Zenza Bronica S2A: infinite focus problem

[ciccioder]

Hi,
i have a Zenza Bronica S2A, never used before, with a Nikkor 75/2,8.
I noticed that if you focus on infinite the image on background in the viewfinder is out focus....is this possible??? Is a problem or there is some technical reason????
thanks

 

[JasonC]

First thing is to check the foam that is pushing down on the ground glass. If the foam is deteriorated, the ground glass will be in the wrong position causing focusing problem.

 

[zebulus]

I have a bronica model C, and nailing the focus is difficult I find, especially when shooting wide open. I just had mine completely repaired and serviced by Jimmy Koh and its still hard to nail the focus. Takes practice I think.

Ive only had one other 6x6 camera (Yashicamat 124G) and nailing the focus on it was even harder.

 

[David A. Goldfarb]

It's a well known problem. Remove the viewfinder, and you'll find a frame that holds down the groundglass, held in place by four screws. Remove the screws, and you'll see foam under the frame that should be pressing down the glass, but usually has deteriorated, if it hasn't been replaced recently, causing the springs under the groundglass to push it up and out of register. You can clean off the foam with a solvent and replace it with the same neoprene foam that is used for light seals, or some people like to use moleskin (the stuff you put on blisters), because it doesn't deteriorate like neoprene. If you do any further disassembly, to clean the groundglass, etc., note which side of the groundglass is up (it should be matte side down), and whether there are any shims under the groundglass that you don't want to lose. The fresnel rests in a well under the groundglass, and offhand I think it should be with the ridged side up, but also take note of that, if you decide to take it out for cleaning.

 

[paul ron]

The bad foam may be the problem, I dopn't work on those cameras but most are basically the same... something doesn't sound right here.

The springs under the screen push up to bring it to focus? So how is the screen adjusted to focus accurately to the filmplane?

Generally the screen n frame unit or the glass screen itself will ride on screws or someting solid under it to shim it up to proper focus.. not push down, as this leaves no way to accurately adjust other than using exact thickness foams to give the exact preasure to bring her in and find in a few months the foam has sagged n the focus is out again? I doubt that.... ummmm.

I'd first try n see if the film plane focus matches the screen then see if this fellow needs a diopter to correct the difference. If neither, the find out how the screen is adjsuted by refering to the repair manual. Screns never rely on foam as the way to keep a sscreen in focus, brass shims, screws.. but foam should have no bearing on it.

.

 

[David A. Goldfarb]

The matte side of the groundglass rests on machined metal rails, and there may be shims between the rails and the glass. The springs are also pressing up on the groundglass and the frame with the foam is pressing down on the groundglass. When the foam isn't deteriorated, it presses down harder than the springs are pressing up, and the matte surface of the glass is in contact with the metal rails, and everything should be in register, and nothing should move around. When the foam deteriorates it shrinks and pulls the glass up, and the springs push the glass up, so that it no longer rests on the rails, and it gets out of register.

Classic Bronicas can have other focus problems, like mirror alignment or back registration issues, but deterioration of the foam is by far the most common situation. I'd guess that virtually every old Bronica (EC-TL or earlier) that hasn't had this attended to in the past five years needs this repair.

Sam Sherman wrote a detailed page about Bronica focus issues some years ago that used to be on Bob Monaghan's Bronica megasite, but the site has moved around and become fragmented, so it may not be so easy to locate.

 

[paul ron]

That is weird they'd do that. Most all the camera screens, including a lot of restorations I did on other vintage cameas, the screen most always sits on someting solid so precise adjsutments can be made easily without having to hold anything down. Springs or foam are generally to keep the screen unit form rattling around onceit is mounted in the frame, not as part of the adjustment system, weird. I have an ETRS and the screen is mounted on a solid rail with shims, no foam to keep it compressing springs underneath. RBs are also solid mounted on 4 adjustment screws as is are Yashicamats n Rollies, Mamiya TLRs... n many more.

I'd be interested in the link to the repair article if you can find it? You've got me curious to see how this works, a first for me.

 

[David A. Goldfarb]

It does seem like an unusually complicated design, but the classic Bronicas are like that. The only reason I can see for having the springs underneath is to make it easier to install and remove the groundglass, but that isn't something that needs to be done very often.

It may have to do with the viewfinder blackout curtain, which is another unusual feature of the S2a and earlier Bronicas. On these cameras, the mirror doesn't flip up to block light from the viewfinder, like on most other SLRs. Instead the mirror slides forward and drops into an opaque black metal sheath when the shutter opens, so that light isn't reflected from the mirror up to the film, and a blackout curtain slides under the fresnel to prevent light leaks through the viewfinder, so the complicated groundglass mount may be necessary to make this light seal with the blackout curtain.

The reason for the falling mirror is so that lenses can protrude into the mirror box, requiring less retrofocus correction than on an SLR with a conventional rising mirror.

 

[ciccioder]

Ok, many thaks at all, really!!!!
I just change the foam (simple operation) as you told me....now it seems to be better than before....but there is still something wrong!!!!
Inspecting the ground glass and the fresnel lens, i note that fresnel is just a bit curved, not plain......and i suppose this may affect the focus but i don't know, because when i put the ground glass, the springs are not able to push the fresnel lens.
I have to try the camera with film...