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Karl Andre Bru

Ye olde 144 degree shutter angle and lightmeter rant

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Hi guys!

 

Im sorry but here it probably comes again....to put it short:

1.shooting on old bolex h16 reflex

2. shooting on 500T Vision 3

3. camera only has 144 degree shutter angle.

4. the light meter is Minolta Auto Meter IV F

5. shooting at 24FPS (not worrying about incorrect speed from the old lady)

7. the light meter can choose between cine mode(choosing FPS) or shutter speed.

 

So with a 144 angle at 24 FPS, at 500ASA I should choose 1/60 as my shutter speed to get the correct reading on my meter, yes? (24x360)/144=60

As a test: About a foot from a non clear(kind of frosted) 40 watt bulb, being the only source in my room I get 5.6 and 3/10 with my meter at 24FPS,500ASA and 1/60 shutter speed.

 

If anyone can be bothered to respond that would be super swell, gosh darn it...

 

Cheerio!

 

Karl Andre Bru

Lighting Assistant/Gaffer/Illuminator

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Yes 1/60sec is the duration the shutter exposes any given point on the film plane

 

but you're forgetting ye even older 'bolex lightmeter adjustment for reflex prism' rant ...

 

Not sure nowadays but I guess we'll see - reckon within maybe 5 posts (?) we'll have someone copy something they found on the net about Bolex reflex prisms that is incorrect :P

 

Anyways, pulling old book of shelf, opening it and blowing away the dust of ancient swiss armpits:

 

Your reflex Bolex has a prism that soaks up a smidge of your light for the viewfinder, just open up your iris above your meter reading a corresponding smidge to account for this ... Search the forum archives for the exact amount and technical discussion ad infinitum regarding how many stops a smidge is - but just between you me and the internet, lets say 1/3 stop for shits and giggles :lol:

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You're saying you have a Bolex reflex with a 144 degree shutter. Are you sure? The only Bolex I know with a 144 degree shutter is the M series cameras, which are non-reflex. Reflex models have a 131 degree shutter (spring wound), while the EBM has a 170 degree shutter. Just that I'd throw that in...

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HA HA,

 

wow - that was TWO posts before someone assed up a number (me!) - :lol: - yes they are 130-ish degrees (the variable shutters are a bit sloppy)...

 

poop, maybe that 144deg thing is someones attempt at accounting for the prism in terms of the shutter angle... (confusing to communicate to others, but ok once you can figure it out on your own terms)

 

So anyways everything I said was correct apart from the fact it should be calculated with 130something/360 * 1/24 = 1/66 - then open a smidge with a reading from that number...

:rolleyes:

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Guest Glenn Brady

Filmmaking was a lot simpler when lightmeters didn't require users to specify shutter angles and filmmakers had instruction manuals at hand. Designers nowadays seem to stuff as many functions as possible into electronic gadgets, making them both unnecessarily complicated and failure prone. I've been using the same battery-independent Sekonic meter for thirty-five years with no problem, never having to specify shutter angles to properly expose film.

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I`m quite sure you have. I guess its ye old inexperience with shooting on film that makes us a bit anal when it comes to clinging to our light meter for dear life.

But im looking forward to see how we did. Should be pretty sweet though, im sure.

Thanks for all the replies!

 

Cheers

 

Karl Andre Bru

Lighting Assistant/Gaffer/Illuminator/etc...

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Actually, I believe the early h16 reflex (the pre rexs' without the variable shutter) do have a 143 degree shutter. I have one, circa 1957, and have always used the 143 or 1/60 with rx lenses. When using non rx lens I add the light loss correction, ~1/80.

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Actually, I believe the early h16 reflex (the pre rexs' without the variable shutter) do have a 143 degree shutter. I have one, circa 1957, and have always used the 143 or 1/60 with rx lenses. When using non rx lens I add the light loss correction, ~1/80.

 

 

This is the kind of incorrect info I talk about. RX or non-RX lenses do not affect anything to do with the light intensity calculations around the reflex prism - they are made to correct for optical issues the prism causes with wider angle lenses - nothing to do with the light loss ...

 

Glenn, most new 'cine' digital lightmeters are just appended versions of a stills paradigm meter and if you want can be used in that mode just as easily as your older model...

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Guest Glenn Brady

Glenn, most new 'cine' digital lightmeters are just appended versions of a stills paradigm meter and if you want can be used in that mode just as easily as your older model...

 

I'm not surprised this is so, but this question about shutter angle comes up so frequently, it suggests many believe a proper exposure can't be gotten without inputting a shutter angle to a lightmeter.

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The thing about 144 degrees is that it's the magic number for shooting NTSC TV sets at 24 fps without a roll bar.

 

 

 

 

-- J.S.

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My Bolex has a 133 degree shutter (Rex 4) that makes it a theoretical 1/65 (rounded) when filming at 24 fps. Now for the prism-light-loss...

If i substract the 25% light loss of the prism viewfinder i get something like 1/81,2 which is the correct exposure time. This matches to my Bolex filmtable (okay: that one states 1/80). Since the Bolex is not crystal speed it's always a estimate. All H16RX seem to have 133 degree shutter above the serial number 200000 which marks the introduction of the Rex 2. EL and EBM have a 170 degree shutter opening.

Regards Oliver

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When using a reflex bolex, the simplest thing to do is to use the cine speeds on your light meter and make the exposure correction with the asa setting. This way, you can readily switch between shooting speeds without having to re-calculate anything.

The correct compensation is 2/3rds of a stop in total, which includes 1/3rd of a stop for the 130 degree shutter angle, and 1/3rd of a stop for the prism light loss. Thus, if you are using 100 asa film stock, set the light meter to 64 asa (which is 2/3rds of a stop slower than 100 asa) then simply set the meter to 24fps if you are shooting at 24, or 12 if shooting at 12 etc..

Here is a chart that puts this correction in terms of real and adapted shutter speed:

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

But as I say, I prefer to adapt the asa rather than the shutter speed.

richard

  • Upvote 2

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So with a 144 angle at 24 FPS, at 500ASA I should choose 1/60 as my shutter speed to get the correct reading on my meter, yes? (24x360)/144=60

Well, sort of. Technically, you've got the formula upside-down - it's 144/(24x360), which is .01666... or 1/60. But you remembered to invert the answer (1/60 instead of just 60) so it all comes out in the wash anyway.

 

Not to mention that "60" is easier to understand than "0.01666".

 

--

Jim

Edited by Jim Hyslop

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I guess I was just trying to point out not all early H16 reflex cameras have a 130 degree shutter. I should have stopped there, sorry for any misinformation:)

 

Thanks Richard, that was useful info and website.

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Nahh, please compensate 25-35% light loss for the prism. The prism is INSIDE / IN FRONT OF the film gate and not in the lens. Please see the following shots i took from Douglas Underdahls 16mm Camera Book.

I recommend it to anyone seriously filming with the Bolex as well as the Bolex Bible by Andrew Alden. Sorry for the lousy iPhone pics...

post-39275-12754904487745.jpg

post-39275-12754904583864.jpg

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When using a reflex bolex, the simplest thing to do is to use the cine speeds on your light meter and make the exposure correction with the asa setting. This way, you can readily switch between shooting speeds without having to re-calculate anything.

The correct compensation is 2/3rds of a stop in total, which includes 1/3rd of a stop for the 130 degree shutter angle, and 1/3rd of a stop for the prism light loss. Thus, if you are using 100 asa film stock, set the light meter to 64 asa (which is 2/3rds of a stop slower than 100 asa) then simply set the meter to 24fps if you are shooting at 24, or 12 if shooting at 12 etc..

Here is a chart that puts this correction in terms of real and adapted shutter speed:

http://www.city-net....ex/shutter.html

But as I say, I prefer to adapt the asa rather than the shutter speed.

richard

Great post! Thanks! I searched high and low for ASA adjustments like you mentioned :)

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Those tables if I recall (and they haven't been adjusted by the website) are a direct copy of Bolex tables originally supplied with the cameras.

 

They are *also* wrong - how do I know? Well if you calculate a ratio or two you'll see they are internally inconsistent.

 

But back to part of my original point, it don't matter! We are talking small amounts, only appreciable by folk shooting reversal with every other factor locked in exactly (lighting etc...).

 

Do you have that much control over your reflections and practicals in incident, or have you mastered the zone system in spot mode and push/pull processing?

 

If not, less stress is best - meter as per normal and then open up a squeak ;)

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Please see the following shots i took from Douglas Underdahls 16mm Camera Book.

 

Looking at second page of the Underdahl book, the line where it says flange/focal distance (FFD) could be a bit clearer.

 

In the Bolex system, again because of the beam-splitter prism, one must differentiate between optical FFD and physical FFD.

 

In a H16RX camera, with the traditional 3-lens turret, the optical FFD is 17.52mm, the C-mount standard. The prism elongates the light path by a distance of 3.24mm. The flange now has to be positioned at 17.52mm + 3.24mm = 20.76mm from the film plane. This is the physical FFD.

 

Now for a Bolex camera with a single bayonet mount. The flange of the bayonet mount is designed to be 5.70mm ahead of the turret flange. So the optical FFD is now 17.52mm + 5.70mm = 23.22mm. The physical FFD is 17.52mm + 3.24mm + 5.70mm = 26.46mm

 

Jean-Louis

Edited by Jean-Louis Seguin

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Hey guys!

 

Digging this up from the past.

 

I have a Sekonic L-478D lightmeter which does not allow me to set my shutter angle to 133 it's either 135 or 130. Regardless of that issue though, I'll set my meter to 130 shutter angle for this experiment.

 

I usually shoot 500T and when I shoot 500T I rate it at 320 on my Scoopic because I like that extra over exposure cushion like many people.

 

But with my Bolex Rex 4 I know I'd have to compensate another 1/3rd because of the light loss in the prism. So if I was shooting 500T with my Bolex Rex 4 trying to match the exposure with my scoopic on the same film stock and using the same principal I would rate my 500T at 250 ASA with my bolex, correct?

 

Just like Richard said I want to just stick to ISO/ASA rating of the light loss. That way I don't have to deal with shutter speeds when I switch frame rates.

 

What I don't understand is that Richard said there is two reasons to light loss; 1.) The prism (1/3rd loss) and then 2.) The Shutter (1/3rd loss) why is the shutter causing a loss in light in this calculation? Is it because it's a spring wound motor?

 

Because if that was the case then according to the 2/3rd light loss just because of the design of the bolex and then the extra 1/3rd exposure adjustment that I personally make to cushion my shadows that would equal me exposing a full 1 stop over to compensate using the bolex.

 

Does anyone still have any more patience with this subject to clarify this, Ha? Also, does anyone have a proper bolex manual that they can link me too? I've been finding them in google searches but they don't have correct information; some state the RX lenses allow more light which is false and some say the bolex is 144 degree shutter which is not true for the REX series.

 

Thank you!

 

Ryan

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I think Richard was adding another 1/3 stop for the shutter because many meters assume a shutter angle of 180 degrees.

 

If your meter has the facility to enter a shutter angle then you don't need to make that compensation.

 

Regarding your meter only having a 130 degree setting, the difference of a few degrees of shutter angle is so insignificant in terms of exposure that you don't need to worry about it. Even the difference between 144 and 133 degrees at 24fps is only 1/60 sec compared to 1/65, which is a small fraction of a stop.

 

Bolex shutter angles varied over the decades of production and different models. Early reflex Bolexes have 144 degree shutters, later electronic models have 170 degree shutters, but most RX models are 133 (or thereabouts). I think the general evolution is as follows:

 

The first Bolexes, up to serial number 100400, have a shutter angle of 192 degrees.

From serial no's 100401 to 195800 (1954 to 1961) they have a shutter angle of 144 degrees.

From around 1962 (a few years after variable shutters had been introduced) it was further reduced to 133 degrees.

EL and EBM models are 170 degrees.

 

You're correct that Rx lenses do not compensate for the prism light loss, they are marked in standard f stops.

 

There are many manuals at this excellent site:

http://www.apecity.com

including a good copy of a H16 Reflex manual (go the version 2 from JL Seguin).

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If I may help with the understanding: Paillard wouldn’t get tired of repeating that the H camera has a focal plane shutter acting very close to the film. The early models have 192 degrees opening angle between strictly radial shutter edges but one reckons with 190 degrees because the shutter edges never depict sharply on the film due to their standing away. The Ciné-Kodak Special, by the way, has its variable shutter closer to the aperture. In the first advertisements with the Movie Makers magazine 200 degrees were spoken of, a publicity exaggeration that got soon corrected.

 

In this perspective we can reckon with 168 degrees, 144, and 133 for the real angles of 170, 145, and 135 degrees. The smaller difference with the 145-144 shutter angles derives from the more critical situation of filming a TV screen. The Paillard-Bolex H-16 M bears that designation not for Marine as I once have stated somewhere but simply for Monoptic. An underwater camera should have the widest shutter opening angle possible. The M has a lower-priced appearance by the diaphragm chart on the front, yet the true target were people who wanted to shoot off screen in the US.

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I think Richard was adding another 1/3 stop for the shutter because many meters assume a shutter angle of 180 degrees.

 

If your meter has the facility to enter a shutter angle then you don't need to make that compensation.

 

Regarding your meter only having a 130 degree setting, the difference of a few degrees of shutter angle is so insignificant in terms of exposure that you don't need to worry about it. Even the difference between 144 and 133 degrees at 24fps is only 1/60 sec compared to 1/65, which is a small fraction of a stop.

 

Bolex shutter angles varied over the decades of production and different models. Early reflex Bolexes have 144 degree shutters, later electronic models have 170 degree shutters, but most RX models are 133 (or thereabouts). I think the general evolution is as follows:

 

The first Bolexes, up to serial number 100400, have a shutter angle of 192 degrees.

From serial no's 100401 to 195800 (1954 to 1961) they have a shutter angle of 144 degrees.

From around 1962 (a few years after variable shutters had been introduced) it was further reduced to 133 degrees.

EL and EBM models are 170 degrees.

 

You're correct that Rx lenses do not compensate for the prism light loss, they are marked in standard f stops.

 

There are many manuals at this excellent site:

http://www.apecity.com

including a good copy of a H16 Reflex manual (go the version 2 from JL Seguin).

 

If I may help with the understanding: Paillard wouldn’t get tired of repeating that the H camera has a focal plane shutter acting very close to the film. The early models have 192 degrees opening angle between strictly radial shutter edges but one reckons with 190 degrees because the shutter edges never depict sharply on the film due to their standing away. The Ciné-Kodak Special, by the way, has its variable shutter closer to the aperture. In the first advertisements with the Movie Makers magazine 200 degrees were spoken of, a publicity exaggeration that got soon corrected.

 

In this perspective we can reckon with 168 degrees, 144, and 133 for the real angles of 170, 145, and 135 degrees. The smaller difference with the 145-144 shutter angles derives from the more critical situation of filming a TV screen. The Paillard-Bolex H-16 M bears that designation not for Marine as I once have stated somewhere but simply for Monoptic. An underwater camera should have the widest shutter opening angle possible. The M has a lower-priced appearance by the diaphragm chart on the front, yet the true target were people who wanted to shoot off screen in the US.

 

Dom & Simon,

 

Thank you so much for taking the time to explain this I really appreciate it and I'm excited to shoot my rex 4 tomorrow!

 

Dom, awesome site to link me to exactly what I was looking for!

 

Thanks,

 

Ryan

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The first Bolexes, up to serial number 100400, have a shutter angle of 192 degrees.

From serial no's 100401 to 195800 (1954 to 1961) they have a shutter angle of 144 degrees.

From around 1962 (a few years after variable shutters had been introduced) it was further reduced to 133 degrees.

EL and EBM models are 170 degrees.

 

 

 

I recently picked up a non-reflex Bolex H-16 , serial number 98890 , so according to what you wrote above it should have the 190 (192) degree shutter , but according to the serial numbers given here :

 

http://www.bolexcollector.com/cameras/h16supreme.html

 

this camera with serial number 98890 was manufactured in 1954 and has a 144 degree shutter.

 

I haven't shot any film with it yet , but I am looking forward to testing it . However, now I'm confused if I should be metering based on a 144 degree shutter or 190 degree shutter. Is there some way to tell for sure if the shutter is 144 or 190 ?

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Well, I found this user manual online ... https://tinyurl.com/Bolex-H16-manual -- based on the exposure time given and the camera models that are referred to in the manual (H-16 Standard , H-8 , H-16 Reflex) I would place the manual's publication at around 1954 - 1958 ... and the exposure time given in the manual for 24fps is 1/60 sec. , which would be a 144 degree shutter. If the Bolex Collector website has the correct info on serial numbers then my camera with serial number 98890 , manufactured in 1954, has the 144 degree shutter.

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