SPRING MOTOR AND FILMING FAQ

SCOPE

This FAQ covers all 8 mm spring motors from 1940's thru 1960'S.

GENERAL

The vast majority of all 8 mm film cameras sold from 1940 up through the 1960's have a flat spring wound motor to drive the film train. A spring made from tempered steel is wound into the shape of a coil. The spring coil is mounted on a shaft. One end of the shaft winds the motor's spring with a folding key.

When the camera's run button is depressed, a one way clutch holds the winding key in the same relative position while the now compressed (wound) spring tries to unwind itself. This unwinding causes the case of the spring motor to turn. The turning motion of the case outer ring gear powers the speed regulator which controls the rate at which the spring motor unwinds. Typical setting are: 8, 12, 16, 24 36 48 and 64 Frames Per Second.

Bolex 8mm cameras (all except the H8 series and Super 8) are infinitely variable with a dial to indicate the approximate frame rate per second (FPS). Other cameras such as Bell & Howell and Revere (and others), use a selector with a specific FPS setting. 

Following the winding procedure found in your camera's manual. The number of winding turns varies depending upon the make of the camera. Bolex cameras are fully wound at 21 1/2 turns or at about 11 full turns. There is a slight variance from motor to motor. Other camera such as Revere's, Keystone, and Bell &Howell's typically are fully wound at approximately 8-10 full turns.

Cameras other than Bolex wind until the spring is fully coiled. The maximum winding is mechanically limited in Bolex cameras. This allows the motor to be wound to a hard stop. Bolex's are advertised as "impossible to overwind" and uses a mechanism to prevent the camera from being overwound. For the most part, it works as advertised. However it is possible to overwind a Bolex. It takes a lot of forcing, but it can be done.

RUN TIME PER FULL WIND

The run time per full winding is shown below:

MODEL:                                                                    RUN TIME

      

       Bolex (All 8mm models except for H8)              20 seconds

       Revere 44                                                             10 seconds

       Revere K-45                                                         25 seconds

       Revere 99                                                             15 seconds

       Keystone K-38                                                     25 seconds

       Keystone K-36                                                     35 seconds

     NOTE:

     The above are average/typical run times measured from full 

     wound to full stop.Not all of the running time is usable, however. 

     Except for the Bolex, all 8mm cameras typically will run from fully

     wound to stop at a speed approximately that which is dialed in.

     I.e., 24 FPS will film 24 frame per second. However, at some 
     time after the initial start, the motor's speed WILL slow down

     and the FPS will become lower.

WHY?

The location (time) of the slow down will vary from camera to camera within the same model designation. It depends on the age and condition of the motor and at what wind point the camera was stored. Spring motors left fully wound can loose their elasticity (springiness) and will not last an average full wind. Spring motor cameras should be fully wound down when not in use.

SLOW DOWN

Slow down means that after developing, the finished footage will play normally (at the selected filmed frame rate) and the will "speed up" at some point in the clip. This "speed up" is due to the filming frame rate of the camera slowing down and the projection rate of the projector staying constant.

OTHER PROBLEMS

Cameras that have been left fully would can sometimes develop a permanent "kink". This "kink" is a weakness in the spring and can be felt while filming with the camera. It feels like a bump, thud or clunk. Sometimes it can be heard - sometimes only felt. The kink, depending upon the severity of the damage, may not be noticeable. The fix for this is usually to replace the motor.

REPLACEMENT MOTORS

There are no new motors available for any 8mm cameras. Nobody rebuilds them. Therefore a donor camera for parts is required. If you purchase a donor camera, be sure get the same model or a corresponding model with the same motor dimensions. Bolex cameras all used the same motor except for the H8 series and possibly the L8 model.

Ask the seller if the motor is usable. Given that these cameras are all over 50 years old, finding a donor camera may result in your having to purchase multiple cameras to get a good motor. Be advised that typical sellers do not know whether or not the motor is usable. The may state, "It winds and runs". They may not notice that the motor is unusable.

If you buy a camera with a bad motor and the seller has NOT agreed to take it back upon your inspection, you can always resell the camera.

USABLE RUN TIME

All camera manuals have information giving the usable run time for a full wind. This information is for a new camera. All 8mm cameras are now 50 plus years old. You will need to allow for this. All spring motors will have lost some of their usability after 50 years. You can wind and run the camera to the point at which you can clearly notice the motor running down.

EXAMPLE

If you fully wind your Keystone K-38 camera and it begins to run down at 17 seconds, you should stop filming and fully rewind the camera after 10-15 seconds. During filming, you can count (in your head) 1,000-one, 1,000-two, 1,000-three, etc. It was and still is good operating practice to fully wind the motor after each shot. Shoot for 3 seconds? Rewind - now. Shoot for 10 seconds? Rewind - now.

BOLEX IS THE EXCEPTION

Bolex cameras are the exception. A Bolex 8mm camera, in good operating order, can film for about 20 seconds. When the Bolex motor reaches the end of the wind it will stop abruptly while turning, and filming at the same FPS.

If a Bolex motor begins to slow down while filming, it is because the motor is weak. Depending on how weak the motor is, it may or may not be serviceable. Because of the limited run time, 8mm film cameras don't do well for interviews or documentaries.

FILMING TECHNIQUE

Good filming technique with any 8mm camera demands that the operator plan each shot prior to shooting. The means the you will need to keep track of the clip (shot) length (counting seconds in your head) and camera distance, focus and location. Failure to plan ahead will mean you will need to shoot more footage and your filmstock and developing costs will go up.

AVOID JUMP CUTS

Starting and stopping a camera can result in a "jump cut". Imagine on overhead view of the subject and the background. If the subject turns to either side slightly, and the camera is stopped and then filming starts in a slightly different location or angle, the subject can appear to "jump" from one place to another. Keystone Cops style. Moving the camera at least 15 degrees off axis between any two consecutive shots at the same distance to avoid a jump cut. Read more on Jump Cuts here:

https://en.wikipedia.org/wiki/Jump_cut

 

Try moving closer or farther away from subject to prevent a "jump cut".  After shooting, you can edit in/out similar angles or distances after filming to better tell the story.  Advance planning always helps. Not planning will waste film and result in a poorly made film. 

TELL A STORY

             1) Parents leaving on a plane for vacation,

             2) Kids graduating,

             3) Cat playing with dog, etc. 

Think of where you'll need to be to get the shots. Make the shots short. 3 to 8 seconds or so. Do not run the camera until wound down for a long shot. It will be boring and you have to edit out the bad parts, anyway. Given the cost of film and processing, this is an absolute necessity. Good footage is built up, shot by shot.

MORE INFORMATION ON FILMMAKING

Plenty of old "how-to-shoot film" books on the internet. Any books on filmmaking will help. If you are videographer, you will need to learn to limit your shots lengths. Books:

https://www.google.com/search?q=filmmaking+8mm+books&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb

 

Remember that film shot is gone forever. No mistakes allowed. No do - over's, etc. Plan ahead.

MY FILM HAS A SCRATCH IN IT. WHY?

The camera had an ExCLA. Working perflectly. Back from the developers, then telecined, the footage had 2 vertical lines. The film developer said:

"The camera is scratching the film".

Really, thats what he said. The camera is scratching the film. I don't think so. Here's why... 

WHO DUNNIT?

It's difficult to tell exactly where the problem is originating. Doe you have the original positive developed film? Can you see the scratches?  If there are NO scratches on the positive film, the the problem is NOT with the camera. The problem does look like scratches were on on the emulsion side of the film. They could be from any of the following situations :

            1) During the manufacture of the film.          

            2) During cutting down of the film from 35 or 16 millimeter to 8mm.

            3) During re-punching of the second set of sprocket holes to 

                convert the film to double run.

            4) During the actual running of the film in the camera to produce

                and image.

            5) During chemical processing of film.

            6) During the telecine process.

            7) During rewinding at any stage of any of the above process

                (except #4).

Basically, we need to know WHEN the scratches occurred.

How do we know which of the above 7 processes(s) are responsible for the scratches? Only process #4 involves the camera itself. The rest are either manufacturing,  developing or  telecine processes.

The ExCla covers disassembly, cleaning, lubrication and readjustment. No repair work on the gate or other parts of the camera. None was noted during the ExCla. There is only 1 part of the camera that actually touches the emulsion side of the film during filming - the gate.And the Gate ONLY touches at the outer edges where it does NOT matter.

The film is wound emulsion side in from the manufacture. It is 100% protected by the backing of the next portion of wound film on the reel. 8mm file is about .008" thick made of polyester. Tough stuff.

The film first passes over the tension roller. The roller touches the film on the backing side. To do any damage the roller would have to scratch the film ALL the way through the films thickness to reach the emulsion. Not possible.

The pressure plate presses the film between the plate and the gate. The pressure plate (flips away to reload film) touches the backing side of the film. Again the pressure plate is not able to scratch the film through to the emulsion.

Finally, the film that passes through the gate and the emulsion does touch the gate, but only at the extreme edges away from the gate open area.  At the point where the film does passes over the gate, it passes only over the extreme edge of the gate. There is nothing to scratch the gate anywhere. I've attached 2 images. One is the gate dimensions. The other is a picture of the Bolex 8mm gate.

The width of the gate opening (horzontally) is .177". The estimated scratch lines, are about .020" to .040" wide, relative to the gate widths. I got this by viewing a still of the footage on my HP 24" monitor and measuring the width of the scratch with a vernier caliper. The .020" to .040" estimate is about 10x to 20x the width of a human hair.

           

If it's anything related to problem 4 above, I will fix it at no charge. Keep in mind, this is not covered under the performed ExCLA. I do have the actual roll of expired film that I used to test your camera. I have inspected it with a 3x lens under strong light and I see no indications of the film's emulsion being scratch when I inspected it.

WHAT I CAN DO TO HELP

The are a couple of things I can do to help:

1) Send the camera to me and I will run another, different roll of test film through and look for scratches.   It there are scratches added to the film's emulsion layer, after passing through the camera, I will locate and repair/replace the problem at no cost to you. If there are no scratches after running the test film, I will return the camera with you paying the return postage.

as an alternative:

 2) I will send you a 1/2 roll of unexposed film and you can run it though yourself. If it comes out scratched similar to the finished film; send me the camera and the film for repair. I will pay the return shipping.

If it turns out to be a problem other than the camera adding the scratches, the problem must be with manufacturing, developing, processing or telecine.

MY CONCLUSION:

Given the size of the scratches, relative constant position, and  the relationship to the gate size, I believe the scratches were caused by 1) Developing, 2) Processing or 3) Telecine processes. As much as I hate to blame anybody, it is most likely the problem due to 1 of those 3.