PL 100-400 for Astro Images....

Discussion in 'Astrophotography' started by D7k1, Aug 21, 2016.

  1. D7k1

    D7k1 Mu-43 Top Veteran

    692
    Nov 18, 2013
    Ok, first my excuses:

    1. trying out new Polar Alignment scope, forgot to check alignment with mount on install. Alignment was way off - 132" - so knew tracking would be not so good even at 30 Seconds.
    2. Just used 3x enlargement on Denb to focus lens.

    Overall I think this lens has some potential. This image is about a 20% crop -perhaps more. 40 30 second subs, no darks or no other subs. With a good polar alignment, darks, lights and no moon it should produce some good stacked images. Shot @ 400 mm @ 30 Seconds .

    a6ac1327855083.57b9ed3d16f1f.
     
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  2. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    How would you say this would compare to a telescope?

    I have my dad's Televue Renaissance 550mm, but I need to figure out the tracker.
     
  3. D7k1

    D7k1 Mu-43 Top Veteran

    692
    Nov 18, 2013
    I also just realized I also left long exposure noise reduction on, should have turned it off, lost stars where Deep Sky Stacker with darks/whites would have kept them.
    Some more info: ISO 800, f6.3, object m27

    Televue is a premium scope, but you would be imaging at 1100mm and that requires very good tracking (an AVX ($800) might work but more likely something like a CGEM ($1500) for unguided.
     
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  4. jdthebigj

    jdthebigj Mu-43 Regular

    35
    Aug 28, 2012
    Fremont, CA
    JD
    I've been contemplating using PL100-400 to take pictures of M31. Have you tried that?


    Sent from my iPhone using Mu-43 mobile app
     
  5. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    The tracker it's on (a Vixen Skysensor) is probably about as old as the scope (1985-1986); it has a DIN connector with a serial (DB9) cable, and there's a DOS laptop which hopefully still works. So I'm guessing it won't be especially good.
    The scope is a Televue Renaissance 4 inch f/5.5 (550mm). It has a little mold on the edge of the front optic; supposedly it won't affect the image much since it's at the edge but it has destroyed the resale value.

    But I'm also wondering how the scope would compare to native lenses as my understanding is most scopes don't have flat-field correction, etc., so they may not look as good from a camera sensor as they do to the naked eye.

    Thanks!
     
  6. D7k1

    D7k1 Mu-43 Top Veteran

    692
    Nov 18, 2013
    Generally refactors and SCTs use focal reducers/correctors, and reflectors use comma correctors to correct any optical issues. Something like a TV101 will have $3K worth of glass and produce images far better than what I would expect from any camera lens including the 4-600mm Canikon monsters. I'd contact TV and see what they would charge to replace the optic with fungus.
     
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  7. D7k1

    D7k1 Mu-43 Top Veteran

    692
    Nov 18, 2013
    Actually, I was just playing around to see if it would work. I will now do MM31 in about a month and I would it expect it to be pretty good. I will use a GX8 next time with the lens and a Gx8 on prime on the C8 at the same time to compare. Will post here.
     
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