C

leading to the required form of the secondary as bs2 = -1+(r^) = -! + (! - Ra)3 , (3.331)

from (3.326) and (3.330). If Ra = 0.25, this gives bs2 = -0.578, a moderate elliptical form. For normal values of Ra, the value of r3 from (3.326) will require M3 to be placed behind the primary in order to provide a reasonable final image position. This implies a perforated primary, as proposed by Baker.

The "aspheric plate theory" of § 3.4 can be applied in exactly the same way as for the Paul system above to prove that field coma and astigmatism are zero, so that the Paul-Baker system gives

Schroeder [3.22(b)] comments on the first large practical realisation of such a Paul-Baker telescope as a transit instrument with a 1.8 m primary working at f/2.2 and an axial obstruction ratio Ra ~ 0.32. He states near-diffraction-limited imagery is given over a 1° field. As with all such three-

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment