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Orion SkyGlow Filter (Light Pollution Filter)

Discussion in 'Astrophotography' started by MadMarco, Feb 23, 2015.

  1. MadMarco

    MadMarco Mu-43 Veteran

    298
    Oct 30, 2014
    Guildford, England
    I live in the middle of a largish town of 70,000 so light pollution from street lighting and other sources is a problem for anyone interested in astronomy. Poor seeing increases the impact of light pollution and in England the seeing is rarely very good.

    I've been looking at LP filters for a while now and was never sure if they would do anything worthwhile or of they are in fact snake oil. After reading a few reviews I went for the middle range 2" Orion SkyGlow Filter which I got for £75. The filter is designed specifically for 2" screw attachment to astronomic eyepieces and the like, although I'm sure that it could be adapted to go on the front of a camera lens.

    P2232203.

    The Orion SkyGlow is classed as a broad-band Light-pollution Reduction (LPR) filter; designed to help improve the visibility of a variety of deep-sky objects by blocking out the common Mercury vapor, Sodium, and some other emission lines from man-made and natural (airglow) sources.

    To test the filter, I took a single 60 second exposure @ISO800 first without and then with the filter. These images were taken with my William Optics ZS71 and Skywatcher Field Flattener.

    Without LPR filter:
    P2151888.

    With LPR filter:
    P2151889.

    Straight away I was amazed at the difference, it completely exceeded my expectations. There is a definite green colour cast to the filter and you are losing maybe a third of a stop of light. The important win is the improved signal to rubbish ratio, there is more good light in comparison to the bad light. To do a further comparison, I made an adjustment in Photoshop to set the grey levels. This is good general fix to eliminate colour cast from light pollution.

    Without LPR filter
    P2151888ps.

    With LPR filter
    P2151889ps.

    Living in an area with light pollution like I do, this is completely worth the money. It opens the door to longer exposures and possibly lower ISO, with the benefits that brings.
     
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  2. Petrochemist

    Petrochemist Mu-43 Top Veteran

    651
    Mar 21, 2013
    N Essex, UK
    Mike
    Very impressive!
    Being cheap I opted for a Didvminium filter (AKA red enhancer) which reduces skyglow at a fraction of the price & available in standard camera sizes. The results from my quick trials certainly wern't as good as your shots, but it does give a significant improvement, with sodium lights.
    Must get out & use it again!
     
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  3. MadMarco

    MadMarco Mu-43 Veteran

    298
    Oct 30, 2014
    Guildford, England
    I've got the 72mm Hoya Red Enhancer (Intensifier) which is a 'didymium' type filter. I've used it quite a bit now and used to blue-tac it to the front of the telescope, it's surprisingly effective although the Orion SkyGlow is a bit of a step up.
     
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  4. maritan

    maritan Mu-43 Veteran

    388
    Oct 30, 2014
    Thanks for the info!

    I looked for one for my current lens - 12-40 pro - just to see what's available. With a 62mm thread, the 2" Orion can't be used. The Hutech LPS might be a good option because they come in various diameters.

    I also plan on getting a UWA lens eventually and most likely will have an even bigger diameter. Maybe I'll just wait for my UWA of choice and then look into these filters.
     
  5. MadMarco

    MadMarco Mu-43 Veteran

    298
    Oct 30, 2014
    Guildford, England
    The 72mm Hoya Red Enhancer is a left over from my Canon DSLR setup, thankfully step down rings can be had for peanuts from eBay.
     
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  6. wjiang

    wjiang Mu-43 Hall of Famer

    What does such a filter do if used for star/landscape scenes rather than deep sky framing? Does it make the terrestrial foreground stuff look really strange?
     
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  7. maritan

    maritan Mu-43 Veteran

    388
    Oct 30, 2014
    Great question by Wjiang. Would love to know the answer myself. There are a few caveats to this approach as I already found out from one of the makers of an LPS.

    If the LPS is an interference filter, the wide angle lenses do NOT go well with them. This is because there is a spectrum shift causing a weird coloring on the edges of the picture. However, IDAS LPS makes a drop in front filter (behind the lens, in front of the sensor) that can fix this. Unfortunately, this solution isn't available for Olympus. He has Canon, Nikon, Sony and Fuji filters.
     
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  8. MadMarco

    MadMarco Mu-43 Veteran

    298
    Oct 30, 2014
    Guildford, England
    The Hoya Red Enhancer is a great filter for making oranges and browns of autumn leaves really stand out, you can use it with anything:

    http://www.hoyafilter.com/hoya/products/coloredfilters/redenhancerintensifier/

    The LPS filter is obviously much more specialist and gives everything a distinctly green tinge, the configuration that I use it in is:

    [William Optics ZS71] - [Orion SkyGlow] - [Skywatcher Field Flattener] - [Olympus E-M10]

    Because of the thread pitch I'm not sure if it would be possible to attach it to the front of a standard lens, I'm sure that someone must make an adapter.
     
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  9. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    Yes., but not terribly. The orion sky glow is a weaker narrow band but still limits the transmission lines in certain visdibnle regions.
     
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  10. Speedliner

    Speedliner Mu-43 All-Pro

    Mar 2, 2015
    Southern NJ, USA
    Rob
    Amazing difference. Thanks for the info.
     
  11. maritan

    maritan Mu-43 Veteran

    388
    Oct 30, 2014
    Found it! I knew I had read this before but didn't refer to it earlier because I couldn't find the link again. Here's what you can expect to see with a LPS filter on the outside of the lens:

    http://www.zdziarski.com/blog/wp-content/uploads/2015/02/Iced.jpg

    Taken from the blog:
    http://www.zdziarski.com/blog/?p=4742

    See that purple ring around the outside of the picture? I believe that's what happens with the spectrum shift along the outside of the interference filter due to the curvature of the front element on wide angle lenses.
     
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