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intermittent overexpose of frames on 16mm footage


Habib Beh

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Hello,

I just got back the results of a test film I ran on a Bell and Howell camera. Unfortunately, the results of my test film did not go as well as I had liked.

The test film shows repeating "bursts" of frames that are overexposed. I'm sorry I'm not being more descriptive, but I've included a link of a few seconds of the test footage I shot:

http://imgur.com/a/hrV9okp

Based off of the footage, can someone tell me what exactly went wrong? I'm trying to figure out what mechanism of the camera is not working properly and if it is even fixable.

I'd appreciate any input! Thank you!

Edited by Habib Beh
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Sounds like your spring motor is sticky and is not releasing smoothly. The spring lubrication gets sticky and as it unwinds, it will create sudden bursts of speed as the grease unsticks.

 

You need to have it cleaned or try another camera.

 

You weren't hand cranking it via the accessory drive at the base of the camera, were you? You were using the ratchet spring motor, correct?

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OH, buy the way.... what model B&H camera do you have? :unsure:

 

I was assuming a DR 70 or variant ...

 

Hi Frank,

 

Thanks for your reply. It's a model 240 and no, I was using the spring motor and not hand cracking the camera. Would you happen to know any places that would be able to service the camera?

 

Thank you!

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Sounds like your spring motor is sticky and is not releasing smoothly. The spring lubrication gets sticky and as it unwinds, it will create sudden bursts of speed as the grease unsticks.

 

I think it's unlikely to be the spring motor. In my experience spring motors are usually lubricated with graphite flakes not grease, and rarely fluctuate so dramatically. To create those blown out frames the camera would seem to be intermittently slowing down quite drastically, and massively overexposing a frame or two every 10 frames or so. Since it happens repetitively it seems more likely to be a gear sticking once per revolution or something like that.

 

Did it make a funny noise as it ran? I would imagine you could hear the camera running intermittently, and perhaps see the shutter slowing down through the lens port (if it has a removeable lens). To completely blow out a frame the exposure must be quite a few stops over, meaning many multiples of the normal exposure time. So at say 16fps the camera must be slowing to 3 or 4 fps for a frame or two, which must be noticeable. Does it seem to run smoothly without film?

 

The only other possibility is an intermittent light leak or processing fault, but I can't quite picture how that would happen.

 

I don't mean to undermine Simon's offer, but given that these cameras are ubiquitous and often sell for under $50, I'm not sure it's worth servicing.

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I think it's unlikely to be the spring motor. In my experience spring motors are usually lubricated with graphite flakes not grease, and rarely fluctuate so dramatically. To create those blown out frames the camera would seem to be intermittently slowing down quite drastically, and massively overexposing a frame or two every 10 frames or so. Since it happens repetitively it seems more likely to be a gear sticking once per revolution or something like that.

 

Did it make a funny noise as it ran? I would imagine you could hear the camera running intermittently, and perhaps see the shutter slowing down through the lens port (if it has a removeable lens). To completely blow out a frame the exposure must be quite a few stops over, meaning many multiples of the normal exposure time. So at say 16fps the camera must be slowing to 3 or 4 fps for a frame or two, which must be noticeable. Does it seem to run smoothly without film?

 

The only other possibility is an intermittent light leak or processing fault, but I can't quite picture how that would happen.

 

I don't mean to undermine Simon's offer, but given that these cameras are ubiquitous and often sell for under $50, I'm not sure it's worth servicing.

 

Hi Dom,

 

Thanks for your reply. I went ahead and took a short video of the camera running with film in it (running at 8, 16 and 24 fps) and without film (running at 8 fps). I'd really appreciate if you or anyone else could be kind enough to take a look at it. As far as I can tell, the shutter seems to be running smoothly, but I'm no professional :)

 

short video of shutter running:

 

http://i.imgur.com/CH076wI.mp4

 

This is going to be a long shot, but do you think that this problem could be caused be a lens issue? I've never used this particular lens here (see below), I was thinking because its a wide angle lens, that it may have been "too wide" and caused distortions? Again, I realize this is a long shot theory but thought I'd ask anyways.

 

Thanks everyone for all of your help so far.

 

Here's the lens I'm talking of:

 

aOoqABJ.jpg7yygBZs.jpg

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No it cant be the lens, this is an intermittent fault, the lens isnt changing.

 

So you cant see or hear any speed variations when you run the camera both with a dummy load and without film? Curious.. If you have some old film, run it through with the door open and see if the film seems to be transporting smoothly.

I cant quite picture how it could be a light leak in the camera.

Maybe it was a weird error during processing?

Or possibly the transfer? How did you digitise the footage?

Might be worth shooting another quick test.

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There will be inside the gizzards of the camera, a centrifugal governor of some sort. For sake of smallness, the governor in a Bolex H16 clockwork camera appears to be controlled by friction of small leather boots inside a polished brass bell.

The frame rate adjustment sets what rotational speed the friction pads engage the inside of the brass bell. Other industrial or internal combustion engine governors use spring resistance against the centrifugal force and some sort of mechanical linkage to a power controller, usually a throttle lever.

What is inside the Bell and Howell I do not know but it will be a centrifugal governor of some kind. If there is any contamination of the friction surfaces in a Bolex, it must be cleaned. Otherwise there will be slight flicking as the governor hunts for correct speed across a wider variation than it should.

If there are varying amounts of friction in the whole drive train, this will force the governor to hunt heavily for correct speed. It likely will not overspeed and underexpose, but at tight spots in the drivetrain, speed will drop back and cause your over-exposed frames before the governor can step back to restore speed.

It is likely a service is needed which includes cleaning old dried lube off gears and thrust faces, relube and cleaning the governor, which should restore your camera.

In the Bolex, a well maintained governor, set against a strobe source whilst the film transport is loaded will hold the camera in sync with a modern sound recorder for about 15 seconds, sometimes more. The Bell and Howell speed control may not be as accurate but there certainly should not be any light frames in each run except at starts and stops.

You also need to be decisive when you button on and off. If you relax the trigger slightly, it may drag on the transport and cause your light frames. You also should not allow the spring to entirely run down before you button off. The high speed part of the mechanism may continue to run on under its own inertia and pull the spring end out of its retention.

As mentioned above, given the price of the camera, you need to decide the cost benefit of having it fixed. Any other cameras out there which are offered for sale, unless they have been recently serviced, will likely have some speed issues, so my personal preference would be to suck it up and have it serviced.

Mechanical devices with plain bearings, gears and springs, do need regular maintenance whether they are being used daily or sleeping on a shelf for six months.Your camera may well have been in hibernation for years.

I was not able to hear sound with your video recording. A sound track with the vision might be more helpful.

Please heed better advice from other folk.

Edited by Robert Hart
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In my experience Bell & Howell cameras run better constantly than Paillard-Bolex but that isn’t the subject. One factor not yet spoken of is the film. OP may have loaded irregularly cut film or film on a bent spool or sticky film. Often a dry take-up friction can have an impact on evenness of run.

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