Light pollution filters

jim wrote:

What's the current thought on these? Are there any out there that are
worth the money?

Yes. But then you could say I was biassed since I sell a specific filter
for photographic use in low pressure sodum light environments.

I already have an Astronomik UHC filter which is pretty good, but I'm
wondering if a more general pupose filter might be better for casual
deep sky stuff from a fairly badly light-polluted location (Stafford,
UK).

The first thing to figure out is do you want a visual filter or a
photographic filter (you can increase a photographic exposure to
compensate, but you cannot crank up the sensitivity of your eye).

The second thing is to look carefully at what sort of street lamps
predominate your local environment? The US broadband LPR filters are
optimised for a US style mercury light environment (cold blue lights).
They are overpriced and not particularly effective here.

Most places in the UK have a mixture of lights but with high pressure
sodium (peachy white) and low pressure sodium (almost pure orange
yellow) in various proportions. New lights almost invariably now HPS.

If you want a visual filter for general use in the UK than the Orion
Optics UK Sodium filter is as good as any (and cheaper than US brands).

http://www.orionoptics.co.uk/ACCESSO...lterspage.html

Photographically I would recommend my own Nonad filter provided that
most of your local light pollution is from low pressure sodium.

http://www.nezumi.demon.co.uk/nonad/nonad.htm

Some Lumicon filters are overpriced in the UK, and although the filters
themselves are very good the custom screwed mountings are terrible
(unless they have improved recently). I have seen some so loose and
sloppy they could drop out of the eyepiece...

The Lumicon deep sky H-alpha filter is still an interesting one
photographically if you want to capture faint galactic hydrogen
nebulosity in badly light polluted conditions.

http://www.scsastro.co.uk/it210014.htm

Orion US filters from SCS and others are pretty good. The Hutech
formerly Tokai photographic filter although very expensive may perform
better than Nonad in a mixed street lighting environment.

http://www.scsastro.co.uk/it210008.htm

This isn't meant to be a definitive review of all filters just a rough
idea to which ones might work for you in the UK.

You should also take a look at David Knisely's filter FAQ. Alas he
ignored UK filters.

http://www.cloudynights.com/item.php...d=63&pr=2x9x42

I second his recommendation of the Orion UHC and Lumicon OIII for visual
use, but in the UK for a first general visual filter I reckon the Orion
optics Sodium light filter is as good as anything and cheaper too!

Be aware that no filter will let you see more stars. The price of a
filter is to make everything slightly dimmer, but to dim the uwanted
light pollution much more than everything else improving the contrast.
White light continuum sources like stars and galaxies necessarily take a
hit along with the light pollution.

You can usually do better by increasing the magnification and using a
wider field eyepiece for star clusters and galaxies.

Regards,
Martin Brown
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