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Adding a video tap


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#1 Nate Yolles

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Posted 20 July 2005 - 06:34 PM

The idea is to put a miniDV camera on my Cameflex CM3 in order to get a video tap and onboard monitor.

The current method that I'm pursuing is replacing a prism with a two-way mirror in order to split the light. It seems to be working so far except for one thing, focus. If I focus on an object, then pull the prism and insert the two-way mirror, I can't seem to get the picture back in focus. I adjust the mirror in, out, check both sides and it's still soft. Just to clarify, it's affecting the focus to the viewfinder, not to the film plane.

Does anyone have any ideas? I hope you enjoy my picture at the least.

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#2 Luke Prendergast

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Posted 20 July 2005 - 08:57 PM

Through the prism is a longer path than off a mirror's surface - a prism refracts rather than reflects. I suspect this is where the issue is. Can you put the mirror in the path of the vewfinder image rather than replacing the prism?
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#3 Rob van Gelder

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Posted 20 July 2005 - 11:12 PM

Yes, your picture of the prism and the lightpath is incorrect. Light bounces 2 times inside the prism and so the path is longer.
That means that if you replace the prism for a mirror, you should take the eyepiece lens further away from it to get focus, but this might introduce other things like vignetting.

The best way is to get a prism which has on one side a 50% reflective layer and the videocamera could look through that......

Otherwise, go for full 100% video assist and operate on a LCDscreen and trust your focus puller.... :)
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#4 Nate Yolles

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Posted 21 July 2005 - 09:46 AM

Rob, you are correct, my pictured prism was reversed. I've updated my "diagram," however, I fail to see how the light bounces twice in each prism, I'd appreciate an explanation of how that works. In experimentation, it seems that I need to get the viewfinder closer to the mirror, however, it's adjusted as far as it can go in that direction already.

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#5 albussi

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Posted 26 October 2005 - 01:07 PM

ABOUT THE ECLAIR CAMEFLEX CM3... // (ARRI 2C)

This seems like a wonderfull camera. I was thinking of buying an Arri 2C then discovered this camera.

Even though I have never seen the camera I seems to have a lot of ADVANTAGES:

*Variable Shutter on most models? (10-200 degree or 15 -200 ??)
*Possible PL mount upgrade
*Apparently the mechanics of this Camera are much more durable,sofisticated and less prompt to have problems with it than the Arri 2b or 2c
*Less expensive than Arri 2c
* Some Models will shoot 16mm AS WELL! but someone told me It's really made to shoot with 35mm and shooting with 16MM could be risky (comments on this???)
* possible S35 and S16 modifications

But it also seems to have disadvantages:
* NO VIDEO ASSIST POSSIBLE
DOES ANYBODY KNOW IF IT IS EASY TO RIG SOME SORT OF VIDEO ASSIST WITH LCD SCREEN THAT CAN BE QUICKLY REMOVED SO YOU CAN ALTERNATE QUICKLY FROM OPERATING WITH THE LCD TO THE EYEPIECE ????

* Not a lot of people know about the cameflex CM3 so it seems it would be risky to buy one because it would be hard to find someone for maintenance / repairs and PARTS..

ANY THOUGHTS OR LINKS ON THE CAMEFLEX CM3 WILL BE VERY MUCH APPRECIATED!
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#6 Chris Keth

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Posted 27 October 2005 - 09:00 PM

I drew a very fast illustration (literally about 20 seconds, so excuse the shotty quality and inaccuracy of the reflection and refraction angles ;) ) of how the prism bounces light. It uses internal reflections to bounce light, so if it's built like my picture, the light would travel a longer path, as well a possibly being altered further by the prism's surfaces.

Edited by Christopher D. Keth, 27 October 2005 - 09:06 PM.

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#7 Glenn Hanns

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Posted 30 October 2005 - 07:13 PM

I drew a very fast illustration (literally about 20 seconds, so excuse the shotty quality and inaccuracy of the reflection and refraction angles ;) ) of how the prism bounces light. It uses internal reflections to bounce light, so if it's built like my picture, the light would travel a longer path, as well a possibly being altered further by the prism's surfaces.



I thought a prism worked like this.

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#8 Luke Prendergast

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Posted 30 October 2005 - 08:07 PM

Yeah CK your pic is upside down.
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#9 Tony Rudd

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Posted 22 November 2005 - 08:23 AM

if i started a camflex group on yahoo for those having or wanting a cameflex, etc, would people join?
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#10 david west

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Posted 22 November 2005 - 11:08 AM

I thought a prism worked like this.



i think it does.... but if you are looking at a subject 10 feet away, doesnt it now look 20feet away after going thru the prism just as if you were experiencing the same illusion by looking into a mirror??
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#11 Rob van Gelder

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Posted 06 December 2005 - 10:00 PM

Reading back my reply I don´t know what i was thinking.....

exchanging a mirror for a prism does basically the same but it there are some issues, like the refraction index of the glass and such, but it has been so long ago that I learned about this....

But you can find yourself a 50% transparent silvered mirror and replace the original with that. You need to make a construction that keeps the light out, also the picture is reversed because it is not mirrorred by the mirror (it goes straight through). Some tiny CCD camera´s have a switch to reverse scan.
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#12 Paul Bruening

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Posted 08 December 2005 - 06:16 AM

Hey guys,

What about mounting the DV cam at the eyepeice? I'm considering this for an XL2 on my Arri IIb. I'll have to see what the eyepeice optics project on a white card in a dark room. If it will render an image 1/3", it may be do-able.
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