Bolex Shutter

I was wondering if anyone knew about the reasoning for the 133 degree shutter on a bolex. Since it takes 1/3 of a stop off, one would think they would go to something near 180. The question was brought up in a cinematography class and i would love to impress the professor with an answer.

Thanx in advance

Sincerely,

Dylan A. Tredrea

The Bolex shutter is at 180 degrees (or 170). The viewing system, though, is a prism reflex, not a mirror. Therefore, 1/3 of the light is deflected towards the viewfinder. Ergo, one third stop difference, giving an EFFECTIVE shutter of 133 degrees, or a shutter speed of 1/80.

At least, it's always worked for me that way.

When pixilating, your shutter speed should be switched over to 1/40, I suspect the reasoning for that is the single frame button is attached to a different gearing system, or motor altogether.

Duraid Munajim

Duraid Munajim wrote :

>The Bolex shutter is at 180 degrees (or 170).

Bolex Shutter Speed at 24 FPS is 1/65th of a second. Taking into account light loss through the reflex optics reduces the effective shutter speed to 1/80th of a second. This is for Exposure compensation only, as far as motion is concerned the shutter speed remains at 1/65th at 24 FPS. Provided the variable shutter is left fully open

Single frame exposure I've been told is 1/30th of a second actual. 1/40th of a second with compensation for the reflex optics.This is with the single frame selector set on "I". With the Single frame selector set on "T" the Bolex acts as your still camera on the "B" or Bulb setting.

I've checked this info with my Bolex H-16 manual, so it should be correct.

Some single frame points. The Bolex manual gives the range on the speed dial as being from 18 to 64 for single frame operation. I have always heard to set the Speed dial at 64. Also the timinmg mechanism is not perfect, and if you look at your single frame footage, you will probably see small exposure variations from frame to frame. They do not seem to show up on projection, or transfer. This info I got from Joe at Swiss Camera in NY. Obviously before he passed away.

Steven Gladstone

Gladstone Films

http://home.earthlinkl.net/~veenotph

>Bolex Shutter Speed at 24 FPS is 1/65th of a second. This is for Exposure Provided >the variable shutter is left fully open

So does that mean the shutter is 170 degrees?

>I have always heard to set the Speed dial at 64 [when using the single frame toggle].

I remember many years ago testing the veracity of that statement - if you set it at 8 fps, do you get more exposure, or is it governed by its own timing mechanism. The results were that no matter where you set your speed dial, the exposure remains the same.

Small diferences from frame to frame? I have shot a short film with the Bolex, all pixilation, as well as several inserts for various shorts, docs, etc., and never had that problem. The bigger problem is registration, which varies from bolex to bolex.

Regards,

Duraid

Duraid, I believe you are incorrect about the shutter angle of the Bolex. The prism does take away a third of a stop as does the 133 degree shutter. The Shutter speed (open variable shutter) for 24 fps is roughly 1/65, but is effectively 1/80 because of the 1/3 stop loss due to the 133 degree shutter.

Not my original source, but a source not the less:

http://www.city-net.com/~fodder/bolex/shutter.html

I am in no way connected to this site or the webmaster btw.

To your credit it would make sense to have a 180 (or near) degree shutter. My experience and knowledge of this camera is actually rather shallow, so any one else's input would be appreciated.

Thank you, Dylan A. Tredrea

P. S: Duraid you sound as if you have shot with a Bolex assuming only a 1/3 of a stop loss when in fact it is a 2/3 stop loss. If you have only shot on B and W reversal, the film has the latitude so that this 1/3 stop underexposure may not be noticeable. Just food for thought

Duraid Munajim wrote:

> So does that mean the shutter is 170 degrees?

Duraid, does it matter once you know the actual shutter speed at 24 FPS? Well Lets go do the math shall we. 1/FPS Times Shutter angle/360 = Shutter speed ( exposure time)

1/65 = 1/24 Times What? ( X)/360 360 (1/65) = 1/24 times X 24 (360/65) = X

X= 132.92307692

Lets call it 133 degrees. This would be with the variable shutter open all the way.

I wll stand by my statement of small differences from frame to frame in exposure using the spring. I got it from a top notch Bolex technician. However, as I also said, these differences are only noticeable when looking at the the film spooled out into your hands, not while running through a projector.

The results were that no matter where you set your speed > dial, the exposure remains the same.

This has less to do with exposure, and more to do with tension on the spring. Perhaps It is just a convention, as I've heard to set the speed lever to 64 when attaching an electric motor, and disengaging the spring. Again, the Owners manual I have for my Bolex H16 only mentions 18 to 64 FPS as the range in which to set the speed selector when shooting single frame, I don't doubt that it works fine set at 8. According to the manual. 1/30 of a second actual, /40th of a second compensated.

Steven Gladstone Gladstone Films Http://home.earthlink.net/~veenotph

Duraid Munajim wrote :

> So does that mean the shutter is 170 degrees?

Duraid, does it matter once you know the actual shutter speed at 24 FPS?

Well Lets go do the math shall we.

1/FPS Times Shutter angle/360 = Shutter speed (exposure time)

1/65 = 1/24 Times What? ( X)/360 360 (1/65) = 1/24 times X 24 (360/65) = X

X= 132.92307692

Lets call it 133 degrees. This would be with the variable shutter open all the way.

The results were that no matter where you set your speed > dial, the exposure remains the same.

Steven Gladstone

Gladstone Films

The reason the spring-wound Bolex's shutter is 133 degrees, rather than the more desirable 180 degrees probably is because of a lack of efficiency in the mechanism. It probably has to allow time both for the frame to be yanked down and settled into proper registration before the shutter can be allowed to open.

More efficient movements, like the Mitchell 16 and Maurer 16 were so efficient they could have 235 degree shutters (1/37 sec. at 24fps), which I wish some modern cameras could emulate. Only one time, in using either of these cameras, did I detect a slight strobing on movement, because the exposure time was long enough to provide motion blur when strobing might have occurred. They also gave 1/3 stop more exposure than 1/50 sec. shutters.

Wade K. Ramsey, DP

Dept. of Cinema & Video Production

Bob Jones University

Greenville, SC 29614

>I was wondering if anyone knew about the reasoning for the 133 degree shutter on a >bolex. Since it takes 1/3 of a stop off, one would think they would go to something >near 180.

Probably this gives the camera enough time to position the claw and register the film properly; Bolex can be very steady - well, some of them (IF maintained/serviced properly that is).

I no longer believe the absolute mythology of pin registration for 16mm - as the Aaton has proven, (altho a Bolex is not an Aaton).

My 16S has been very very steady and weave-free, but a Bolex (Rex 4 or 5 at least) (*see above re service*) not too shabby.. BUT the venerable "S" and its pin registration is like an insurance policy !

Imagine a springwound Bolex with motor option, retaining the built in single frame and way cool time exp mode, make the shutter 170, keep the plane shutter (variable) _with_ spinning mirror reflex viewing and showed the entire frame or more in the vf (easy change to S16 wd be nice) I'd trade my 16S in on one ! (It'd be like having a lightweight portable "S35R for 16mm")

WHAT a useful camera it would be. (Wd make a nice to complement the A-Minima !)

OK, jp, can you work with the folks across the lake ?

-Sam "it would be progressive and you could scan the output" Wells

P.S. Arri could counter with a '416ES' ....

Ooops, my mistake about the shutter. I didn't think that extra second and just let it slide. And you're right, it is a 2/3 difference in exposure from 180, not 1/3 - that was just a typo.

It seems to make sense Steven, Wade, that the 133 degree shutter is there to allow for the claw to come in and out in enough time.

As for the exposure differences from frame to frame, well ... I was in the editing room with my film for three weeks and never noticed a change from frame to frame. And then having to sit through it over the different festivals - never noticed any density shifts. While I write this I'm jogging the VCR forward frame by frame on my film - nope, nothing doin' - mabe I was lucky.

...plus, MY top-notch Bolex technician has nothing to say about switching the speed dial to 64 when pixilating or about frame to frame changes. The Bolex seems to be the camera of choice in 16mm when doing single frame animation, go to any animation film school and ask what they send their students out on the field with. If there were slight exposure differences from frame to frame, believe me, the pupppet animation students would notice. Having said that, maybe

Keep in mind I'm saying all this half tongue in cheeck. Maybe we can pit our respective post-humous Bolex technician's against each other :-)

BTW, I have nothing against the practice of setting the speed dial to 64 when shooting single frame on the bolex. Before I roll the camera on the first day of a shoot, I always tap a tripod leg (or dolly wheel) gently. It kinda helps with my exposure :-)

Kind regards,

Duraid Munajim

>Ooops, my mistake about the shutter. I didn't think that extra second and just let it >slide. And you're right, it is a 2/3 difference in exposure

I even asked my school-mates and it turns out we were all under the misconception that the Bolex shutter is about 180 degrees and that due to the light being deflected to the viewfinder, we lose about 1/3 of a stop of light.

I hope I am not wasting my time here in film school. It would be very embarrasing to get out into the professional world and be misinformed. I am so glad to have joined CML-101.

>1/3 of the light is deflected towards the viewfinder. Ergo, one third stop >difference

That's what I learned in class too... I wonder if the teacher has actually asked a trick question. That's something to think about before responding in class.

Sincerely,

Fatima Mojaddidy

>That's what I learned in class too... I wonder if the teacher has actually asked a trick >question. That's something to think about before responding in class.

What's the point of a trick question if the student isn't given the means of determining the correct answer ?

A teacher could, say, provide reference works: I just grabbed off my shelf AC Manual 4th Edition. page 150 "H-16 Rex has 130 degree adjustable shutter (giving 1/65 sec. at 24 f/p.s.) ...."

Now, I don't remember, is it really 132 ? 132.5 ? Shall we dissasemble one in class and measure it ? No, but above gives some working information. Admittedly, this AC Manual does not specify the ammt of light loss in the reflex prism system, but at this point the teacher *might* want to cover reflex systems in general, prism vs spinning mirror, who, how, why. So you then might be inspired to ask "how much light loss is there in this (or other) prism or pellicle mirror reflex viewfinders ?"

Get David Samuelson's Hands on Manual (I'll join you at the bookstore, I need one myself) and you'll have a film school you can take with you...

-Sam "don't dissasemble your school's cameras especially if they're spring wound" Wells

Sam Wells wrote:

>Sam "don't dissasemble your school's cameras especially if they're spring wound" Wells

Au-contraire Mes Amis.

I took home a filmo that no longer ran at settable speeds. Taking it apart was great fun, until the spring shot out and ate the sweater I was wearing. I really liked that sweater. Took me an my father ten tries to wind the spring tight enough to get it back into the case. Turns out something called the Idler ( Eidler?) gear broke. Swapped the gear out with one from a filmo that had been dropped one time to many, and bingo. I still have the dissasembly manual I wrote as I took the filmo apart.

You do need to watch that Spring. Ah College, I remeber it as if it was a dozen years ago.

Steven Gladstone

Gladstone Films

>1/3 of the light is deflected towards the viewfinder. Ergo, one third stop difference Be careful. Assuming that 1/3 light IS deflected (that's another part of the discussion), then 2/3 makes it to the lens.

One third of a stop difference would be caused by deflecting 20% or 1/5th of the light to the viewfinder.

Stops are logarithmic - it's dangerous to mix them with percentages.

Dominic Case

Group Technology & Services Manager

Atlab Australia

www.atlab.com.au