Trutek IR blocking filter for visual?

[Moonshane]

Hi all

I have been offered three filters for a good price, two of which I will use but the other is an IR filter which is described as a visual filter but what applications do they work with? I had always assumed that they were for imagers?

Any advice appreciated. I can always sell on if of no use but I fear I may be missing out

Cheers

Shane

[ronin]

I think a good use for one is when viewing Mars. Seems Mars throws out enough IR that it "fuzzies" what you see, so an IR block is useful for that.

I think it is a case that the eye does not "see" IR but there is no specific cut off, for the eye so the near IR causes some reaction at the eye and thus an IR block helps.

That is however the only aspect for one I am aware of, there could well be others however that I have not heard of.

[Moonshane]

Thanks Ronin, that's a great post. I wonder if using it with my Baader Neodymium might improve the view further than the latter does.

[michael.h.f.wilkinson]

It depends what the cut-off wavelength of the IR filter is. If it lies beyond about 800nm, it will have no effect, if it cuts off well below that value, it could have some effect, but only on objects bright enough to trigger the cones in the retina, as the rods cannot even see H-alpha very well (if at all). If you put the filter on a white sheet of paper and it has a colour cast (most likely very pale blue) then it might be blocking some red. If it looks essentially white, i do not see what it could do visually. 

[Moonshane]

cheers Michael. You make an obvious point which I had not even considered!

[ronin]

Looking at a Baader Neodymium filter the combination would start to pass at 350 then I guess cut off at 700-750(ish) with the IR block, I would guess 700nm. Cannot locate anything on the Trutek.

Wouldn't think a combination would deliver much visually - except the Baader would remove of whatever is at 570-600nm which I presume is the sodium emission.

Since however it looks like there is no great problem in combining them, you do not seem to end up with a 98% ND filter or a narrow band effect give it a try.

[Moonshane]

I think you are right Ronin. worth a go come what may. I'll report back once I give it a try.