[E_ri_k (Erik)]

Originally Posted by JA

Hello Erik,

If you have the filter itself you could calculate it, based on measurements of the critical angle for total internal reflection, using perhaps a laser, accurate angle measurement and the refractive index of air and the relationship that binds them together solved for the index of refraction of the glass that you want to know.

Best
JA

Thanks JA, a little beyond my capabilities I think but good to know!

Originally Posted by Merlin66

99% sure it’s BK7 glass that’s used.
Why do you need to know?

Thanks, oh just calculating extender lengths and taking into account optical filters.

Originally Posted by blink138

there would be no reason for it to be anything other than hard crown glass (1.523) i would i think
pat

Thanks for the info Pat

Originally Posted by Merlin66

I've contacted Baader and asked the specific question Re the filter material.
Erik - why the question??

Thank you, sorry for not getting in touch with you sooner, work had different ideas!