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Teleconverters to use 16mm zooms with 35mm cameras?


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#1 Zachary Vex

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Posted 03 March 2007 - 05:10 PM

Is it possible to get full 35mm coverage using a 2X telezoom converter on a 12-240mm Angenieux zoom (presumably designed for 16mm coverage)? I realize the disadvantage is the loss of light... how do I calculate coverage using a teleconverter and how do I calculate the number of stops lost, based on the X2 (or X1.4, X1.6) factor found on teleconverters?
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#2 chuck colburn

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Posted 03 March 2007 - 06:15 PM

Converters are optical attachments that mount on the front of a given lens, they do not increase the circle of coverage of a lens. Extenders mount between the lens and the camera and with the proper configuration can enlarge the image enough to cover 35. We use to do a lot of them back in the sixties and seventies. You need an optical bench to hold the lens, extender optics and a ground glass to figure out the physical spacing of the componets and the design and fabricate a housing to tie it all togeather to the lens and what ever type of lens mount it is you are going to use.
2x extender = appx. 2 stop loss
1.4 or 1.6 around 1 stop loss
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#3 chuck colburn

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Posted 03 March 2007 - 07:42 PM

Is it possible to get full 35mm coverage using a 2X telezoom converter on a 12-240mm Angenieux zoom (presumably designed for 16mm coverage)? I realize the disadvantage is the loss of light... how do I calculate coverage using a teleconverter and how do I calculate the number of stops lost, based on the X2 (or X1.4, X1.6) factor found on teleconverters?


That 12-240 will end up being a bit slow, (around T-9). Mayby this lens might serve you better.

http://cgi.ebay.com/...VQQcmdZViewItem
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#4 Zachary Vex

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Posted 04 March 2007 - 03:44 PM

Converters are optical attachments that mount on the front of a given lens, they do not increase the circle of coverage of a lens. Extenders mount between the lens and the camera and with the proper configuration can enlarge the image enough to cover 35. We use to do a lot of them back in the sixties and seventies. You need an optical bench to hold the lens, extender optics and a ground glass to figure out the physical spacing of the componets and the design and fabricate a housing to tie it all togeather to the lens and what ever type of lens mount it is you are going to use.
2x extender = appx. 2 stop loss
1.4 or 1.6 around 1 stop loss


Sorry if I created confusion by using the word "converter." The piece I was describing goes between the lens and the camera, and says "Birns and Sawyer X2 TeleZoom Angenieux-ECLAIR." According to this article it seems one can use tele-extenders to cover 65mm with 35mm lenses:

http://www.cinematog...es_For_65mm.htm

I assume that this "TeleZoom" is actually a tele-extender... please tell me if this is not so. What I'm looking for is the formula for calculating coverage and aperture change based on X1.4, X1.6, and X2. Strangely, if you look up "teleconverter" on google you'll find lots of articles about what seem to be tele-extenders made for 35mm still cameras. In this instance, is "teleconverter" the same as "tele-extender?"

That 12-240 will end up being a bit slow, (around T-9). Mayby this lens might serve you better.

http://cgi.ebay.com/...VQQcmdZViewItem


Wow, that is a monster, and a c-mount to boot! Great for super 16mm coverage, but it wouldn't work for me... I need 35mm coverage (ultimately), a 20X zoom, and Cameflex mount. The 12-240 starts at 3.5 so it should end up 5.6 plus a half when using a X2 tele-extender, right? And if i could find a X1.4 tele-extender presumably I'd save yet another stop.
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#5 chuck colburn

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Posted 04 March 2007 - 04:57 PM

Hello Zachary,

An extender that is made to work with a given lens mount to a given camera (Nikon to Nikon etc.) is not being used to increase the circle of coverage but is being used to increase the focal length of the taking lens by a given factor (sorry about all the givens!) such as 2x, 1.6x etc. So an Angenieux 25-250 with their 1.6x extender mounted to it becomes a 40-400mm lens but still only covers the 35mm format. What was happening when we took the optics of still or cine extender to blow the image up from 16mm to 35mm coverage was that we were changing the physical spacing of the extender from the taking lens untill the magnification factor was enough to cover the larger film format. This is why they required a new housing to be fabricated to hold the extender optical group. This also caused the "T" stop to be appx. T-9 on the 12-240/24-480 conversion. The lower power extenders (1.4x and 1.6x) required such large spacings that we ran into curveture of field problems. This is why I said we used an optical bench so that we could see the circle coverage and keep it as small as possible for the required aspect ratio (full, 1:85, 1:66 etc.).
Just as a sidebar, when we were fitting lenses to the Showscan CP-65mm camera, the commercial extender optics I tried with the Cooke 20-60 and 25-250 zooms were not up to the standards we required. And these were the best of the best ( Zeiss Mutars etc.). We ended up having a custom unit designed for are use.

Chuck
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#6 Zachary Vex

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Posted 07 March 2007 - 05:10 AM

After careful open-air measurement I've determined that my X2 TeleZoom attachment works exactly as a tele-extender, and increases coverage by exactly double.
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#7 John Jaquish

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Posted 08 January 2014 - 07:46 PM

This is an old thread, but I'm curious about this -- what I don't understand is that many of the older extenders seem to have a "universal mount" scheme on one end (I'm guessing because they're designed for 35mm zooms).  Are there Arri bayonet-mount extenders to attach to the 16mm zooms? Or, do the older 16mm Angenieux zooms in fact have a universal mount? Or, in the cases this is done, are the mounts mechanically removed from the 16mm zooms? I've seen references to people doing this somewhat simply, seemingly without an overhaul of the lens.


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#8 Dom Jaeger

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Posted 09 January 2014 - 01:16 AM

There are Universal mount extenders for older 35mm pro zooms like Angenieux 25-250s (as far as I know Universal mount was only 35mm), but there are also extenders made for other 35mm and 16mm lenses. The rental house I work for has 16mm versions in PL and Bayo mount by Optex and Zeiss, and 35mm ones in PL by Optex and Century. The main issue is how far the optics protrude in both extender and lens, many combinations simply don't work because the optics hit before the lens is seated. The older ones in particular were designed primarily to be used with telephoto lenses which don't protrude behind their mounts. The Zeiss Mutar was designed for the Zeiss 10-100 and 11-110 so has a bit more room, but it still won't fit most Angenieux 16mm zooms. The Optex "Colcine Super 16" 2x extender has the most room of all our extenders.

 

Some 16mm extenders:

 

cslb.jpg
 
 
and some for 35mm:

kuo9.jpg

 

FWIW, I haven't found any 16mm zoom with 2x extender combination that properly covers a S35 frame, including the Angenieux 12-240, though I suppose it's possible if you custom fabricated something on an optical bench.  But the enlarged image circle is often quite degraded in quality at the edges anyway.


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#9 Jean-Louis Seguin

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Posted 09 January 2014 - 09:02 AM

See: http://www.cinematog...?showtopic=8187

 

Jean-Louis


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#10 John Jaquish

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Posted 09 January 2014 - 09:39 AM

Thanks Dom and Jean-Louis both. Dom, those pictures are very much helpful. I was trying to find out all the extenders that were available. It seems like this is very much a "try-and-see" notion, but not to expect much.


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