Ha Flats

[martin_h]

Carrying on from by binning question.....

Taking flats with a Ha filter in line with a EL panel....has anyone tryed it?

I'm getting some wierd results, my max value increases when I increase the exposure time (as you would expect) but the average value doesn't increase in the same proportion!

I'm getting near saturation on max value but only a few thousand mean value.

I'm wondering if the EL panel is outputting light in wavelengths that is being cut by the Ha filter.

Does anyone else do Ha flats with an EL panel, if so what results do you get?

[Merlin66]

Ha is such a narrow band that flats are not normally required!

The El panels give a broadwavelength "flat" spectrum, but I'd question their performance in Ha.

[FraserClarke]

I've taken a spectrum of an EL panel, and that one had a long wavelength cutoff about 650nm (H-alpha is 656nm). I don't know if all panels are the same, but it wouldn't surprise me if they have an IR cut-off -- don't want them getting too hot!

I suspect your bright panel is not very bright at H-alpha...

[martin_h]

I've taken a spectrum of an EL panel, and that one had a long wavelength cutoff about 650nm (H-alpha is 656nm). I don't know if all panels are the same, but it wouldn't surprise me if they have an IR cut-off -- don't want them getting too hot!

I suspect your bright panel is not very bright at H-alpha...

No its not!!!

I usualy do flats at about 1.5 secs, but with the Ha I was up to 10 secs and getting dodgy results. So I resorted to using "white light" flats and hope there was no grot on the Ha filter.

[ollypenrice]

I daresay it depends on the panel. Mine, till it died, was fine in Ha though notably slower than in other filters. No surprises there. Didn't Gerd Neumann of Astronomik source an appropriate panel?

I find my new light box won't generate flats in either Ha or blue and unfortuunately I can't change the darned bulbs without redesigning it from scratch. Groan.

Olly

[FraserClarke]

Do also remember that H-alpha is typically ~10nm wide, compared to ~150nm wide for a broad band filter (BVR). So even if the light source is bright, it's still going to take ~15x longer in H-alpha than a broadband...

I typically take sky flats with ~2--5s in BVR and ~30s in H-alpha...