Is this normal? nikon 24-70 2.8 vs 50 mm 1.8

Discussion in 'Photography Equipment & Products' started by hao, Sep 18, 2009.

  1. hao

    hao TPF Noob!

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    I made some shots in my room during the evening with the room light which was not very bright with those two lenses (Nikon 24-70mm 2.8 and Nikon 50mm 1.8). Both lenses were set to 50mm @ f2.8 and the same shutter speed.

    What I have found is that the images produced with 50mm were somehow brighter than 24-70.

    So was it that the physical length of the lens that affected the intensity of light coming to the camera sensor? or it was because that 24-70 has more glass elements in the lens which could block some friction of light?

    Is it normal? thanks!
     
  2. robertwsimpson

    robertwsimpson No longer a newbie, moving up!

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    Unless I'm mistaken, a prime lens is always going to pass more light than a zoom.
     
  3. Dao

    Dao No longer a newbie, moving up!

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    Technically, I believe they are suppose to be equal. But usually it is off a little bit.

    i.e.

    Photo A: Prime Lens A at 50mm, 1/250, F/2.8, ISO100
    Photo B: Zoom Lens B at 50mm, 1/250, F/2.8, ISO100

    Both are technically same exposure (with the same EV), so it suppose to be the same. However, I learned that lenses are not create equal.

    Even Brand A 50mm lens maybe different from Brand B 50mm lens with the same F stop.
     
  4. bigtwinky

    bigtwinky No longer a newbie, moving up!

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    can you post the images?

    was the ISO set to auto or was it set to the same value for both images?
    what mode were you in? maybe if you were in a semi or full auto mode, the camera may have made some adjustments for metering...
     
  5. hao

    hao TPF Noob!

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    I dont have the image right now,
    but you can definitely tell the difference.
    I can post the image later after I get home
     
  6. Big Mike

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

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    That's not all that uncommon. Some lenses pass more light at given apertures than others. Part if it might be inconsistencies in the actual size of the aperture opening. What the lens/camera thinks is F4, might actually be F4.5 or something like that.
     
  7. 5DManiac

    5DManiac TPF Noob!

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    I wouldn't worry about it. Technically given the same settings, the apertures should be consistent but due to the lenses being different, there may be slight variation as the above guy said. ive seen the exif on my 50 1.8s pics and i think ive seen 1.75
     
  8. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Was your ISO set to AUTO?
     
  9. hao

    hao TPF Noob!

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    I rarely shoot with AUTO ISOs.
    ISO was set to some value, but not AUTO
     
  10. Derrel

    Derrel Mr. Rain Cloud

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    Nikon | Imaging Products | AF-S NIKKOR 24-70mm f/2.8G ED (2.9x)

    15 elements

    Nikon | Imaging Products | AF Nikkor 50mm f/1.8D
    6 elements

    Nikon Nikon 24-70mm f/2.8G ED AF-S - Lens Review from Experts at Popular Photography- Photo Tips
    "24-70mm (24.78-68.86mm tested), f/2.8 (f/2.86-3.05 tested)"

    What you observed is pretty common. Every single air-to-glass surface loses some amount of light, even with modern anti-reflective coatings. Prior to lens coatings, light loss of up to 3 percent per surface was common; with coating, it has been brought down to around 1 percent or slightly less, per air-to-glass surface. f/stop is a function of focal length and the width of aperture in relation to focal length. f/stop is a mathematical formula, not a measure of light transmission; this is why lenses for cinematography use have a precisely measured TRANSMISSION value, known as the T-stop.

    As you can see by the Pop Photo lab tests, the 24-70's actual,measured f/stops are just slightly slower than f/2.8, across the focal length range.
     
  11. hao

    hao TPF Noob!

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    thank you everybody for the input.
    I dont think that is an issue then. Plus, I could not find any one complaining such issue as a defect on the Internet. There are defect issues such as bad focusing, dark edges, loose lens mount..
    but not this one, or I am just too picky.
    Anyways, you guys have been very helpful
     

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