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Thread: Stupid cheap widefield

  1. #1
    Galaxieman's Avatar
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    Default Stupid cheap widefield



    Bought a 200mmf/3.5 ($20), a 300mm f/5.5 ($18), and a 400mm f/5.6 ($48). Total with shipping and adapters for all 3 was under $120. Mounted each piggyback on the big scope. Got a set of ten 10-second frames of Andromeda with each to see how they do for astro-work. Here are thumbnails of each stack sized so they show approximately the same FOV (click for larger image):

    200mm, f/3.5:


    300mm, f/5.5:


    400mm, f/5.6


    More pictures and a longer write-up are up over on my blog. On initial glance, the 200mm is going back on eBay as a decent terrestrial lens, but not one suited for astro-work (very obvious coma issues). I'm torn between the 300mm and the 400mm, and would appreciate any input you folks have about which you might think is better and why. On my initial eval, I think the 400mm has slightly better contrast and less star bloom, but the stars that do bloom have more coma. I realize these are NOT high-end APO instruments, and as such I don't expect them to output pinpoint stars across the field, etc, etc. But when the most expensive of the 3 lenses was just over $60 all told, and they all fully illuminate a full-frame 6D sensor... I'm really happy with the results. When cost is so low, benefit doesn't have to be too high for the cost:benefit ratio to slew quickly. I think I'll try some shots centered on M42 to see how these compare with some bright stars near the center of the field for round 2.
    Scope: Celestron NexStar 8 GPS, HD wedge on CPC HD tripod, f/6.3 reducer/corrector, Telrad Finder, Celestron 9x50mm Finder w/ Orion Starshoot Autoguider;
    NexStar GT Mount on Magnum XG tripod (poor-man's EQ wedge)
    Camera: Canon 6D ........... Lenses: Rokinon 14mm f/2.8, EF 50 f/1.4, Sigma 70-200mm f/2.8, Vivitar 400mm f/5.6 (manual focus)
    Stacking software: DSS, Registax ..... Image Software: Lightroom, Photoshop
    Please visit my blog at: http://www.galaxieman.com

  2. #2
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    Default Re: Stupid cheap widefield

    The 300 and 400 image quality look very similar. Pretty nice images for the prices you paid. However, if I'm going to stay up late to get pictures, not sure either of them would make my cut. A bit too much blue around the bright stars.

    The 400 would make a very nice entry level starter setup. Cheaper than an Orion ST-80.

    All of this is just my humble opinion for what it's worth.

    Thanks for sharing.

    Steve
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    Default Re: Stupid cheap widefield

    If you don't mind my asking, why bother with the little scope? Why not just use the big scope on which the small scopes are riding piggyback?

    Clears,
    Joe
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    Default Re: Stupid cheap widefield

    Looking for a wider field?
    John

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    Default Re: Stupid cheap widefield

    Using a 300mm or 400mm in lieu of an entry-level scope for wide-field was my basic idea. The 6D + focal reducer combo on my NexStar 8 GPS is wider than the T1i was, but for targets wider than 1° across, it's too narrow a FOV.

    I have a Celestron TravelScope 70 which has near as makes no difference the same aperture as the 400mm f/5.6, and has similar fall-off in the corners of a crop-sensor camera that the lens does on a full-frame. CA and coma are also worse with that scope. Not as bad as the 200mm shot above, but notably worse than the 300mm or 400mm Vivitars. The big thing, however, is the focuser. Granted, the focuser assembly on something like a ST80 would be a good step up from the TravelScope, but without something like a dual-speed upgrade, the focuser on a lens just seemed more stable, and less prone to flex when tasked with holding up a dSLR. I read about how some of these older lenses did reasonably well for astro work, but it was hit or miss between lens designs, or even between different manufacturers of the same design. It's sort of a 'roll-the-bones' affair as far as quality controls, how well a lens may have been maintained / stored, whether or not it will focus to infinity properly with an adapter... etc. So I scrubbed a couple of auction sites and found these three lenses to experiment with.
    j.gardavsky and STEVE333 like this.
    Scope: Celestron NexStar 8 GPS, HD wedge on CPC HD tripod, f/6.3 reducer/corrector, Telrad Finder, Celestron 9x50mm Finder w/ Orion Starshoot Autoguider;
    NexStar GT Mount on Magnum XG tripod (poor-man's EQ wedge)
    Camera: Canon 6D ........... Lenses: Rokinon 14mm f/2.8, EF 50 f/1.4, Sigma 70-200mm f/2.8, Vivitar 400mm f/5.6 (manual focus)
    Stacking software: DSS, Registax ..... Image Software: Lightroom, Photoshop
    Please visit my blog at: http://www.galaxieman.com

 

 

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