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    andrei23's Avatar
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    Question Filter Help: Alpha/Betas vs. LRGB



    Hi there...

    I have a question regarding filters for CCD imaging. I read an excellent comparison of filters: http://mysite.verizon.net/vzeed81b/f...rformance.html

    But is seems this author is comparing single shots? My impression (and I admit I'm new to this so could use some words of wisdom) was that the H-Alpha, H-Beta, O-III, and S-II filters were meant to replace the LRGB set in monochrome imaging of nebulas? Meaning used together (well, in separate exposures) as opposed to singly? Or am I way off the mark?

    I currently have a Deep Sky Imager II (one-shot/color not the PRO monochrome)... can I make still use of these to improve my results by taking separate exposures and forcing them to monochrome in Photoshop? Or am I better off sticking to one-shots using a UHC filter instead (and should I consider replacing my DSI with the PRO version)?

    I live in a fairly low-light rural area, and use a 10" reflector - what would the more experienced astrophotgraphers here say are the first filters I should add to my toolbox for capturing images of DSOs?

    Thanks in advance!
    Last edited by admin; 08-12-2011 at 05:30 AM. Reason: edited link - that information was stolen from its original source on the other forum
    Binos: Optolyth 8x56
    Scope: Celestron C10 N-GT, CG-5GT German Equatorial mount, JMI MotoFocus
    EPs: Explore Scientific 4.7mm, 14mm, 30mm 82 FOV; Orion 20mm illuminated
    Filters: Baader Ha, OIII, SII, UHC, Skyglow, Blue interference; Astronomik UHC
    Photo: Meade Deep Sky Imager II

  2. #2
    Mothywood's Avatar
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    H-alpha, O-III, and S-II filters are used to view the amount of these elements within nebulae. They block all wavelengths other than light being emitted by these elements. When sets of images are exposed through these filters separately then combined as an RGB it creates a false color image. H-alpha data is often used by astrophotographers as luminance data for the RGB info to add color to. Narrowband filters are not meant to "replace" RGB filters, each have their place in astrophotography.
    As for whether you could use them with your one-shot color... Not with good results. Because OSC cameras have a Bayer matrix (that is, RGGB filters in front of it's pixels) only 1/4 of the sensor's pixels can detect the color red. So if you wanted to use a H-alpha filter, only 1/4 of the pixels would be able to read that data. This would only lead to a low signal to noise ratio image with low resolution.
    If you are looking to get better images of nebulae, and your problem is light pollution, I would suggest purchasing a broadband filter such as the one offered by Orion.
    Mounts: CGX, CGEM
    Telescopes: Orion 102mm f/7 ED Apo w/ MoonLite focuser and autofocuser, WO Star71 71mm f/4.9 Apo w/ MoonLite autofocuser
    Cameras: Orion Parsec 8300M, SBIG STF-8300M, Canon 6D, StarShoot autoguider
    Filters: Baader LRGB, Ha, OIII, SII, UHC-S
    Software: Photoshop CS5, MaxIm DL, Registar, DSS

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

    admin (08-12-2011),andrei23 (08-12-2011),Vali x (08-12-2011)

  4. #3
    andrei23's Avatar
    andrei23 is offline Main Sequence
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    Thanks for the explanation and the suggestions, Mothywood! I've been doing some further reading, and picked up a UHC filter in order to get the most out of my DSI II. To stretch this entry-level camera to its furthest (noticed you have a Parsec... droool), and to do any meaningful color-separated photography, debayering seems to be the key. I've just downloaded Nebulosity, as its VNG algorithm seems to be the best for OSCs. Ultimately, I know I will need a better (and monochrome) camera. All in good time - I still have plenty I can learn and practice with on this one.
    Binos: Optolyth 8x56
    Scope: Celestron C10 N-GT, CG-5GT German Equatorial mount, JMI MotoFocus
    EPs: Explore Scientific 4.7mm, 14mm, 30mm 82 FOV; Orion 20mm illuminated
    Filters: Baader Ha, OIII, SII, UHC, Skyglow, Blue interference; Astronomik UHC
    Photo: Meade Deep Sky Imager II

 

 

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