Cross-sectional diagram for Mamiya 90mm KL?

[paul_ong1]

<p>I am looking for a cross-sectional diagram for the Mamiya 90mm KL lens. Basically, the diagram shows the basic shapes of the lens elements and their layout. My RB67 Pro-S manual has that information on the non-C 90mm lens (page 42). The manual for the Pro-SD or the RZ might have a diagram for the KL. I searched the web for a newer manuals and for a lens diagram of the KL, but no luck. I am hoping that someone has the image and are willing to share.</p>

<p>Thanks.</p>

[david_mcniven]

<p>Hi Paul, Mamiya's website is unclear on even the number of elements/groups. In one place it says the construction of KL's is the same as the equivalent RZ lenses - but if you compare their numbers for RZ & L lenses they differ - and the C lens is different to both.<br>

I don't have or recall having seen a diagram but I do have an unmolested 90KL lens - obviously I'm not going to dismantle it but there is another way of comparing number & position/orientation of elements with limited accuracy by using reflections.<br>

It's a last resort really though, a diagram will be better if you can find it.<br>

Good luck. You do seem to be having to fight for every step forward!</p>

<p> </p>

[steve_rasmussen]

<p>I have an old Mamiya brochure that says the 90mm KL has 8 elements in 7 groups. My guess as to its design is Double Gauss with 4 elements on either side of the stop.</p>

[paul_ong1]

<p>David, thanks for your response. Yes, I have had a hard time figuring things out from the MCA web site. I will try emailing them next week to see if I can get some help. If I cannot get a diagram, I may get back to ask you if you can describe what you see on the intact lens. The good news is that the non-C 90mm is working out much better than expected after stopping down 2 f-stops. Had a chance to make some panoramas by moving the back standard on the Toyo.</p>

<p>Steve, thanks. That is a good starting point.</p>

[ondebanks]

<p>Bob Shell's Mamiya book gives the RZ lens as 6/6 el/gr, the K/L lens as 8/7. The K/L does not look to me like a Double Gauss - the large number of elements, the flattish surface of the front element (going by the picture in the book), and the long barrel together make this unlikely. With no more evidence than that to back me up, I'll go out on a limb and say that I suspect that it is more like a mildly retrofocus wideangle in design.</p>

[paul_ong1]

<p>Ray,<br>

Thanks. What is interesting is that the 90mm is close to the register length (112mm between the focal plane and flange), so a mildly retrofocus is very much possible. From another thread here, I learned that symmetrical lenses are both easier to build, less costly and performs better in many respects. If nothing else, I am getting a basic education in lens design.</p>

[steve_rasmussen]

<p>Given what Ray has said, plus the long register distance and the fact that the lens is of moderate speed (f/3.5) it is doubtful that the lens is Double Gauss. Double Gauss designs are generally faster than this.<br>

The advantages of symmetry are that coma, lateral color and distortion were automatically corrected. Modern designs have moved beyond dependence on symmetry to be able to correct these aberrations. So today's asymmetrical designs perform as well as the symmetrical ones. Even the modern Douible Gauss and Plasmats are not fully symmetrical like they were when they first came out.<br>

In Double Gauss designs, the front and rear elements are close to the same diameter. If your lens varies from this, it is probably some sort of Reversed Telephoto (Retrofocus, Distagon, Super Angulon-R etc.).</p>