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NB filters reduce skyglow!

Demonperformer

By Demonperformer
in The Astro Lounge

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Demonperformer

Demonperformer

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OK, like a newspaper headline, no great revelation there -  you probably all know this already, but I thought it would be interesting to attach some numbers to this from an urban area. So I went outside with my SQM & NB filters and got some. Not particularly "scientific" as it was just holding the filter over the sensor and the "rim" around the edge of the SQM means that light from one or other of my streetlights might have been creeping in under the filter edge, but it gives some idea.

With no filter: 18.85, +Ha filter: 22.11, +OIII filter: 21.11, +SII filter 22.43.

So, that gives me an improvement in the background of between 2¼ & 3½ magnitudes. From what I have read, it was no great surprise that the OIII was the worst of the bunch in this respect, but even there I am getting down to what is, in effect, a 21m sky. All in all, I find this somewhat encouraging, but I am left wondering whether (and by how much) 3nm filters would perform better. I can feel a purchase coming on ...

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festoon

festoon

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Thank you for posting, really helpful information for those who have not got a sky quality meter. If you have one - it would be great to see the effect of a skyglow filter like the Baader Neodymium :)

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Demonperformer

Demonperformer

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Actually, to complete the list, I also checked my CH4 filter, which gave me a 4.0 mag improvement, but I'm not sure how much of that would be down to the fact that the waveband is outside the visual spectrum. And anyway, as it is used for planetary, the lack of skyglow aspect is less significant.

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dph1nm

dph1nm

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On 22/05/2018 at 04:41, Demonperformer said:

So I went outside with my SQM & NB filters and got some. Not particularly "scientific" as it was just holding the filter over the sensor and the "rim" around the edge of the SQM means that light from one or other of my streetlights might have been creeping in under the filter edge, but it gives some idea.

With no filter: 18.85, +Ha filter: 22.11, +OIII filter: 21.11, +SII filter 22.43.

So, that gives me an improvement in the background of between 2¼ & 3½ magnitudes. From what I have read, it was no great surprise that the OIII was the worst of the bunch in this respect, but even there I am getting down to what is, in effect, a 21m sky. All in all, I find this somewhat encouraging, but I am left wondering whether (and by how much) 3nm filters would perform better. I can feel a purchase coming on ...

Hmm - not sure this makes much sense. As I understand it the SQM already has a 'visual' broad-band filter, and the results are calibrated to work for that. So if you stick another filter in front surely the calibration will not be right? I mean I could stick a neutral density filter in front and get as faint a sky as I liked.

NIgelM

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