Mamiya C330 Focusing Screen Light Seal Gone

Ari · Jun 25, 2021

I just received a Mamiya C330 today and noticed some black dust inside the camera.
I removed the WLF and saw that the dust was coming from under the ground glass. The light seal had dried out and was crumbling.
I removed as much as I could so that dust wouldn't fall onto components inside the camera, but I wonder if the loss of this seal means the ground glass/focus is now out of whack.
Here's the part and where the seal is dried out. The GG assembly is on its back in the photo.
Is this an important light seal or was it just a seal that merely kept the two glass pieces together?
Will I have to re-calibrate focus? Anyone know how I'd go about that?
I ask because after screwing down the top metal square, it still has play, so the seal must have kept those two pieces from moving as well.
Thanks in advance.

Ari · Jun 25, 2021

Thanks, Gregg.
I found this as well, but not sure if it will work with the C330 (non-F version): https://uscamera.com/product/mamiya-c330f-screen-seal/

MattKing · Jun 26, 2021

Technically, that isn't light seal material - it is merely foam separator that ensures that the screen itself presses against the adjustable screen height setting studs in the mirror box.
If you haven't already looked at it, here is the link to the relevant section in Graham Patterson's excellent Mamiya C series TLR reference - http://grahamp.dotinthelandscape.org/mfaq/mfaq-09.html
Graham posts here regularly under grahamp - perhaps he will chime in.

Ari · Jun 26, 2021

Thanks, Matt!

Ari · Jun 26, 2021

And found this just now: https://www.photo.net/discuss/threa...screen-foam-replacement-advice-please.295125/
Thanks, gents!

grahamp · Jun 26, 2021

The C330 and C330f screens are identical, and do need the foam support.

The C330s did away with the framed screen units and the screen slots into the camera - rather like removable screen 35mm SLRs eg. the Olympus OM series.

Ari · Jun 26, 2021

Thanks, Graham. Good to know!

Neil Grant · Jun 27, 2021

The C330s did away with the framed screen units and the screen slots into the camera - rather like removable screen 35mm SLRs eg. the Olympus OM series.[/QUOTE]
..there 's foam in a C 330s screen frame under the top half of the frame. So it's slightly different from an interchangeable screen in an OM or Nikon Fxx. It's purpose, I think, is to push the screen against the lower part of the frame. The screen will then sit properly on the three adjustable screw heads that contact it through cut-outs in the lower part of the frame. The foam deteriorates, just like in the earlier models, but the focusing accuracy isn't effected. The screen rattles in the frame though, and foam debris is distributed into the camera.

grahamp · Jun 27, 2021

True. I was mostly highlighting that the C330/C330f exchange the frame/screen as a unit, while the C330s keeps the frame with the camera body. One of the reasons the 's' screens are not interchangable with the earlier models. At the risk of over-generalizing, screens are pressed against a reference surface or a three-point defined plane by some sort of spring or compressible material.

Ari · Jun 28, 2021

I got the foam today, installed it and crossed my fingers as I shot a test roll. Installation was easy, if a little delicate.
I shot a roll last week without the foam, and honestly, it didn't look back-focused, just perhaps about 1/5mm off.
Anyway, I'll see what today's test roll shows.
Thanks for everyone's help!

Ari · Jun 28, 2021

Thanks, Gregg, I'm waiting for film to dry, but if I need to tweak the focus I'll be sure to use this method.
I have some GG around here somewhere that I can cut and use.

Neil Grant · Jun 28, 2021

grahamp said:
True. I was mostly highlighting that the C330/C330f "
...my post may prove useful for owners of the comparatively rare C 330s that have to deal with degraded foam around the focusing screen. Very little is written about them and owners may wrongly believe that the foam is of critical importance for focus accuracy as is the case with the earlier C 330 models.

Ari · Jun 28, 2021

Well, the film looks pretty good, but I have a nagging feeling that focus is off by a hair and a half.
I really don't relish the idea of having to tweak the focus screws. I'll check again with a loupe and a spare ground glass before doing anything.

Neil Grant · Jun 29, 2021

Old Gregg said:
@Neil Grant I see why you said that. It makes perfect sense when examining the C330s focusing screen housing. But the degraded foam did cause back-focusing for me. The reality of old deteriorated materials is messy. The old foam turned into sticky crumbs which spread around, under and on...

...useful info for C 330s users!

Grim Tuesday · Jun 29, 2021

Old Gregg said:
@Neil Grant I see why you said that. It makes perfect sense when examining the C330s focusing screen housing. But the degraded foam did cause back-focusing for me. The reality of old deteriorated materials is messy. The old foam turned into sticky crumbs which spread around, under and on the edges of the screen, leading it to happily exist in elevated state without rattling. I have several rolls to prove it.

Here's the shot with deteriorated foam. The focus is on 24"/2F mark and the pencil.

The foam got replaced. The focus is on the 12/1F mark and the dishsoap bottle.

I was about to comment in this thread confirming Neil's opinion that deteriorated foam cannot affect focus position (because gravity pushes the screen down as well, usually) but your experiment reveals the messy nature of real life, and the experiment is much better than theory! Thanks for doing it and sharing it here, it has inspired me to replace the foam on mine when I get a chance!

Ari · Jun 30, 2021

I think I fixed the focus issue I was having after I'd installed some new foam.
Looks pretty sharp in this photo, but some other photos it still looks off by a hair.
My eyes must be going soft on me.
Anyway, thanks for all your help!

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