Sunday, February 28, 2010

Stereo Realist Panoramic Conversion by Gene F Rhodes

 I remember this '625eq' camera while browsing the links in Robert Monaghan's site long time ago. Recently I rediscovered the same while I again started browsing  Robert's archived site. 

The camera was handmade by Gene F Rhodes well known for his  website Though the original website is now defunct, you can retrieve a good amount of information from the archived website available here.

This 35mm converted stereo camera is known as '625eq' because it offers the same aspect ratio what a 6x25 medium format panoramic could provide. The description as I copied exactly from his website is as follows: 
A hand built, fixed lens,  35 mm wide-angle / wide-image panoramic camera made from a damaged Stereo Realist camera body and a  47 mm  f8  view camera lens.  If this were a medium format camera it would be 6 x 25 cm. The Realist's frame and film advance gearing were rebuilt to accommodate a new enlarged 24 x 102 mm image frame.  Three scans are required to load each 102 mm negative into the computer. According to Ron Leven of Schneider Optical the 47 mm  f8 super angulon lens has an image circle of 113 mm at  f11, and a 40.5 mm  filter thread. After many light drop-off tests I find this lens to be unusable without some kind of center filtering, and B&H Photo accepted a  special order for a Heliopan center filter, but they never delivered. This project was my most interesting, but it is now terminated

 This is so far the most detailed description I found about  the panoramic conversion of a stereocamera:
Job 1--Film Advance:    In a Stereo Realist the film take-up spool pulls the film through the camera. The film drives a star wheel sprocket which is shaft connected to a slotted disk cam in the upper chamber.  A cam follower rides on the edge of the disk and is shaft linked to a spring coil brake around the shaft of the take-up spool. When the follower drops into the slot the brake is applied and the film stops. A reset pushbutton moves the cam follower out of the slot, releases the brake and allows the film to be advanced. For stereo format the star wheel makes one turn per exposure but in the new camera the star wheel makes 2.2 turns. The first job was to separate the star wheel and cam with gears to get the 2.2 :1 ratio. The star wheel bearing support was in the image area of the new camera and had to be removed and a new bracket had to be created to support the star wheel, gears and a new cam disk. This required the cam follower to be modified to align properly with the relocated cam. (The gears and bearings were scrounged from my junk box as was the items below.)

Job 2--Lens Mount:      I didn't want to do any unnecessary machining so I decided to use a screw thread focusing technique much like screwing a lid on a jar. In this case the jar is from a pressure transducer bought at an aircraft surplus store and a matching 55 mm threaded lid. The lens is mounted through the lid creating an assembly that is compact and easily removed. The jar was shortened and modified so the front cover could clamp it to the camera. The lens mount was something to be proud of until I discovered severe light leaks. Now it is light tight but kludged.

Job 3--Center Filter: The light drop off at the ends of my negatives is 2-3 stops, and none of my many hand made filters were usable.  I have been using Picture Publisher software to correct the light drop off by using a especially created filter mask. This was satisfactory for a time, but is not a permanent solution.  (See above photos for before/after comparison.)

Job 4--Focus Calibration:   1/8 turn = 20',   1/4 turn = 10',   1/2 turn = 7',   3/4 turn = 6',  1 turn = 5',    2 turns = 3',    4 turns = 2',   9 turns = 1'   and 12 turns = lens fall off.

Note:  The viewer lens is from a one shot Kodak pan camera, but it brackets the image and shows the horizon. When in doubt, I use the yellow bubble balance.

You can visit this page for the description.

The bottom  picture compares the film sizes obtainable by this camera with others.

I thank Mr. Rhodes very much for providing the picture and information on his great handmade panoramic camera.

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