Ok John. But would you agree that same spherical figure, produces a different wave front error in a faster system.
Or does it produce it produce the same wave front error?
Spherical aberration is produced I believe because the image plain itself is flat, hence distance from the edge of the mirror is shorter that that from the center of the mirror. If the image plain itself was a sphere, then there would be no error, no matter how fast the optics.
Again, does the same turned edge produce produce a different wave front error in a faster system or the same wave front error?
Quote:
Originally Posted by ausastronomer
Wulfgar,
I think you are confusing the terms "spherical mirror" and "spherical aberration".
Here is a 2006 thread which ran on Cloudy Nights which explains the Rayleigh and other criteria for establishing at which aperture and F-Ratio a mirror needs to be parabolised.
In simple terms as the aperture increases the F ratio at which the mirror needs to be parabolised increases.
A 6"/F5 spherical mirror would be useless for anything except low power widefield views. A 6" spherical mirror needs to be about F12 to be diffraction limited or better.
Cheers,
John B |