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Red Markings on Som Berthiot Primes


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#1 ymkulkarni

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Posted 21 February 2009 - 11:08 PM

Hi,

I have 2 Som Berthiot RX Primes that came with my Bolex. The 75mm and the 25mm both have red markings in the middle of the lens with arrows pointing out above/below the 4. I figured that you were supposed to use the red arrows to set the f/stop and focus point but does anyone know what the other numbers stand for and when I would use them. The numbers are in this order 22|11|4|11|22 for both the lenses. Also, the f/stop settings don't click exactly on the 4 but rather click at odd intervals between the various f/stops available. Does anyone know if my lens needs to be repaired so that the markings are aligned? I don't know if this is a good explanation of my problem but hopefully someone has these same lenses and knows what I am talking about. Thanks! :]
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#2 Ryan Thomas

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Posted 22 February 2009 - 11:09 AM

Hi,

I have 2 Som Berthiot RX Primes that came with my Bolex. The 75mm and the 25mm both have red markings in the middle of the lens with arrows pointing out above/below the 4. I figured that you were supposed to use the red arrows to set the f/stop and focus point but does anyone know what the other numbers stand for and when I would use them. The numbers are in this order 22|11|4|11|22 for both the lenses. Also, the f/stop settings don't click exactly on the 4 but rather click at odd intervals between the various f/stops available. Does anyone know if my lens needs to be repaired so that the markings are aligned? I don't know if this is a good explanation of my problem but hopefully someone has these same lenses and knows what I am talking about. Thanks! :]


Those markings give you a good estimation of how much DOF you have at each F-stop. Handy for figuring out hyperfocal distances and the like. I'd have to see a picture to be positive, but that's what it sounds like it is.

Edited by Ryan Thomas, 22 February 2009 - 11:10 AM.

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#3 ymkulkarni

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Posted 22 February 2009 - 01:29 PM

That makes sense. Thanks a lot!
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