What is a blocking filter function?

[NightPhotographer]

I want to use my telephoto lenses for solar prominence imaging. I need to use front mount filters since rear mount filters mess with focus. Lunt offers front mount Etalon but I have difficulty finding a front mount blocking filter. Is there any other filter with the same function that can be mounted in front?
Cheers

[rsfoto]

Hi,

From my experience that will not work for H-alpha imaging. You need a blocking filter near the chip. So far have never seen a blocking filter right after an etalon.

[Merlin66]

The blocking filter is an extremely narrow band (10A) filter centred on Ha. This is mandatory with an etalon type filter to effectively "sort" the myriads of band passes obtained to just allow the one at Ha to pass through.

I think your application with the telelens may have to be re-assessed.

[marktownley]

The only way you could do it is with a camera Quark from Daystar, but even then I don't recommend a DSLR for solar imaging.