Mamiya Press 150mm F/5.6 lens dissasembly

[Marcelo Paniagua]

Recently I bought a lens from a japanese store on ebay. Seller described it as EX-5 (whatever it means) and that it has a slight haze. Received the lens yesterday and it turns out there is huge fungus/haze on the middle element of the lens.

I was willing to accept a slight haze but nothing compared with the condition of the lens.

I contacted the seller and explained the condition and send them a picture, asking for refund. To be honest, seller service was great, since he promptly provided a refund and told me to keep the lens.


Now I'm on a possession of a lens that may try to clean. I've cleaned similar conditions on some lens in the past, with mixed results. Since the lens was free and probably will be sitting on my shelf, I think I will try to disassembly the lens module to get to the middle element (if possible) and try to remove as much fungus as possible.

Does anyone have any tip on disassembling the back lens element part? Should I build some tool to remove it since is pretty deep into the lens body? Any thoughts?.

 

[lobitar]

I seem to remember you may unscrew the front lens group from the shutter, just like you unscrew the front lens group from any other large format shutter. However, expect the front group to be screwed into the shutter VERY tightly! But once having successfully unscrewed the front group there will be no need for unscrewing the rear lens group, as you can then access the inner surface of the rear group from the front.

 

[reddesert]

Mamiya Press lenses are like large format lenses, there is a front cell and a rear cell that screw into a leaf shutter. The shutter itself is held to the lensboard/focusing mount with a retaining ring at the rear. I believe the 150/5.6 lens is a Tessar type design, meaning the front cell is two elements with an airspace and and the rear cell is a cemented doublet. Because the focusing mount is deep and the rear group is hard to access, as you mentioned, the path of least resistance is likely to remove the front cell - it should just unscrew - and lock the shutter open on B. Then you can clean the exposed surfaces of the front and rear cells, reaching the front surface of the rear cell through the shutter.

If the damaged surface is in the middle of the rear cell, it might be a cemented surface that has gone bad (again relying on my memory that it's a cemented doublet), which is much harder to deal with, and in that case you should probably keep the lens for parts in case you can find one with good glass but a bad shutter, or something like that.

 

[gordrob]

Here is a link on Youtube of probably what not to do but it does show you the front part of the shutter. You have to pay attention to the wire for the flash sync. so you can get it back to where it belongs.
There is also another video which may or not help, of how to disassemble the Mamiya 100mm f3.5 which is similar. The first 2 or 3 minutes shows how to get at the rear element.

 

[Marcelo Paniagua]

Thanks for the replies. Will try to remove the back element and see if there is anything to do

 

[Marcelo Paniagua]

Oh well, removed back element and turns out (as expected) that is cemented. Not much to do but reassemble and wait for a donor lens.

A shame since lens body is on great condition. Thanks for replying.