Quarter Moon Shadow in Mamiya-Sekor c 1:4.5 f180mm lens

[peter k.]

Dang... just noticed this, looking through the lens, unattached from the RB67, there is a light darken area hugging the edge of the lens, like a quarter moon shadow.
Haven't shot with this lens or camera since June, but looking at those c-41 negs, don't see any evidence of it in the shots that I used this lens on. Everything seems to be in focus ect, and no shadow or whatever showing.
Hmmm... So what could it be?
If I used some B&W film.. what kind of shot set up would I do, to perhaps 'expose' its condition and see if its affecting the image?
thanks for your help..

 

[shutterfinger]

1. Shutter open or shutter closed?
2. Looking into from the front or rear?
3. Position of shadow from top when mounted on camera, use clock numbers.
4. ISO 400 normal exposure/normal development; sand dunes or similar light colored subject(s).

 

[peter k.]

1) Off the camera shutter open..
2) Looking both front or rear its there
3) Off camera originally, it was at 2 o'clock.. put on the camera focused close and across room, took off and it was at 3 o'clock.. put it on again and moved and adjusted f stop ISO ect, then took it off it moved up slightly between 2 & 3

When its on the camera, through the waist level viewer, can't notice anything.

 

[summicron1]

When its on the camera, through the waist level viewer, can't notice anything.

i am having trouble understanding what you mean by a "lighten darken area" as you look through -- does it seem to be a de-cementing of the lens on the edge?

In any event, I bet you anything the images you get will be fine. At wide-open, when you are using that area of the lens, it may introduce some slight softness, but not so much as to be noticeable ... it may cause some flare. I'd shoot with the lens and not worry.

 

[Kirks518]

Balsam separation.

EDIT - I thought the moving around was from the way the OP was holding it. NM then.

 

[shutterfinger]

Mount the camera on a tripod, open the shutter on T or equivalent, open the film holder and look through the lens. Is the defect visible?
Balsam separation will not move around unless the element is loose. Some shutters have secondary shutter blades that are short and go on over the ends of the main shutter blades to ensure light tightness throughout the blade movement. One could be loose or worn enough to let stray light reflect back onto the lens provided the shutter uses them.
Are any of the shutter blades silver colored?
Does the angle of the light entering the lens affect the defect position?
Another possibility is the shutter goes past full open off the camera and just goes to full open on camera.

 

[MattKing]

Do you have a hood or filter on the lens?

 

[tedr1]

I have seen lens element separation in a Mamiya 180 that has the appearance you describe. Exposures made with the lens wide open (f4.5) may be degraded very slightly by this optical defect. When the lens is used at smaller apertures (f5.6 for example) the separated region of the lens elements may be covered by the lens iris when it stops down for the duration of the exposure and the image quality is then not affected at all. Repair is possible, by a skilled optical shop, however the cost may exceed the replacement cost of the lens (about $100 - $150 in the USA)

 

[peter k.]

Daylight so could get a picture taken against house siding, lens at 4.5 with open shutter set on 'T'
Film back is off. Taken from back. Area is now staying consistently at 3 o'clock
>Balsam separation?
Hmm... from the pictures on the internet.. don't think so.
> No hood or filter on.
May well be a lens separation I guess... F11 is all clear..
Soooo... will have to go give it some shots and see how it affects the image on f8 to 4.5.

 

[paul ron]

take a pic of the lens you have? Depending on the model, the front cell may unscrew like a light bulb. I may have a good front cell from my junker closet.

Sounds like it may be separation.

 

[peter k.]

Well is it a light bulb... or a lens seeking the light..
Have not tried to unscrew or see if its lose.. please let me if the lens matches what you think it may be..
thanks..

 

[Kirks518]

I'm going back to my original statement - Balsam Separation.

 

[paul ron]

View attachment 165205
Well is it a light bulb... or a lens seeking the light..
Have not tried to unscrew or see if its lose.. please let me if the lens matches what you think it may be..
thanks..

Looks the same.. move the front of the lens around in the sun n see if that half moon shows?
The cell you the looks the same as mine. Mine has very little separation on the edge but its not enough to effect the image.
You need to take out that front name plate. First turn the cone to unscrew it a bit so you can get a good grip on the name ring. That will take the preasure off the ring. AFter teh ring is out you can unscrew the cell inside the cone.

Once the cell is out you can see it better in the light if its separation or whatever.

 

[peter k.]

First turn the cone to unscrew it a bit so you can get a good grip on the name ring.

Cone??? In your picture, is the cone the third item back from the front?
And if so it unscrews counter clockwise?

 

[paul ron]

cone is the part closest to the body of the lens in my pic

 

[peter k.]

Hmm ok loosened the cone, but how the heck do you get a grip on the name ring?
Tried an eraser.. not griping name ring..

 

[paul ron]

rubber glove?

 

[peter k.]

Nope.. undid the cone as far as it will go.. to try to get a better grip on the ring... gonna try again with something else I have..
Hmm... there is a small mark on that ring.. think someone has been here before.. can't see it in my picture of the lens (#11) as it is at the bottom in the reflective sun light area..

 

[paul ron]

Keep trying n youll get it.

tty later.

 

[peter k.]

yeah... later.. uncomfortable messing with it.. will shoot some images with the lens more ope and see what it tells..
thanks.. will update when I develop..

 

[peter k.]

Tried a B&W..placed a sheet of 2x3 in the roll film holder.. as you can see it did not stay straight.
f5.6/8 @ 400
Simple Epson Scan, nothing done to it.. First is full image.

Second is zoom on affected area
Not really a good test shot, as it is not consistent of just a light colored area as Shutterfinger suggested in post#2
But going to go shoot a roll, whatever is wrong does not seem to be causing to much stress in the image, so will give it a full roll and find some sand or large light area.

 

[paul ron]

well if its not imposing on the image, leave it. perhaps using small apertures will minimize its effect.

but at certain light angles will reveal the defect either as flare or a soft focus haze.

the cell i have is much less than your half moon.its at the edge. if you decide to swap them, ill be here. its not going anywhere. just pm me.

 

[shutterfinger]

Peter, as soon as I saw the picture of the lens I concurred with the separation diagnosis. Edmund Optics sells UV optical cement that is currently used in place of Balsam. The only difficult part to recementing is getting the cells correctly aligned. Start by marking alignment lines on the side of the pair. SKGrimes has some information on how to do it. http://www.skgrimes.com/library/old-news/old-lenses-can-be-restored-by-re-cementing
I would make alignment marks of 2 or 3 parallel with a second set 90° from the first on the side of the elements with a scribe or fine tip permeate marker and a straight edge.

Its been a hundred years since I had a Mamiya RB lens apart, Paul has it well covered so put that pry bar down.

 

[Theo Sulphate]

Last year I bought a Mamiya 180/4.5 - some dust in the optics - and just now I see a very minor darkening similar to what was shown above. It's at the very edge of the element(s) and I don't think it would have an effect even wide open.

Is the area likely to expand? If so, how rapidly?

Also just realized the shutter is behind the rear element - it could be touched.

 

[paul ron]

it seems in the last 10 years Ive been seeing more of these lenses separating like that otherwise it was rare to see mamyia lenses doing that. But its mostly the 180s separating. I wonder why?

very weird. BTW its easy to open that cell, the top just unscrews by hand. The element group seaparating is that top one. I was going to try my hand at gluing but never got around to it. I may just give it a go later this week if peter doesn t want this one.