Baader refractive index

[E_ri_k (Erik)]

Hey guys, I'm looking for the refractive index of Baader 36mm filters. Endless googling has left pretty much nothing.

Does anyone here have any information regarding this?

Erik

[billdan (Bill)]

I can't give you an exact answer Erik, but I would imagine they would use BK7 crown glass with a refractive index of 1.52.
Unlikely they would use the more dense flint glass, which can range from 1.6 to 1.8.

[JA]

Originally Posted by E_ri_k

Hey guys, I'm looking for the refractive index of Baader 36mm filters. Endless googling has left pretty much nothing.

Does anyone here have any information regarding this?

Erik

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

[Merlin66 (Ken)]

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

[blink138 (Pat)]

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

[Merlin66 (Ken)]

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

[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!

[Merlin66 (Ken)]

Baader got back to me...
They use “optical glass” for their filters....not very informative!!

[E_ri_k (Erik)]

Originally Posted by Merlin66

Baader got back to me...
They use “optical glass” for their filters....not very informative!!

Haha, no not very! It’s ok, I gathered 2 pieces of information I found online and compromised in the middle. Fingers crossed.

Thanks for your efforts.

Erik