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  1. #1
    Howard's Avatar
    Howard Guest

    Default Which Light Pollution Filter?



    Hi,

    I am in need of some advice about filters.

    I'm looking for a good sodium light pollution filter (1.25"). I know
    the filter will dim the stars but I'm sure it will help me see them
    too.

    The two I have in mind are,

    Orion (US) UltraBlock Narrowband Filter (£77)
    or
    Orion (UK) Sodium light pollution visual Filter (£62)

    I have searched the forums and cant find any posts comparing the two.
    Which one should I buy?
    Are there any other makes/types which I should add to the possibles?

    Thanks in advance.
    H.


  2. #2
    Martin Brown's Avatar
    Martin Brown Guest

    Default Which Light Pollution Filter?


    Howard wrote:


    I should declare an interest first. I sell a photographic filter Nonad
    effective against low pressure sodium light.

    Have a look at David Kniselys filter FAQ
    http://astronexus.com/node/4
    But remember it is US-centric, assumes mercury streetlighting and
    ignores most products from UK & Japan.


    Sadly it will always dim the stars no matter how gentle the filter (and
    visually they have to be pretty brutal to work). What it does do is
    make nebula line emission seem much brighter by making the sky a lot
    darker.

    Photographically you can just increase the exposure time to compensate,
    but alas the eye has no such feature.

    If you want to see more stars (ie white light continuum emssison) then
    increasing the magnification is usually a better choice. The stars are
    unresolved and stay compact whilst the light pollution is spread over a
    larger angular area.

    I have both of them. I would recommend the Orion(UK) Sodium visual
    filter as a first introduction because it is more generally useful in a
    mixed sodium light environment. The UltraBlock will get you better
    nebula contrast but at the same time it crucifies stars. There is no
    free lunch. You can only make things dimmer with a filter.

    If the filter is well matched to the light pollution you make the sky a
    lot darker without losing too much light from the object you are trying
    to study, The effects of both filters on various light sources are on
    my spectra page.

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

    There is now a much better high resolution set of spectra on Maurice
    Gavins page

    http://home.freeuk.com/m.gavin/grism2.htm


    For a first filter you can't really go wrong with the Orion Optics (UK)
    one. It is the cheapest too...
    (avoid overpriced US made broadband filters unless you have a lot of
    mercury lighting nearby)

    Regards,
    Martin Brown


  3. #3
    Ian Newham's Avatar
    Ian Newham Guest

    Default Which Light Pollution Filter?

    In article <1168901477.540372.9120@m58g2000cwm.googlegroups.c om>, Howard wrote:

    I can't compare the two but following Martins advice (and very
    informative webpage, thanks Martin) I bought the Orion UK filter and
    have been very pleased with it. Using a filter takes some getting used
    to but it has proven very versatile. Its very effective against low
    pressure sodium and trades off a little high pressure sodium performance
    to leave you with quite a reasonable view of stars when you consider
    you're filtering quite a bit of their light out, certainly good enough
    to star hop to nebulae etc. It's performance on nebulae has impressed
    me, I'm surrounded by a lot of light pollution and many are just
    invisible without.

    --
    Ian Newham
    mailto:ian@ourshack.com
    http://www.IanNewham.com

  4. #4
    Howard's Avatar
    Howard Guest

    Default Which Light Pollution Filter?

    Thanks Martin and Ian for your input. I have gone with your advice and
    put an order into Orion (UK) for their Sodium filter.

    Thanks once again.
    Howard

    Howard wrote:


 

 

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