Specification for Focus Adjustment, binds and squeaks

[RFrazier]

Working with a Specification on a new lens design. I am trying to find some industry specification that addresses the design requirement and/or tolerance of focus adjustment.

Example #1: Manual focus of 50mm lens, shall require no more than XX in-oz of torque to operate focus ring and no less than XX in-oz of torque.

Example #2: Manual focus of 50mm lens shall not bind or squeak... Anyone know of a reference that may cover binding and/or squeaking?

Example #3: Iris operation shall not bind or squeak... Anyone know of a reference that may cover binding and/or squeaking?

All of these examples have been observed. As I stated earlier, is there any industry specification for these types of issues? Only feedback I get is my 35mmSLR lens does not squeak, bind and moves rather freely!

Your consideration and feedback is appreciated.
Roger F.

 

[drawoh]

RFrazier,

I am not aware of a specification like this. When I design lens mounts, I ask the optical designer what they want. If they don't care about squeaking, I don't.

I have not had binding problems since I swore never again to use un-anodized aluminium to mount optical components. I understand that 300 series stainless steel binds, but I have no experience with it. I regard binding as unacceptable. If components that bind halfway assembled so that they have to be taken apart by a machine shop, make the optical designer happy, I can accomodate them.

The focusing torque depends on the application. If this is a one-time alignment by a scientist, you can make them use a tool. It will be harder for unauthorized people to mess it up, later. If the tiniest woman or child you can find is comforable focusing the thing, then the torques are low enough.

Commercial camera focusing mechanisms are really nifty, but they are mass produced, which means there is lots of opportunity to amortize design effort. I do not know how accurately camera lenses are centred. I don't think it matters to them, but it might matter to you. This tends to be critical with my applications. A series of threaded tubes with locking rings is often a good one-off design.

JHG