Focal length/lenses!

Discussion in 'Photography Beginners' Forum' started by jvw2941, Sep 21, 2009.

  1. jvw2941

    jvw2941 TPF Noob!

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    I recently read an article in Digital Photography on focal length and what lenses do best. But I still feel very lost in the whole focal length category. What is focal length and what affect does it have on your lens, camera, processor etc.

    Also, I'm trying to find the right lens for when I buy the Canon EOS 50D. I love macro shots but also need a wide angle for landscape and more wide-scale photographs. I know this isn't much info and I do know a good bit about lenses but I'm just looking for some pointers from any pros on lenses and focal length.

    Thanks so much,
    Jameson
     
  2. fokker

    fokker No longer a newbie, moving up!

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    Focal length = zoom (effectively)

    focal length of 300mm is super telephoto - taking closeups of birds from a long way away

    50mm is 'normal' range, supposed to be equal to about what the human eye sees

    15mm is wide angle, suitable for landscapes, architecture etc (think of it as being zoomed right out so you can fit lots of stuff in the frame)
     
  3. jvw2941

    jvw2941 TPF Noob!

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    thanks, it's a LOT more simple than I though ha
     
  4. jvw2941

    jvw2941 TPF Noob!

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    one more thing, if a lens says F/1.4. Is that the only aperture value it can go to?
     
  5. Dwig

    Dwig TPF Noob!

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    NO.

    The f/stop or aperture listed as part of a lens' specifications, and usually marked on the front of the lens, is its maximum aperture (widest f/stop). Almost all lenses have adjustable apertures and can bet set to a range of f/stops smaller than the maximum.

    For a proper definition of focal length read this:

    Focal length - Wikipedia, the free encyclopedia

    Any "translation" of focal length into "telephoto", "wide angle", or "normal" has to specify the image format (sensor or film size) to be valid. A 40mm lens is "normal" when using 35mm film, "wide angle" when using medium format, and a slight "telephoto" when using a typical APS-c "crop sensor" DSLR. In each case, the focal length remains 40mm.

    You will often see the term "equivalent focal length" used. It has nothing directly to do with focal length; the relationship is indirect. On any one format, a particular focal length produces a particular field of view (FOV). When "equivalent focal length" is used, sometimes written like 50mm-e, what is being said is that this lens used (e.g 20mm) on the format being discussed (e.g. APS-c crop sensor such as Nikon's DX) produces the FOV of a different focal length (e.g. 30mm-e) on 35mm film. The common reference format for such "equivalences" is 35mm full frame (aka "Double Frame") film.
     
  6. flyin-lowe

    flyin-lowe TPF Noob!

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    If you have a prime lens like a 50mm 1.4. Then 1.4 is the largest aperture you can go to but you get get a lot smaller (higher number). If you have a zoom lens that is like a 75-300 4-5.6 then the 4 is the largest aperture you can have at 75 mm and 5.6 would be the largest you can have at 300mm. Again you can also change it to 22 or something but the above numbers are the largest you can go at the extreme focal lengths of the lens. Another thing that confuses many beginners is that the smaller the number the larger the aperture. 4 is larger then 5.6
     
  7. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Or focal length = Reach

    15mm is a very short reach. 100mm is a medium reach. 500mm is a long reach.
     
  8. Eyetattoo

    Eyetattoo TPF Noob!

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    What is the relation of aperture to the DOF?
     
  9. fiveoboy01

    fiveoboy01 TPF Noob!

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    Wider aperture(smaller number) will give a more shallow DOF than a stopped down(larger number) aperture.

    Also on the subject of zoom, one thing to add is that when handholding, the longer the focal length, the easier it is to incur image blur due to camera shake.
     
  10. djacobox372

    djacobox372 No longer a newbie, moving up!

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    Just when you thought so... I'll make it more complicated for you:

    The field of view (zoom level) is just one aspect of focal length. Perspective, or foreshortening, needs to be considered as well.

    Longer focal lengths will have less foreshortening--they bring objects in the background closer to the subject. Whereas shorter focal lengths will exaggerate perspective--distant objects will get very small very fast.

    To me this factor is far more important then the field of view, because perspective can not be adjusted via cropping, or moving closer/further from the subject.

    This is why 100mm lenses are more flattering as portrait lenses then a 35mm lens. The perspective is flattened with the longer focal length, so the subjects nose doesn't look as big and the effects of body posture have less of an impact on proportions. This is also why professional photographers use medium format cameras when shooting models, it allows them to take wider shots while still using a more flattering focal length. Many people think full-frame, medium and large format are all about resolution--it's not.

    There is a misnomer that states that 35mm is a "normal" lens for digital slrs because the sensor is cropped--a 35mm has a similar field of view on digital as a 50mm has on a film camera. The problem with this assertion is that it ignores the impact on perspective, which cropping has no impact on--this is why a 50mm lens looks like what we see, it has nothing to do with field of view--human vision is far wider then 50mm on a 35mm camera, yet the focal length that creates the most "true to life" perspective is about 45mm.

    If you understand this you'll be ahead of a lot of so called experts that go around claiming 35mm is "normal" on a digital slr.
     
    Last edited: Sep 23, 2009
  11. fokker

    fokker No longer a newbie, moving up!

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    Interesting, I never knew that. Thanks!
     

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TRUE PERSPECTIVE IN 35MM CAMERA