Nikon Lens sizing question.

Discussion in 'Photography Beginners' Forum' started by Alan92RTTT, Apr 14, 2010.

  1. Alan92RTTT

    Alan92RTTT TPF Noob!

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    I get confused by this all the time and maybe someone can help.


    I have a D5000 which I know is designed for their DX series lenses.

    If I use a lens like this [ame=http://www.amazon.com/Nikon-70-300mm-4-5-5-6G-Digital-Cameras/dp/B000HJPK2C/ref=wl_it_dp_o?ie=UTF8&coliid=I28XQD5YR87W4I&colid=2P202WL2S3K9K]Amazon.com: Nikon 70-300mm f/4.5-5.6G ED IF AF-S VR Zoom Nikkor Lens for Nikon Digital SLR Cameras: Camera & Photo[/ame] which is not a DX series lens it will act like a 105 - 450 lens.


    My question is about the DX branded lenses. I have seen some pages/posts that indicate that they will do the same thing and other pages/posts that indicate the will act like their listed mm's.

    Which is it? Are the MM's on the DX lenses accurate or is my 18-55 is really a 28-82?

    Thanks
     
    Last edited: Apr 15, 2010
  2. Breaux

    Breaux TPF Noob!

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    This is a very confusing issue.

    The mm for any lens stays the same. The camera you put it on is what changes the angle of view, or as you say, makes it "act like" a different focal length; more specifically it's the size of the sensor or film that counts.

    Any 70-300 lens on the D5000 (DX or not) will give the perspective of a 105-450 lens in 35mm terms. The reason is that your sensor is 1.5 times smaller than a 35mm film frame. The DX lenses are designed to give a smaller image area, which allows them to be smaller, lighter, and sharper, but it does not change the relationship between focal length and perspective.

    So the mm of 18-55 is the actual focal length of the DX lens, which results in a perspective (and magnification) similar to about 28-82 on a 35mm camera.

    This website has an angle-of-view table and calculator and might help clarify the issue: http://www.brooksphotopedia.com/definitions/angle-of-view.shtml
     
  3. Alan92RTTT

    Alan92RTTT TPF Noob!

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    Thanks, thats what I thought. I just keep seeing comments that make it see like the DX's were different.
     
  4. Big Mike

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

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    As mentioned, the focal length for any lens stays the same...it's always what is listed on the lens. It's the camera (size of the sensor) that changes, which is why we have this 'crop factor'.

    My question to you is...are you used to using a 35mm film SLR camera? If not, then don't give any of this a 2nd thought.
    All Nikon lenses will fit onto your camera and the view will be what it is.
    When they say that a lens will 'act like.....' they are comparing it back to the old standard of 35mm film cameras. If you have no preconceived notion of what lenses act like on that...then the comparison means nothing.

    One thing to consider, is that (I don't think) you camera has a built in AF motor, so if you want AF, you need to buy lenses that have their own AF motor.
     
  5. Big Mike

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

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    Well, technically they are. They have a smaller image circle, only big enough for the size of sensor in your camera. So all DX lenses will work with your camera, no problem.
    But if you someday get a 35mm film SLR or a 'full frame' DSLR like the D700....then those DX lenses won't have full coverage.
     
  6. Alan92RTTT

    Alan92RTTT TPF Noob!

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    AH so their is a difference.

    The main reason I care is to be able to compare two lenses. For example a tamron 18-250 to the nikon 18-200 whats the real difference to me in use. knowing that the listed mm's are always on the same scale make the comparison simple.
     
  7. Big Mike

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

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    Yes, the focal length on both lenses will be the same at any given setting.

    When comparing lenses, you can look at the numbers for direct comparison. The focal length and the maximum aperture are the main numbers to look at, which is why they are part of each lens's name.

    What you won't neccessarily see in the numbers, is the quality of the lens. Both the physical (build) quality and the optical (image) quality. These have to be looked at on a lens by lens basis...usually by reading reviews of the lens.
    A quick way to roughly gauge the overall quality of a lens, is just to look at the price. For the most part, higher quality lenses tend to cost more than lesser quality lenses. But of course, there are exceptions to the rule.
     
  8. cnutco

    cnutco No longer a newbie, moving up!

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    Big Mike
    You would be correct.


    Alan
    Only the D90 body and larger, (meaning size of body not model number,) has the AF motor.
    Also, if you are thinking about getting into speed lights later down the road, then make sure you get a lens that will communicate with the camera body.
     
  9. D-B-J

    D-B-J Been spending a lot of time on here!

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    yes, make sure you get lenses with an af motor. Also, the mm scale is only true on FX (full frame) cameras, and 35mm cameras. They are all based on the same scale, but when put on a smaller (DX) sensor, the field of view will become "longer."

    So a 70-300 on a DX camera would seem like 105-450mm. And 70-300mm on a Full Frame camera.
     
  10. Alan92RTTT

    Alan92RTTT TPF Noob!

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    I knew about the AF motor issue but thanks for watching out for me :)
     

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