Zenit EM complete CLA ongoing thread (pic heavy)

jaeae · Dec 29, 2020

Next step would be installing and adjusting the mirror assy. This is fiddly and important, because it will also affect the 1st curtain.

The newer Zenits (like 12XP and 122 from 80 - 90's) are easier to adjust because they have clamping springs for the big mirror mechanism screws, the EM does not...

1. Loosen the big screws on the mirror assy mechanism "slide"
2. Install assy in the camera body
3. cock the shutter and test
4. if the mirror does not go up OR does not come down again you either have too tight setting that stops the 1st curtain altogether, or the flipper wheel is @ the wrong tooth (there's only one right gear tooth it works correctly at)
5. adjust mirror mechanism height
6. remove mirror assy from camera and tighten the screws
7. re-install assy to camera and check mirror again (re-do 3-6 again if not ok)

The mirror slide mechanism height adjustment screw is next to the prism behind aperture lever mech

Here's the sliding mechanism that affects how much the mirror flipper pin is pressed towards the mirror flipper wheel

Here's a video how much there should be play. Maybe not more than this, because the mirror may start blocking light from lens back element

AgX · Dec 29, 2020

jaeae said:
And when you open the shutter in "B" mode, the 1st curtain blade should be just outside the film opening at the left. 2nd shutter blade should be "waiting" at the right, optimally some millimeters before film frame opening (not just at the edge).

Is there a reason for this?

jaeae · Dec 29, 2020

AgX said:
Is there a reason for this?

I believe it makes the curtain movement more stable, since the curtain can start it's acceleration before the actual film opening. The 1st curtain also starts well before the opening, like 5mm.

I checked a couple of bodies I have, they both have the 2nd shutter waiting for release in "B" setting, something like 2 .. 3 mm before the film opening.

jaeae · Dec 29, 2020

When I had everything assembled I put new foams to the prism holder, under viewfinder lens and to the side of the prism holder.

I didn't bother glueing the foam, I think it will stay in the slit just by tucking it in. Easier to dissasemble again. It's purpose is to block some dust and light from the metering window from getting into the mirror chamber. The piece that is under the viewfinder lens, I put some glue on it so it stays in place.

jaeae · Dec 29, 2020

Next thing; shutter adjustment

I tried using different methods for adjusting the curtain tensions.

1. Just by eye. Suprisingly, if one fiddles with the adjustments and practices looking the shutter, it can be adjusted just OK.
2. Record sound from "B" and "1/30" settings and compare them. Using software that shows waveform (like Audacity), one can determine the curtain travel times.
3. Use digital camera video, with a camera where you can set the shutter speed very high manually. I used my Panasonic GX80/85 and set the video shutter speed to 1/2000. You can release the shutter several times and you will be able to catch the curtains photographed going @ different places on the film opening.

For initial setting, good starting point:

Here's results for the EM. I used Olympus sound recorder, microphones about 5cm from the camera. Camera back door open. The recorder was on a piece of foam, and I kept the camera body in my hands, to avoid any structural noise.

"bulb" setting. The long silence is me keeping the shutter open ( = no noise).

Here's 1/30:

Note that my interpretations may not be 100% correct, but after looking at 20 different recordings I think the times are like that. What was suprising, NONE of my several Zenit shutters were under 1/30 when adjusted. Ok, if you adjust Zenit 122 to very slow settings it might be like 1/25, but when the shutter is adjusted to be snappy and consistent, the 1/30 is always more like 1/35, even 1/40. My fastest was a factory-spec-not-fiddled-with-Zenit 130, which had almost 1/45.

So the tolerance seems to be 1/30 +0, -0.5 stops for these

You can pretty safely set the shutter as slow as you can and it'll be OK. Of course you should not set just 1 rotation of adjusting screw. If the springs are very loose, the curtain speeds will likely vary their speed more with temperature, weather, camera orientation etc.. So, 2-3 rotations seems to be OK for the models with the conical helper spring. But you probably need more for the ones without it (like 12SD and 122). The helper spring is the one next to the mirror flipper wheel. It's tension can also be adjusted, it should be so that there is no tension when shutter is uncocked. Or it can be very slightly pushing the shutter curtain to "closed" direction. But not other way around.

jaeae · Dec 29, 2020

The curtain blades are about 4mm wide, so one can estimate slit width with that in mind.

The film frame is 36mm wide. So in principle, for different speeds, the curtain slit:

1/30: 36mm
1/60: 18mm
1/125: 9mm
1/250: 4.5mm
1/500: 2.25mm

It's worth noting that the E has no way of adjusting the slit. If the curtains are poorly glued to the drums in wrong places - and you find that out during adjustments - you must disassemble it and re-do everything.

In newer models like 11 or 12 (with the shutter speed knob that does not rotate along with the shutter drum) you can fine tune the slit. Which is an excellent feature.. !

You don't need to test any other speeds other than 1/30 and 1/500. Others will follow OK.

Here are 1/500 photos. NOTE: the curtains are of course perpendicular. The obliqueness is because of digital camera "rolling shutter" effect. Google it.

Shutter at start:

Middle-ish:

End:

You may ask why is the slit wider at the end? The curtain is fastest at there. And slow at the beginning. I have read somewhere that you should adjust the slit that way, and it so far it seems to be true. I have some other Zenits around and they are adjusted this way, and shooting clear skies at 1/500 show no banding or uneven exposure. I believe "one stop" of difference might be OK then? The slit is very accurately 2-3mm at the beginning and probably 4-5mm at the very end of the curtain travel. This is accomplished by setting the 2nd shutter travel time / speed just a bit slower than the 1st.

mohmad khatab · Dec 30, 2020

jaeae · Dec 30, 2020

I tried to adjust the shutter 1/500 by looking through the camera towards bright-ish flat light source and releasing shutter several times. If you look carefully, you can see the left part of the film opening getting darker than right, if there's too much tension on the 2nd curtain and it catches up the 1st. And vice versa.

When the shutter is ok, the camera can be assembled and then there's only focusing fine-tuning left.

I used a loupe + focusing screen from a 122 to check focus. What you want is actual focus on film plane to match with viewfinder. You can use "Bulb" mode for this. The mirror rest screw in the mirror chamber is used for the fine tuning. It's a bit hard sometimes to wrap your head around on which way to turn the screw Note also that you should loosen the lock screw below it before ajusting and lock it again before re-checking focus. I have checked focus @ 1m and infinity.

One example:
If your 58mm helios standard lens (recommended!) reaches infinity @ end stop or just a bit before it using film plane, but in the viewfinder you cannot reach infinity --> your mirror is too far from the lens.
The lens goes closer to mirror when you focus far away.
So in that situation you must rotate mirror rest screw counter-clockwise to set mirror higher = closer to the lens rear element.

If you want to be quick, the infinity check is enough, other distances should be just OK if you can reach infinity using the viewfinder (or just slightly beyond).
With my Helios 44M-4 lens, the lens barrel shows also 1 meter pretty accurately, depending on the camera body. It seems to be maybe within 5cm of the actual 1m focus @ film plane.

jaeae · Dec 30, 2020

For reference here are most tools I used in this project:

For lubrication, just standard "sewing machine oil" / white oil and the usual lithium grease.
For the screwdrivers I would recommend getting a cheap set with several different size flathead drivers + a small file. You can fine tune the tips of screwdrivers and pliers to fit. This way you can avoid ruining screw heads etc.

As lens spanner I have used a metallic caliper/compass/divider (what do you call it?) of which tips a have filed to fit lens retaining rings.

AgX · Dec 30, 2020

jaeae said:
One example:
If your 58mm helios standard lens (recommended!) reaches infinity @ end stop or just a bit before it using film plane, but in the viewfinder you cannot reach infinity --> your mirror is too far from the lens.
The lens goes closer to mirror when you focus far away.
So in that situation you must rotate mirror rest screw counter-clockwise to set mirror higher = closer to the lens rear element.

At all cameras the mirror-rest adjustment only has gradual affect on the image. Misadjustment will result in a gradual reduction of focus along the vertical.

Tel · Dec 30, 2020

Your work on shutter timing is excellent. I've always been fearful of this but I might give it a try....

jaeae · Dec 30, 2020

AgX said:
At all cameras the mirror-rest adjustment only has gradual affect on the image. Misadjustment will result in a gradual reduction of focus along the vertical.

Yes, these Zenits seem to have some shims the focusing screen rests on, those are probably put there in factory in some kind of jig. The shims are quite thick though, so the fine tune probably always has to be made with the rest screw. Getting the focus screen out of the mirror assy and back again, without scratches - has to be the fiddliest job in Zenit (don't try it!)

AgX · Dec 30, 2020

I had it about the mirrior, not the screem.The point is that at adjusting the mirror rest one part of the image will be much stronger affected. The image swings into focus.

jaeae · Dec 30, 2020

AgX said:
The point is that at adjusting the mirror rest one part of the image will be much stronger affected. The image swings into focus.

Yes got it

I meant that one can avoid that issue by shimming the screen, but it's a lot of work

AgX · Dec 30, 2020

No, you cannot avoid it. If screen and optical axis are at 90°, the mirror has to be at 45°. The mirror-rest is to achieve this. As this far awwa of the mirror hinge amd the hinge is more or less coinciding with one edge of the mirror, you got the effect of the image plane swinging into focus. With the mirror shim one basically adjuts the rather static part of the image.

jaeae · Dec 30, 2020

I see, hmm maybe not as simple as I thought. That got me thinking what would be the best practice to set focus on these - maybe adjust mirror box/assy back/forwards (it has some play) if the focus is way off ? And use mirror rest adjustment as last resort.

ic-racer · Dec 30, 2020

Very nice. Your pictures and text explain more than some of my threads.

AgX · Dec 30, 2020

I never did such. But I guess the way would be to first set the mirror angle so that the sharpness is even over the whole image and then if necessary adjust the screen height.

We likely need one of those KMZ girls to tell us how to do...

jaeae · Jan 22, 2021

Did some cold weather testing

Seems that -10 celcius is a bit too much for the shutter. The 1st curtain slows down to maybe 1/3 of the original speed and it does not have enough momentum to release the 2nd shutter. Well sometimes yes. It feels like the mirror flipping mechanism and 2nd curtain drum are the biggest reasons for friction - since the 1st curtain axle rotates within the 2nd curtain drum. The drum is aluminium and I'm 90% sure it does not have any lubrication from the factory and I did not put anything there myself. The surface area is quite high and I believe if you would put some grease in there, it would slow down even more in the cold weather. The higher speeds work much better, probably because both curtain drums rotate at the same time.

Again I think the newer Zenits are better in this respect also - the 2nd curtain drum is plastic in those (as are some rollers) and it probably has less friction and mass. The 12XP is probably the best overall model..

AgX · Jan 22, 2021

jaeae said:
Did some cold weather testing
The drum is aluminium and I'm 90% sure it does not have any lubrication from the factory and I did not put anything there myself. The surface area is quite high and I believe if you would put some grease in there, it would slow down even more in the cold weather.

In general synthetic oils are less affected by low temperatures. To what extent this also applies to greases our lubrication nerds may tell us...

jaeae · Sep 17, 2021

I was doing some focus fine tune and general check (going to use this EM soon again). Did a comparison of EM vs Olympus XZ-2 shutter speeds and resulting lightness of image. I shot these through the film opening, zooming in so that the XZ-2 lens view angle was narrow and no component of the EM darkens or shades the image. Looks pretty good !

Niglyn · Feb 26, 2022

Hi,

Thanks for the detailed breakdown of the EM. I did a curtain repair on an EM few years ago, what a nightmare.

The bit, I still do not understand, is how the shutter speed selection works. Any explanation would be most helpful. There seems no way to adjust the speeds (many of my Zenits only get to about 1/125, then the speed only slightly increases)

My guess is that the curtain tension controls the curtain speed and the slotted washer under the shutter speed dial controls the release of the second, curtain, but I can't still cannot see how.

I have made a shutter timer/tester using an Arduino & two lasers. It is quite simple to make (happy to share if peeps want to make one) I am able to measure shutter speed and both first and second curtain travel.

As an example, the Zenit sitting in the tester now shows a curtain speed of around 8mS for both first and second curtain. Shutter speeds at 1/30 and 1/60 are fine, but 1/125 is actually 1/94, 1/250 is actually 1/147 and 1/500 is actually 1/210

4season · Feb 26, 2022

jaeae said:
Also I noticed that the upper curtain string has worn for some reason.

Thanks again for this how-to guide: My Zenit 412 broke a lower shutter curtain ribbon. As far as I could see, the only sharp or abrasive objects in the area were the metal portions of the shutter curtains themselves. So I smoothed out the rough edges with sandpaper. Unfortunately, the shutter curtain itself couldn't be salvaged because it had stretched out of shape, but I was able to rebuild using new materials from Aki-Asahi.

jaeae · Feb 26, 2022

Niglyn said:
Hi,

Thanks for the detailed breakdown of the EM. I did a curtain repair on an EM few years ago, what a nightmare.

The bit, I still do not understand, is how the shutter speed selection works. Any explanation would be most helpful. There seems no way to adjust the speeds (many of my Zenits only get to about 1/125, then the speed only slightly increases)

My guess is that the curtain tension controls the curtain speed and the slotted washer under the shutter speed dial controls the release of the second, curtain, but I can't still cannot see how.

I have made a shutter timer/tester using an Arduino & two lasers. It is quite simple to make (happy to share if peeps want to make one) I am able to measure shutter speed and both first and second curtain travel.

As an example, the Zenit sitting in the tester now shows a curtain speed of around 8mS for both first and second curtain. Shutter speeds at 1/30 and 1/60 are fine, but 1/125 is actually 1/94, 1/250 is actually 1/147 and 1/500 is actually 1/210

Sounds quite slow, if adjusted properly, 1/250 and 1/500 should be closer than that. 1/100 for 1/125 is only 1/3 stop different so it would be perfectly OK.

Yes, tension controls curtain speed and the slots control the slit of curtains. When you press shutter button, first curtain releases and at the same time second curtain is stopped by a latch. The latch is released when the shutter speed selector in its chosen slot hits it. The first curtain rotates/pulls the slotted washer.
See this video:
The E/EM/B models have no adjustment on this. Later models with "rotate anytime" shutter speed knob have a better mechanism, where you can fine-tune the curtain slit. On E/EM/B models, you just have to glue the curtain precisely to get about 2..3mm slit at 1/500 setting.

Note that the Zenit shutter is actually quite fast if adjusted and lubricated properly. The 1/30 should be more like 1/35. If you try to adjust it to 1/30 I suspect the tension springs may be a tad loose and curtain movement may get a bit variable, since the mechanical parts are so coarse.

Niglyn · Feb 27, 2022

Thanks for the speedy reply. The video makes things clearer.

After adjusting the second curtain, which was visibly dragging, the camera developed another fault. Now, the first curtain only partially opens when the shutter is pressed. When releasing the shutter button, it then fully opens & the second curtain closes. Carefully pushing the first curtain or turning the speed dial to fully open the first curtain, then allows the second curtain to fire & close.

I have tried varying the tension on first and second curtain, but still the fault persists. I'm guessing there must be an issue with the shutter mech, worn or sticky oil. Although stripping an E is easier than a camera with a Zenit with TTL metering, not sure I want the hassle.

Zenit EM complete CLA ongoing thread (pic heavy)

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