Exposure Advice

Steps to achieve accurate Exposures

To achieve accurate exposure with a Bolex H16 camera there are two main steps you need to address and find the answers to:-

1 Find out what the Bolex camera you are using’s shutter angle is.

2 How the type of light meter you will use with it will affect how easy it is to shoot and gain accurate exposure and deal with any exposure compensations you may need to do.

There is a 3rd thing but so long as you have accurately took care of the above 2 it’s kind of negligible, but for completeness you need to remove a 1/3 of a stop off any reading due to light lost to the viewfinder via the prism otherwise you will over expose by a 1/3 of a stop. The latitude of modern negative film stocks makes this difference not worth bothering about but if you’re using reversal film where there isn’t much margin of error either way your exposures might benefit by doing so.

Step 1 Determining Shutter Angle

There is unlike other film cameras a lot of confusion and uncertainty out there about determining a H16 cameras shutter angle. This I think is due to all the subtle differences in models and revisions plus a lot of printed historical inaccuracies, confusion, wrongly applied compensations, web forum posts and misinformation. I aim to explain why these inaccuracies have come about so as to once and for all banish this long standing confusion and leave no lingering doubts.

You’ll be pleased to know that it’s actually very easy to find out what the shutter angle of your camera is please consult the easy to follow flowchart below:-

Bolex H16 Shutter Angle Determinator Flowchart

For those of you who think it can’t be this simple based on reading other sources or want to know why there is so much confusion read on or otherwise having found the shutter angle jump to step 2 below if you don't want to know the confusing history.

Timeline of Shutter Angle Changes

1930’s Serial Number 0001
The First Bolex H16 Camera was introduced in the 30s with a fixed 170 Degree shutter and so that stayed the same until…

1955 Serial Number 100400 (Addendum 1)
The Camera claw is totally redesigned to allow backwards as well as forwards movement and better registration. From Bolex Reporter Extra Edition Titled “School Issue” Page 8 from 1967 I quote “In 1955, Bolex rejected the ordinary claw movement and introduced a new claw mechanism, under the name of “Registration Claw”, proven ever since to be the utmost in accuracy and reliability. All Bolex H cameras manufactured since 1955 which includes all H16 Cameras above Serial No 100400 are equipped with this new claw movement.” Although not mentioned in this article its clear Bolex changed the shutter angle at this point as well as on Page 13 of “Petersons Bolex Guide to 16mm Moviemaking” (published 1973) tables show the same serial number as a reference for finding out if you have a Non Reflex camera with a 170 degree or 143 degree fixed shutter angle. So 20 years later from 1955 checking to find out if you had a serial number above or below 100400 was still useful but back in 1955 the H16 Reflex camera hadn’t been released yet although they were getting it ready as a year later…..

1956 Serial Number 116001
The first Reflex camera “Rex Original” arrives with no variable shutter so it has a fixed shutter angle still of 143 Degrees as all new cameras have got since last year’s Addendum1. But the first seeds of confusion are starting to be sown somewhere in the distant past. The Bolex Collector website and other sources has this one down as 144 degrees? Did they really make a new shutter angle 1 degree different for this model only 1 year from the new edict? Don’t think so! Anyway it’s so miniscule a difference not to matter anyway but I’m still going to say it’s 143 Degrees until someone can prove me wrong by sourcing this 144 degree figure as I can’t! Then….

1959 Serial Number 162306
The Rex 1 camera is released the first Bolex camera with a variable shutter which is introduced with a 1 page write up on Page 4 of Bolex Reporter Spring 1959 Issue and supposedly has a 145 degree shutter. Did you get that right editorial staff at Bolex Reporter in 1959? Or was it actually 143 Degrees still? Did they really make a new shutter angle now 2 degrees different from the new edict 4 years later?  Bolex Collector sources this as where he got this figure so blame Bolex Reporter for this historical inaccuracy I still think it’s 143. Anyway its clear to me Bolex decided not to make the max shutter angle any different on making their 1st Reflex camera and there 1st Reflex camera with a variable shutter, they both used the same angle they’d used since the Addendum 1 of 1955.  They were still deciding as to how they were going to go forwards with the new Reflex idea just as how they dropped the DV marking on their Reflex lenses at this point and settled on RX. It seems the first two Reflex cameras were a bit of a try out even though they were released to the public they didn't have everything set up as Bolex wanted it going forwards so……

May 5th 1962 Technical Bulletin Official Bolex Service Manual Modification Sheet (Addendum 2)
Thanks go to Martin Stent for digging me up this official addendum to the original service manual sent to factory trained Bolex service personnel back in the day which states proudly “The aperture of the fixed blade is reduced from 143 to 130 degrees”. So from now on Bolex are producing two types of shutter angle one for cameras with variable shutters (130 Degrees Max) and one without (143 Degrees Fixed).  Now we need a camera to start making this change on….

1963 Serial Number 200001
The Rex 2 Camera is released the first new camera with a variable shutter after the 2nd addendum. From this point onwards everyone should be in agreement every Camera with a variable shutter has its shutter angle as 130 Degrees. But there not! Why? Bolex collector has the shutter angle pegged at 133 Degrees not 130. This seems to have come from Page 20 of Andrew Alden’s Bolex Bible book which states Reflex Cameras have a variable shutter of 133 degrees and this seems to have been restated by lots of people subsequently but I can find no reference to it anyway prior to 1998 when his book was published.

However Andrew in his book stating the shutter angle is 133 when its actually 130 is a clever fudge to be able to shoot film with a normal cine light meter and still get good exposure. It is a virtual value to use to compensate light meter readings took off normal light meters; the real physical shutter is still 130 Degrees (I talk about this compensation in Step 2 Next). This however seems to have been accepted as fact by a lot of people and I can see guides colleges have wrote for their filmmaking classes making out the variable shutter is anywhere between 133-145 Degrees. Its Not! He states below Serial Number 100400 the shutter angle was 192 Degrees which is completely wrong where he gets this from I’ve no idea. For Non Variable shutter cameras above 100400 he says 144 Degrees not 143 for some reason. He also agrees with Addendum 2 found by Martin Stent that there was a change to alter the shutter angle prior to Reflex cameras as he says up to the introduction of the reflex cameras the shutter angle was 144.

We also have 135 Degrees Mentioned in various places where does this value come from? Well it seems to come from Bolex themselves. This though isn’t the Bolex of five thousand workers making thousands of handmade cameras a year it’s the fairly recent modern day operation of 1 or 2 people running things. I have a July 2000 Price list from them and they talk about the technical specs of the available wind up variable shutter cameras H16 SBM and H16 REX5 and state they have a 135 Degree variable shutter angle. Since when did you tack an extra 5 degrees on sometime between 1962 and 2000 Bolex? If so from what serial number? I think you’re confused about your own products!

So in Summary:-

170 Degree Shutter Cameras
H16 EBM & H16 EL or Any H16 Spring Wound with No Variable Shutter and a Serial Number Below 100400 Camera I.E The ancient Supreme, Leader and 30’s 40’s and early to mid-50s cameras.

130 Degree Shutter Cameras
H16 Spring wound + Variable Shutter Cameras I.E. Rex Series, SB and SBM.

143 Degree Shutter Cameras
H16 Spring Wound + No Variable Shutter + Serial Number above 100400 H16 J, T, M Series + others.

It appears that if you were a Bolex Rex Original or Rex 1 owner you have been misled by all official Bolex booklets and advice in books such as those discussed above as anyone would assume that both cameras as being reflex would have a 130 degree shutter but both have a 143 Degree one.

Step 2 Light Meter Compensations

Bolex have never produced a camera with a standard 180 degree shutter angle which is a problem as it is assumed everywhere apart from the odd exceptions (Bolex most definitely included) that all cine cameras will have a rotating mirror shutter with half the light when shooting going to the viewfinder and the other half to the film. So your exposure readings will be some stops out unless you are using one of the first two options below:-

1 Use a Bolex Zoom Lens with a light meter built in or the hand held Bolex light meter or have a Bolex light meter built into your camera as the EL does as standard or use a camera where Bolex has retrofitted a light meter (Discussed below).

2 Use a modern cine Light Meter which allows you to enter the shutter angle as well as fps and film speed to get accurate exposure.

3 If you actually have to use a Light meter that even if it does have a fps scale (it might just have shutter speeds for still cameras) does NOT allow entry of shutter angles. Any meter that does not will be calculating readings assuming your camera has a rotating 180 degree mirror shutter angle when we know this isn’t the case with a H16 Camera.

Option 1 requires no compensation to be applied at all they even factor in the 1/3 of a stop loss due to the prism. Option 2 for total completeness you need to make sure you drop a 1/3 of a stop off your reading for the prism as discussed at the start not necessary with modern negative stocks might only help with reversal ones it’s kind of negligible anyhow and your own personal choice to apply or not. If using option 3 though you will have to apply some form of compensation as it’s a big drop taking a reading on a meter that assumes a 180 Degree shutter when the cameras angle is actually 130 degrees and even more so if you have the variable shutter nearly fully closed at position 1 where the shutter angle decreases to 35 Degrees so your readings will be quite some way off and you won’t get good exposure.

The 133 Degree Mystery Explained

What I’m going to discuss next will explain how Andrew Alden got the whole 133 Degree shutter angle confusion started and why the shutter angle for cameras with a variable shutter (except Rex 0 and Rex 1) is definitely 130 Degrees.

A common quote in Books that talk about Bolex Reflex cameras and exposure is the following taken in this case from American Cinematography Manual 4th edition “H-16 Rex has 130 degree adjustable shutter (giving 1/65 sec at 24 fps)” umm now clearly 24 frames per second or 1/24 could be set on a meter but they are assuming your using a meter that assumes a fixed 180 Degree shutter angle so you’d get wrong exposure. Instead you can either alter the film speed by a factor or the fps rate to compensate for the shutter angle difference that you cannot alter on these meters. So you instead set the fps to 1/65 rather than 1/24 to get an accurate reading with the variable shutter at 130 Degrees on a meter stuck at 180 degrees and this is the compensation at work.

Now this is the commonest speed and shutter angle someone would use and it gets quoted quite a lot. It can be traced back to the original Bolex Manuals which come with the cameras as well! Have a look and there’ll be an exposure table which will include the 24 fps 1/65 value in it (see table 2 below). So where does the 133 Degrees shutter angle come from that Andrew quotes in his book Bolex Bible? The only thing Andrew has done is look behind the curtain and do some maths and find with Bolex’s compensated fps rate they were not being 100% truthful.

All he did was take the compensated values he was being quoted and put them in the following standard formula:-

Shutter Angle = (Frame per second)  x (360) / (Shutter Speed)
Shutter Angle = (1/65)  x  (360) / (1/24) = 132.9

Which is very close to 133 Degrees. So things don’t add up and Bolex were hoping you didn’t notice or do the maths all this time and no one did until Andrew. Bolex should of wrote in there Instruction manual the following “The Maximum open shutter angle is physically 130 Degrees but to get a table of easy to memorise and nice to look at numbers that go up by nicely rounded off fractional increments that you should be able to find on all meters easily rather than ones that looks all over the shop we base our calculations around a 133 degree virtual shutter angle. The 3 degree difference making a small but we think negligible shift in correct exposure." The same shift is at play with the variable shutter set to its other two positions.

Exposure Tables

Table 1 Non Reflex Cameras.

H16 Cameras Below s/n 100400 Shutter 170 Degrees H16 Cameras Above s/n 100400 Shutter 143 Degrees
Filming Speed Exposure Time Filming Speed Exposure Time
8fps 1/18 8fps 1/30
12fps 1/25 12fps 1/40
16fps 1/35 16fps 1/45
24fps 1/50 24fps 1/60
32fps 1/70 32fps 1/80
48fps 1/100 48fps 1/120
64fps 1/140 64fps 1/60
Single Frame 1/25 Single Frame 1/30

Table 2 Reflex Cameras with Variable Shutter "The Fudge Table".

Filming Speed Variable Shutter Open Variable Shutter at 1/2 Variable Shutter at 1
130 Degrees 65 Degrees 32-35 Degrees
  Real Adapted Real Adapted Real Adapted
12fps 1/33 1/40 1/45 1/55 1/75 1/94
16fps 1/45 1/55 1/60 1/75 1/100 1/125
18fps 1/50 1/60 1/70 1/87 1/110 1/137
24fps 1/65 1/80 1/90 1/112 1/150 1/163
32fps 1/90 1/110 1/120 1/150 1/200 1/225
48fps 1/130 1/160 1/180 1/225 1/300 1/375
64fps 1/180 1/220 1/240 1/300 1/400 1/500
Single Frame 1/30 1/40        

The Positions that the the variable shutter switch can be be set to and how this affects the open angle of the variable shutter and how it would actually look if you could fully see the shutter complete a rotation is shown below. White is the 230 Degreee Fixed area of the shutter. Black is the variable shutter. The open angle of the shutter is shown by the empty space where you can see the prism and its this open shutter angle needed for exposure calculations.

Bolex H16 Shutter Angle Coverage

Table 3 Reflex Cameras with No Variable Shutter H16 EBM and EL.

Shutter 170 Degrees
fps Real Adapted
10fps 1/20 1/25
18fps 1/40 1/45
24fps 1/50 1/60
25fps 1/53 1/65
50fps 1/100 1/125

Modern Meters Can be set to Bolex 130 Degree Shutter AngleSo if you are using the values from table 2, with a standard cine light meter there is a 3 degree shutter angle shift on all of them this won’t introduce much of an exposure difference so feel free to carry on using it.

The books and guides are all old and do not assume (which was the case at the time) that any amateur would have access to an advanced light meter where you could specify the shutter angle exactly as they were probably for high end studio work at the time and very expensive.

So if you have one now such as the Sekonic L508 Cine I own shown left put the exact 130 degrees shutter angle into it and don’t bother using the fudge table above and gain yourself an even more accurate reading with the shutter fully open.



Bolex Retrofitted Exposure Meter

After all the discussion above you may be thinking of spending some money to get a decent light meter which allows you to enter all the exact shutter angles and avoids all the hassle of the fudge table. What if you could for a similar price dispense with entirely having to even use a separate light meter and get true Through The Lens metering of a scene? This only being available as standard on the H16 EL camera although implemented in a different way.

The EL has a popup cell that measures the light of a scene by popping into the filming path and moves out when filming. In the retro fitted conversion a number of reflective mirror strips are applied to the shutter as when the camera isn't running the shutter always closes over the film at an exact point it's natural stop position so a reflective strip can be placed centrally to reflect light into the tiny cds cells to take a reading prior to shooting.

Difference between Bolex H16 EL and Retrofitted Metering shutter components

The meter also takes into account every variable shutter position as you set it and frees you up to be less burdened by the exposure side of things and work more quickly and more creatively and dare I say it? More point and shoot. Available if you send your spring bound H16 or EBM back to Bolex and shown on their price list as "800300 Light meter setting into H16 RX, RX5, SB, SBM and EBM camera" here’s the text from Bolex’s own Leaflet promoting it with pictures from my own SBM Camera that has undergone the conversion.

Bolex camera – owners have been waiting for it….Now a Dutch electronics-firm has successfully solved the problem; TTL light metering installed in all spring driven Bolex-reflex cameras 16mm, DS-8 or standard 8 can now be equipped with it, making these reliable workhorses even more versatile. Many movie-makers find the spring- driven models a blessing under many operating conditions, but up to now they had to do with hand held exposure meters now they can have the optimal accuracy of TTL metering even for extreme macro and telephoto work or submarine cinematography.

As the illustrations show, the installation of TTL metering has been carried out in a technically elegant way and leaves all normal camera functions intact.

Bolex H16 Retrofitted Meter Film chamber components

A small knurled knob directly below the lens turret allows a line-up of the fps (12 to 64 fps) and Film Speed (12 to 800 ASA or 12 -30 ISO / DIN), as shown as 24fps 100ASA (21 DIN / ISO) .This knob has the necessary potentiometer and the battery clip attached in the film chamber. The system is activated by pressing a small button in the camera base, this will apply battery current for approx 20 seconds.

Two tiny cds cells are attached to the beam splitting prism, these cells “read” the light coming through the lens and give an accurate and effective “integral” measuring of the picture area. Further electronic components are positioned in the viewfinder tube and include two LED’s, the 20 sec switch allows plenty of time to turn the diaphragm ring to a position where both LED’s glow with the same brightness indicating “correct exposure”. The shut off eliminates battery drain.

On all the 16mm models, operation of the camera with any of the factory set shutter openings is taken into account automatically adjusting the measuring accordingly, this cannot be accomplished on the 8mm models. Power is supplied by a 6 volt battery of the PX-28 type or Lithium equivalent, the lithium type being preferred for longer life and for being less affected by very low temperatures, at any rate the system works reliably down to a voltage drop of 20%.Back

For use under submarine conditions it is necessary to switch the 20 second shut off over to continuous a read out remains possible only as long as the camera drive is off. Pull the knob outwards and the LED on the side lights continuously to show your now in continuous mode when done press the knob in.