[ATM] 1.25in Versus 2inch focuser.

["Marco" <marco.miglionico@btinternet.com>]

Which should I consider for the following scope:

20in F5 mirror. I ran SEC and consulted my local mirror
supplier and 83mm (3.27in) seems to be the best match
in both Kriege/Berry's book and in SEC.

However in Berry's book it is recommended that in a scope of this
size, parameters give a practical limt of around 0.5 degrees FOV.

Doing some calculation tells me that I only need a 1.25in focuser
as a 24mm panoptic will supply me with a field of around 39 arcmin
which is more than ample.

My question is, what advantage would I get from fitting a 2in focuser if
the 1.25inch eyepiece gives me my maximum practical field of view.?

For that matter, is there any point in fitting a 2in focuser to anything F5 
or faster?

any illuminating ideas?!!

Marco. 

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