[richardda1st (Richard)]

Hi Mark.

As the original secondary is 63mm (2.48") I'd better check my dimensions again. If my numbers are correct I will choose the 2.14” 1/18 PV.

I do not fully understand the illuminated field. I would have thought that if the secondary is large enough to receive the full cone of light, allowing for alignment issues and secondary imperfections near the edge, the illuminated field stays the same. I can only see the illuminated field reducing when the secondary is too small to receive the full cone of light. What I’m trying to understand is why does the 1.83” give a 6mm diameter fully illuminated field and the 2.14" give a 15mm. More to learn.

By the way, did you notice that my original concern with this new primary’s fl was in the opposite direction, being longer and not shorter? You were right the Meads stated specs is just nominal.

I have not had much observing at the moment due to the conditions, but what I have done so far is good.

Richard
-----------------------------------------------------------------
ps

Thanks astro744
I knew I should have checked for a new post before I submitted mine.
I will check them out tomorrow. As I said above I will check my dimensions.