Re: [ATM] Focal Length Accuracy

[Mike Lockwood <melockwo@uiuc.edu>]

Anthony,

Anthony Anconetani wrote:
> You have asked why I want the focal length to be as close to 36 inches
> as possible.
> 
> No particular reason really. Just practice. 8-)

You are getting lots of measurement experience right now, and you will 
start to find out what are more dependable and less dependable methods 
for focal length measurement as you progress through your work on this 
mirror.

My advice is to keep good notes to document your measurements, and 
then after you polish for 0.5-1 hr you can do a quick Foucault test do 
determine the true ROC.  Then you will be able to see quite clearly 
what method worked best.

My personal preference is a very precise, carefully used spherometer, 
but that is overkill for a mirror that does not require precise 
control of the radius of curvature.

	Mike Lockwood

>>-----Original Message-----
>>From: atm-bounces@atmlist.net 
>>[mailto:atm-bounces@atmlist.net] On Behalf Of Jim Burrows
>>Why do you have to have the "focal length as close to 36" as 
>>possible"?  Has the OTA already been built?  Otherwise, 
>>there's no requirement on the focal length - long, look at 
>>planets; short, look at dim fuzzies.


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