lens fires when I hit the shutter pre-release

[jamie]

Yesterday I wanted to use my 150mm f/4 C on my 501CM for a 1-second exposure and noticed that when I hit the shutter pre-release the shutter gets tripped. However the shutterblades then don't close until I click the shutter and when I do they close very slowly.

What's the problem here? The lens or the body? I would guess it's the lens since I don't have that problem with my 80mm, however, I had the body CLA'd a while ago and it's still under warranty until the end of this month so I want to make sure it's ok.

 

[EmilGil]

When you press the MLU-button, the lens should close, the mirror go up and the auxillary shutter open. If the central shutter doesn't close until you press the release-button, your lens is in need of CLA.

It sounds like the slow speed timer in the lens is a bit sticky. What happends if you use the other times? Remove the back and look through the aux. shutter. Try 1/2s, 1/15s, 1/125s and 1/500s. Same behaviour?

 

[Woolliscroft]

The Mamiya RB67 sometimes does this. The work-around seems to be to re-set the mirror up switch for each shot.

David.

 

[jamie]

The lens shows the same behaviour at almost all shutterspeeds but at some shutterspeeds it happens more often than others (and at 1/500s the shutterblades sometimes get stuck midway). What I find strange is that whenever this happens the shutter actually fires, i.e. I can hear the timing mechanism, but it doesn't close.

When I don't use the pre-release everything works fine and the shutter is really "snappy".

It seems pretty clear that the lens needs a CLA. I'm just not sure if I'm willing to have it CLA'd for $150+ because I'm planning on replacing my old C lenses with newer CF lenses.
At the moment I can work around it by just not using the pre-release with this lens but I'm afraid that the problem could get worse if I ignore it.

 

[Mike Kovacs]

On a leaf shutter SLR the sequence to mirror up goes something along the lines of:

start position - lens open, aperture open, rear flap closed, mirror down

mirror lockup - lens closed, aperture stopped down, rear flap open, mirror up

or trip shutter w/o mirror lock - lens closed, aperture stopped down, rear flap open, mirror up, shutter tripped (black viewfinder at end)

I agree with the 2nd poster - if you see the lens slowly closing down its shutter is probably in need of a service. What happens when you shoot it on bulb without locking the mirror? If the shutter blades are oily/dirty and sluggish, they should be sticky regardless of how you trip the shutter.

That complicated sequence is the bane of all leaf shutter SLR designs. They are finicky and need to be serviced from time to time to keep them in shooting condition.

 

[jamie]

I just tested the lens again and now I think I see what the problem is. The shutter blades are clean and they don't seem to be sluggish but I noticed that when I fire the shutter the shutter (sometimes) only closes when the exposure is completed but not before the exposure starts. Instead of going through the closed-open-closed procedure the shutter only does the open-closed part.

I think it's time to call my repair guy and ask for a quote. However, I might just leave it like that and save up to buy a CF lens.

 

[John Koehrer]

Shutter blades aren't the only thing that can get gummed up,
The blades are moved by the "blade operating ring" & just a tiny poo dab of grit or oil will cause it to slow down just from the additional drag between the BOR & the housling.

 

[jamie]

thanks everyone for the help!

I think I'll have it CLA'd next week. I'd like to do more portraits in the future so I really need it and should I decide to sell it later on I will probably get a lot more if it has recently been CLA'd.