I have an Esprit 120 ED on order and want to get a Bahtinov mask to use with it. I am considering the William Optics Diffraction Spikes mask for 172mm-235mm diameter dew shields. According to SW support, the outside diameter of the dew shield is 6.9" (172.7mm), so it seems it would be a tight fit. However, I found another source that gave 165 mm as the OD.
Does this WO mask (or perhaps another) fit the Esprit 120 ED? Is there another mask that would work better?
A more general question from a refractor proto-newbie*: With my present scope, an SCT, I use a mask that sits down inside the dew shield, almost against the corrector plate. Does putting the mask on the end of the extended dew shield on a refractor work? Would I use it with the dew shield retracted or removed?
Thanks for any information and suggestions!
* Proto-newbie: someone who is about to become a newbie.
Edited by mborland, 28 June 2020 - 12:10 PM.