Bolex Shutter Timing Guide:

[Tyler Fukuda]

I'm sorry if this topic has beat to death but i'm researching to understand this camera fully inside and out and want to better grasp the shutter / pull-down claw timing from the manual and from what I've read here.

To start this off, i'm going to use the example of re-placing the front "Lens Holder" (as referred to in the service manual) on my Bolex REX-4:

Before the Lens Holder (or Turret sometimes called) is replaced, a few things have to be in order(?):

1) Camera must have tension on the mainspring (A few winds of the handle).

2) Pull-down claws must be set towards the lowest position on the eccentric post/shaft?            

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 -  "Wind the spring motor a few turns and operate the camera through the frontal release knob. Fit the nylon gear (a) and the washer with the squarish

shaped hole (b), making sure that the eccentric (c) is inclined as per sketch. The angle displacement (d) must be of 1 tooth."

 

3) The "Lens Holder" with the Variable Shutter assembly now is ready to mount onto the body, but i'm a bit confused at the information here.

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Next you put on the front section with the shutter in a position where both blades cover the aperture.  Make sure both claws are turned back against their rests. Slowly lower the front and observe shutter, turret swiveled 180 degrees, reflex double prism swung out. Shutter should not turn far. Once in place, hold it there while pushing the side release knob to P(ICTURE), the single-frame functions switch set at T(IME). Shutter should stop with leading edge just above aperture, Paillard specified 1,5 mm. If not, repeat sequence until you’re near. If unsatisfactory, loosen the three set screws of the helical gear on shutter shaft, turn about 20 degrees, retighten.

If i'm not mistaken and according to the manual, the first part is ONLY to be followed if you've disassembled the variable shutter from the lens holder? If you were only replacing the Lens Holder back onto the body, you would skip to the second half of where the shutter blades lie just above the gate, and by finally seating the lens holder, it will correct itself into the position in the diagram: 1.5mm above the gate is the end position after front lens holder is secured?

4) Then you would set the camera to "T" mode and position the run button to "P" (Sadly my camera doesn't seem to move into T mode currently??) observing the timing between the pulldown claw position and the shutter open/close position.

 

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To check the shutter timing, when set to extended single frame the shutter should pause in the open position with the edge of the shutter just visible through the lens port above the gate opening.

The pull down timing should be set so that the film is advanced just after the shutter closes. With the motor disengaged you can manually advance the movement and observe when the claw tip begins to move forward relative to the shutter. To double check, mark some film with a sharpie and observe through the lens port as you manually advance the film, there should be no movement of the film visible before or after the shutter closes.

 

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There are a few things to be set correctly.

• The shutter should be halted with its leading edge one to two millimeters above the aperture in the TIME function when side release is held to front;
• The shutter should cover the aperture entirely before the claw begins to exert pressure on a hole edge;
• The shutter should not free the aperture before the claw has cleared a perforation hole after a pulldown. Variable shutters set fully open.

4) Additional information regarding if you decide to remove the claw gear and it isn't recentered correctly? and/or you reposition one of the take-up/feed sprockets

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When you load the film with the loop formers closed, and it runs through the gate, it should be picked up by the claw just as a perf reaches it, and then the same with the lower sprocket. So you need to slowly hand crank the film through and first set the rotational position of the upper sprocket so that the claw picks up a perf just as it begins to move forward, and then set the rotational position of the lower sprocket so that a tooth cleanly picks up a perf when the film reaches it. If these are misaligned, either the film will jam or when you open the loop formers the loop will shift up and be off centre.  It can be tricky to set correctly. There are two screws holding each sprocket in position, and when you secure them again you should also try to keep the sprocket height the same as you found it, with slight clearance above the guides. I have a tool to help set the height

Am I reading into this correctly? Just want to make sure i'm doing this the correct way when doing this for the first time.

Edited September 8, 2025 by Tyler Fukuda

[Tyler Fukuda]

[Tyler Fukuda]

[Dom Jaeger]

Sent you an email.