Not a good pic, but tech questions related

Discussion in 'Photography Beginners' Forum' started by Tom3, Jan 14, 2009.

  1. Tom3

    Tom3 TPF Noob!

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    I was playing with the camera the day the moon was very big:
    [​IMG]

    None of the pictures turned out good...

    The pics were done using a D200 with the following settings: f/5.6, 4sec exposure, 100 iso, 98mm focal length.

    The blue halo you see was caused by the polarizer on the lens.

    but this triggered two questions:

    - When I did shots with a wide aperture, I got a warm tint, while when I did it with a small aperture, it was very monochromatic; Could it be that the wider opening lets street light come in more? I mean the same trees (lit by street light) were in the same shots, but the yellow tint was gone with the small aperture.

    - I assumed that I could do manual focus and set the lens on infinity: it turns out that no... at infinity the moon is blurry! a tiny tiny bit less and it was sharp; what is the reason? (it's a sigma 18-200, could it be the cheap construction?)
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Good question. I'd guess it has something to do with the different angles that the light is bent at for different aperture. Diffraction and maybe some chromatic aberration etc.

    By setting it on infinity...did you just turn the ring all the way? On many lenses, this would indeed be past infinity focus....just a little bit. This might have something to do with lesser quality lenses, zoom lenses or maybe it's there to allow for expansion/contraction or slight misalignment.
     
  3. OldClicker

    OldClicker TPF Noob!

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    Way over exposed if you actually want to see the moon. Try f/16 at 1/125 sec. - TF
     
  4. Josh66

    Josh66 Been spending a lot of time on here!

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    I think it's like that to prevent the autofocus system from taking/causing any damage from hitting the mechanical stops. Every lens I own will go past infinity (the 135 f/2.8 will go waayyyy past infinity).

    On Canon lenses the vertical part of the infinity mark (looks like an "L") is infinity.
     
  5. Tom3

    Tom3 TPF Noob!

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    right, now thinking of it, it makes sense to have a little slack at the end.

    oldclicker: yes, it is overexposed; this shot was to demonstrate that the wide aperture will let the street light in; I should have posted the ones with the small aperture: you can only see the light from the moon, absolutely no tint from the street.
     
  6. Josh66

    Josh66 Been spending a lot of time on here!

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    Did you change the shutter speed and the aperture?

    If you changed the aperture without also changing the shutter speed, that is why the wider aperture is letting you see more of the street light.

    If the small aperture shots used the same shutter speed as this, they would be exposed less.


    The above photo was at f/5.6, 4 sec. If the other photo was at f/16 the shutter speed would have to be 32 seconds to get the same exposure. If it was f/16 and 4 seconds, it would be exposed 3 stops less that this one.
     
  7. Tom3

    Tom3 TPF Noob!

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    yes, I did somewhat match the shutter speed / aperture to get constant exposure, so the street light did not come from the longer exposure, the color was really tied to the wider aperture.

    Big Mike's theory is probably right.

    I would venture to guess that, with a large aperture, it gives more opportunity for light that wouldn't have made it to enter sideways and possibly bounce a couple times inside the lens before hitting the sensor.
     
  8. Josh66

    Josh66 Been spending a lot of time on here!

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    Interesting...

    Can you post the other one too?
     
  9. Tom3

    Tom3 TPF Noob!

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    this one:
    [​IMG]

    Is still 100 ISO, but f/40 and 30 sec exposure

    As you can see, there is no tint from the street
     
  10. Sw1tchFX

    Sw1tchFX TPF Noob!

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    Shoot at f/8, spot meter on the moon, ISO100 or 200 and get that polarizer off, it has no buisness being on there when you're in anything but broad daylight and want to cut out reflections.

    You do that, you'll have great shots.
     
  11. Josh66

    Josh66 Been spending a lot of time on here!

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    f/5.6 to f/40 is a difference of about 5 1/2 stops, while 4 seconds to 30 seconds is only about 3 stops. Your f/40 picture would have had to be somewhere around 140 seconds to get the same exposure.

    That's why it's so much darker, even at 30 seconds it's still exposed about 2 1/2 stops less than the first one.
     
  12. Tom3

    Tom3 TPF Noob!

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    it makes sense now; so I guess, with a 140 seconds exposure, the same tint would have appeared.
     

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