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Blocking filter mirror.

Posted: Wed Apr 29, 2015 8:38 am
by GUS
Found this diagram, have seen the LS60 one before but not this one. It gives some details of the mirror in the diagonal, can someone explain its safety role in the BF, ( and whats meant by long wave pass). I noticed with my two BFs that they have a purple tint and are not as reflective as a standard diagonal mirror.

Re: Blocking filter mirror.

Posted: Wed Apr 29, 2015 11:22 am
by GreatAttractor
From what I gathered elsewhere on SolarChat, I believe it has to do with preventing the long infrared (>1200 nm) from reaching the eye/camera. Note that the front ERF (the RG630 element) blocks only to 1200 nm. Similarly, for the same purpose we use e.g. a Beloptik KG3 IR/UV-cut filter in mods.

I'm sure the experts will give a more precise answer.

Re: Blocking filter mirror.

Posted: Wed Apr 29, 2015 12:35 pm
by GUS
Thanks for the response GreatAttractor, so in a straight through BF is this blocking applied to one of the filters.

Re: Blocking filter mirror.

Posted: Thu Apr 30, 2015 4:15 am
by swisswalter
Hi Ivan

yes we discussed that with pics some years ago in that forum. The diagonal has some sort of golden mirror. I do not know how that IR pass is realised in a straight through blocking filter. Never had a chance to take one apart. Note, on the above pic they called the filter ahead of the blocking filter an ITF filter. Now a days Rikki speaks from a blue glass filter.

Re: Blocking filter mirror.

Posted: Thu Apr 30, 2015 8:36 pm
by mdwmark
Like my grand daughter's books, what is wrong with this picture.
Mark W.

Re: Blocking filter mirror.

Posted: Thu Apr 30, 2015 11:12 pm
by marktownley
mdwmark wrote:Like my grand daughter's books, what is wrong with this picture.
Mark W.
That's funny, you made me laugh :)

Re: Blocking filter mirror.

Posted: Fri May 01, 2015 7:51 am
by mdwmark
The front element shows it as a polished RG630 window. But RG630 has the same profile as the "filter glass" window in the back. The front would need to have a short pass coated on it to get that profile. And it would probably turn back on at 800-1200nm.
The "filter glass" would be red so that when you are looking into the scope you would not see you eye looking back at you off of the blocker.This would either be a silver or gold looking mirror depending on the design.
Mark W.