Over the last two days I've read various thread on numerous forums about Bahtinov masks with great interest. These discussions have raised a couple of questions in my mind which I don't recall have been fully explored in these threads.
1) My 8"LX200 has a very long dew sheild. Does it make any significant difference how far in front of the scope mirror/lens the mask is placed.
2) I have an Orion 80ED and an 8" LX200. The LX200 can have anything from a f3.3 focal reducer to a 4x barlow shoved on the end meaning the focal length can vary from 660cm to 8000cm. The formulae for designing these masks includes the focal length of the system, yet the one of the commercial retailers for these masks (
http://www.spike-a.com/) just sells them by OTA diameter. So is it really necessary for me to have 5 different masks for my LX200 (f3.3 focal reducer, f6.5 focal reducer, normal, 2x barlow and 4 x barlow) or is a single mask adequate?
3) In relation to question 2 ,are the sensitive of masks to different focal lengths more, less or insensitive to whether the mask is a first order or a third order mask?
4) What are the advantages of a 1st order mask over a 3rd order mask?