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Vario-Switar 8-36 Help Needed


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#1 andy oliver

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Posted 29 April 2010 - 12:12 PM

Hi, i've trawled the net in search of some info regarding the 8-36 vario switar lens for the H8rx. There are 3 markings on the barrel, attached is a photo, i'm afraid i've blacked out two of the markings either side of the screw. My question is, which mark do i use for setting the exposure?. When the trigger is pressed, the iris opens up, then closes down, but the iris always presets back to approx one third over exposure, ie if i set the lens to 5.6, i press the trigger, the lens opens up to 4.5 !! Thus, i'm tending to over exposure footage with this lens...
Any help/info would be greatly received...

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#2 Jean-Louis Seguin

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Posted 29 April 2010 - 03:44 PM

Hi, i've trawled the net in search of some info regarding the 8-36 vario switar lens for the H8rx. There are 3 markings on the barrel, attached is a photo, i'm afraid i've blacked out two of the markings either side of the screw. My question is, which mark do i use for setting the exposure?. When the trigger is pressed, the iris opens up, then closes down, but the iris always presets back to approx one third over exposure, ie if i set the lens to 5.6, i press the trigger, the lens opens up to 4.5 !! Thus, i'm tending to over exposure footage with this lens...
Any help/info would be greatly received...


Hi Andy,

My guess is that the other marks that you blacked out indicate where to set the aperture for when the camera's variable shutter is closed to the 1 or the 2 position. So the white line that's still there is the good one.

It's been my experience that the aperture presetting feature on this kind of lens just doesn't work very well.
Not just yours but a lot of them. There's an identical system in the 18-86mm non-EE version and it also behaves badly.
Something to do with the balance of spring tensions inside the mechanism.
I guess you will have to assume that the correct aperture is the one when you are pressing the trigger all the way and the diaphragm closes to the set aperture. Forget where the aperture ends up when you are not depressing the trigger.

Cheers,
Jean-Louis
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#3 andy oliver

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Posted 29 April 2010 - 05:17 PM

Hi Andy,

My guess is that the other marks that you blacked out indicate where to set the aperture for when the camera's variable shutter is closed to the 1 or the 2 position. So the white line that's still there is the good one.

It's been my experience that the aperture presetting feature on this kind of lens just doesn't work very well.
Not just yours but a lot of them. There's an identical system in the 18-86mm non-EE version and it also behaves badly.
Something to do with the balance of spring tensions inside the mechanism.
I guess you will have to assume that the correct aperture is the one when you are pressing the trigger all the way and the diaphragm closes to the set aperture. Forget where the aperture ends up when you are not depressing the trigger.

Cheers,
Jean-Louis


Hi, many thanks for the reply, i'm tending to obtain slightly over exposed footage with my 8-36. Just wondering if the iris is kicking back to compensate for the bolex prism? something i've already compensated for? Although i'm setting the iris ( on the white line ) for f5.6, once the trigger is fully depressed, i'm finishing up with aprrox f5.0-ish...... Perhaps the answer is not to use the trigger release mech on the lens.

Thanks again

Andy
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#4 Jean-Louis Seguin

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Posted 29 April 2010 - 06:17 PM

Hi, many thanks for the reply, i'm tending to obtain slightly over exposed footage with my 8-36. Just wondering if the iris is kicking back to compensate for the bolex prism? something i've already compensated for? Although i'm setting the iris ( on the white line ) for f5.6, once the trigger is fully depressed, i'm finishing up with aprrox f5.0-ish...... Perhaps the answer is not to use the trigger release mech on the lens.

Thanks again

Andy



I would say set it completely manually if you can.
The preset mechanism is not reliable.

Cheers,
Jean-Louis
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#5 Simon Wyss

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Posted 01 May 2010 - 01:22 AM

To do away with mechanical backlash always turn the iris ring in the same direction to the intended point. Most operators close the diaphragm from full open. An iris free from backlash existed with the Benoist-Berthiot Cinor. Vive la France !
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