[ATM] How many zones

[toolontop at yahoo.com (Mark Cowan)]

Hi Jonathan:

4 would work but 5 is better, and Nils web-page
calculator recommends 4.6.  The number is a balancing
act between

a) Accuracy
b) Readability
c) Patience

C) will run out faster with too many, or too few.  Too
few will reduce accuracy, and if taken to extreme also
make it hard to pin down the zones crossing as you
start to see the "hump" on the portion of the curve. 
Too many will also reduce accuracy, as the zones
become too small and too similar on a slow mirror to
read easily. 

Remember all mirrors of the same f/number appear to
have the same size under the Foucault tester, so
distribute your zones accordingly. :)

Hope that helps a bit, and good luck!

Mark Cowan
Salem, Oregon

--- Jonathan Bishop <jonathan_bishop@sbcglobal.net>
wrote:
> Hi,
> 
> I am figuring an 8" f5 mirror. Can someone recommend
> the number of zones to measure? <snip> 
> Since I am new to this probably 4 zones is easier,
> but will it be sufficient?
> 

__________________________________
Do you Yahoo!?
Yahoo! Finance: Get your refund fast by filing online.
http://taxes.yahoo.com/filing.html