ATM diagonal sizing an spiders

[Barger Kyle <kbarger@haverford.edu>]

I am just curious about calculating the size of the diagonal--Texerau 
recommends using 31 arc-minutes (the size of the moon) as an appropriate 
value for the size of the fully-illuminated field.  Is this still 
considered a good standard?

Second, that's mostly academic, it looks like I will be going with a 1" 
secondary for my 4.25" f/6.  But nobody seems to have secondary holders 
in that size. I called up University Optics to see if they had a smaller 
size than listed in their catalog.  The guy I talked to said they usually 
recommend a single-stalk mounting for 1" and smaller.  Any opinions?  I 
had hoped to go with a commercial adjustable holder to make fine-tuning 
the alignment easy.  In thinking about it, the single-stalk seems 
problematic in terms of keeping accurate collimation, and I know a lot of 
people complained about that on the Orion dobs before they changed them.