Finding focus distance

[Ihrke052]

Sorry if this has been answered before but I have an older focus assembly and was just wondering if anyone has any good solutions to finding the focus point? Can you simply measure the diameter of the lens or is it more complex than that? I've run lights and laser pointers through it but havnt gotten a real fine point.

Thanks!

[Guldberg]

Trial and error.

Put a piece of cardboard or wood on the bed with a pencil or something similar under one end. Fire the laser for a similar time over the length of th paper. As the distance from the lens to the object changes the dot size changes. When you find the smallest dot size, measure the length from the object to your reference point and make a focus block this length. Usually you want the focus block a fraction smaller (0,5 mm) than what you measure.

For a rough start, its probably somewhere between 2-4" from the mirror to the object.

[Meshal]

So helpful , thanks