Coulter mirror markings

I pulled the mirror from my dob to clean and noticed that the side of
it is marked with -4. Does anybody have an idea as to what this means?
The mirror is from an older red tube 10 inch.
Thanks
Roger

In article , rhinso19
@wideopenwest.com says...
I pulled the mirror from my dob to clean and noticed that the side of
it is marked with -4. Does anybody have an idea as to what this means?
The mirror is from an older red tube 10 inch.
Thanks
Roger


I was told (by J. Braginton, IIRC) that a similiar marking on an old
Coulter 10" mirror I had was a "comparator index", meaning (I
suppose) it shows the relative discrepancy between the target focal
length and the actual. That's why my first "f5.6" mirror had a -44 on
the side - It was actually an f4.5 mirror that was thought to be f5.6
and given a correspondly large error when checked against that scale.

At least that's what I gathered from the conversation I had.

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-- Len Philpot - --
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