leica M, Medium Format and film speed

What?

What?

I repeat my earlier point: there is only one point in space which is theoretically in focus. If your equipment is calibrated properly and the film is flat, that point will be at the distance you have focused at. If you focused at 1 m, only objects at 1 m from your film plane are in focus, what's at 0.99m and what is at 1.01m are not in focus.

A lens is designed to gather light rays and focus it to a point that you decide, regardless of the size of the lens. This is why I say that focus has nothing to do with format.

DOF is a separate matter. How large the DOF is depends on various factors, such as aperture, distance, focal length, etc. You can look up the formulas, but in brief, the DOF of a medium format lens is shallower than that of a 35 mm lens basically due to the longer focal lengths involved.

As for why min aperture decreases with format-- I've never asked. I've never associated it with a COC issue. I always felt it was an engineering consideration, ie f64 is so small on a 35 mm lens it's hard to make the aperture blades stop down to that precision. Considering 35 mm lenses can be as short as 10 mm, it's not surprising.

Nevertheless, even if one can't build an f/64 35 mm lens, one can still do the theoretical calculations for DOF of a 35 mm lens stopped down to f/64. I'm sure it's larger than a 6x6 lens stopped down to f/64. If it's soft it would be because of diffraction, which is not a COC issue.

The only relation COC has to format is an indirect one, ie degree of enlargement. However, this may be counter-balanced by the fact that a MF lens has a shallower DOF compared to a 35 mm lens.

We can have a separate discussion on COC and DOF if you want. I know people argue a lot about these things. Eg I've seen heated discussion on whether DOF changes with crop factor on DSLR's. But my own experience with MF and 35 mm shows that for the same aperture, the DOF is much shallower on my Hassys, so I'm getting much more blurred backgrounds in my Hassy portraits compared to my 35 mm. I'm not sure if the lower enlargements from 6x6 fully compensates for the shallower DOF, I think that would make an interesting discussion.


Finder said:
Well, if the coc is not related to format, why does the minimum relative aperture decrease with the increase in format? Digital P&S have a minimum aperture of f/8 or f/11. 35mm, f/22, 4x5, f/64, 8x10, f/128. coc DOES change with format as what is considered "sharp" (a subjective quality) is a matter of the angular resolution of the human eye and, as you pointed out, "sharp" will be different for different folks.

This is why there is not one plane of focus, but a small range where an image will be "sharp," termed "depth of focus." This is also dependant of relative aperture. At f/64, a 35mm frame will be soft no matter how hard you try to focus.

"Sharpness" is a subjective quality. Format impacts it.
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waileong said:
My point is clear: there is only one point in space which is theoretically in focus. If your equipment is calibrated properly and the film is flat, that point will be at the distance you have focused at. If you focused at 1 m, only objects at 1 m from your film plane are in focus, what's at 0.99m and what is at 1.01m are not in focus.

A lens is designed to gather light rays and focus it to a point that you decide, this has nothing to do with format. This is why I say that focus has nothing to do with format.
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Actually, you are confusing the plane of focus with depth of focus. The plane of focus is an optical plane, but it does not indicate sharpness. Depth of focus indicates the space in front and behind the focal plane wher an image will appear sharp. The depth of focus is part of lens and camera design as it defines the tolerances in the design.

Do not confuse depth of focus, which descibe image space, with depth of field, which describes object space.

DOF is a separate matter. How large the DOF is depends on various factors, such as aperture, distance, focal length, etc. You can look up the formulas, but in brief, the DOF of a medium format lens is shallower than that of a 35 mm lens basically due to the longer focal lengths involved.

As for why min aperture decreases with format-- I've never asked. I've never associated it with a COC issue. I always felt it was an engineering consideration, ie f64 is so small on a 35 mm lens it's hard to make the aperture blades stop down to that precision. Considering 35 mm lenses can be as short as 10 mm, that's not surprising.

Nevertheless, even if one can't build an f/64 35 mm lens, one can still do the theoretical calculations for DOF of a 35 mm lens stopped down to f/64. I'm sure it's larger than a 6x6 lens stopped down to f/64. If it's soft it would be because of diffraction, which is due to the laws of optics.

The only relation COC has to format is an indirect one, ie degree of enlargement. However, this may be counter-balanced by the fact that a MF lens has a shallower DOF compared to a 35 mm lens.
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There is no mechanical limit to the aperture size. It is simply because resolution decreases because of relative aperture because of diffraction. Larger format can handle larger spot sizes caused by diffraction and still appear sharp. Just because you can calculate DOF does not mean the image is "sharp." But the effect of diffraction is evident in a single system. A 35mm image will be sharper at f/8 than f/16 regardless of DOF.
 
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Perhaps you can then enlighten me on why there are no F1, 1.4 or F2 lenses for medium format, and certainly for large formats. Certainly there are no diffraction issues at play here, so I've always thought these were due to engineering considerations (ie weight, size, DOF being so shallow that the lens is too difficult to produce and use, etc) and cost. Do you know any other reasons?

The plane of focus should be the film plane if the equipment is calibrated properly. Depth of focus varies with format, and I think you're saying MF has a larger depth of focus than 35 mm.

Tell me, does that make up for the smaller depth of field? Because I know that shooting close up portraits at F4 on 6x6 gives me almost no room for depth of field, it's almost as if I'm shooting at F1 on 35 mm.


Finder said:
Actually, you are confusing the plane of focus with depth of focus. The plane of focus is an optical plane, but it does not indicate sharpness. Depth of focus indicates the space in front and behind the focal plane wher an image will appear sharp. The depth of focus is part of lens and camera design as it defines the tolerances in the design.

Do not confuse depth of focus, which descibe image space, with depth of field, which describes object space.


There is no mechanical limit to the aperture size. It is simply because resolution decreases because of relative aperture because of diffraction. Larger format can handle larger spot sizes caused by diffraction and still appear sharp. Just because you can calculate DOF does not mean the image is "sharp." But the effect of diffraction is evident in a single system. A 35mm image will be sharper at f/8 than f/16 regardless of DOF.
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waileong said:
Perhaps you can then enlighten me on why there are no F1, 1.4 or F2 lenses for medium format, and certainly for large formats. Certainly there are no diffraction issues at play here, so I've always thought these were due to engineering considerations (ie weight, size, DOF being so shallow that the lens is too difficult to produce and use, etc) and cost. Do you know any other reasons?
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Cost is one. A 150mm f/2 lens on a 4x5 camera is huge.

Another is tolerance. There is more variation to the image plane with larger pieces of film. It is easier keeping a 35mm frame flat.

[/QUOTE]The plane of focus should be the film plane if the equipment is calibrated properly. Depth of focus varies with format, and I think you're saying MF has a larger depth of focus than 35 mm.

Tell me, does that make up for the smaller depth of field? Because I know that shooting close up portraits at F4 on 6x6 gives me almost no room for depth of field, it's almost as if I'm shooting at F1 on 35 mm.[/QUOTE]

Depth of focus is related to the angular size of the light cone in image space - depth of field is the angular size of the light cone in the object plane. Depth of focus is aperture dependent. At f/8, depth of focus is the same regardless of focal length. Manufacturing tolerances mean the image plane must fall within the depth of focus in order for the image to be sharp. Since film and other componants - ground glass, rangefinder calibration - are never perfect, this lets the engineer know how good the system needs to be.

But that is not the whole story as the coc defines "sharp." The smaller the aperture, the greater the affects of diffraction. At f/64 with the film at the focal plane, the image will appear sharp depending on the format. Permissible coc are based on a relative point size. If the point (Airy disk) is too large, it will look soft.

Let me see if a CCD will make this clearer - I am going to exchange Airy disks for pixels. In order for a pixel to look sharp it must be small enough so its dimension cannot be seen - same with coc. If I have a few CCDs with a 7 micron pixel, will it produce a sharp 8x10 print? That would depend on how big the chip was. If the chip is only 640 x 480 pixels, the print will look soft as the pixels are getting too big. If it is 6400 x 4800 (and hense a larger format because we are keeping pixel size constant as well as field of view), then the print pixels will look sharper.

Larger format sizes don't require the same Airy disk sizes as smaller formats. Sharpness has nothing to do whether an image falls on a focal plane, but the quality of the image itself. If the Airy disk size is too large, then the image will look soft. So 4x5 images can be shot at f/64 and look sharp, but 35mm images cannot. Sharpness is relative and dependent of format. One of the biggest problems in optical design now for P&S digital cameras is making lenses with enough resolving power to create a sharp image on the small high-res chips.
 
I sold the medium format rig earlier this year. Basically because it's too heavy to carry around on a daily basis like I do with a small format camera. So basically it always stayed indoors; such a waste.. But one thing's certain; not a day goes by that I don't long back for the MF's image quality. No matter how high resolution the small format lenses are that I have, 35mm just can't match MF as far as image quality is concerned. In the end, portability won over image quality..
 
As a rule I would say that medium format is best suited to situations where there is a lot of light. I've found that a dull winter's day the limit for my Pentax as 1/250 at 5.6 is the lowest really practical hand holdable shutter speed and aperture combination. I have shot a f2.4 but with the 105mm but this can be very tricky so you have to shoot more and with 10 frames per roll, this starts to present its own problems. I'm sure that mamiya 6's can be hand held at lower speeds but you'd still have the DOF issues, which are of course exacerbated if you're shooting anything moving. To be honest from the testing I've done digital gives the best practical image quality in low light situations, if you like the 'look'.
 
some 120 delta 3200 that I ran through my yashicamat before came back surprisingly clean, probably similar to 135 xp2.

I had a mamiya 6 before to but sold it for the (for me) more versatile and easier to deal with 35mm format, plus the camera kept falling apart on me on my long treks so it got the boot. I say go for the 35mm option with your mamiya's, it will work great.
 
[on selling MF after buying a Leica...

QUOTE=jaffa_777]Why is that Matt? I would be interested to know your reasons as I don't have own a leica body or glass.[/QUOTE]

Image quality is perhaps best substituted by Image Characteristics. Sometimes I want coarse grain and this is therefore the best image quality for my creative intent...

I would warrant though that the Leica did not produce finer grain, smoother tonality or better perceived detail/resolution at larger prints sizes. I can think of many reasons to shoot 35mm SLR over 35mm RF or either or one in particular rather than MF....but these decisions relate to teh image characteristics I want AND handling considerations.

I would NEVER choose Leica 35mm over MF if I desired super smooth tonality, fine grain and great resolution on larger prints, say 20x16. I would however stick with teh Leica even for this if the slower MF handling prevented me getting ths shot I wanted....which is actually quite often if travelling very light, unobstrusive etc. Naturally MF RFs help in thsi regard but are still not 35mm in handling due to bulk, film change frequency, lens speed etc
 
Toby said:
As a rule I would say that medium format is best suited to situations where there is a lot of light.
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I can handhold my Rolleiflex for longer than I can my M6, and the image quality of even very fast b&w MF film helps compensate for the relatively slower lens. It's more comfortable to carry on long walks too, it's physically larger but also lighter.

Ian
 
iml said:
I can handhold my Rolleiflex for longer than I can my M6, and the image quality of even very fast b&w MF film helps compensate for the relatively slower lens. It's more comfortable to carry on long walks too, it's physically larger but also lighter.

Ian
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while I never particularly got on with my Rolleicord Va, that shutter was so quiet and smooth that with a cable release (no prob with the WLF) attached it sooooo smooth and very possible to shoot at very slow speeds, so I agree about that. also remember that ANY MF RF camera is great in low light as there is no shutter slap that can be excessive on MF SLRs. A Mamiya 7 with 400 film and f4 gives the same shutter speed as a 35mm at f2 with 100 speed. If you have a tripod it becomes irelevant and one can shoot 100 speed in the MF RF too. DOF is about the same I think with an 100/80mm f4 vs a 50/40mm f2.
 
trittium said:
All I know is I stopped shooting my MF equipment once I bought a leica. :)
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All I know is I want more MF, Leica or not ;)

My only worry is that they stop producing 120 roll film format, which IMHO is the most versatile film format ever produced. Say, can you buy 120 format in bulk? seems it would be easier to hand-roll than those 35mm canisters.
 
I too got out of MF after getting my Leica. I find the 'look' I get with the Leica glass, even on that tiny piece of film is better to my eye. I've detailed my reasons for liking the format better on this threads ugly twin- for me it all comes down to the print, and the prints are just better. I shot Pentax 67, Hasselblad, Fuji over the years and find a sparkle and snap to my prints with my current kit that I never had before. As a long time LF shooter MF was my 'easy' kit- no tripod, lots of images for the weight, etc. but over the last year and a half I've gotten better prints, so for me, it is Leica over MF.
 
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