RE: ATM what did I do wrong????

["Jerry" <wa4guu@verizon.net>]

Well, If you are using a flashlight at the center of curve to focus on a
paper at the center of curve and you are 98" away from the mirror with both
the infinty focus will be 49". 
Hope I understood you correctly. If so you are only 1" off from your desired
focal length.

Jerry 



-----Original Message-----
From: owner-atm@shore.net [mailto:owner-atm@shore.net] On Behalf Of c f
Sent: Sunday, January 18, 2004 9:38 PM
To: atm@shore.net
Subject: ATM what did I do wrong????


Hello to all,
I am working my first mirror, a 6" f8,  sounds simple enough,  got through 
the 80, measured and I was right on, .0468 for a depth in the center.  I did

all my grinding TOT.  I then went to 120, did a focal check, used the sun, 
bingo, + - 48 ".   On to 220, 30 Micron, 15 micron. all with TOT.  
everything looks awsome, did a sharpie on the 15 micron, and the grid came 
out in 2 wets, and it came out evenly,  checked under a magnifying glass, 
not a pit in site that isnt of the same size as the others. that tells me 
good things.

But............ I wet the mirror, put up a peice of paper, flashlight, and 
took another focal reading. and SOB, it is wayyyyyy off.  in the other 
direction to boot!!!!!!!!!!!!!!!!!!!  instead of a 48" +- focal,  I have a 
freeking 98" focal!!!!!!,  I went from .04687 to .03125!!!!!!!!  this was 
done with the TOT, using a "W" stroke, 1" over hang during the stroke.  Now 
with all the reading I have been doing, it says that if you keep the TOT, 
then you will dig a deeper hole so it is suggested to swap them.  well, I 
decieded to not do this, and keep the TOT to maybe bring it closer to a F/7.

can anybody tell me what I did wrong??  because at this time, it looks like 
I am heading back to 120 maybe 220 to get this back to the correct focal.  
but it would be nice to know what I did so I dont repeat this again.

thanks to all for helping out the newbie

Charles in wilmington ma

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