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need info about lens KERN VARIO-SWITAR1:1.9 f= 16-100 POE BOLEX H16 RX


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#1 Giovanni Savino

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Posted 15 October 2006 - 11:16 PM

I need to use this lens on a Bolex REX 5 but there are a couple of things I am unsure about:
there is a small push button to run the camera from the lens body right below the screw-in hole to attach the "remote" start stop cable.
This push button can be swung to the left and to the right against two small symbols ( two circles, one with a small black dot and the other with a big black dot in it) and appears to affect the built in metering.
All info about how to use this properly would be greately apreciated.

Thank You
:unsure:
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#2 Sir Alvin Ekarma

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Posted 16 October 2006 - 05:07 PM

There's an archived Poe Zoom manual on the main page of the site if that helps.... http://cinematograph...ens_and_mag.pdf
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#3 Nick Mulder

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Posted 17 October 2006 - 12:35 AM

Did the link at the other website help you out at all ?

(http://www.apecity.com/manuals/)
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#4 Giovanni Savino

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Posted 17 October 2006 - 07:32 AM

Did the link at the other website help you out at all ?

(http://www.apecity.com/manuals/)


Thank you very much. I was able to download a manual for the lens.

Now the problem appears to be with the f stop values expressed from the lens. At a setting on the lens of 50 asa and 24fps the built in meter reads f11 when my sekonic spot meter says f8 on a grey card.
So I try to match the two readings by lowering the asa dial on the lens to 25 ASA. By doing that I get the same reading both on the lens and the spot meter (off a grey card).
Are there any side effects if I do that ?

thanks again
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#5 Nick Mulder

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Posted 17 October 2006 - 02:35 PM

Thank you very much. I was able to download a manual for the lens.

Now the problem appears to be with the f stop values expressed from the lens. At a setting on the lens of 50 asa and 24fps the built in meter reads f11 when my sekonic spot meter says f8 on a grey card.
So I try to match the two readings by lowering the asa dial on the lens to 25 ASA. By doing that I get the same reading both on the lens and the spot meter (off a grey card).
Are there any side effects if I do that ?

thanks again


I think the POE lens has two settings to account for whether or not it has been connected to a mechanical Bolex with 130deg shutter or electric EBM or EL with the 170 deg shutter -

On the top knob thingy you will see two settings - 'E' means the Electrical 170deg - at least it does on the PTL which I own... I have vague recollections that the POE might have little shutter icons, choose the one with the smaller hole (ie. the 130deg shutter in the RX5)

That could be set incorrectly on E the POE and correctly at 130deg on your lightmeter - the difference isn't a full stop, but enough to make a difference ...

maybe ??
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#6 Giovanni Savino

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Posted 17 October 2006 - 06:13 PM

I think the POE lens has two settings to account for whether or not it has been connected to a mechanical Bolex with 130deg shutter or electric EBM or EL with the 170 deg shutter -

On the top knob thingy you will see two settings - 'E' means the Electrical 170deg - at least it does on the PTL which I own... I have vague recollections that the POE might have little shutter icons, choose the one with the smaller hole (ie. the 130deg shutter in the RX5)

That could be set incorrectly on E the POE and correctly at 130deg on your lightmeter - the difference isn't a full stop, but enough to make a difference ...

maybe ??


thank you Nick,

I am experimenting quite a bit with different light meters and somehow getting there.
What I would really would like to know- carved in stone- once and for all is:
The bolex REX 5 manual says that the shutter speed is 1/80th of a second at 24fps but because of the prism deflecting 20-25% of the light passing the actual shutter speed to be used(when using RX lenses that compensate for the light loss) is 1/65th of a second.

So: I am using a REX5 with a RX lens at 24fps and I set my hand held light meter at :
Shutter angle 130 degrees
Shutter speed 1/65th of a second

is this CORRECT ?? :blink:
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#7 Leo Anthony Vale

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Posted 18 October 2006 - 01:42 PM

So: I am using a REX5 with a RX lens at 24fps and I set my hand held light meter at :
Shutter angle 130 degrees
Shutter speed 1/65th of a second

is this CORRECT ?? :blink:


No. Use the 1/80.
RX lenses don't compensate for light loss by the prism,. They compensate for abberations caused by the prism. There are many threads that have gone over this.
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#8 Nick Mulder

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Posted 18 October 2006 - 04:12 PM

thank you Nick,

I am experimenting quite a bit with different light meters and somehow getting there.
What I would really would like to know- carved in stone- once and for all is:
The bolex REX 5 manual says that the shutter speed is 1/80th of a second at 24fps but because of the prism deflecting 20-25% of the light passing the actual shutter speed to be used(when using RX lenses that compensate for the light loss) is 1/65th of a second.

So: I am using a REX5 with a RX lens at 24fps and I set my hand held light meter at :
Shutter angle 130 degrees
Shutter speed 1/65th of a second

is this CORRECT ?? :blink:


that table confused me for a while as well - its for people who cant do math (or can, depends how you look at it) - regardless, it causes confusion for many - At 24fps with a 130deg shutter your actual shutter speed will be:

(1/24)*(130/360) = ~ 1/66 of a second (as you have correctly worked out)

..but to account for the light loss of the prism Bolex prefers just to give us a table of relative shutter speeds in which to set our light meters at.

(1/80 = 0.0125) < (1/66 = 0.015)


..as you can see 1/80 lets less light through.. It is the equivalent of 1/66 with about %17 of the light taken out according to my dodgy rounded math.

So 1/80 isn't the physical shutter speed at all - problem is most of us need to work with the actual shutter speed when playing around with special effects, speed effects, lighting sync, oddball tinkering etc... So basically, we all need to understand and remember the reasons for this table to have a happy Team Bolex.:ph34r:

The table has been around for decades so we can reasonably expect the same question to pop up now and again for the rest of the time 16mm film is around, searching the forums here will yeild heaps of info (as has been suggested by Leo) -

Anybody else keen on a Bolex sub-forum in the 16mm forums ? with a sticky on the subject ?

Edited by Nick Mulder, 18 October 2006 - 04:14 PM.

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