Sinar Compatible Front Standard on Arca Swiss 5x7

[Bernice Loui]

Needing a lower weight monorail 5x7 the choice was made to modify an Arca Swiss monorail to accept Sinar lens boards and Sinar shutter. This is a must as the collection of lenses are on Sinar boards and most are in barrel.

This is the Arca Swiss front standard rails with associated parts to be made. The frame is from a Horseman L series monorail. This frame already has three holes drilled into the side. Two are 0.168" ID, the center hole (on lens center line) is threaded M5 x 0.80 pitch which is the same as Arca Swiss.

The plastic blocks use are made of HDPE (High-density polyethylene) which is tough, durable and agreeable to being cut on machine tools with reasonable stability.

Here are the raw parts to be worked on:



Arca Swiss front standard rails have a 11mm radii on the post. Using a 22mm solid carbide end in the milling machine, a single 11mm radii grove was cut into the HDPE block. Once this was done, the overall thickness of the bock was cut down using a flycutter in the mill to trim the HDPE blocks to match the Horseman L frame to Arca Swiss rails.



Mounting holes were drilled and tapped to connect the HDPE blocks to Horseman L frame allowing the assembly to fit into the Arca Swiss rails.



There is a special M5 threaded stud made on the lathe that is not shown. This connects the M5 threaded center hole on the Horseman L frame to the Arca Swiss thumb nuts (M5 threaded, same as Horseman) used for adjusting front standard rise.



What remains is to order up a special bellows with dimensions that fit the Arca Swiss rear bellows frame with Sinar front bellows frame.


Part two, on camera fit test.



Bernice

[Bernice Loui]

The modified Arca Swiss front frame put back on the Arca Swiss blocks to test fitment and sort out other problems.

The Horseman L frame ended up with the lock bars side ways or rotated 90 degrees from there they normally sit. For lenses in shutter, this proved to be not much of a problem. Overall rise adjustment of the modified front standard turn out to be pretty similar to as delivered Arca Swiss.

This is what the modified standard looks like with a Rodenstock 115mm f6.8 Grandagon.



With a 12" f4.5 Kodak Ektar in #5 Ilex shutter. About a big a shutter commonly used on lenses. No problems.


Test fitting the Horseman L frame with a Sinar shutter proved to have interference with the fold over lens board retainer bar. Flattening out the bend cleared the Sinar shutter. Note the Sinar shutter sits 90 degrees rotated from it's normal position. This is due to the mounting hole location on the Horseman L frame. A new set of holes could have been drilled and tapped into the Horseman L frame that would have oriented the Sinar shutter into it's normal position, placing the Sinar shutter in the position orients the shutter release downward allowing a straight cable release to be made and used with the Sinar shutter (future project). There is no retainer slot on the side of the Sinar Shutter which is why it cannot be rotated and locked into the front frame.

Front view with Sinar Shutter and 10-3/4" Dagor in barrel.



Rear view with Sinar shutter and 10-3/4" Dagor in barrel.



Last up is to have a bellows made to fit Arca Swiss rear, Sinar front. Then we run test with film on this hybrid camera.

Bernice