Mamiya C330S/80mm Sekor S infinity focus problem

[FrankB]

I've recently become the (mostly) happy owner of a secondhand Mamiya C330S TLR. It came with an 80mm f2.8 Sekor S lens and I've added a 180mm f4.5 Super to it.

I've put a couple of rolls through it and had (by my unexacting standards) some pretty okay results. However, I was out in the Dales with it yesterday and noticed that with the 80mm I can't focus on infinity; the rack closes completely before I can get a sharp image at distance.

The lens plate appears correctly mounted, the camera is in good condition with no visible dents and the rack moves smoothly throughout it's range. It's only a problem with the 80mm (the 180mm will focus beyond infinity) and at the apertures I tend to use (f16, f22) it's probably not going to be a major hindrance. Given my mindset though, if it is a fault I'm probably going to want it fixing.

Any advice would be very much appreciated!

Thanks in advance,

Frank

 

[dr bob]

There is only about 3mm of margin left on my 80mm lens after focusing at infinity. There must be something causing your lens to extend slightly more than "normal". My C330f has a slight interference problem with the cocking lever. When mounting a lens, except for the 180 and 250, the lever has to be depressed slightly to allow the lens body to seat properly. I have forgotten this on several occasions

I also found my previously owned (original owner) 180 to have apparently been reassembled incorrectly after a CLA. The last element in the taking lens was reversed. All is A-OK now.

I performed a focus test a long time ago on all my lenses and found them to be excellent. There have been discussions here indicating that, e.g., “The 180 is not sharp.” And the next, “My 180 is the sharpest”. Both APUGers were probably correct. I have found that the lenses for the C-series require good maintenance practice. I thought my 180 was un-good until I found oil (?) on an interior surface. Disassembly and cleaning corrected the problem. I also hear that the 55mm is not the sharpest. I won’t argue about it but only to state that mine is OK.

There are a lot of things affecting focus on the C-series. One major cause of problems is the ground glass mounting system. I have heard several complaints from clients after they replaced or modified their gg. As you have no apparent problems with your 180, I doubt that is a problem.

Good hunting and best wishes.

 

[benjiboy]

Have you checked that the distance scale revolving knob in front of the distance scale window is set on 80mm before you fit the standard 80mm when changing from the 180mm lens? I have just tried it with mine after reading your posting, and this may be the cause of your problem, if not , I would remove the folding focusing hood, and check that the screen is seated correctly this is a possible cause of focus error , failing this as Dr. Bob says it may have been inexpertly taken apart and reassembled by a previous owner, or suffered impact damage resulting in it being put out of collimation, which would need reassembling on an optical bench by a repairer, it would probably be cheaper to get another one . If you could find a shop or someone who has one and try theirs

 

[grahamp]

Unless there is some severe mis-alignment of the lensboard, or you are not mounting the lens properly (unlikely), I would suspect a problem with the focus screen. You need to check the focus at the film gate and the screen with both lenses using a piece of ground glass or some taut transluscent sticky tape.

What type of focus aid do you have? If it is a microprism or split image type, what is the number on the screen? You will have to demount the screen to see the label. There are some screens that are designed to work well with the longer lenses.

I find it interesting that the 180 is giving better results than the 80mm. I would have expected problem to show up the other way.

The parallax setting on the side of the camera has no effect on the focus, by the way.

 

[FrankB]

Thanks to all for the responses. I don't know if the focus issue will show up on the film as well as on the screen, as I haven't been able to process the film yet. I'll try a few things with the camera tomorrow (including reseating the screen and lens in different ways) and report back.

Graham - the focus screen number is B2 and it's a split-prism type.

Thanks again,

Frank

 

[grahamp]

The B2 is a 6 degree split-image, so it should be better with the 80mm than the 180mm. I was expecting a B, given he problem.

 

[paul ron]

Best thing to do is check the focusing at the film plane first. If that is OK then just a readjustment at the focus screen is needed and you are in business again.

It sounds like the screen was changed because the standard screen was a ground glass style, not a split image. That may be the cause of your missalignment. It's not a big deal to adjust either. If you had the older TLRs, it would be a different story, they didn't have replaceable screens and adjustment was done by subtracting or adding a shim under the lens.

 

[Marco Gilardetti]

The parallax setting on the side of the camera has no effect on the focus, by the way.

Exactly the same applies to the revolving distance rod, of course :rolleyes:.

I agree that you should check the mirror and ground glass position before taking any step. Take some pictures at full aperture or - even better - place a control ground glass on the film rails, and compare it with what you see on the reflex glass. A piece of matt adhesive tape on the central portion of the image frame works as well, provided that you don't push it towards the lens while checking the focus.

 

[FrankB]

I've just done a quick test and, after reseating the focussing screen, I can now focus at and (a smidgeon) beyond infinity without difficulty. I think this must have been the problem. I'll run a roll through focussing on various objects at various distances wide open, but I think that it'll be okay.

Very many thanks for all the responses!

All the best,

Frank