How do you calculate FWHM of the primary beam of the telescope from wavelength and dish size?
Ian S asked:
How do you calculate FWHM of the primary beam of the telescope from wavelength and dish size?
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How do you calculate FWHM of the primary beam of the telescope from wavelength and dish size?
I assume there is some simple formula, and it goes something like Field of View ~= Lamda/Dish Diameter.
July 18th, 2010 at 2:45 pm
Resolution angle
Theta = 1.22 Lamda over D
Lamda = wavelength
D = diameter
Use the same units for Lamda and for D
For very small angles…Theta = sin Theta…see trig books
Read down for variants of the formula . . . . .
The usable field of view varies with the quality and size of the collecting surface and for very large telescopes is only a few minutes of arc.
For visual telescopes the Dawes Limit is 4.56″/D in inches = 114″/D mm
Where ” = seconds of arc.
A mirror or lens 4.56 inches in diameter resolves 1″
That is for a specific set of criteria…two close 2nd magnitude stars in a dark sky background with good seeing. jonal
July 21st, 2010 at 6:24 pm
It’s not “field of view” it’s “full-width at half maximum” beam size.
The field of view is set by aberrations and field curvature. c