Mamiya RB 50mm Floating Element

[brett_kosmider]

After reading a few posts about the 50mm C Sekor lens for the Mamiya RB here on

photo.net it occured to me that I never knew it has a floating element.

 

Since I have this lens, could someone please explain to me how the floating element works

and what it really does. I read that there is a Mamiya "lens manual" out there somewhere

that explains the functionality of this lens but I was unable to find it anywhere on the net.

 

Thanks,

 

Brett Kosmider

[User_502260]

In the days of folding medium format cameras there were two types of lenses. The first type was known as a front element focusing lens. When you focused it, only the very front element or the first few elements up front would move back and forth in a small helical mount. This was adequate for subjects at a distance but produced less satisfactory results for close subjects. The other type of lens had what is called unit focusing. A larger helical mount allowed all of the elements to move back and forth at one time as a unit. This was better for close subjects and with normal to telephoto lenses. Wide angle lenses either did not focus to very close distances or produced poor results at close distances. Typically there was curvature of field and the corners had poor sharpness and light falloff.

 

When the technology for making zoom lenses improved, it was discovered that as the zoom lens was focused at close distances and when the focal length was changed, it was advantageous to have some of the elements move at different rates when measured from the focal plane. The fact that the lens elements were no longer being moved all at the same time as in unit focusing meant that certain elements were "floating."

 

Early zoom lenses mostly had front element group focusing and this prevented them from focusing very close. The front helicoid could be only so long. Examples of this design are the 80-200mm f/3.5 Konica Hexanon and the 80-200mm f/4.5 Nikkor. When Vivitar introduced the 70-210mm f/3.5 Series 1 zoom lens, a form of floating element design allowed much closer focusing and similar designs were adopted by other companies. It was around this time that some lens manufacturers decided to use a floating element design on fixed (non-zoom) wide angle lenses. One of the first lenses withg this design was the 35mm f/2 Canon FD lens. It was made to fit the new Canon F-1 and FTb SLR cameras which had full aperture metering. I have one of these and it works very well.

 

In 1976 Konica introduced its first non-zoom lens with floating elements. It was the 28mm f/1.8 UC Hexanon. Vivitar's 28mm f/1.9 Series 1 lens also had a floating element design. This not only gave close focusing but very decent quality at the close distances. Eventually this design feature made its way into medium format lenses like the Mamiya RB 50mm wide angle lens. One annoying problem with floating element lenses is that over time the lubricant used inside of them can break down. It may leak onto the aperture blades, dry out or show up on the lens elements. If this lubricant is used in the small part of the lens which moves the floating element or elements it can be very difficult to clean out and replace.

[chris_waller]

I have an RB and know about the floating element in the 65 and 50 mm lenses. When the lens is focussed on the subject, you turn the adjusting ring to same distance and this moves the floating element to the position of optimum sharpness. I'll have a look in my RB lens manual and try to be more precise.

[mag_miksch]

65mm has a floating element?

[marck mcgill]

65 with floating element? Please double check...

[photom]

Responding to Mark and Mag on 65 mm floating element. According to the Mamiya USA site the RB version has a floating element and the RZ version does not (at least not mentioned). Interesting.

 

http://www.mamiya.com/cameras.asp?id=1&id2=15

[joseph_e._forks]

I believe there are at least three versions of the sekor Z 65mm.

 

1) older 65mm (non W, non LA - I own this one)

2) 65mm W non LA (not positive about this one, should have in between aperture settings)

3) 65mm LA (floating element with in between aperture settings, pictured on Mamiya Web site)

 

Best

Joe

[brian_caldwell]

"Early zoom lenses mostly had front element group focusing and this prevented them from focusing very close. The front helicoid could be only so long. Examples of this design are the 80-200mm f/3.5 Konica Hexanon and the 80-200mm f/4.5 Nikkor. "

 

Front group focusing is still extremely common in zoom lenses since it automatically maintains the focus distance regardless of the focal length setting. Virtually all of the compact negative-positive zooms used in digicams these days use front group focusing, for example. Close focus is not necessarily compromised with this type of focusing, either. The Vivitar 90-180 macro zoom and the more recent Nikon 70-180 macro both use front group focusing, and both are famous for their close-focus performance.

[brett_kosmider]

Hey, thanks for the in depth. That really clears things up, er, sharpens I guess

[User_502260]

Brian is correct. I have a 90-180mm f/4.5 Vivitar Series 1 lens and it is quite good. In about 1976 Konica replaced its very heavy 80-200mm f/3.5 Hexanon with the lighter and smaller 80-200mm f/4 UC Hexanon. Both lenses have front element group focusing. The UC lens focuses to about 2 feet. There were two versions of Vivitar's 24mm f/2 manual focus lens. The earlier and larger one was made by Kino and the later and smnaller one was made by Komine. I had a lot of trouble with an example of the Kino version. It was seen by three different repair shops before it worked properly. The lubricant in the floating element mechanism was gummed up. From my experience the wide angles with floating elements (on 35mm cameras) perform much better at close focusing distances than similar lenses without the floating element design. It makes sense that this should be true for medium format wide angles too.

[marck mcgill]

Tom, was <a href="http://www.mamiya.com/lenses.asp?id=1&id2=15&id3=17&id4=260&id5=265">this</a> the link you wanted to post? Well, sure this 65mm has nothing to do with the 65mm I've always seen around for the RB (please note that I own the first model, that is non-S and non-SD). If one wants a 65mm with floating elements, sure must keep eyes open to the overall look of the lens and to the production year. What a mess.