[Ben_Edict]

Someone with technical knowledge could step in here please...

Since medium format lenses have approximately half the resolving power of SLR lenses (30-45 lines per mm vs 60-90 lines per mm--depending on who does the testing and what the parameters are). Wouldn't that result in less sharpness than shooting with high quality SLR lenses?

I know that in analog form, since 6x7 system produces a much larger image--4.5x larger than 35mm--you need less magnification to print and thus "buy back" the resolution in reduced magnification to achieve the final print. I get that, but I also realize that digital doesn't translate quite as easily into "final print magnification".

So even if you are only using the center "sweet spot" of the MF glass, if that still has lower resolution than, say a Limited lens, wouldn't the Limited produce much sharper images than the 6x7 lens with adapter? Even "standard issue" DA lenses have higher resolving power than the best 67 lenses and thus should produce sharper images...

Again, someone with expertise please help!

You are completely right. The larger the film format the lens was computed for, the lower the resolution. That is the general rule. But there are ofcourse quite a few exceptions, like the digitally optimized large format lenses by Schneider (extremely expensive, though), which have such a high resolution, that they should work nicely with a DSLR. Also the Mamiya 645 200mm APO is great on APS-C as are some MF macro lenses. But in general I would only use those MF/LF lenses, which I already have and which I don't have for 35mm/DSLR. Buying MF lenses expressedly for use on a DSLR is mostly just a nice way of experimenting. Or you might have the need for the larger image circle for shifting/tilting etc.

Ben

[Ron Boggs]

Glad to know I'm not partying with Phelps on this issue...

I love my 67 system lenses just as you enjoy your Mamiya stuff, but really Ben, you aren't trying to say the Mam. 200 has 80 or 90 lines of resolution are you? Not to be a jerk, but it sounds like you are trying to justify your MF lens to yourself. What is the resolving power of that lens, and actually, without a direct adapter to use it on Pentax digi bodies, is it relevant at all?

[Ron Boggs]

Sorry about the tone in that last post, Ben. As a Pentax medium format shooter, I've gotten tired of hearing Mamiya this and Mamiya that all the time for the past ten years. When you brought up your Mamiya lens rather than any of the ED Pentax * lenses, it felt like you poked me in the eye with a stick. That's my personal problem. Didn't mean to throw it back at you like that...

[Ben_Edict]

Sorry about the tone in that last post, Ben. As a Pentax medium format shooter, I've gotten tired of hearing Mamiya this and Mamiya that all the time for the past ten years. When you brought up your Mamiya lens rather than any of the ED Pentax * lenses, it felt like you poked me in the eye with a stick. That's my personal problem. Didn't mean to throw it back at you like that...

I don't mind. I don't use any of my Mamiya lenses on the small DSLRs (I only have Mamiya MF and no Pentax, so I can't write about the quality of those!), as I have pretty much covered all focal lengthes for the Pentax DSLR with zooms and primes double and threefold. No, but I have seen images with a Nikon D300 and the Mamiya 200mm Apo by a colleague and these were absolutely en par with any other lens of this focal length dedicated to 35mm.

The only thing I am contemplating is using my 4x5 cameras with an adapter back for Pentax, to make panoramas with a simple back shift. That is convenient and very exacting - but I have no clue yet, whether my LF lenses will be any good with such a dense sensor.

Ben

[Jewelltrail]

FeverBeaver: It is a self-made adapter. One Rear Lens Cap 3rd-party, one old bayonet from a F 35-80 and the Auto Extension Tube 19mm.

That is cool! I love it when I am able to use my creativity and mechanical skills to make things like this--nice work!

[calicojack]

It is a selfmade adapter. One Rear Lens Cap 3rd-party, one old bayonet from a F 35-80 and the Auto Extension Tube 19mm.

Yes, a nice piece of creative craftsmanship. I assume you can't focus to infinity though.

[feverbeaver]

Yes, a nice piece of creative craftsmanship. I assume you can't focus to infinity though.

Focus to infinity is no problem. The flange focal distance of 6x7 is 84.95 mm the one of the K-mount is 45,50 mm.
My adapter is 20,40 mm, the extension tube 19,00 mm.
Total: 39,40 + 45,50 = 84,90 mm

I can focus beyond inifinity.

[calicojack]

Focus to infinity is no problem. <> I can focus beyond inifinity.

Nice! I forgot how big the 67 body is.

To infinity and beyond! (I seem to remember that from somewhere.)

[Jewelltrail]

Ron Boggs: Since medium format lenses have approximately half the resolving power of SLR lenses (30-45 lines per mm vs 60-90 lines per mm--depending on who does the testing and what the parameters are). Wouldn't that result in less sharpness than shooting with high quality SLR lenses?

I know that in analog form, since 6x7 system produces a much larger image--4.5x larger than 35mm--you need less magnification to print and thus "buy back" the resolution in reduced magnification to achieve the final print. I get that, but I also realize that digital doesn't translate quite as easily into "final print magnification".

So even if you are only using the center "sweet spot" of the MF glass, if that still has lower resolution than, say a Limited lens, wouldn't the Limited produce much sharper images than the 6x7 lens with adapter? Even "standard issue" DA lenses have higher resolving power than the best 67 lenses and thus should produce sharper images

Ron: I am definitely not someone with technical expertise, but I do have 2 decent eyes and an opinion, so I just did a quick test to put them to work.

I took a shot with my Tammy 17-50mm @ 50mm and f5.6 manually focused. Then by slightly moving the tripod back a little bit to try and offset the tad extra reach my Pentax 67 SMC 55mm f4 lens has, I took another shot @ f5.6 with it.

A quick but careful comparison of the images shows nothing conclusively, except the Tamron renders a bit more underexposed when both lenses are with identical EXIF, something I already suspected about the Tammy.

I manually focused both shots, so there is a margin for error. My first observations do not support that MF lenses, in general, tend to have half the resolving power of good APC glass. I will need to do more shooting, within set parameters, but it is possible that the MF Pentax 55 is sharper than the Tamron 17-50 is @ 50mm. Do you have any thoughts? Does anyone for that matter? I would love to hear and learn more.

I do have a very nice copy of the Tammy. And I believe the resolution figures, though not immediately available to me, are impressive.

[Ben_Edict]

Ron: I am definitely not someone with technical expertise, but I do have 2 decent eyes and an opinion, so I just did a quick test to put them to work.

I took a shot with my Tammy 17-50mm @ 50mm and f5.6 manually focused. Then by slightly moving the tripod back a little bit to try and offset the tad extra reach my Pentax 67 SMC 55mm f4 lens has, I took another shot @ f5.6 with it.

A quick but careful comparison of the images shows nothing conclusively, except the Tamron renders a bit more underexposed when both lenses are with identical EXIF, something I already suspected about the Tammy.

I manually focused both shots, so there is a margin for error. My first observations do not support that MF lenses, in general, tend to have half the resolving power of good APC glass. I will need to do more shooting, within set parameters, but it is possible that the MF Pentax 55 is sharper than the Tamron 17-50 is @ 50mm. Do you have any thoughts? Does anyone for that matter? I would love to hear and learn more.

I do have a very nice copy of the Tammy. And I believe the resolution figures, though not immediately available to me, are impressive.

I don't know about the Tamron. But a more valid comparisson would be between the FA 50 and the 67 55mm lenses - both being primes. I don't think a standard zoom (whether it be the Tammy, a Sigma or a Pentax or Canon etc.) can reach the peak MTF of a fixed focal length lens. Especially not, as they cover quite a wide reach from wide-angle to a light tele on APS-C.

On the other hand, you sure profit from the sweet spot behaviour of the 67 lens on the tiny digital sensor. Published lens data suggest, that resolution for larger formats goes down heavily, compared to 35mm. So you will find tele lenses for 4x5 or larger, that are considered to be solid performers with resolutions as low as 30 lp/mm and even less.

I think the point is, that MF and LF lenses do not need the high resolving power, but that does not prevent the lens designer to achieve high res with such a lens sometimes. Maybe the Pentax 55mm falls into this category?

Ben

[Ron Boggs]

Wouldn't it be nice to start with a chart listing the resolution of each Pentax lens--and all tested under the same parameters. "Tested" meaning establishing a resolution measurement with a lines per mm figure. With in-camera sharpening of JPEG's and computer screen resolution variables, an "eye test" really isn't what I was hoping for.

And note that resolution certainly isn't the only measurement of a lens' output. Things like color pop, minimal diffraction effect, and killer bokeh produced by 67 system lenses may well be worth halving the resolution?

Just as it is general knowledge that medium format lenses have approximately half the resolution in lines per mm than the small format lenses...medium format lenses have far less "issues" with diffraction at tiny apertures. However, since APS-C has greater diffraction problems than 35mm which has greater diffraction problems than medium format...will the smaller sensor diffraction issues prevail? Or will the lower diffraction problems of the lens win out? Ah, if this stuff was easy everyone would do it.

Since I already own some very nice 67 lenses, including two M* EDIF models, I have a vested interest in learning about the issues we've been discussing in this thread. Can I cross-apply my 67 lenses to my digi bodies and still get publication quality images? My interests are not simply "will it work" or "will it work fairly well". I need to know if the results are competitive with the finest images competing in the marketplace--or at least in the magazine editor's marketplace. I'm hoping to learn from others because I don't trust my ability to analyze digital images. It's all just a bunch of electrical current to me.

[vizjerei]

XD Good that I didn't get a 645 300mm lens as my telephoto lens for K10D ( at a time there are many cheap ones on ebay...)

[Ben_Edict]

Wouldn't it be nice to start with a chart listing the resolution of each Pentax lens--and all tested under the same parameters. "Tested" meaning establishing a resolution measurement with a lines per mm figure. With in-camera sharpening of JPEG's and computer screen resolution variables, an "eye test" really isn't what I was hoping for.

And note that resolution certainly isn't the only measurement of a lens' output. Things like color pop, minimal diffraction effect, and killer bokeh produced by 67 system lenses may well be worth halving the resolution?

Just as it is general knowledge that medium format lenses have approximately half the resolution in lines per mm than the small format lenses...medium format lenses have far less "issues" with diffraction at tiny apertures. However, since APS-C has greater diffraction problems than 35mm which has greater diffraction problems than medium format...will the smaller sensor diffraction issues prevail? Or will the lower diffraction problems of the lens win out? Ah, if this stuff was easy everyone would do it.

Since I already own some very nice 67 lenses, including two M* EDIF models, I have a vested interest in learning about the issues we've been discussing in this thread. Can I cross-apply my 67 lenses to my digi bodies and still get publication quality images? My interests are not simply "will it work" or "will it work fairly well". I need to know if the results are competitive with the finest images competing in the marketplace--or at least in the magazine editor's marketplace. I'm hoping to learn from others because I don't trust my ability to analyze digital images. It's all just a bunch of electrical current to me.

Diffraction is a function of the open diameter or aperture diameter. That means, it is independent of the lens' design. Whether a 200mm lens is computed and made for APS-C or for 4x5 makes no difference for diffraction.

The question of the format is a different one. The smaller the sensor, the higher the resolution must be in order to achieve an acceptable final image size (print). Per definition a airy dsic of 0.025mm should be achieved (basically the same criterion, that applies to the definition of depth of field). For larger formats the airy disc can be much bigger, up to around 0.1mm for the large medium formats. For APS-C you also have to take into account that the photo sites are smaller than simply dividiing the physical sensor size through the pixel number. I calculatet the acceptable airy disc size to be around 0.01mm or just under half the acceptable size for 35mm film.

This is the reason, why diffraction visibly degrades image quality for APS-C sensors at larger apertures than for FF or 35mm film.

If I rememmber rightly we had a recent thread, where I was explaining that more in-depth, but as a general summary, I think, that is enough...

Ben

[Ron Boggs]

Yes, I remember the thread, but the content sometimes outweighs my brain!
So, in essence, the diffraction--caused by the lens design and unavoidable--is the same on each format. But the smaller formats make whatever diffraction that exists appear worse than it appears on the larger formats. Again, back to magnification of the diffraction. You have to magnify it more on APS-C, thus making it more noticeable and less tolerable. In medium format situations, the diffraction is less magnified on the final print, thus less noticeable and more tolerable?

[Ben_Edict]

Yes, I remember the thread, but the content sometimes outweighs my brain!
So, in essence, the diffraction--caused by the lens design and unavoidable--is the same on each format. But the smaller formats make whatever diffraction that exists appear worse than it appears on the larger formats. Again, back to magnification of the diffraction. You have to magnify it more on APS-C, thus making it more noticeable and less tolerable. In medium format situations, the diffraction is less magnified on the final print, thus less noticeable and more tolerable?

Basically your summary is correct. I would like to change just the wording at the beginning. Diffraction is not so much a question of lens design, but of physics and cannot be circumvented. Otherwise your conclusion is quite correct.

Ben