when my desired DOF would be @f4 as judged by the on-lens scale I stop down to 8.

Mamiya has been criticised many times on this forum for "stretched" depth of field indications, but I measured my Mamiya 7II lenses, measureing the change in extension for indicated DOF change, and they are in line with some of my Hasselblad lenses! Maybe the lenses are so sharp (and they are sharp, sharp, sharp!) that they are more noticable when they fall off focus slightly. Or maybe the materials and design result in slightly less actual DOF. Contrary to often repeated dogma, DOF for different lenses of equal focal can vary according to design, Zeiss will confirm this.

 

Bringing a little more confusion into it, I have measured the change in extension of the 38, 50, 100, 120, 150, 180, 250SA Zeiss/Hass lenses, and there seems to be no logical change in extension/DOF ratio as you go lens to lens. The change in DOF markings don't progress as a funcion of focal length, but rather go up and down as you go from one focal length to the next up. Either Zeiss is marking DOF based on actual experience with each lens (I doubt it as there are some dramatic indicated DOF changes for small focal length changes from one lens to the next, some of which make no sense based on my experience with the lenses) or they have changed their thinking over a fairly short period of time. The production of these lenses is all within 6 years of each other.

 

I prefer the way I do it with my RZ, to measure change in bellows extension when focusing on near and then far objects, and use my own factor to get to DOF. If the subject has much severe detail or sharp edged contrast, where focus might be more noticeable in the image, I bump up an extra stop.

 

There are many reasons why a great familiarity with your lenses and their rendition of the image is important, and this issue of DOF is one of them.

About four years ago I opened my brand-new 501CM and 80mm lens, shot a test roll and was dissapointed with the max DOF transparencies. I called Hasselblad and they asked for the slides, which I sent. A week later I received a detailed letter stating that the focus range was exactly what Hasselblad had determined it shoulb be. In other words, they considered some softness at either end of the range "acceptable." After that I just set focus for +2 stops when I needed max DOF and greater sharpness. I think that even if there is a "standard" COC, it's an arbitrary standard. After being frustrated ith 6x6 for a year I went back to 6x7. I don't own an M7, but the DOF scale on my RZ lenses seems more accurate than the Zeiss 80.