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    Default 5x Barlow for planetary imaging with a 6" reflector



    I am evaluating the possibility of increasing the magnification of my imaging setup by stepping up from a 2x Barlow to a 5x Barlow. I am aware that by increasing magnification I will lose contrast and some detail. My OTA is a Celestron Omni 150 XLT which has a highest useful magnification of 354x. I know that manufacturers tend to overstate this but I am thinking about giving it a try. Has anyone in the forum paired a 5x Barlow with a 6" reflector with good results? Your insight will be greatly appreciated.

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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    I have used a 3x barlow on an XT8 (f6) and while it works it is very tricky to work with. Focus range is very, very tight and getting the target in the field of view (and keeping it there) it there is difficult.

    I can only imagine a 5x barlow would be even more difficult.
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  4. #3
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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    I've not done much in the way of planetary but I've been looking into getting a barlow, so I've been researching it myself. According to Starizona, your choice of a barlow should be based on pixel size.

    For the ASI1600 that is 3.8*825 = 3135. That tells you the optimal focal length based on your camera.
    Divide your focal length into that (3135/750 = 4.18 or a 4x barlow). If you had excellent seeing, you could probably use a 5x, but those times would probably be rare.

    Another site recommended a image scale of around 0.33 arcsec/pixel for 1 arcsec seeing conditions. If I plug your info for your camera and scope into this calculator (3.8 micron pixel & 750 FL * 3x barlow = 2250 FL):
    Image Scale and Field of View Calculator
    I get a image scale of 0.348 arcsec/pixel, which is pretty close to the recommended amount.

    A 4x barlow (3000mm FL) yields 0.26 arcsec/pixel (Starizona recommended 0.25 "/pixel). So my guess is your best bet would be a 3x or 4x barlow.
    Rob

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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    This is very helpful, thanks very much!

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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    Hi Tom! I thought so...but a 3x won take me where I want. On the other hand the 5x is too much. Based on the pixel size of my AS═ 1600 maybe 4x is the way to go, but Gosh! there are not many choices and the ones available are so expensive!

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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    3x is the highest usable magnification for Planetary work in my opinion. My best rig and results are from an 8 or 10" SCT with a 3x barlow and asi120MC CCD camera. The smaller chip actually helps here.
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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    Quote Originally Posted by Leveye View Post
    3x is the highest usable magnification for Planetary work in my opinion.
    With any scope or with your SCTs? Your 8" SCT with a 3x barlow has a focal length of around 7000mm. Since his scope is f/5 (150/750mm) even a 5x barlow will make his focal length only 3750mm. His image scale with a 3x barlow would be about equal to your scope without a barlow.
    Rob

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    Default Re: 5x Barlow for planetary imaging with a 6" reflector

    Interesting discussion. But doesn't the resolution of the telescope limit that? If the scope has 150mm aperture, then the resolving power is 0.8", right? So, going below 1/3 of that many arcsec/px won't make much sense, and that's about 0.27 arcsec/px.
    Even more important: won't the image be too dim to get a decent video?

 

 

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