prismatic viewer/gate focuser for RX bolexes - any leads?

[Richard Tuohy]

Hi,

I'm keen to get one of the little Bolex gate focusing pisms - often called the critical gate focuser or prismatic focuser.  Does anyone happen to have one they don't need or have leads on one?

many thanks

richard

 

[Simon Wyss]

I strongly discourage to use those. You risk scratching the polished film rails with the rough glass prism. Glass is much harder than steel and the aperture plate is made from structural steel, nothing of raised tensile strength or hardened.

[Richard Tuohy]

7 hours ago, Simon Wyss said:

I strongly discourage to use those. You risk scratching the polished film rails with the rough glass prism. Glass is much harder than steel and the aperture plate is made from structural steel, nothing of raised tensile strength or hardened.

Interesting point Simon!  
But it is hard to think of a better way to check critical framing.  I use these viewers in 'film out' setups (ie video back to film).
Any suggestions appreciated!

[Simon Wyss]

A number of manufacturers made cameras sporting a critical focuser in conjunction with a lens turret. Bell & Howell had begun the system in the early teens on the 2709 design camera and brought it back on the Eyemo 71-M/N/O/P/Q as well as the Filmo 70-D/H/K/S series. The three-port turret Filmo Eights have it also. Then you have the Victor models 4 and 5 that give an enlarged view of the image of a lens behind a port away from the taking position and Paillard where a front frosted prism is accessible from H-16, nr. 7531 on. The ETM-P 16 and 9.5 afford a ground glass in the same plane as the film is, magnified by an instantly retractable finder in a tube. Together with an adjusted rackover support (called focusing alignment gauge by B. & H.) you eliminate parallax precisely. An advantage of that system is that the camera can be loaded with film, an other is that the ground glass or prism receives 100 percent of the light coming from the lens to be set. More than that, an assistant can focus a different lens while you shoot and follow through a side finder on the opposite side of the camera. When needed, you can switch lenses in an instant. I never get tired of explaining the rackover method. Mitchell used it, Fox, Keystone, Sankyo, and more.

[Simon Wyss]

An alternative, it takes a little investment, is to have the front face of the prism polished. CADRO or CADIL is then used behind a piece of frosted leader in the gate.