Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Reflection spectrum from a herschel wedge


Paz

Recommended Posts

I was reading about uv/ir cut filters and read that the baader filter blocks out to about 1100nm and passes ir beyond that. I read there are other filters that block further into the ir such as the beloptik kg3 that blocks out to 5000nm or so.

So it looks like if only considering the filters that longer ir may pass through (e.g. I assume polarising filters and the baader solar continuum filter dont take long ir out).

But then there is the question of what does the wedge itself transmit, i.e what is the reflection spectrum for a glass surface? Its evidently flat enough in the visual spectrum because we can observe in white light well enough but does it reflect/pass uv and ir in the same proportions or something different.

I ask as I am considering a kg3 filter but I understand they do some of their work by absorption thus keeping some heat in the scope but if a wedge doesnt reflect ir then the extra blocking would not matter.

Link to comment
Share on other sites

I coated glass will reflect according to fresnels law, the incidence angle is likely 45degrees though the back of the wedge will be different so it’s reflection is dumped and doesn’t make the eyepiece. https://en.m.wikipedia.org/wiki/Fresnel_equations

you can look up a typical glass refractive index curve (https://en.m.wikipedia.org/wiki/Dispersion_(optics)  and plug the numbers in. I’d expect reflection across a very wide band, so it you’re worried about the longer IR being an issue then I’d specifically filter for them. Not many glasses trasmitmtoknfar into the harmful UV, but many will transmit UV-A, so some form of filter to trim this off might keep the cataracts at bay a little longer (assuming you always wear sunglasses).
Your eye lens will block beyond 1400nm (or so), so beyond that you don’t need to worry about retina damage (your cornea will be smoking long before then!), https://lasersafety.com/resources/laser-safety-guide/

peter

  • Like 1
Link to comment
Share on other sites

On 02/04/2022 at 17:08, PeterW said:

Your eye lens will block beyond 1400nm (or so), so beyond that you don’t need to worry about retina damage (your cornea will be smoking long before then!).

Thanks very much for the comments and links. This comment did make me laugh - it's good to know my retina will be fine!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.