Re: [ATM] Re: ATM Digest, Vol 17, Issue 10

["David Harbour" <scarab2@cox.net>]

Arjan-

Don't be embarrassed on my part; I know you are a good mathematician (better
than me!)  Me? I just hire Professor Schwartz when I need a computation. My
brain is too worn out anymore to trust with this kind of stuff.

Anyone could tell you just plugged in a wrong value somewhere; I can't keep
necessary and useful formulae in my head (like I am sure that you can) but I
seem to understand things better when I can keep "ball park figures" for
orders of magnitude in my head.

You would have found your own error quickly anyway- I am certain of it, as
you double checked it again and again, as any good and meticulous
mathematician, such as yourself, would have.

Well done, Arjan-

Davey


----- Original Message ----- 
From: "Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>
To: <atm@atmlist.net>
Sent: Thursday, May 12, 2005 2:34 PM
Subject: [ATM] Re: ATM Digest, Vol 17, Issue 10


> Yeah, formulae were right, but I filled in the wrong x value in the sphere
> one.
> I said it could be wrong, didn't I?
> It's just like my daughter, she does understand math but screws up tapping
> it in on the calculator.
>
> Cheers,
> Arjan
>
>
> > This sounds reasonable to me- it is in the right "order of magnitude"-
> Arjan
> > must have just made a mistake somewhere with some term. Anyone can do
that
> > (I am so stupid with math that no one would want to trust me with
> > calculations for a trip to the moon- we'd smash on the rocks).-
>
> > Arjan wrote:
> > > > Equivalent formulae (equal paraxial ROC = R) would be:
> > > > sphere:     x^2 + (y-R)^2 = R^2, or y = R - sqrt(R^2 - x^2)
> > > > parabola:  y = (x^2)/2R
> > > >
> > > > so for x = radius = 5.5m and R = 33, the sag would be
> > > > sphere:    929.8 mm
> > > > parabola: 458.3 mm
> > > >
> > > > This deduction may, of course, be wrong.
> ...
> > > .sagitta (Y, r, -1)
> > [1] 458.3333
> >
> > ... and the sphere:
> >
> > > .sagitta (Y, r, 0)
> > [1] 461.5612
> >
> > So, the difference is 3.228 mm
>
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