Zenzanon S 80 mm lens shutter irregular

[Cor]

I was wondering: a have a very basic knowledge about electronics: so this solenoid magnet gets magnetized when the there is current running through the solenoid. The magnetic force is retarding the shutter for a fixed time (ie as long there is current going through the solenoid). When the current is cut, de magnet demagnetize, and the shutter is released. Than the magnet isn't a magnet anymore ? If so why would "re-charge" that magnet with a strong neodymium magnet again ?

Thanks,

Cor

 

[koraks]

If so why would "re-charge" that magnet with a strong neodymium magnet again ?

This is a typical solenoid construction:

(Source: Magnet-Schultz)

The coil is an electromagnet; it only acts as a magnet as long as there's current flowing through it (DC in a solenoid).
However, the solenoid works because the electromagnet expels a permanent magnet (the plunger/armature).
So there's both a temporary electromagnet, and a permanent magnet. The combination of the two is what makes the solenoid do its thing.

The problem is that if you take a typical ferromagnetic material and you place it in the vicinity of another magnet, the fields start to align. This other magnet can be the actual electromagnet that's part of the same solenoid, but it can also be another magnet nearby - or even the core of the earth itself in weak/low-quality permanent magnets. Ultimately, all magnets that are kept stationary in relation to the earth's magnetic field will align with the latter. In low-quality/low-strength magnets, I can imagine this happening within decades.

A further problem is that magnets tend to demagnetize once they heat up. The temperature at which this happens, depends on the material, but is generally (well) outside the temperature range a typical camera lens should experience (>80C). I can imagine that prolonged exposure to high temperatures may result in loss of strength in some materials. The same is true for extremely low temperatures btw; -40C or so.

In the case of your lens, it's unclear whether the intermittent problem is due to the permanent magnet balancing on the brink of being strong enough to do its job, or if it's a bad electrical contact in the coil circuit somewhere (not necessarily in the coil itself).

 

[Cor]

Thanks !

Best,

Cor

 

[itsdoable]

This is a typical solenoid construction:

Thanks for posting this. I've got a PG 100mm with a shutter that won't close reliably. All other camera functions are operating properly, and my 150mm works perfectly.

This video indicates that the solenoid magnet may have become demagnetized over time. If the permanent magnet has weakened, the mechanism may not be able to pull the shutter closed properly. That makes sense. I hope it is the case, as it should be a relatively straight-forward fix.

I'd be careful about the video linked in post #19, the Seiko shutters do not have a permanent magnet component. The part that the video calls a "magnet" is the Anvil, and is not a magnet, just ferromagnetic steel. Over the course of use, it may become mildly magnetic, but it's function is not to be magnetic. It just closes the magnetic loop when the coil is energized. If anything, it may need a degaussing.

The electro-magnetic switch on these shutters is not technically solenoid (which has a moving rod pulled by the coil, as shown by koraks), it's a horseshoe-anvil release. None of the parts are permanent magnets (neither are any parts of a solenoid). Note that later electromagnetic releases did use a permanent magnet (Hasselblad, Nikon, Canon, Pentax, etc...) but that design came later, associated with the development of neodymium magnets.

In the Seiko shutters, the horseshoe component becomes an electro magnet when the coil is energized, attracting the anvil to the ends, the linkage from the anvil prevents the shutter from closing. Releasing the Anvil allows the associated linkage to release the shutter, which then closes. The Anvil only moves ~1mm.

The coil is on one leg of the horseshoe, and the anvil pivots on a linkage to the pin to it's left, which is linked to the lower arm in the photo, which holds the shutter open.

The coil rarely breaks, and is easy to test with a meter. The usual issues are with old lube on the linkage, making it stiff, or a failure in an electrical components resulting in low current to the coil. In the latter, the shutter dose not work for longer times, as the Anvil is not held against the horseshoe properly.

If the shutter is not closing, then the Anvil is not releasing from the horseshoe, which can be caused but stiffness in the linkage, or a combination of that and the horseshoe and anvil retaining some magnetism, so there is a weak force holding it together. Cleaning the linkage, and degaussing the Anvil and horseshoe would help (although degaussing is usually not necessary).

The other thing to look at is oil on the shutter blades (especially near the pivots where you cannot see it), this causes the shutter to stick when open. This is more common on mechanically times shutters, as they have a lot more lube in the area. The shutter blades, pivots, and associated components are designed to run dry.

 

[koraks]

@itsdoable thanks for setting us straight on that; good points. I also agree that gummed up grease or maybe fouling is a potential cause of the lack of a reliable release, or stickiness of the shutter blades. I'd expect the latter to be visible from either the front or the rear of the lens with the shutter closed.

 

[dizot]

I'd be careful about the video linked in post #19, the Seiko shutters do not have a permanent magnet component. The part that the video calls a "magnet" is the Anvil, and is not a magnet, just ferromagnetic steel. Over the course of use, it may become mildly magnetic, but it's function is not to be magnetic. It just closes the magnetic loop when the coil is energized. If anything, it may need a degaussing.

The electro-magnetic switch on these shutters is not technically solenoid (which has a moving rod pulled by the coil, as shown by koraks), it's a horseshoe-anvil release. None of the parts are permanent magnets (neither are any parts of a solenoid). Note that later electromagnetic releases did use a permanent magnet (Hasselblad, Nikon, Canon, Pentax, etc...) but that design came later, associated with the development of neodymium magnets.

In the Seiko shutters, the horseshoe component becomes an electro magnet when the coil is energized, attracting the anvil to the ends, the linkage from the anvil prevents the shutter from closing. Releasing the Anvil allows the associated linkage to release the shutter, which then closes. The Anvil only moves ~1mm.

View attachment 362316
The coil is on one leg of the horseshoe, and the anvil pivots on a linkage to the pin to it's left, which is linked to the lower arm in the photo, which holds the shutter open.

The coil rarely breaks, and is easy to test with a meter. The usual issues are with old lube on the linkage, making it stiff, or a failure in an electrical components resulting in low current to the coil. In the latter, the shutter dose not work for longer times, as the Anvil is not held against the horseshoe properly.

If the shutter is not closing, then the Anvil is not releasing from the horseshoe, which can be caused but stiffness in the linkage, or a combination of that and the horseshoe and anvil retaining some magnetism, so there is a weak force holding it together. Cleaning the linkage, and degaussing the Anvil and horseshoe would help (although degaussing is usually not necessary).

The other thing to look at is oil on the shutter blades (especially near the pivots where you cannot see it), this causes the shutter to stick when open. This is more common on mechanically times shutters, as they have a lot more lube in the area. The shutter blades, pivots, and associated components are designed to run dry.

I appreciate the additional details, @itsdoable. I had presumed the the anvil was a permanent magnet based on the video, and its role was to pull the solenoid back to close the shutter (a job usually accomplished with a spring). Given your explanation, I would agree that it is more plausible there is a mechanical issue that may be resolved with proper cleaning. I don't see any oil on the blades...but as you mentioned, they could be gummed-up in their mount where it is not visible.

I have cleaned oily aperture blades on other lenses, so I'm not afraid to get in there and take a look. At worst I'll end-up with a non-functioning lens, which is where I am already.

Thank you!

 

[Cor]

Thanks for the further clarifications itsodoable ! In the mean time I have obtained a newer 80 mm PS lens (less nice than my S lens, it has some fungus, but the shutter works, I ran a test roll, and it seems sharp enough). So I feel less worried opening up the S lens..maybe...

Best,

Cior

 

[choiliefan]

I bought an 80mm 2.8 PS with a damaged helical a couple years ago and mounted the cells in a manual Copal shutter. It's a terrific "modern" lens and works great on my Century Graphic.
I did the same with a damaged 40mm Zenzanon (645) which I use in a customized Speed Graphic for Instax film.
There's more than one way to skin a cat.

 

[Cor]

I bought an 80mm 2.8 PS with a damaged helical a couple years ago and mounted the cells in a manual Copal shutter. It's a terrific "modern" lens and works great on my Century Graphic.
I did the same with a damaged 40mm Zenzanon (645) which I use in a customized Speed Graphic for Instax film.
There's more than one way to skin a cat.

Interesting suggestion !

Thanks,

Cor