lens advice - confused on DX conversion

Discussion in 'Digital Photography' started by puckhead193, Jun 22, 2011.

  1. macrumors G3


    May 25, 2004
    So I'm thinking of picking up a Nikon 14-24 f2.8 OR a 24-70 2.8. Now I know there will be a crop factor of 1.5 on my D90. Now my question is this, on my kit 18-105 DX lens what does that equal to in full frame. If I look at my 35mm 1.8 DX lens what is that equal too in a fx camera?
    Which lens would be better for my D90?

  2. macrumors 65816


    Nov 2, 2007
    A crop factor of 1.5 means you just multiply everything by 1.5.

    18 - 105 would be 18*1.5 - 105*1.5, which is 27-157(ish). The 35mm is 35*1.5, which is 52.5mm
  3. thread starter macrumors G3


    May 25, 2004
    so when i'm using my 35mm 1.8 DX lens it really is a 52.5...
    so nikon DX lens are for lack of word labeled wrong. I thought that my 18-105 would be equal to 18-105 if i could magically put it on a full frame body w/o the crop factor....very confusing. :p
    so i'm thinking in terms of a normal lens for my D90 the 14-24 is a better choice.
    Is one lens better then another in terms of sharpness?
  4. macrumors 68020

    Apr 14, 2001
    Fukuoka, Japan
    No, it's not. You should get a 17-55 mm f/2.8 Nikkor if you have that kind of money. It roughly corresponds to a 28-80 mm bread and butter zoom.
  5. macrumors 65816

    Jun 9, 2009
    They are not labeled wrong. The 18-105mm signifies the focal length of the lens, which is a property irrespective of what body you mount it on.

    The 1.5 multiplier comes in when you are calculating effective field of view. Although field of view and focal length are closely related, they are not the same thing.

    If you have to ask about the sharpness of the 14-24 or 24-70, then you probably should not be buying them. You should not buy one or the other "because it is sharper".
  6. macrumors 65816


    May 8, 2008
    Hilo, Hawai'i
    Ruahrc explains it properly.

    But about the 14-24 f/2.8. Have you handled one? It's seriously large and heavy. I have one and I love it, but it's a big sucker. And it's really expensive.

    The 14-24 wouldn't be a "normal" lens for your D90, assuming that by "normal" we're talking about the traditional 35mm "normal" 50 mm lens. With the 1.5 crop factor, a 35mm lens would be equivalent to the traditional normal lens.

    The 14-24 on a DX sensor would be equivalent to 21-36 full frame, which in the full-frame world would be very wide to moderate wide. Definitely not "normal."

    Play around with Google and "field of view," and you'll find many calculators and examples.
  7. macrumors 6502a


    Sep 30, 2008
    Dallas Metroplex
    On the D90, I would recommend the 24-70mm f/2.8 since that would be a great walk around and portrait lens due to the crop factor.

    I wouldn't get the 14-24mm f/2.8 on a crop body because it's not wide enough. I would go with the Tokina 12-24mm f/4 or Sigma 10-20mm f/3.5 for wide.

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