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Re: [ATM] convex secondary

Heck, I messed it up again. I went with an f/2 primary, while the one at 
hand is f/3. Here's an aplantic 400mm f/11.45 Loweday with an f/3 primary:

R1=-2400mm
K1=-1.0353
primary to secondary: -900mm
R2=-630mm
K2=-1.3632

On best curved surface (r=500mm) field is diffraction limited at 30mm 
off-axis (nearly 0.4 degrees). More than can be used. On flat surface, blur 
size 12mm off-axis is ~0.012mm - less than the Airy disc. The system is 
somewhat slower than f/9, but it is fairly compensated by
better field quality and lower undersampling.

Vlad


> An example of a system that could be made with your mirrors is this f/7.75 
> aplantic Loweday:
>
> R1=-1600mm
> K1=-1.0372
> distance to secondary: -600mm
> R2=-413.333mm
> K2=-1.2949



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