# What is the bluest narrow band filter mounted on ground based telescopes?

If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that?

I mean under the circumstance that its lyman alpha shifts to 3300A.

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Are you asking what is the bluest commercially available filter, or the bluest ever commissioned by a professional observatory to make special observations? The former might be feasible to answer, but I cannot imagine that the latter will be, short of someone happening to know every single filter available to astronomers at every facility. I also don't quite understand the reason for your question. People are imaging ly-alpha sources and studying them spectrographically, so yes that is feasible. But why are you qualifying the question for ly-alpha sources red-shifted to 3000 Angstroms? –  Jeremy Apr 10 at 20:33
There are only certain windows of visibility for ly-alpha due to the atmosphere, requiring satellite/probe observations for frequencies outside those windows. –  Jeremy Apr 10 at 20:37
Just want to do a narrow band photometry. I find Gemini-N (gemini.edu/?q=node/10420) has a poor response at 3300A and the u-band filter is no longer available now.What is the bluest commercially available filter？ As far as you know, what is the bluest ever commissioned by a professional observatory? –  questionhang Apr 11 at 1:26
Do you want to do photometry with your own equipment, or do you want to approach a facility to use theirs? Are you trying to source a filter for yourself (and if you find a place using a suitable filter, you will endeavour to also source one from where they did?) I think most U filters will be weak at 330nm. However, if you have special needs for a filter centred on 330nm, and you can fund it, I'm sure you could commission something... Who knows what others might have commissioned. –  Jeremy Apr 11 at 5:28
I find someone bought a suitable filter for their Keck observation. I know the absorption by the atmosphere at 3300A on the earth is large. If we want to get a 3300A narrow image,a space telescope,i.e. hst, is necessary? –  questionhang Apr 11 at 7:43

You probably will have difficulty imaging Ly$\alpha$ from a z=1.7 quasar at 330nm.