Wednesday, February 14, 2018

Common Problems When Loading/Running 8mm Film

It’s common practice on spring wound film cameras to fully rewind the motor after each shot and to run down the spring motor at the end of filming for the day. This is recommended by Bolex in all their camera manuals. Older cameras may or may not have weaker motors. If they do, it is typically at or near the end of the spring motor stopping point.

Do NOT film to the end of the wind, as this can cause the footage to be filmed slightly slower. When run on a projector the film will appear to run slightly faster than filmed.

2) Make sure the film is put in correctly. 8mm film has a glossy side and a satin finish side. The satin finish side is the emulsion side. Its typically a different color which is no help if you are using a changing bag or a dark room.

The emulsion side always faces the front of the camera. A little practice with a fingertip will tell which side is which. If film is accidentally shot on the wrong side, reload it making sure the satin or emulsion side faces the gate (and lens), and reshoot the film. Both ends of the film, for a foot or so, will be unusable.

3) If installed improperly, the leader of the film slips out of the take-up reel slot at any time, resulting in a lack of pulling force on the film through the gate. This can, in turn, cause the claw to not fully engage the film’s sprocket hole and the shutter mechanism will automatically stop the camera. This is a very common problem.

If you suspect the film has slipped out of the take-up reels slot, cover the camera with a jacket or use a changing bag, open the door, pull the pressure plate release lever and while your fingers hold the top reel (feed reel) from turning, rotate the take-up reel and try to manually wind film onto the take-up reel. If the take-up reel continues to turn and no tension is felt on the feed reel (top reel), there is a very good possibility that the film end has slipped off the take-up reel.

Most people install the top feed reel of film onto the top spindle, then thread 6” or so of film thought gate and then and then tuck the loose end of the film into the slot of the take-up reel and drop into onto the take-up reel. Then they flip the pressure plate lever, close and lock the door and finally, wind the camera. If the film hasn’t slipped from the slot, it’s still possible it can slip later.

I recommend loading 2-3 full turns of film manually onto the take-up reel outside the camera. The extra turns will hold the film in the slot securely. Film comes off the top spindle feed reel at the bottom of the reel. You do not need to see this when loading film. Your fingers can confirm this inside a changing bag or under a jacket. Once loaded, I place the feed reel on the top spindle with my right hand re-confirm than the film is coming off the bottom of the reel.

Then, while holding the take-up reel with my left hand, I thread the film through the gate with emulsion side facing forward (toward the gate), and finally drop the take-up spool onto the lower spindle. If you need a little more film, pull from the feed reel.

Then, with fingers, I hold the top reel and turn the bottom reel clockwise to take up the slack. Then I push the pressure plate lever forward to close. Pressure plate is now firmly against the film gate. Lock the door and fully wind the camera.

4) Make sure the pressure plate is full forward towards the front of the camera when the pressure plate lever is pushed toward the lens of the camera.  The door cover will not shut if the pressure plate lever is pulled back.

If the pressure plate has been removed, make sure it has been correctly repositioned. It IS possible to reposition one the pressure plate’s two “legs” outside of the corresponding 2 flat spring clamps. With the pressure plate removed, you can see both clamps.

The pressure plate must be touching both sides of the film to exert equal pressure on the film. Otherwise the camera may mis-register and stop while filming. Correctly installed, the pressure plate will open and close with both sides touching the gate area at the same time.

5) Make sure you are using the correct film. Yes, it is possible to load and run the wrong film. Standard 16mm film will for a 16mm camera, will in fact load onto the reels, thread and run. For about 1 frame. Then the registration holes will not align and the camera will stop.

8mm double run film is exactly the same width as 16 mm standard film except 8mm film has an extra hole punched between the 2 existing standard 16mm film sprocket holes. This is not a common problem but more than one person has tried to run 16mm film because:

“Hey! It fits!”.

Yes, it does...

“And they sold it to me! Cheap!”

But it still won’t run :(

6) Another common problem occurs when the user films a few shots and then puts the camera away for later. The camera and the reels get bumped around and the next time the camera is used, the claw mis-registers the film and the camera stops. See LEADER SLIPS/MIS-REGISTRATION.

7) Excessively cold temperatures (below 40 degrees F or 4 C) can cause the grease in the lower clutch take-up reel’s overriding clutch to drag excessively resulting in the mis-registration of the claw onto the film’s sprocket holes.

If the claw misses the hole; the camera will stop running. The camera is designed to stop if mis-registration occurs. Leaving the camera in the car’s boot/trunk overnight on a cold night can cause this problem. The fix is to keep the camera inside where it’s warmer.

8) The camera’s take-up reel overriding clutch is lubricated with grease. The grease is between two friction plates. One plate is highly polished steel, the other is bakelite (plastic). If the camera has not been properly service, this grease may be dried out or become “too sticky”.

This can result is too much friction and the film will mis-register when running. The fix is to overhaul the clutch. For the ‘do-it-yourself’ person, a hint: DO NOT lubricate with oil. This will lower the friction and the camera will still mis-register as the clutch now has too little friction.

9) Use old film (out of date, exposed - not good) to practice loading film. Mark this "practice reel" so you don’t mix it with fresh film.

10)  Older film tends to dry out, become brittle and  especially after many years past the  expiration date, it may not be suitable for accurate film color. Some people prefer the ‘look’ of old, out-of-date film. Some don’t. You can find old film on

See the prices? Outrageous. $5.00 is a fair price for out-of-date film. Make sure it's 8mm double run. You can also used developed film. The camera doesn’t care. You can’t develop film again once it’s been through the process, but all that matters is that it can be used as practice film.

Super 8 film will NOT work. Wrong sprockets hole locations and size. Wrong aspect ratio. See link below. Regular 8mm or Standard 8mm film has many different names. More information in your camera's manual or check here:

Not sure? Tell the seller what kind of camera you have. I.E, Bolex D8L, B8L, P1, etc. If they do not know if the film fits; shop elsewhere. Link to film sellers:

11) Film can be loaded in the dark to avoid exposing the film to excessive light. Or use a “Changing Bag” or other alternatives can be used:

You can place a jacket over the camera to shade the film, or you can load the film in a closet or other dark area. Film can be loaded indoors or outdoors – just avoid harsh, bright or direct sunlight.

8mm double run film is sold with the emulsion side of the film (the side that collects the image) oriented toward the inside of the reel. This means if you pull out 8” and expose it to light, it will capture that light. This is not a problem. Consider the first 8 to 12” of the new reel "expendable".

After loading, run the camera for few seconds to expose new footage. You are now ready to film. This is normal camera practice for ALL film cameras. The reels used with ALL Bolex cameras have solid sides. This prevents light from exposing the film’s edges. Always use solid sided take-up reels.

If you need additional take-up reels, plastic or metal are okay. Make sure when you send your film in to the developer, that you DO NOT send in your original Bolex reel. If you do, make sure you tell the developer to return your original Bolex reel to you.

The proper way to avoid sending in the wrong reel is as follows:

      1)    Load with new film onto the top spindle.

      2)    Place the original Bolex or the other take-up reel that you want back, onto the bottom spindle. This will be an interim (temporary) take-up reel.

      3)    You will run the full new film twice through the camera. The 1st time pass films on ½ of one side of the film. At the end of 25’, the camera ‘clicks’ signaling you that 25' of film is exposed. Open the film door (same precautions as loading new film), exchange bottom and top reels and re-thread film leader to the empty bottom take-up reel. The Bolex reel will now be on the top spindle.

4) This is how the double run system works. Two 25’ passes are made with one 25’ reel of 16mm wide film, exposing ½ a side at a time. When finished filming, your original Bolex reel will be empty and still on the top spindle. The bottom reel with the exposed film on it is the one you send in to the film developers. When it's gone, replace the original reel onto the bottom spindle.

     5)    Any questions? See your camera’s manual. It's all in there :)

Tuesday, July 4, 2017


Need an 8mm camera? I suggest a Bolex 8mm camera series as follows:  D8L, P1, D8LA, P2 or P3.  In that order. I recommend staying away from: B8 (2 lens), C8 (1 lens), neither has a light meter. Also L8, 155, 160 series, K1, K2, P4. These camera are much more complicated and very expensive to repair. Avoid B8SL or C8SL – controls are minimized for non-photography oriented people (beginners).
More information here on all Bolex models: 

Bolex D8L and P1 are the most popular and both have very good resale value. A used Bolex D8L, D8LA, or P1 in typical for its age, and in good running order (or not) , with lenses and a metering system working normally, is worth $75 - $100+ on eBay depending on accessories and lenses. Switar lenses are top of the line Bolex and can raise the price significantly. A Switar 0.9 lens, alone, sells used for $350-$500 on eBay.

Because most Bolex 8mm cameras are 50+ years old, a minimum service of a CLA (Clean-Lubricate-Adjust) or EXCLA (Extended Clean-Lubricate-Adjust) should be performed. Bolex recommends a CLA every year – see Bolex manual. You can get by with less. 2-5 years is typical for a CLA. An EXCLA is required ONLY when camera has sat in the closet for 35+ years or has motor damage or other problem necessitating a teardown.

Service is a judgment call as most Bolex owners do NOT know the maintenance history of the camera they possess. However, the camera may have been maintained by the previous owner and is in good working order and is ready to shoot film. This would be an exception to the rule. Most camera owners don’t know if the camera can or cannot shoot film. Especially so if they have never shot film.

“Got it at a yard sale – don’t know the condition.”

This is a common statement on most eBay cameras. Most Bolex 8mm cameras are obtained at eBay, Goodwill, St. Vincent De Paul, yard sale, or elsewhere. If the condition is unknown or not stated outright up front, assume the camera will need maintenance and possible an overhaul (more $$$). Adjust the buying price accordingly.

If you are new to film cameras, you will learn quickly why to avoid the “mediocre –** SL series” or “too complex - the “K” series, ”. Why? Repair and maintenance costs. Do NOT go cheap. The **SL series has minimal controls. Easy to use. You’ll outgrow that on the 2nd reel of film stock.

All cameras should have a working meter. If not, you can use an external meter such as  Sekonic L-398x series. This meter has NO batteries, does reflective or incident light metering, is accurate, has a Frame Per Second (FPS) and shutter angle dial adjustment. Both of which are ABSOLUTELY necessary for movie film cameras.

A manual for the L-396 can be downloaded here:

These meter, and meters like it, can be found used or eBay for $25 and up. New L-398A meters are about $218.00 at  Given the cost of film stock and processing, a good metering system is a must. 

The metering system on ALL Bolex 8mm cameras does NOT allow for backlight conditions. Backlight exists when the light BEHIND the subject is brighter than the light in FRONT of the subject.

Example: You light for the subject face. The camera “sees” all the light. Including the subjects face and from behind and around the subject. It gives an average reading turn out to be about 1 to 2 stops to much light. You will set the camera according. Film will be appear to be exposed 1-2 stops too dark for the face.  You remember the face. It’s the subject. Light for the subject.

I know, you might be saying “it should be the other way around”. No. Your setting the light value based of the light that the meters see. And it sees everything. Then it tells you to set for the brightest light seem. But your subject’s face is in the “shaded area” of the light. Hence, the light the camera sees will be LESS than needed to see and light the subject’s face properly. Their face will be 1-2 stops darker than optimal. How do you get around this?

Bolex cameras DO NOT allow for backlight. No backlight button or lever or button to push. It’s up to you to recognize a backlight condition and manually compensate. It’s easy. Bright light behind subject? Close iris 1-2  stops. Bright light from the side? ½ - 1 stops. It’s a judgment call. Experiment.

If you planning to shoot a lot of footage, the 1st reel of film should be for testing. Shoot backlight, shoot normal, shoot low light. Keep records. You can use a sheet of cardboard with f-stops, distance, location of sun, printed on it etc. Go outdoors. Have the subject hold the cardboard it in front of them when you shoot 10 seconds of footage. Change the cardboard information. Shoot with sun behind you and in front of you.

When you review the developed film on a projector, you will be able to tell the difference (visually) that the location of the sun makes in setting of the f-stop. Remember that backlight conditions can exist wherever there is light and that includes indoors. Especially when you use extra lighting. 

Use the local library to check out books on motion picture film making. That is what you are doing. When you are asked about what you are doing, you say: “I am making a motion picture”. And, you are. You are a now, officially, a filmmaker. Can’t find any library books? Look on eBay. For a few bucks you can get all the information you’ll need to learn moviemaking. Here’s a few links:






Whatever you search for, select “lowest price” from the eBay put-down at the top of the page. This will bring up the older, less costly books that nobody wants. And it’s just the “stuff” you’re looking for but the seller doesn’t know that.


Good Luck!


Wednesday, April 15, 2015


A customer writes, " I need the light meter battery and the zoom control batteries for my Bolex P3. Can you help?

Yes. We have the P3 cap $12.00 postpaid, USA. It also fits the P1 and P2.

The light meter battery: Mallory HG450r, RM450, etc, are no longer manufactured as they contained mercury.

We sell a replacement light meter kit consisting of a custom machined spacer,  battery of the same voltage as original, and installation instructions.

There is also an additional instruction sheet showing how to check and adjust a "sagging" battery well contact spring.

Installation is a drop in fit. No modifications or adjustments. Leave it in the camera. Lasts 1-2 years. Replacement batteries are available everywhere.

More information here:


The battery kit is at bottom of page. 

To order please contact me and I'll send payment instructions.

The Mallory ZM-1 or RM-1 batteries are no longer made or available but there is a replacement battery:  PX01 - 1.5 Volt. Alkaline construction, same as, LR50, V1ALK, etc. These are available from Amazon: 

Alkaline batteries are not rechargeable. Also sold in other places. Here is a link to search Google for more locations including those outside the USA: 

PX01 batteries were used in several models of the Bolex 8mm reflex cameras. The don't last long if you use them in the P3's zoom.

I would consider the battery cost plus shipping and buy at least several sets.

Monday, April 6, 2015

Saturday, September 27, 2014


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

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.

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


     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.

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 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.

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.

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.

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.

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 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.

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.

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:

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. 


             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.

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:

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

Wednesday, September 3, 2014


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... 

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.

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.

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.

Saturday, June 7, 2014


Customer writes to BolexRepair saying they just shot a roll of film and had it developed. Its all black. Why? And can we fix the problem? Yes, we can fix the problem (if there is one) and do we work on a B8L cameras. Here's our reply:

We do work on Bolex 8mm cameras such as your B8L. All Bolex cameras should be checked every year or two. Bolex recommends that the camera be cleaned, lubricated and adjusted on a yearly basis. 
This is called a "CLA". Most likely the camera has not be checked for 40 - 50 years. A lot of these cameras were sold and after a few years, retired to the closet or were replaced by camcorders. In any event, cameras can and do stop running for no apparent reason if not in serviceable condition. For more information, click on link:

It can be one of several things:

1) Old film. Was the film fresh? If not fresh, the most obvious answer is that the film was the problem. When I see film that's marked: "Best used by Feb 1987" or whatever, I know it's "out of date". No good. Customers sometime ask, "Is it any good?" My reply:
     "No. Even if it was stored in a refrigerator for 27 years, it will still be degraded. Some people like to argue film is film and its good forever. No, not really..."

2) The iris was not set properly. The B8L uses a it's onboard light meter to calculate the iris opening. Keep in mind that the iris opening suggested by the camera's meter is for ASA 25 or ASA 40 film. Both are no longer available.

ASA 100 is available. If you use ASA 100 film, the meter will STILL assume its 25-40 and all film will be overexposed by about 1.5 to 2 stops. The fix is to select proper calculated ASA and then close iris by 1 to 2 stops. The exact amount will depend on light available. 

A better option is to use a light meter made specifically for cinema (motion picture) cameras, such as the Sekonic L-398. The film's ASA, metered light, shutter angle and FPS are pre-calculated by the meter to give the iris opening as an lens F-stop. Just dial-in the calculated number on the lens.
Given the cost of film and developing, this is the safest option. Used L-398 meters can be found on eBay for $75 and up. Click this link to download the manual:

3) The film was processed incorrectly. Not very likely, but it does happen. Because 8mm processing uses chemicals, exposed film is typically saved until there is enough film footage to process economically. Maybe a week or two (or more). Then the chemicals are mixed fresh and ALL the processing is completed.
The chemicals once used don't stay fresh for very long and must be discarded. Not sure? Ask the people processing the film:

     A) What is their policy regarding processing chemicals, 
     B) Are the chemicals fresh?, 
     C) Do they send the processing out to an outside vendor? 
     D) Do they process in-house?
I recommend buying fresh film and if possible, have the seller do the processing. Not everybody sells AND also does processing. See the link below for film sources and processing:


4) If the film failed to go through the camera, it will not be exposed. When developed, the film will develop as black.

If you are not sure which service is necessary or if the camera even needs to be serviced, we will evaluate your camera for a flat fee of $45.00 (includes return shipping and insurance, USA, only) and notify you of the camera's condition and any cost for repairs.  

The $45.00 fee also applies to any work to be done. In the event that no work is done beyond the initial evaluation, we will return the camera postpaid and insured along with a written estimate of the camera's condition and a recommendation of any work necessary to return the camera to operating condition.