Universal Panoramic Camera Viewfinder

STOP DO NOT USE, REVISION IN PROGRESS TO CORRECT AN ERROR

Universal Panorama Camera Viewfinder is a viewfinder system suitable for wide to normal lenses on panoramic cameras. Currently the development is geared towards 6x17 panorama cameras and cameras with multiple 6x framing options.

I abandoned the telephoto version of the finder due to a fatal design error.

Development Background

I was designing a panoramic point and shoot camera which also converts to a roll film back for use on my panoramic field camera. So I needed a viewfinder system for use in point and shoot mode.

The 120 roll film back can also use film plane masks to allow me to shoot in 6x17, 6x14, 6x12 and 6x9 formats. That meant I'd need flexibility in the design to be able to use various formats and lenses, and I'd need a large objective lens not only for a bright viewfinder but also to have a wide enough element to accommodate a range of framing masks.

This entry has now been updated to Version 2 of this viewfinder with a better method for mounting the rear lens element, and now requires users to have a calibrated 3d printer.

I've designed two different methods of mounting to a camera, a traditional cold foot mount that requires a 1/4-20 heat stake threaded insert to attach a cold shoe adapter and the purchase of a cold shoe adapter.

My preference is the wide foot mount for 3D printed cameras which uses M4 mounting screws set 72mm apart. This version requires two M4 heat staked inserts in the camera body and a M2.5 insert and cap screw in the main housing to mount the foot to the housing.

The build requires the purchase of two lens elements. The lens sets are readily available and will cost about $70USD for uncoated optics, and slightly more for magnesium fluoride coated lenses. The quality is worth the expense. I'm using the following lenses from Edmund Optics:

45-037
32-862

The housing accepts swappable 50mm diameter frame masks to represent the angle of view for a number of lenses commonly used with 612 and 617 cameras so the user only needs a single viewfinder but gets better benefit from having multiple viewfinders.

I will be uploading additional sets for wide angle lenses in each negative format. 

Tip:
Print the frame mask sets in different colours for ease of identification.

How I Designed This

Viewfinder Design Specifications

The Front Element is a plano-concave lens - diameter 50mm, lens focal length minus 100

The Rear Element is a plano convex lens – diameter 25mm, lens focal length 125

The focal distance between lens elements is 25mm, and the viewfinder has a magnification of 0.8

The focal planes of each element are located within the lens body, so when designing the housings the back focal distances from the rear of the lens element is used to calculate distances. In this design the rear element faces are 19.4mm apart.

The formulae for calculating the mask opening dimensions for various negative and lens combinations is:

K = (j*m*d)/f

K = width or height in mm

j = negative width or height in mm

m = magnification (either 0.8 for wide or 1.33 for tele)

d = the viewfinder focal distance which for both option is 25mm

f = the chosen lens focal length. 

Example for 617 wide angle finder:

k = (170mm x 0.8 x 25) / 150mm

k = 3400 / 150

k = 22.666 mm wide

k = (60mm x 0.8 x 25) / 150mm

k = 1200 / 150

k = 8 mm high

The 150mm lens mask is 50mm diameter x 1mm thick with a 22.7mm wide x 8mm high aperture.