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Manual for Kern Vario-Switar 12.5-100mm MC Zoom Lens


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#1 Robert Lewis

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Posted 22 January 2011 - 04:19 PM

I would like to get hold of a copy of the Manual for the Kern Vario-Switar 12.5-100 MC Zoom Lens (the later of the two types which did not have the automatic exposure system included. Does anybody have a copy scanned which they could let me have. There is nothing very complicated about the lens, but on the aperture ring there are both red and white setting lines, which I suspect are related to the fact that the lens has a macro setting. I think it is possible that one line is for use when the macro setting is not in use and the other is for when it is, and I would like to be sure about this. Any advice would be welcome.
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#2 Chris Millar

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Posted 22 January 2011 - 06:00 PM

I know my PTL version (the motor/auto exposure one) has T-stops marked in orange - could be that ...

The Aspheron switch is basically a back focus adjustment - you can do pretty nice macro but the focal plane wont sit still with a zoom ... In lieu of two operators this has been helpful on occasion :lol:
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#3 Robert Lewis

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Posted 23 January 2011 - 07:25 AM

Chris. Thank you for your response. I am attaching a picture of the relevant part of the lens. Apologies for the quality, but I think you can see that on the barrel of the lens there are two line markings. The white one lines up with the f22 white line marking on the aperture ring. Just below the aperture ring white marking there is a red line marking. It is the purpose of that line marking I am puzzled about. As you can see there are only f.stop markings on the aperture ring, but the red marking on the barrel must have a purpose. The question is what is it? Any information is welcome.
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#4 Robert Lewis

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Posted 23 January 2011 - 07:31 AM

Apologies picture attachment didn't link to the above message.

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#5 Chris Millar

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Posted 23 January 2011 - 03:59 PM

I was going to suggest it still might be T-stops and they all had the same offset from standard but the orange mark seems to be on the wrong side of the white witness mark in that case ...

I'm shooting a commercial tomorrow doing some macro bolex stuff and the director happens to own the lens you have there ... I'll ask him ;)
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#6 Dom Jaeger

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Posted 23 January 2011 - 10:26 PM

The red mark would be the T-stop, as Chris said.

It's on the correct side - a little over a third of a stop higher, meaning a geometric aperture of f/2 say, is around T2 and a third for exposure purposes.

The manual is only one page (reproduced in 4 languages), and not much help really. Most of it is explaining the Aspheron accessory use.
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#7 Chris Millar

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Posted 23 January 2011 - 11:40 PM

It's on the correct side - a little over a third of a stop higher, meaning a geometric aperture of f/2 say, is around T2 and a third for exposure purposes.

I'm having a nightmare lately with things like this - got basic focal length/DOF theory all wrong the other day too - yes it is on the correct side.

I second guessed myself this morning and got all in a twist ...

Heh, got a proper shoot tomorrow also - just you wait until I mess that up !

Edited by Chris Millar, 23 January 2011 - 11:41 PM.

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#8 Robert Lewis

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Posted 24 January 2011 - 04:16 AM

Thanks Chaps.

As I see it, T-stops are not marked on the aperture ring. Instead, what is shown is a reference point on the barrel which indicates at all times the difference between any selected F-stop and the "related" T-stop. That being the case, and since I work in F-stops, I can ignore the mark.

I like it when an "issue" turns into a "no issue".
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#9 Chris Millar

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Posted 24 January 2011 - 05:03 AM

Thanks Chaps.

As I see it, T-stops are not marked on the aperture ring. Instead, what is shown is a reference point on the barrel which indicates at all times the difference between any selected F-stop and the "related" T-stop. That being the case, and since I work in F-stops, I can ignore the mark.

I like it when an "issue" turns into a "no issue".

Unless you're exclusively dealing with specific DOF/focus for technical reasons (and dealing with exposure in other ways) why 'work in f stops' when T stops are given ? Sure it aint much of a difference, but you may as well nail it if you can yeh ?
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#10 Robert Lewis

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Posted 24 January 2011 - 08:58 AM

Unless you're exclusively dealing with specific DOF/focus for technical reasons (and dealing with exposure in other ways) why 'work in f stops' when T stops are given ? Sure it aint much of a difference, but you may as well nail it if you can yeh ?


I accept what you say Chris. It is just that the camera I use with the lens in question has a behind the lens exposure meter (Bolex EL), and my other lens is a Kern Vario-Switar POE (which I use on my Bolex SBM) has a built in exposure meter. Generally therefore, in my particular situation, as I read things, both set-ups take light loss in account.

That having been said, I appreciate your help and now realise that on those occasions I use a hand held exposure meter, the light loss needs to be taken into account and using the T-stop scale in those cases where the lens is marked with it is the appropriate way to do so.

Many thanks.
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