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Alternative Imaging Methods
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Old October 12th, 2006, 09:46 AM   #1
Inner Circle
Join Date: Dec 2003
Posts: 4,439
Letus mods.

In the course of designing an advanced mount for the Letus35 to provide a facility for precise backfocus for zoom lenses, Fujinon ENG camera lens style (more or less) and maybe a little ability for macro, I have mined around inside and made some observations which for people who might attempt to make innovation, I feel I should pass on as they are cautionary in nature.

If anyone is contemplating cutting a 0.7mm per mm or 1.2mm per mm internal thread inside the lens mount hole of their Letus to securely hold a deeper adjustable cylindrical base for a lens mount, please DO NOT, unless you are very seriously skilled and know exactly what you are doing.

(If you are going to go ahead and do a silly thing regardless, do not cut a 1.2mm per mm thread to its full depth in any event as it is not being loaded in tension in this application and does not need a lot of bite. The matching thread on the cylinder and flange needs to be likewise under-dimension but cut to full depth.).

In keeping with sound engineering principles relating to dimensional stability of plastics or cast metals, the front end of the Letus which supports the working guts of the machine as well as the lens mount, has reliefs or holes between the lens mount hole and the outer rim which face inwards and cannot be seen. This part of the appliance is machined precisely and should be respected.

There is only about 1mm of wall thickness there which does not give you much leeway to make a mistake and consequently weaken the structure.

By the way, I have not ruined a Letus35. I have retreated gracefully before going that far and am doing some more design first.
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