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C 645 Lens Quality

budding

New Member
I've looked at a lot of images taken with Zeiss optics - absolutely stunning! So, I'm a bit confused by the references to the Pop Photo article that claims that Mamiya 645 lenes are better than Zeiss 645 lenses (Mamiya publishes a summary on their own site). See
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for a representative s&le of Zeiss bashers.

I found a site,
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, that does extensive lens testing, and they seem to rate a lot of the Zeiss leneses highly. Anyone care to comment about differences in methodology? Perhaps someone can shed some light on this for those of us that aren't optics experts!
 

derekcooper

New Member
Hi,

If you're blown away by the results of the Zeiss lenses, then why = confuse the issues with all the mumbo-jumbo posted on photodo and the = Contax-bashing site. It's a little like religion - once you're in love, everything else = is second-best, even if everything else is as good.

Mamiya makes great gear - top shooters like Annie Liebowitz use it, so = it can't be bad. A lot of shooters use Contax 645, so it can't be bad = either. Getting caught up in all those comparisons of lenses is a waste of time = if you're already impressed. Just think, you could be out shooting instead = of wading through all the stuff on those two sites.

Probably not what you wanted to hear, but I couldn't resist! Personally, = I shoot with the Contax 645 and am constantly blown away by the quality = and wouldn't switch for anything. I have used Mamiya gear on some = assignments, and have never been blown away by their quality. Build tolerances = aren't, in my experience, nearly as tight at the Contax gear. I've used the Ixpress back on the RZ and can actually rotate the back slightly when it's in = place, which isn't good, obviously. Found the same with the prism finder, = lenses, etc.

Cheers,

Derek Cooper
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fotografz

Well-Known Member
Hi Robert,

I shoot with both. Mamiya 7II and RZ as well as Contax 645. I chose the Contax 645 over the Mamiya 645 solely based on image differences I could detect between each lens system. Often the comparisons are about "sharpness" which many of the Japanese makers are quite good at. However, there are other aspects which make up an image...like color rendition and Bokeh. Plus that mysterious 3D feel some glass gives you.

Leica M glass has similar charactistics and while "scoring" at or below other chart comparisons, is clearly superior in the look you achieve with them.

In short, your eyes aren't decieving you.
 

albert4321

Well-Known Member
I agree with Derek and Marc,

I also shot with the Mamiya RZ, Hasselblad, and the C645. I choose the C645 because of its handling and the image quality. Beside the color rendition, Bokeh and 3D feel that Marc mentioned, lens flare and distortion control are one of the best.

I would not care what other reviewers say, for one they can be biased, the images that I see and love on the light-box is what I count.
 
K

kerryjapan

My two cents worth:

Have you ever seen an advertisement for Contax in any Pop Photo magazine??? Proably not....

Have you ever seen an advertisement for Mamiya in Pop Photo???? Yeap, all the time. I think that the editors for the magazine are just ensuring future business...

But, I'm also a cynical type person :)

Kerry
 
M

mike_nunan

Hi Robert,

In addition to re-iterating the "use your eyes" advice given in the messages above, I would also recommend you spend a little time reading up on the meaning of the various types of lens test results that you're referring to. The best place to start is Photodo.com, which gives a decent explanation of the type of testing - MTF testing - which they perform. It's really not massively difficult to understand, and a half hour's reading will put you in a much better position to make informed judgements.

The medfmt site's analysis of Contax 645 glass is based entirely upon old-style resolution tests, quoting performance in terms of lines pairs resolved. This kind of test sets out to determine the finest detail that can be distinguished at a given aperture. A lens which performs well in this test may not actually provide good contrast for slightly larger image details, meaning that it will not look as punchy as another lens which is a worse performer in an outright resolution test.

I would definitely recommend Photodo.com as one of the more reliable available sources of lens sharpness data. Many people don't look beyond the summary scores, but it's well worth learning how to read the whole report as it contains much useful information. For ex&le, look at the figures for the 80mm f/2 Planar. This lens has an overall rating of 3.8, which would tend to indicate that it's pretty good. However, the weighted MTF figures for each aperture are revealing: f/2 0.56, f/2.8 0.67, f/4 0.76, f/8 0.82. In broad terms, these figures show how sharp the lens is at each aperture. A (physically impossible) perfect lens would record 1.0 everywhere. The 0.56 figure at f/2 indicates that the lens is indeed fairly soft wide open. This is exactly the same situation that exists with the 85mm f/1.4 Planar for Contax 35mm cameras -- the lens behaves almost like a soft-focus lens wide open, such is its softness. The situation changes dramatically as soon as you stop down a bit, though. You see a big jump in contrast even at f/2.8, but by the time you are at f/4 you're definitely "cooking on gas". These are MF lenses, so shooting at f/4 is going to be dicey in terms of depth of field, never mind f/2, therefore in practical terms this lens is going to be a stellar performer. If you want to shoot at f/2 for creative effect you have the option -- something the other manufacturers are unable to offer.

The second set of weighted MTF figures show how much contrast the lens preserves when it images test patterns at three different spacings, chosen to produce frequencies of 10, 20 and 40 line pairs per millimeter at the film plane. The figure for the coarse pattern will always be better than the lower ones, for reasons which are hopefully obvious. Counter-intuitively, it is the ability of a lens to provide good contrast for relatively large features which gives the much of what we perceive as punch and sharpness in the image. Therefore the first thing you should look for is a decent showing in the 10lpmm figure, and the 80/2 scores 0.89 which is a very good result. The 0.75 score at 20lpmm is also good and the final figure of 0.51 at 40lpmm is passable. (Interestingly, the figures are almost identical to those for the 80/2.8 Planar for Hasselblad.)

It's also worth mentioning (since the author of the medfmt article seemed unaware of it) that although it is indeed true that the 645 lenses are made under license by Kyocera, the same applies to the Contax/Yashica 35mm format lenses and these are rightly regarded as among the worlds finest optics. In the end the designs are all prepared by Zeiss, and it seems that Japanese standards of assembly and test are well up there with the best that German firms can achieve.

As a final comment regarding the lenses, I would fully agree that background blur (bokeh) is a huge factor in lens choice, and this is where Mamiya and others cannot compete with the best German designs. I speak from experience as a (very satisfied) Mamiya 6 shooter. Much as I love that camera, there is no doubt that my 35mm Zeiss glass has the edge when it comes to smoothing out the background, which can make all the difference to portraits, especially.

As regards the body and the rest of the system, I would only suggest that you go along to a store and try handling one for yourself. I picked one up in an idle moment recently, and was absolutely gobsmacked by the rightness of the handling. The Canon-style ability to override the AF just by turning the ring is a boon, and ring itself feels like a proper manual focus lens. I wasn't aware of the small viewfinder coverage, but that is a bit of a shame I guess. The viewfinder itself was clear and usable thanks to the fast glass. I didn't feel the AF was particularly slow or unstable despite the poor interior light in the shop. If I had the money for a 645 SLR system right now, I think the Contax would be a very strong contender. I would certainly select it in preference to the H1 at this stage.

HTH

-= mike =-
 

skimmel

Member
Mike: Just reading along here. Thanks very much for a great explanation of things! I have one (probably stupid) question: You mentioned that "These are MF lenses, so shooting at f/4 is going to be dicey in terms of depth of field...." Can you explain this for the uneducated.
 
M

mike_nunan

Hi Stephen,

The short answer is that you get less DoF at the same aperture for the same field of view in MF as compared to 35mm. Obviously you have to use a longer focal length to get the same coverage in 645 (e.g., an 80mm lens is about the same as a 50mm for 35mm cameras) and although the reduced enlargement factor of 645 is good for the apparent DoF in the final print, the impact of the longer focal length wins out.

If you want the full explanation with accompanying mathematics, have a look at Norman Koren's excellent page on the subject:

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If you look at the subsection entitled "DOF limits, diffraction, and format" you will see that you need to stop down by nearly two stops to obtain the same DoF in 645 that you got in 35mm (if you were comparing against 6x7 it would be almost exactly two stops).

Regards,

-= mike =-
 

afranklin

Well-Known Member
Hi Mike,

> The short answer is that you get less DoF at the same aperture for the > same field of view in MF as compared to 35mm.

Hum...I don't agree with that:

For 35mm, with a CoC of .025, 50mm lense f2.0 1M = 0.038m For 6x6, with a CoC of .06, 80mm lense f2.0 1M = 0.035m

Seems about the same... What focal length comparisons and CoC numbers are you using that makes you believe this? I'd believe, intuitively, they should be the same...as that is the premise OF the concept of DOF.

Regards,

Austin
 

albert4321

Well-Known Member
What Mike mentioned kind of make sense to me. DOF for f/16 with a standard lens in 4x5 is nothing comparing to 135 format. I have never paid attention in MF, which now Mike got me thinking.
 

skimmel

Member
Thanks Mike! That is very helpful. I have never used MF, so never thought of this before. How does this affect DOF in digital images? (After I read through Normen Koren's page I hopefully can answer this for myself, but....)
 

afranklin

Well-Known Member
Hi Steven,

> I have never used MF, so never > thought of this before.

The DOF calculator contradicts what Mike claimed. It showed that for a 50mm lense at f2 on a 35mm camera, vs an 80mm lense at f2 on a 6x6, they both produce the same DOF.

> How does this affect DOF in digital images?

DOF is purely based on imager size/CoC (film is the imager in the case of using film, and the imaging sensor is the imager in the case of digital)...so, you simply need to know the size of the imager, and given it's size, you can calculate the CoC for it.

A full frame sensor, like the N Digital, will have the same CoC as 35mm film, .033mm. A half frame sensor, which is more typical of the "other" cameras (24mm x 18mm), the CoC would be ~.018mm.

So, I'm saying, because it's digital has no bearing on the DOF, it's the same for film or digital if the imaging area is the same.

Regards,

Austin
 

johnf

New Member
Hi Austin,

Not sure I'm qualified to wade in on this subject, but what you are saying doesn't seem to make common sense to me.

Surely, DOF is a function of focal length and aperture only and independent of image size. If I put a smaller piece of film (or sensor) behind my 50mm lens set at f8 then the DOF (and Coc) will be identical -- the smaller piece of film is essentially just a crop of the full frame.

John
 

afranklin

Well-Known Member
Hi John,

> Surely, DOF is a function of focal length and aperture only and > independent of image size.

Correct, but the assumption is the larger the image, the further it's being viewed.

> If I put a smaller piece of film (or > sensor) behind my 50mm lens set at f8 then the DOF (and Coc) will be > identical

No. I believe the part you are missing is that DOF is a visual trick, and only exists because of the way our eyes work. In reality, there is only one very thin plane of focus. Anything else in focus before and after that plane is simply because our eyes can only see so well (visual acuity) (or because we have reached the limit of the recording medium). Remember, you have to enlarge the smaller image more to get the same size image as you get from the larger format. This is why the CoC for larger formats is larger than it is for smaller formats.

It makes no sense that you would want a different film format to give you a different DOF if all the other parameters are the same (image size/viewing distance and visual accuity). Obviously, a 35mm frame has to be enlarged more than a 645 frame to produce an 8x10 image, and that is why the CoC for 35mm is .033mm and for 645 is .050mm.

I would suggest taking a look at this web site:

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Regards,

Austin
 
J

John_bird

Hi just to add in fact there is no DOF only a plain of sharpness and then various degrees of unsharpness ie a points will become small circles that increase in size as you move away from the plane of focus(known as the circle of confusion) the phenomina refered to as DOF comes from the eyes inability to resolve a very small circle from a point Hence finished print size will have a direct effect on DOF as the more you enlarge the larger the circle will become.
 
M

mike_nunan

Hi Austin,

I know this seems counter-intuitive in some respects, but I spent a good long while poring over the maths (I was a bit rusty in that department so it came down to hauling out some of my old text books) and proved to myself that Norman's workings are correct. I worked from first principles and got the same outcome, and I also plotted a bunch of Excel charts to help convince myself. There is an assumption that the subject distance is much greater than the focal length, so the rule doesn't hold for macro work (I didn't try to find out if any rule of thumb DOES hold there, because I'm not enormously interested in macro work) but the following conclusion from Norman's page is correct I believe:

"Depth of field is constant when the f-stop is proportional to the format size, i.e., DOF is the same for a 35mm image taken at f/11, a 6x7 image at f/22, a 4x5 image at f/45 or an 8x10 image at f/90"

If you still have trouble believing this, it's worth sitting down with a big sheet of paper and working through the maths in detail. If you come out with a different result then please let me know, but I wasn't able to find a flaw in Norman's presentation. Also, as Albert points out, the results do agree with practical experience; consider the very thin DoF of large format or the endless DoF of small-sensor digicams.

-= mike =-
 
An intriguing twist to Mike's post is to include camera shake and "graininess" (using Kodak's Portra grain scores)into the calculations when bench-marking medium format against 35mm.

For any given size of print you end up with about one stop of "quality advantage" with 645 versus 35mm. In other words you get about one additional stop with 645 that you can choose to use for more DOF with a smaller aperture, less grain with a slower film, or less camera shake with a faster shutter speed.
 

afranklin

Well-Known Member
Hi Mike,

I haven't looked at Norman's work, but I know for a fact what you apparently believe (is being said by Norman) is simply wrong, and that my statement is %100 correct, and is supported by Kingslake, and just about everyone else who has spoken/written about this subject. It's also how every DOF calculator I've seen, and corresponds to every lense DOF marking I've seen.

I have specifically done experiments using both MF and 35mm, shooting at the exact same aperture/distance/FOV, and the DOF is as identical as can be discerned. It's simple arithmetic (as Kingslake shows), and this follows completely with reality

Now, on to this statement:

> "Depth of field is constant when the f-stop is proportional to the > format size, i.e., DOF is the same for a 35mm image taken at f/11, a > 6x7 image at f/22, a 4x5 image at f/45 or an 8x10 image at f/90"

I can't say if that statement is right or wrong. It's missing a LOT of information You can't calculate DOF without knowing subject distance, and focal length. That statement needs more qualifications for it to actually mean anything.

I'll take a look at that web site when I get a chance. My guess is you're somehow misreading/understanding what is being said, or the web site is simply wrong...

Regards,

Austin
 
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