Yashicamat aperture problem

[s._katz]

just bought a Yashicamat - the basic 120 only, no meter, with rapid wind crank and self timer. It has the 3.5 Yashinon lens but the aperture control jams at 5.6. It works fine from 5.6 to 22. If I try to push the control below 5.6 I can see 1 or 2 of the aperture blades flex outwards but I don't want to force it. The actual lens opening appears to be 5.6 to 22 so the control link probably didn't just slip. How do I get to the diaphragm mechanism to find out what is hanging it up? Thanks.

[rodeo_joe1]

It's probably due to oil or grease on the aperture blades causing "stiction". A common problem that affects iris mechanisms of all makes and kinds. The blades may also have been permanently damaged by being distorted, or have popped out of their bearings.

 

The only solution is to dismantle the lens and shutter to the point where the aperture blades can be wiped with a cotton bud (Q-tip) soaked in methylated spirit or lighter fluid to degrease the blades.

 

This still may only be a temporary fix, since once contaminated by oil the problem will likely come back unless the iris mechanism is completely dismantled and thoroughly degreased.

 

FWIW. The lightmeter in Yashimats is next to useless IME. I wouldn't fret about not having one built in.

[Bill Bowes]

Hello everyone. If your YashicaMat is functioning OK but for this "problem", I would not sweat it for the present. Unless you plan on shooting rock concerts or just have to have the f3.5, wait until the camera REALLY needs help. The Mat's have one major "problem", that being the film advance crank strips it's gears, and that is a major rebuild.

Several ways to push this further out. Cock the self-timer lever before advancing the film crank. Yes, you must now use the timer, but if your work requires a tri-pod, again, a minor problem.

Do you really need the f3.5? 90% of my 3 Yashica Mats (EM & two 124's) are used with 100 or 400 asa materials. Out doors, exposures are in the f11-22 / 125 sec range with the 100 stuff & "indoors" you have f8 @ 1/30.

Joe is right on about the meter, even my 124 cd's meters are off. . . a Weston 5 or even the Gossen Pilot's are more accurate, and no batteries are needed!

You will probably find that moving the f stop wheel past f22 will give you a "real" f32 to work with.

Pic is from my EM, a 1966 PX purchase while in Germany. 400Tmax & 510-Pyro. V600 scan. Aloha, Bill

[John Seaman]

You can unscrew the whole front lens group on Yashicas with the Yashinon lens (but not the earlier Lumaxar), giving access to the shutter blades which are in front, and the aperture blades behind them. Then by opening the shutter on B, preferably using a locking remote release, very lightly and carefully clean the aperture blades with a Q tip moistened with a little lighter fluid or similar. Be very careful not to get anything on the shutter blades as these are very much more vulnerable to oil contamination than are the aperture blades.

 

If the blades don't respond to this its likely that there is some kind of mechanical jam, and as Bill says, you could perhaps live with it. A lot of shooting is at F8, 11 or 16.

[s._katz]

All good suggestions - thanks. BTW, I consider the lack of a meter a feature. Not using f3.5 seems like the most practical suggestion, especially since It is hard to focus accurately in dim light through this viewfinder anyway. I still need to see if the film advance, while apparently working, provides even frame spacing. Eventually I will not be able to resist taking the camera apart and I will try the limited degreasing idea first. When that time comes, is there a good source for disassembly instructions?

[Bill Bowes]

Be careful when "testing" the cranking lever. If any "catch" or "skipping" occurs, your camera is almost at that failure I mentioned. Even using my delay cocking before cranking, my EM has had two rebuilds (since 66) and one of the 124's is starting the dragging. Bill

[thirteenthumbs]

Stop the aperture down to f32, open the shutter on B, carefully inspect the aperture for any trace of foreign substance or deformations.

The bladed are blued steel .0015 to .002 inch thick. Check the aperture from both the front and rear. The opening should be a equal sided geometric pattern. The pattern will depend on the number of blades used in the aperture. If all is good at this point the problem is the mechanical operation. Aperture blades have a pin on each end (some are staked holes in the blades) with one end fixed and the other in a movable ring attached to the selector lever.

 

The main ingredient in Lighter Fluid is Naphtha which will damage plastics and rubber. I will not use/have never used lighter fluid for any cleaning application.

The best contact cleaner on the market uses a combination of Naphtha and Alcohol. 90% Isopropyl Alcohol is a good degreaser and the 10% water is far less harmful than pure Naphtha or the additives in lighter fluid.

 

Extra fine powdered graphite works well to lubricate aperture and shutter blades.

[s._katz]

All good suggestions - thanks. BTW, I consider the lack of a meter a feature. Not using f3.5 seems like the most practical suggestion, especially since It is hard to focus accurately in dim light through this viewfinder anyway. I still need to see if the film advance, while apparently working, provides even frame spacing. Eventually I will not be able to resist taking the camera apart and I will try the limited degreasing idea first. When that time comes, is there a good source for disassembly instructions?

[thirteenthumbs]

Favorite Classics / Free Camera Repair Manuals

Yashica D at the very bottom of the page, unknown if its similar to your mat or not.

Be sure to read the paragraph at the top of the page before trying a download.

[s._katz]

The aperture blades look clean and even from both sides, and work smoothly between 22 and 5.6; must be a mechanical problem then. In fact, the camera is in near mint condition otherwise. I'll just use it as is for now.

Also, great car photo, Bill.

[thirteenthumbs]

f number=lens focal length divided by entrance pupil diameter.

A ballpark measurement is to divide the marked lens focal length by the diameter of the aperture opening when viewed through the front lens element(s).

Also the approximate entrance pupil diameter can be determined by dividing the lens focal length by the f number.

A 75mm lens at f5.6 should have a 13.4 mm entrance pupil, at f22 a 3.4mm entrance pupil.

A 80mm lens at f5.6 should have a 14.3 mm entrance pupil, at f22 a 3.64mm entrance pupil.

 

An accurate measurement will require an optical measurement of the lens as it can be off a little from its marked focal length and the actual diameter of the geometric shape formed by the aperture blades.

 

A quick check will show if the aperture scale is correct or if the aperture was incorrectly assembled.

[andyfalsetta]

Also, great car photo, Bill.

 

I agree. That is a great shot!

[chazfenn]

It sounds like 1 (or more) blades have "unhooked" from the hinge or adjuster collar. It won't jam & bind up to a point but then it binds & twists.