Critical Gate Focuser
Bolex Product Code :- CADRO & CADIL
The Critical Gate Focusser also gets named as the Prismatic Focusser or simply the Gate Focusing Attachment. All three names however refer to the same device which consists of a prism and a magnifying lens. After opening the film chamber door it is inserted into the gate of the camera in place of the film pressure pad which is removed.
When attached it points sideways out of the camera body and enables an operator to view the subject to be filmed directly through the actual taking lens so therefore offers full reflex viewing. However you can't actually film anything while it is in place! You use it to determine your focus then you remove it, replace the film pressure pad and load the camera with film to take your shot.
The Critical Gate Focusing attachment is intended to be used before the camera is loaded. If you require to use it when a partially exposed film is in the camera you must first backwind the film using the hand crank and remove the spool. Some adjustment for individual eyesight can be obtained by the experimental tweaking of the packing ring below the plastic eyepiece.
This Prismatic focusser allows great accuracy when focusing and framing a subject at close range when using a Non Reflex Bolex camera, where the closer your subject gets to the camera the bigger the parallax error between what the camera sees and what your viewfinder sees.
The Critical Gate Focusser can be used on all Bolex H16 Cameras. However this device is superfluous when you have a Reflex Camera as you have full reflex viewing through the taking lens all the time. The Image that it produces when viewed will appear upside down which makes it quiet uneasesy to use. Although it can be usefull to own if you own a H16 Reflex camera for other reasons explained below.
The Bolex Rackover Device replaced this item for cameras which have the Critical Focusing Screen installed. Older cameras without it have no choice but to use this device, the only other alternative is to get a C mount lens which has its own reflex viewfinder built in.
You would never really use this device with a camera now doing multiple setups as the process of opening camera door, removing pressure pad, inserting device, focussing lens / framing shot using it, removing device, loading film / spools, closing camera door taking a shot then for next setup rewinding the unexposed film before opening camera door removing the spools and starting all over again is just too time consuming. It was only ever intended for critically setting up the camera say on a titling bench or animation stand something that needs to be done and checked occasionally for critically accurate work where the camera was going to be locked tightly in position for some time.
The only use this device serves now is either to perfectly align a Bolex H16 cameras used as the main component of a JK or other manufacturers optical printer, detecting where optics faults lie in a camera by means of using the device to lay blame with either the Viewfinder or Prism optics. Or fully checking what exactly the film that is exposed sees that the slightly cropped viewfinder image may not show.
To tell the two apart
There are two versions of this device "CADRO" the earlier version has a plastic eye cup with more shade for the operator to see what he/she is framing whereas the later version "CADIL" has a metal eye piece and no shading.
Left later version "CADIL" of the critical gate focusser in box. Bottom Earlier version "CADRO" of the critical gate focusser in box.
Instructions for use
In order to use the device correctly the camera should be mounted somewhere it can be locked in position. The best idea being a tripod or titling bench so that once it is correctly set up and the lens focused using the device it cannot be knocked. The basic procedure is:-
1 Open the film chamber door, remove the pressure pad from the gate by lifting the pin from one end and removing the screw from the other and then replace the pressure pad with the gate focusing attachment.
2 Disengage the camera motor by placing the clutch lever on to the "O" position. Push the continuous release control on to position "M" and open the shutter by using the shutter release knob.
3 Adjust the camera for the right field of view and focus the lens with your eye to the plastic eyepiece of the gate focusing attachment.
4 Lock the camera in position and remove the Critical Gate Focusing Attachment. Replace the pressure pad and load the camera with film.