Yashica-Mat 124G Optics

[evan_ludeman]

<also posted to rec.photo.equipment.medium-format>

 

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I recently acquired a Yashicamat 124G and noticed immediately that

my photos varied in sharpness depending on the aperature setting.

Photos shot at f3.5 - 4 were a little soft, while photos shot at f11

just about leaped off the page. Being of an experimental bent and

since it was raining like hell that weekend, I decided to burn a

roll of film in pursuit of some quantitative numbers.

 

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The camera in question is a 124G in great shape, date of manufacture

unknown, with the standard Yashinon f3.5 80mm taking lens.

 

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Procedure was to set up several USAF 1951 style resolution targets

(thanks go to David Jacobson for his terrific post script file) on a

vertical wall with the camera supported by a tripod 3.2m away,

measured to the front of the lens. A 500 watt halogen shop lamp was

used to illuminate the target and the camera was fired via the self

timer. Focussing was done with the view finder and built in

magnifier -- the graduations on the focussing knob are spot on, btw.

Kodak T400CN (C-41 process) B&W was used as the test film --

something like tech pan or Tmax 100 would be a better choice, but

that's what I had available. Films were read under a stereo

microscope with diffuse transmitted light.

 

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Resolution on the film was calculated as:

 

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Rf = Rt * (D-F) / F, where

 

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Rf is the film resolution in lines / mm

 

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Rt is the periodicity of the target which is just resolvable as

separate lines on the film, in lines / mm on the target

 

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D is the distance from target to front of lens in mm

 

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F is the focal length of the lens in mm

 

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Tests were run at all aperatures at 3.2m. The view finder field of

view was also marked out on the target wall in black tape, so that

view finder coverage could be determined.

 

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Results:

 

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Resolution, Distance to target = 3.2 meters, magnification factor

1/39.6 Resolution (lines / mm)

 

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f center corner

 

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3.5 35 25

4.0 44 29

5.6 63 32

8 63 44

11 79 50

16 71 50

22 56 44

32 35 35

 

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Exposed negative size: 56.1mm tall by 56.9mm wide, width of exposed

negative outside viewfinder field of view at 3.2m: 4.5mm top, 4.1mm

left side (photographer's left, facing subject), 4.1mm right side,

2.1mm bottom. This is about 86% coverage left to right, 88%

coverage top to bottom, 76% of total area. The view finder's field

of view at 3.2m is 203cm tall x 198cm wide.

 

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Comments:

 

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There is a 12% "step size" between successive resolution targets,

which is pretty coarse. This should tend to yield errors that are

conservative rather than strictly random. There is a clearly

visible difference, for example, in the films from f5.6 and f8,

although the best resolution is reported in both cases as 63 l/mm at

center. At f8 I would guess it's probably closer to 67 or 68 l/mm,

but not quite good enough to split the next target (71 l/mm).

 

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Measured length of the image of a 11" (27.9cm) sheet of paper (the

center resolution target) on the negative was 0.706cm, which yields

an apparent magnification of about 1/39.6. Using this value leads

to an estimated actual focal length of 78.9mm. 1/39.6 was used as

the basis for calculating resolution on the film.

 

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My exposures were a little on the low side throughout -- I used the

built in light meter and the subject was a white wall with a few

photo targets. Doing it over again, I'd increase exposure a stop or

two. Increased exposure would make the film a bit easier to read and

might have made have tipped one or two of the measurements above

into the next higher bracket. Exposures were dead even across the

field at all aperatures.

 

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Conclusions:

 

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Overall, I would use caution against comparison of these results

with those that have been recorded and published elsewhere. Test

methods and individual cameras, interpretation of film, etc. will

all vary. My specific purpose here was to develop a quantitative

feel for how resolution varied with aperature setting, not to make

any particular claims about the quality of the optical system in

this make of camera. As others have pointed out, there is also a

hell of a lot more to a good camera that the ability to split

resolution test patterns.

 

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The results back up my observation that the photos I shot at f8 -

f22 were noticeably sharper than at 3.5 - 4.0. Others have

commented on this characteristic of Tessar - formula lenses as well.

Clearly, where maximum sharpness and detail is required, shooting

at f11 and f16 will be beneficial. Where a slightly softer focus is

preferred (e.g. portraits), one can work toward either end of the

aperature range, depending on depth of field and shutter speed

requirements. What was surprising to me was both the very high

maximum resolution and the very wide range of variation with

aperature. Given that the usual driving force for MF over 35mm is

better resolution for bigger enlargements, this is very useful

information to have.

[evan_ludeman]

The best laid plans...

 

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It seems that the form submission process for this site has a nasty habit of corrupting tabs and single carriage returns, rendering my nice little results table of resolution values unreadable. I will try this again, double spaced. Apologies (doubly ;-)) if it fails to yield the intended results.

 

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Also, I have been asked for a link to the USAF1951 charts that I used. Here it is: http://www.photo.net/photo/optics/index.html

 

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Results:

 

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Resolution, Distance to target = 3.2 meters,

 

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magnification factor 1/39.6 Resolution (lines / mm)

 

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f center corner

 

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3.5 35 25

 

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4.0 44 29

 

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5.6 63 32

 

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8 63 44

 

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11 79 50

 

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16 71 50

 

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22 56 44

 

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32 35 35

[anov]

I assume that the lens in Yashica Mat 124 is the same as the one in 124G, that is a Yashinon. Am I right? Is there any significant differences between the two? Thank you.

[randolph_carlisle]

Yashinons are four element Tessars. I believe they are all the same. The other lenses found on Yashica TLRs are Yashicors - 3 element lenses.

[francisco_alonso_valdis1]

Yashica Mat 124 Tessar lens i a copy of Rollei Tessar lens. The four elements lens is coated. The diference with Yashica 124G lens is that this ultimate is multicoated. I got a mat124 and a mat124G and both of them are subjectively sharply but mat124G is more contrasty. both of them get flare very easy and use of hod (or a shade) is always preceptive. Although optically mat124G is a little superior, the camera's got more plastic parts and its not so hard work ressistant. overall quality in plain mat124 is higher than 124G.

[francisco_alonso_valdis1]

Yashica Mat 124 Tessar lens i a copy of Rollei Tessar lens. The four elements lens is coated. The diference with Yashica 124G lens is that this one is multicoated meanwhile plain 124G is single coated. I got a mat124 and a mat124G and both of them are subjectively sharply but mat124G is more contrasty. Both of them produce flare very easy and use of hod (or a shade) is always preceptive. Although optically mat124G is a little superior, the camera's got plastic parts (not at all in plain124) and its not so hard work ressistant. Overall quality in plain mat124 is higher than 124G.

[gene_crumpler6]

Your results are typical of a four element lens. One suggestion in doing these types of tests is to use a flash in a dark room, open the shutter for about 10 seconds before firing the flash. This will eliminate any chance of camera shake.

For comparison, here are my results for an 80mm Mamiya TLR lens:

 

F-stop Center only

 

4.0 - 45 lp/mm

 

5.6 - 48

 

8 - 72

 

11 - 72

 

16 - 72

 

32 - 42

[gary_helfrich]

At one point in my infatuation with TLR's I had a Rolleicord V, a Mamiya C330, and a Yashica 124. I've always been perplexed at the postings of the optical similarity between these cameras. Perhaps if all you ever shot was a 2-dimensional test chart with black and white film, there might not be much difference between these three cameras. Most of my friends quickly loose interest in shots of the 1951 test chart, however.

 

Almost all my shooting is color transparancies. The Mamiya and the Rollei are very close to each other. The Mamiya is better when it comes to flare, but the tiny lens hood on the Rollei is easy to just leave on the camera. The Yashica was pretty poor by comparison. I had high hopes for it considering the postings that I have read on this forum. Sure, the images were sharp on all three cameras, but the contast was lower than even the old Rolleicord. The Mamiya just walked away from either the Yashica or the Rollei when you opened the lens up beyond f/8.

 

All of three cameras had been serviced by Paul Ebel at Lens Services, so I doubt that there was a problem with the Yashica. There is just something blah about color images with the 124.