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  1. #1
    dodea100's Avatar
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    Default Mercury Vapour Filters



    Hi there,
    I am newbie and have been trying out my first scope, a 115mm Skwatcher reflector in the back garden for a couple of months now but I have quickly discovered the perils of bad light pollution! Living in a built up area in Herts ( Welwyn Garden City) not far too from London is bad enough but I have the added joy of a row of four high intensity multi-head mercury vapour security lights that light up the mainline rail line less than 100m from my back garden! These monstrosities are kept on ALL NIGHT and all but kill any chance of seeing any DSO in half the sky.
    I've read about light pollution filters you can buy so was wondering if anyone can comment on whether they actually work in severe cases like this and recommend a filter that might allow me the pleasure of seeing a galaxy or nebula or two?

    Declan

  2. #2
    Celestron's Avatar
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    Default

    From what I understand they work better for astroimaging than viewing. Not sure about that though, I'm partly just bumping your post so someone else can answer.
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  3. #3
    skaven's Avatar
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    Default

    A broadband light pollution filter such as the Celestron UHC/LPR, the Lumicon Deep Sky, and the Orion SkyGlow filters are designed to specifically cut Mercury, some Sodium, and a few other emission lines associated with urban lighting.

    If the lights near your property really are mercury vapor (and not the new fangled high pressure sodium lights), then one of these filters should help.

    Note however that the best a filter can do is *cut* the amount of light making it to the eypiece. It can't make anything brighter. If you have loads of mercury spectra in your local sky glow, a LPR filter may help. But in addition to the filter, make sure you're creating a dark adaptation-friendly area for you to observe. It's critical that you observe in an area that is dark enough for your eyes to fully dark adapt (this is a chemical change that takes ~30 mins, in addition to the quick reaction of your pupil opening). If local lights (say, from the house or neighbors) are interfering with the darkness, rhodopsin levels in your retina will not increase enough for you to have full low-light sensitivity.

    Try making your local observation area darker to start with, and if that doesn't help, I recommend trying a LPR filter.

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  4. The Following 3 Users Say Thank You to skaven For This Useful Post:

    dodea100 (04-04-2012),SpaceTrees (04-03-2012),Voyager3 (04-03-2012)

  5. #4
    epeddy1's Avatar
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    Default

    They are not miracle workers. I have rarely seen anyone hop and skip at the results of their LP filters. They usually slightly help contrast. From what I understand, they actually help more in moderate LP than heavy LP. Your best bet is finding a dark site. Or there's always this option:

    I'm always learning, so PLEASE correct me if I sound misinformed. I will not be offended if you tell me I'm wrong. Thanks for your patience!
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  6. #5
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    Default

    I should note that the reason I called out the high pressure sodium lamps is that as opposed to the older low pressure sodium lamps that emitted in a narrow range of light, the newer high pressure sodium lamps emit light across most of the visible spectrum, rendering traditional broadband light pollution filters useless.

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  7. #6
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    Default

    Hello Dodea100,

    the whitish/bluish Mercury vapor lamps simply kill the DSOs. In your case, as you can't see any DSOs, I'd recommend an UHC filter for the clusters, and an OIII filter for the nebulas. The best solution for the clusters under the flood light are the very narrow-band filters, like the Astronomik UHC,
    and for the nebulas the OIII filters, like the Thousand Oaks, and the Baader 8.5nm OIII. the Baader OIII 8.5nm has the CCD grade, and it passes nothing (and absolutely nothing) outside the OIII line double. Most of the other makes have some transmission side bands, passing more light pollution.

    I am mostly using the Baader 8.5nm OIII filter, and the Astronomik UHC. Both filters work well with apertures as small as my 70mm binoculars.

    Best

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  8. #7
    dodea100's Avatar
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    Default

    Quote Originally Posted by epeddy1 View Post
    They are not miracle workers. I have rarely seen anyone hop and skip at the results of their LP filters. They usually slightly help contrast. From what I understand, they actually help more in moderate LP than heavy LP. Your best bet is finding a dark site. Or there's always this option:

    Thanks - The option you suggest is very tempting but not sure of my catapult aim is what it was

  9. #8
    dodea100's Avatar
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    Default

    Quote Originally Posted by j.gardavsky View Post
    Hello Dodea100,

    the whitish/bluish Mercury vapor lamps simply kill the DSOs. In your case, as you can't see any DSOs, I'd recommend an UHC filter for the clusters, and an OIII filter for the nebulas. The best solution for the clusters under the flood light are the very narrow-band filters, like the Astronomik UHC,
    and for the nebulas the OIII filters, like the Thousand Oaks, and the Baader 8.5nm OIII. the Baader OIII 8.5nm has the CCD grade, and it passes nothing (and absolutely nothing) outside the OIII line double. Most of the other makes have some transmission side bands, passing more light pollution.

    I am mostly using the Baader 8.5nm OIII filter, and the Astronomik UHC. Both filters work well with apertures as small as my 70mm binoculars.

    Best

    JG
    Great advice, Thanks. I'll certainly give those a try and report back. The other option is to take up the wife's suggestion and move to the country!

  10. #9
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    Default

    A move to the country is always nice. I have the Orion Skyglow and it does help but its not a miracle worker. I live in a white zone for LP.
    Clear Skies

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  11. #10
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    Default

    my suggestion is to get a tarp, 4 sticks and 4 zippers.
    make 4 panels that zip together from top to bottom and build a little shack
    just zip down your observing side until the scope clears the V

    im making one for this summer!

 

 

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