Old Lumicon Ha filter

[Gordy]

Hi everyone. Well its time to get back into harness which was helped by attending a decreased estate sale.

The only item of interest was a Ha filter made by Lumicon back in the 1980s. This filter looks like it is only deep red coloured glass without any reflective coatings. There are no labels or markings except "H-Alpha PASS Filter - LUMICON".

I bought it as I would like to start doing some Ha astro imaging. Anyone here with a modern Lumicon Ha filter version, and if so, does yours have reflective coatings? (Perhaps the one I bought is obsolete technology.) Regards.

[JA]

Hi Gordy,

The filter you have is not a narrow-band Hydrogen Alpha filter, but a wideband or more correctly low pass filter which starts just before the Hydrogen Alpha wavelength with 50% transmission at ~640nm and ~90% transmission at the Hydrogen Alpha wavelength and near 100% transmission at the SII wavelength and beyond. It would certainly be useful for limiting light pollution, but its wideband characteristic may take in too much into the deep red/infrared to the extent you may see some star bloating, if the optic you are using is not extremely well corrected. See graph below...



Best
JA

[Gordy]

Thanks JA.
I thought as much now I will start looking around for the real thing. Regards.

[JA]

Originally Posted by Gordy

Thanks JA.
I thought as much now I will start looking around for the real thing. Regards.

It's still entirely useable to help eliminate light pollution and gives you the Hydrogen Alpha band, just not as narrowly as with a typical narrowband filter.

Try it.

Best
JA

[Gordy]

Originally Posted by JA

It's still entirely useable to help eliminate light pollution and gives you the Hydrogen Alpha band, just not as narrowly as with a typical narrowband filter.

Try it.

Best
JA

Will do! I just need to find a good Ha source currently in view and see how well the filter performs blocking moonlight.

[AlexN]

I used to use an old Lumicon Ha filter (same as yours - deep red glass) a very long time ago... My camera at the time (QHY8) had a UV/IR block on it, so essentially, it was just an extreme LPF.

I'd do a set of images with the filter, even during 50~75% moon, extract the Red channel, then at new moon, shoot without the filter.

You can then blend the extracted red channel into the OSC image's red at ~25% to 40%, and add it as a luminance layer too.

Did a fantastic job for the $80 odd I payed for it. At the time, a $400 6nm Ha filter was absolutely out of the question for me...

[Gordy]

Thanks Alex. Your suggestion makes good sense. Regards.