Re: [ATM] Focal Length Accuracy

[Mike Lockwood <melockwo@uiuc.edu>]

Dominic-Luc,

Dominic-Luc Webb wrote:
> I ended up using an "effective" ring
> diameter, calculating back from a couple of mirrors with "known"
> ROCs. This brings me back to our earlier discussions about the
> accuracy of a spherometer, now that I actually have one in my
> hands with a decent guage.

I calibrated my spherometer in the same manner, using several mirrors 
with known ROCs.

> How does one calibrate a spherometer such that you would
> put more weight on the readings from this than a Foucault or
> other optical test where you measure the point where light
> is actually focusing?

One generally doesn't weight mechanical measurements more than optical 
ones, because the optical method is obviously better.

The spherometer is simply a time-saving tool that allows one to 
quickly measure ROC and/or changes in ROC while the mirror doesn't 
readily reflect light, or to quickly measure the approximate ROC of a 
polished mirror when setting up a knife-edge test is inconvenient.

There was a thorough discussion of this topic recently on this list.

	Mike Lockwood


_______________________________________________
ATM mailing list http://www.atmlist.net/