Re: Need advice regarding Watson metallurgical microscope

Kevin Cunningham wrote:

<snip>

Chris, Thank goodness modern makers don't use draw tubes. Most
objectives had a tube length specification of 160 mm, there was some
slight variance in this but assume 160 mm. The draw tube was used to
change mag by a little bit. Changing the draw tube length also
eliminated any chance of parfocality. I'd set it at 160mm and forget
it. The objective should say whether its designed for a cover slip or
not. The markings on the objective should be:
type of objective, no marking = achromat Achromat
Power of objective/NA 40X 0.65
tube length/cover glass 160/0.17

This is what your 40X probably looks like.

A 50X metallurical objective looks like this:
Type Plan Achromat
Power / NA 50X 0.70
tube length/cover glass 210/-

Hope this helps!

Watson obviously didn't label their lenses in quite the fashion you describe. Here's what the first on I picked up says:

x10
Watson B7420
PARA 16 mm NA .28

I'll try it and see!

Best wishes,

Chris

.

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