FED-2 shutter tensioning

[evan.kubota]

The shutter on my FED-2 was capping at 1/500s. Other speeds were fine and "B" worked correctly. I disassembled it to diagnose the problem, and did more than I had to, accidentally removing the first curtain ribbons from the drum. I repaired the ribbons and reassembled the camera, but the capping issue remains. If I reduce the second curtain's tension so 1/500s doesn't cap, the second curtain does not close reliably on "B" and 1/25s. If I increase the second curtain's tension so "B" and 1/25s work, 1/500s resumes capping.

Increasing the tension on the first curtain may fix 1/500s without reducing the second curtain tension to the point where "B" and 1/25s no longer work, but the first curtain is already tensioned strongly.

Also, the orientation of the camera affects whether the second curtain closes with light tension – it closes easily with the left side held up (shutter moves "up"), but closes slowly with the right side held up (shutter moves "down"). Why is this the case?

Comments and suggestions are welcome. Thanks.

 

[fidget]

Welcome to the forum...
What do you mean by "capping"? I ask this because a release problem is frequently seen as "capping" whereas capping is actually (as you have identified) when the second curtain catches up with the first.
I've seen many instances of shutter release problems, usually seen as an unexposed vertical area on the LHS of a neg, or when looking through the open back whilst firing the shutter, a dark area on the RHS.

Have a read of the Shutter tension "HOW-TO" at the top of this FSU section.

Congratulations on getting your FED back together again, BTW.

 

[evan.kubota]

Actually, it is on the right side of the film gate. When you say it could be a release problem, why would it work correctly at 1/250s but not 1/500s? What is the most common release problem? What should I do to fix the release?

 

[fidget]

On the RHS of the gate, that's good..as it is easy to fix. Messing with the curtain tension will do very little to help this, but a lot to make other aspects of the shutter problematic.

Get the top off and watch the operation of the release catch on the top of the curtain drum. It looks like a metal crescent. This should move down smoothly with the operation of the shutter button. It sits on a shaft which can become gunked up.

If not smooth. clean it to fix it.

Note that there is a notch in the end of the crescent which traps the tab of the second curtain. The crescent must move down to trap this before the first curtain tab strikes the cam of the crescent and releases it. This crescent is sometimes too high to trap the tab every time, it's worse for the fastest speed as this starts very near the cam.

So, check that the crescent is low enough to trap the tab.
If it's too low, all works well except the B setting, which may never release the second curtain.

There's more than one other thread about this, IIRC with drawings etc.

PS be careful and gentle with the fine spring which acts on the crescent, it must push in and down.
Dave

 

[fidget]

For what it's worth, I've always been puzzled by the action of the curtains in this problem. I can not figure out why the curtains start out without a gap or even overlapped, but then open a little and then maintain a gap (which may not correspond to any particular speed).

Also note that increasing the tension of any of the curtains to fix this "capping" fault is very likely to make it much worse....

 

[evan.kubota]

I understand how the second curtain release works, but the crescent, shaft and spring seem fine. The crescent does look slightly high, but what is the repair for this, filing the end? I'm not sure I understand why the delay in the shaft moving down causes problems only at 1/500s – if the crescent is not trapping the tab for the second curtain release, this would seem to affect all speeds, because the only difference between the speeds, the position of the speed selector that strikes the crescent and releases the second curtain, depends on the crescent holding the second curtain tab. If the problem with 1/500s is that the crescent is not holding the second curtain, but rather allowing it to begin at the same time as the first curtain (thus the absence of a slit until the first curtain outpaces the second because of its greater tension), why do the other speeds work correctly?

 

[fidget]

I understand how the second curtain release works, but the crescent, shaft and spring seem fine. The crescent does look slightly high, but what is the repair for this, filing the end? I'm not sure I understand why the delay in the shaft moving down causes problems only at 1/500s – if the crescent is not trapping the tab for the second curtain release, this would seem to affect all speeds, because the only difference between the speeds, the position of the speed selector that strikes the crescent and releases the second curtain, depends on the crescent holding the second curtain tab. If the problem with 1/500s is that the crescent is not holding the second curtain, but rather allowing it to begin at the same time as the first curtain (thus the absence of a slit until the first curtain outpaces the second because of its greater tension), why do the other speeds work correctly?

That's a good question. Bearing in mind that in my last post I did write that the reasoning behind this particular behaviour of the curtains is a bit of a mystery to me, clearly I cannot provide a detailed answers your question.

Perhaps others can and will.


It may be a mistake to assume that the other speeds work correctly, however. The operating gap between the curtains may be changed by this event. The effect will be less noticeable as the speeds (thus gaps) get longer.

See how the release works? The crescent is lowered to trap the second curtain tab. This is released when the first curtain tab strikes the cam and knocks the crescent off the second curtain tab, thus releasing it. When on B, the cam is never struck by the first curtain tab, so the second curtain tab is only released when the crescent is lifted off it.

The crescent is made of a soft metal and is easy to bend down to catch the tab earlier. Others on this forum prefer to shorten the shaft.
The effect of lowering it a little too far is that it should work well, but B may be effected. It is easy to bend it back up fractionally to adjust for this, a little more difficult if you have chopped a lump off the shaft.

Don't forget to get your curtain tensions back to sane levels. Recommendations on this forum might be to have 2.5 turns on the second and more on the first.

 

[evan.kubota]

I oiled the release mechanism and shutter; it winds much more smoothly now, and I could reduce the tension on the second curtain without it hanging on "B." It was still difficult to get "B" and 1/500s both working, but I think I succeeded.