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Bolex B8 Shutter Speed Adjustment

Ron Forch

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Hi there, 

I'm clearly very new to this forum, and also very new to 8mm movie cameras (still haven't even bought a roll of film, but I'm rather experienced with 35mm film photography). I know that having a reliable camera, which provides repeatable results is fairly essential to troubleshooting technique & for general enjoyment of any medium. I know my limitations, and have dabbled in still camera repair for quite a while. To get started on my 8mm adventure, I have purchased several of the less popular Bolex B8 cameras to study, repair, and use. At this point, I've disassembled, cleaned, lubed, and reassembled a few of them. The blog posts by Cinetinker (whom I saw is a member here) were absolutely pivotal to helping me get started. I use all the correct precision screwdrivers, wash parts ultrasonically in closed containers with waterless watch cleaning solvents, lubricate with Rocol & Nyeoil, then reassemble. So far, the results are great, and I'm pretty excited! 

Now, I've come to the point of dialing in the shutter speed. In reassembly, I've aligned the shutter speed cam & indicator wheel so that 64fps & 8fps are in their correct locations at the extremes of the adjustment dial movement. Between what I worked out on my own, talking to a coworker whom operated high-speed movie & video cameras professionally for 20+ years, and watching the film "Teaser: Paillard Bolex” on Vimeo, I understand shutter timing is set with a stroboscope. Anyway, long story short, now I have a General Radio 1531-AB stroboscope to store with all my other test equipment...

So, armed with a well running camera & stroboscope, I set the camera frame rate to 16 FPS, set the stroboscope to 960 RPM, loosened the adjustment screw on the governor, & turned the silver governor eccentric until the claw eccentric stopped moving in the strobe light. Then, I tightened everything up, confirmed the speed, put everything back together, and did a final check just like the woman in "Teaser: Paillard Bolex”. The results were about 10 FPM slow, but that's around 1%, so it seems good(?). I thought I was done, however, when I try to run the camera at 8 FPS, the shutter doesn't move - the governor limiter is pushing the governor shaft against the rear bushing & preventing it from moving. 

At this point, I was wondering if anyone with repair experience could give me some suggestions. I'm really only assuming the shutter frame rate without film should be set to 16 FPS - should I be setting it to a higher rate and assume it will slow when the system has drag from the film? I figured the governor would account for any drag the film would impart and keep the frame rate constant, but that could be a wrong assumption. I don't currently have any scrap film to run through the cameras to test the effect. 

Anyway, sorry that's so long for a first post! I appreciate any help! 

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Hi Ron, 

I’m very happy my service guide was helpful to you.

It sounds like you’re pretty on top of everything, even getting yourself a stroboscope! In terms of adjusting the speed, it may slow a little when the system is under load, or towards the end of the spring run. I tend to set the speed at the start of the spring wind while holding the take-up spindle, which adds some load.

If the governor is fouling at minimum speed, even though you have set it correctly at normal speed, it could be that the system is running a little fast due to wear. (Let’s assume the stroboscope is correctly measuring the speed.) You could experiment with trying to adjust the governor springs but I’m not sure it’s worth potentially damaging the camera. Since it’s more important to have the speed correct at 16fps than be able to reach 8 fps, I would just avoid shooting at minimum speed.

I would suggest getting some old or exposed dummy film and double-checking the stroboscope by running 10 seconds at 16 fps and then checking that roughly 160 frames were moved through. Also good to have dummy film to practice loading and check that the transport is working ok.

Then you can get to the fun part of actually shooting film! Good luck!


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Thank you for replying to my thread, and for confirming I'm on the right track! I messed with it a bit more this afternoon, and it looks like I have the speeds sorted out so they work as expected at 8, 16, & 32 FPS. I believe my issue may have been one of technique. I did switch to a different stroboscope this time since the xenon tube on my General Radio 1531-AB is nearing end-of-life, making low-speed calibration difficult (which is a real shame because its oscillator is easier to adjust & more stable than my more modern digital stroboscope). Anyway, I found that if I set the camera speed selector to 16 FPS, then adjusted the governor, the shutter did not run at 16 FPS again if I moved the selector to some other speed then back to 16 FPS. What seemed to work the best was to set the stroboscope to 960 RPM, set the shutter speed selector for 24 FPS, then run the shutter while decreasing the speed on the selector until the claw eccentric stopped moving in the light. Then, I could look at the selector to determine if the shutter was running fast or slow, make an adjustment to the governor eccentric, and repeat. Once 16 FPS was dialed in, I checked it at 8 FPS, and it worked! Then I confirmed 32 FPS as well. 

I hadn't thought of holding the take-up spindle to simulate the film load on the system. To do that while keeping one hand free to adjust the speed selector, and the other to operate the shutter, I whipped up a little 3D printed tool, and I think it worked out pretty well. 

My next project bodies have variable shutters. Could you tell me if the moveable shutter blade should be at all visible when the shutter is full-open, or should its edge be just behind the edge of the fixed shutter?

Thanks again for the help! I attached a picture of the finished camera, and the little 3D printed spool load tool I made. 

PXL_20220407_001311853 (Small).jpg

PXL_20220407_003031343 (Small).jpg

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Great stuff Ron!

Sorry it’s been a long time since I worked on one of these and I don’t recall the shutter alignment. I imagine the variable shutter should be behind the fixed blade when fully open, but a small overlap is no big deal, only a tiny fraction of a stop in terms of exposure. 

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The camera has got a locking mechanism on the spring barrel, as you know now, a sun and a planet gear. By it a section of the spring’s torque range is available. Basically, the spiral spring can be wound together until it’s almost entirely rolled onto the core and unwound until it rests in the barrel. Depending on the state of the actual spring the gears should be so engaged that the moving section provides the most uniform runs.

A run is never perfectly even. You have more torque at the beginning, less towards the end. As I have always understood the concept speed is adjusted to an average over the run. A stroboscope is a nice thing to have, yet, I find it enough to ensure that, say, the length of 528 pitches is transported within 33 seconds. The adjustment will therefore be a little higher than by your method, thus just freeing the governor for the lowest speed. The adjustment is made with film loaded.

Amateur movie making was never with synch sound until the advent of cameras having an electric motor. That was at the end of the 1950s, early 60s. Pocket or handbag cameras were meant for mummies to take pictures of their children. No one cared about whether the images moved a little slower at the beginning of a scene and a little faster after 20 or 25 seconds in projection. We can’t call professional dibs on these mechanisms. As you will understand with some thought runs can be best for one speed only. The technician needs to know at what frame rate a spring-drive camera will be used predominantly.

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Thank you for taking the time to explain how the shutter is driven. I understand the little B8-style cameras use a simple governed spring motor, and are mostly a toy when compared to their larger siblings. However, they are charming, and since I can now make them run seemingly well, one will be very useful in my bag along with my other travel cameras. 

I like your technique of considering the average number of frames transported over a period of time. Unfortunately, I don't yet have any exposed film to use as a trial, so tracking down a stroboscope was the only way I could think to get everything timed. Once I get a practice roll done, I'll definitely use your method to confirm the average speed over the motor duration!

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