A&P Veil Nebula region

Discussion in 'Lifestyle' started by EWhytsell, Sep 26, 2008.

  1. EWhytsell

    EWhytsell New Member

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    Here's a wide field shot of eastern veils (bottom) and western veil (top). This one took a huge amount of processing to get them to show up and they are at the limit of what the canon 75-300mm can see. Total exposure time is 1 hr for this one.
    I can't think of a way to reduce the amount of stars in that field. There's just so many that is overwhelming so the shots not that great.

    [​IMG]
     
  2. QWIKSNK

    QWIKSNK New Member

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    is it possible to use a standard tripod, and just focus on the same star for every shot? cause you do like 40 shots combined into one right?
     
  3. EWhytsell

    EWhytsell New Member

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    That shot would be impossible on a standard tripod since it was 50 or so 90 sec exposures.

    I got a question about lenses though. As an astronomer I want the biggest front glass possible in a telescope. It allows more light to get to my eye/camera. Is this the same with camera lenses? I used the 75-300mm here which has a filter size of 58mm so it has about a 58mm glass. Now I can use my 28-135 which has a 72mm size, but would it get me more light? In telescopes it sure does, but as I understand it lenses might be different.

    Evan
     
  4. tetsuo

    tetsuo And shepherds we shall be...

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    with lenses, the bigger aperture (lower f-number) the more light gets in.
     
  5. EWhytsell

    EWhytsell New Member

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    So glass size should have no bearing?
    50mm front lens diameter at F/5 vs a 72mm front lens at F/5, which one gathers more light? I'd think the larger one would.
     
  6. Tedrzz

    Tedrzz New Member

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    the larger one technically would except your totally ignoring the f/stop factor. that's the whole point of an aperture, to accurately let in a certain amount of light to make a certain exposure. even if the front element was a meter wide and your aperture was f/5 it would get the same amount of light as your 50mm "front lens diameter" (in photography you call it front element)

    so you'd want to find something with a bigger f/stop...like a 70-200 f/2.8 which lets in a whole stop more light than the lens you're using right now.
     
  7. EWhytsell

    EWhytsell New Member

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    Hmm that doesn't add up to me. My scope has a front element of 206mm and is fixed at F/10 and it lets in many times more light than one that is a 50mm F/4.

    Is there a standard size in mm that an F/5 aperture equals? I'm kinda thinking that its more complicated than that and that its a ratio of the front element size or something similar.

    If F/0 were possible with all lenses then that would be 100% of the light. Then as you stop down your reducing the light hitting the lens.

    If this is the case then a larger front element will definitely increase the light at any given F number so a larger lens would require a higher F number in order to reduce its light to match a smaller one at the same shutter speed.

    Sound at all reasonable?
     
  8. jared_IRL

    jared_IRL OT Supporter

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    typically, lenses with larger apertures have bigger front elements.

    For example, go look at a 300mm f2.8 and compare it to your 300mm 5.6...

    The front element would be close to twice the size.

    However, it's not just the front element that controls how much light hits your lens. Inside the camera lens are focus motors, moving zoom mirrors, etc.

    So your 28-135 may have a larger front element, but may not let much more light hit the sensor due to the inner workings and how light is reflected.
     
  9. Tedrzz

    Tedrzz New Member

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    When calculating f/stops they use this equation: f/stop = f/d

    where f = focal length
    where d = pupil diameter

    so lets say i have a 400mm lens that i shoot at f/4..the f/stop size (or pupil diameter) is 400/4 so the pupil size would be 100mm. i have another 200mm lens i'm shooting at f/4...the pupil size would be 50mm but both will transmit the same amount of light to the sensor of your camera.

    note that when i'm talking about 400mm and 200mm, i'm talking about focal length, not about front element size.
     
  10. kill_turu_kill

    kill_turu_kill Turu the Terrible OT Supporter

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    Nice shot Evan-

    I tried to shoot last night-piggy backed on a 16 inch Meade at an observatory. Usually from my home I can get around 25 seconds before fogging the shot, but last night the max was only 8 seconds. Not even worth processing. But I did get to visually see M13, M27, and M56 through that scope. The Ring was pretty impressive.
     
  11. EWhytsell

    EWhytsell New Member

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    Nice I've always loved looking at the ring. M27 is really cool, but you need very dark skys to see the detail. M13 is also nice, but requires you to look at it for quite awhile to sorta train your eye to see it well.

    At a star party I got to look at M13 through a guys home built (freaking huge) binoculars. They were a pair of 6" 1500 or 2000mm telescopes that he built and had a prism system set up where we could use them both on the same object. Very impressive to see the true 3-D image of that cluster.

    I'm going to West Virginia to a star party next month so maybe I get some neat pics at that true dark sky site.

    Evan
     

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