ATM Re:Building a 3" diameter, 75mm eyepiece; Moon Viewing

[epabcc@epa.ericsson.se (Bratislav Curcic)]

> 75mm diameter, 250mm/or 400mm  focal length Plano-convex lens

Still too long ...

> The smaller of the two is only 1" diameter...too small??
> vignetting?

Well, there is more to a lens than its outside diameter, really.
But in any case, yes, 1" for an eye lens in a 75mm f.l. Kellner is
too small. It looks that you'll have to check somewhere else
(Melles Griot - but they aren't cheap). 
I do suggest that you check some references for eyepiece design too.
A good starting point is Rutten & van Venrooij, they have nominal
100mm f.l. eyepiece designs than can be scalled to any focal length.
ATM books have sizeable section on eyepieces too.

Bratislav