ATM TERMINOLOGY - F

 

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f:

Focal length.

 

Fast scope:

A scope with a focal ratio of f/4.5 or less. Note: the 4.5 is an arbitrary definition, but seems to be generally accepted.

 

fl:

Focal length.

 

Figuring:

The last process in making a mirror. This process changes the spherical shape of the mirror into a paraboloidal. This process may be omitted when the difference between the sphere and the paraboloid is less than 1/8 wavelength. (Note : strictly speaking this is not the last process, but most ATMers don't silverize/aluminize their mirrors themselves. So practically it is the last step.)

 

fp:

Focal plane (also focal point).

 

fr:

Focal ratio.

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