Question: I can not get the shutter of the Schneider Kreuznach 135/3.5 Xenotar to open.
I tried to explain what I know in this picutre:
![image](https://i.imgur.com/6hnafsOh.jpg)

Anyone any idea?
I'm afraid I don't have a manual for the lens and haven't found one online.

Answer: 
With large format, unless you have an oddball focal plane shutter (I've seen some - more often in a press camera, which you *might* have here), the camera that you have has a *leaf* shutter - the aperture and the shutter are between the front sent and rear set of the elements.

I'm personally most familiar with the Copal brand shutters:

[![enter image description here](https://i.stack.imgur.com/retL0.jpg)](https://i.stack.imgur.com/retL0.jpg)

In this image you can see the f/stop select (silver triangle) which is part of the lens, the shutter select (red line on ring), the shutter release (top of the image), and the lock open (bottom black triangle).

Another view of a Copal shutter (that first one was a #0, this is a #1):

[![enter image description here](https://i.stack.imgur.com/3yO47.jpg)](https://i.stack.imgur.com/3yO47.jpg)

To shoot a photo, one would typically:

1. open up wide (f/5.6 for this shutter)
2. then push that black triangle to the lock open position
3. do your focusing and standard adjustments
4. then stop down to what you want for the f/stop to be to check for the depth of field
5. release the lock open position
6. insert the film holder
7. select the shutter speed
8. cock the shutter
9. release the shutter (cable release)

Now, lets look at this for another view of a variation on this lens:

[![enter image description here](https://i.stack.imgur.com/PDyYY.jpg)](https://i.stack.imgur.com/PDyYY.jpg)

You can see the similar parts - the shutter speed select, the aperture select at the bottom, the shutter cocking. However, this shutter doesn't have the lock open that the Copal shutters do.

What you will need to do there is set the shutter to either 'M', 'B', or 'T' depending on the labeling of the shutter so that it it is open for a long period of time. It is possible that these are different things - you will note that 'T' and 'B' are both on the Copal shutter - one is a bulb (as long as you hold the [bulb](https://i.stack.imgur.com/Ea2RR.jpg) tight it will stay open - the 'T' is for a timed release where you press it once to open, and press it again to close.

You *will* want a cable release.

You may find that watching [this video](https://www.youtube.com/watch?v=eG0ODIugSFI) of a Copal No. 1 shutter being twisted about and worked with or a 6000 FPS [video](https://www.youtube.com/watch?v=co7J2_DkdL4) of the shutter opening and closing - note that the shutter and the aperture are different things, though *really* close together.

That green knob that you didn't mark... it *may* be a lock open. Though, I'm not familiar with that shutter.
Finally. "user47638" was basically right:

![image](https://i.imgur.com/UyBfVhH.jpg)