Which 2" IR/UV Cut filter ???

[Skipper Billy]

I am looking for a 2" IR/UV cut filter to go in my imaging train.

It's a SX H9C, SW 0.86 flattener/reducer with a 2" nosepiece into a SW ED80. The filter will be going on the end of the flatteners nose piece.

I am looking at the Baader and the IDAS

http://www.firstlightoptics.com/uv-ir-filters/baader-uvir-cut-filter.html

http://www.firstlightoptics.com/uv-ir-filters/idas-heuib-ii-uvir-blocking-filter.html

The IDAS filter is twice the price of the Baader - is it worth it ???

I would rather buy right and once but if there isnt much to choose I am happy to save £70 !!

Any thoughts ???

[ronin]

From the information I have they both are a bit "odd".

The Baader curve I have cuts off at 680-700nM in the IR but there is no cut off shown for the UV, at 420nM it is happily passing 90% plus.

The Hutech starts passing at 400-420 then passses wavelengths until 600, drops to effectively zero transmission for 600 to 650 then passes a narrow band from 650 to 680, so just squeezes the Ha line in at 658. However it has cut out the red at 600-650?

As said little odd, I will assume that the Baader follows the Hutech and start passsing at the 400-420 range and it is just not shown.

The Hutech will/should pass Ha but I cannot think of a reason for blocking 600-650, you might detect Ha from nebula but things like Betelgeuse/Arcturus etc will no longer be red as that bit from them is blocked.

I suppose the question is: Is there LP at the 600-650 section that it is trying to block.

[Skipper Billy]

Thanks Ronin - that is a bit odd !!  More research I think !!

[Merlin66]

The Baader is 400-700nm bandwidth.

I have the transmission curves somewhere.

[ronin]

The Baader is 400-700nm bandwidth.

I have the transmission curves somewhere.

The transmission curve I have sort of stops at 420nM, what occurs at 400nm is "hidden".

http://www.astrosurf.com/buil/filters/curves.htm

The Hutech was from elsewhere.

[Merlin66]

To quote:

◾Extremely Sharp Cutoff at 690nm (leaves all the visible red, including the important 656nm H-alpha emission line).

◾Sharp cutoff below 400nm. Eliminates violet halos around bright stars (more effectively than simpler so-called Minus Violet photographic filters).