Digital Prime Lenses?

Discussion in 'Digital Discussion & Q&A' started by MBasile, Jun 15, 2009.

  1. MBasile

    MBasile TPF Noob!

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    So I know with the smaller frame DSLR's the focal length is multiplied (~1.5x for mine). Knowing this, wouldn't getting a 30mm (well, 33 would be optimal) prime lens make more sense than a 50mm? 50mm on film gave the perspective of the human eye, and unless I am missing something, it seems to me that 30mm on an APS-C sensor would be the digital version, correct?
     
  2. Josh66

    Josh66 Been spending a lot of time on here!

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    More or less...

    But you would also get the perspective changes and distortion that you get as you go wider. It wouldn't look exactly the same as a 50 does on a 35mm camera.
     
  3. MBasile

    MBasile TPF Noob!

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    Thanks for the input... I'm still trying to wrap my mind around the how the lenses act in the digital world.
     
  4. musicaleCA

    musicaleCA TPF Noob!

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    Yeah, not exactly the same, but pretty darn close.

    On an APS-C sensor, the crop factor is 1.6. ;)
     
  5. MBasile

    MBasile TPF Noob!

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    Sony's has always been listed as 1.5, I think Canon's is around 1.6, but don't quote me on the Canon number :lol:

    So basically, it'd give me a similar field of view as a 50mm on film, but some wide-angle-like distortion?
     
  6. musicaleCA

    musicaleCA TPF Noob!

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    Maybe a little; but that distortion is worst at the edges anyway, and those are getting cropped-out.

    My bad; yeah, Sony's are 1.5. Silly brain.
     
  7. Josh66

    Josh66 Been spending a lot of time on here!

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    You would probably notice the difference on, say - a close-up of someone's face.

    Other than that, I wouldn't spend too much time worrying about it.

    I also wouldn't worry about crop factors too much. If what you have now isn't wide enough, get something wider. If it's not long enough, get something longer.

    Does it really matter if it's the same as it was on 35mm?
     
    Last edited: Jun 16, 2009
  8. Garbz

    Garbz No longer a newbie, moving up!

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    Wait Wait Wait. Take your ultra wide angle and crop it in the centre. All that distortion appears at the edges of the frame.

    What you get when you mount a 35mm on a APS-C type camera is the equivalent field of view as a 50mm, meaning all perspective distortion etc is as it would appear mounting a 50mm on film. Think about it, how else could the 3-10mm lenses on point and shoots get a usable picture.

    The only thing that changes is the depth of field, because now you have a 35mm lens with the middle croped out so your effective camera to subject to background ratio changes. Thus the only difference is that a 35mm f/1.4 on APS-C would have less depth of field as a 50mm f/1.4 on film. Everything else is pretty much the same.
     
  9. Josh66

    Josh66 Been spending a lot of time on here!

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    What would you call this?

    I guess it's more the distance to the subject than the actual focal length that causes it - but shorter focal lengths will require you to move closer to the subject get the same composition as the longer one.

    Or the effect seen here. (half way down the page)


    Maybe 'perspective distortion' is the wrong term, but something is going on and I don't really see how cropping would fix it.
     
    Last edited: Jun 16, 2009
  10. KmH

    KmH Helping photographers learn to fish Supporting Member

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    You shoot from farther away to minimize the distortion and then crop.
    Some of those short FL model images, the lens was almost touching her nose.
     
  11. itznfb

    itznfb TPF Noob!

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    nikon is also 1.5
     
  12. Josh66

    Josh66 Been spending a lot of time on here!

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    That doesn't seem like a very good solution.

    I wouldn't use a lens that required me to crop just to get a decent image...

    I'm not sure that that would completely fix it anyway. Not to mention that you would be throwing away the majority of the frame...

    Don't get me wrong - I'm not saying wide angle lenses are crap, just that they shouldn't be used for portraits. Not head & shoulders shots anyway. It would probably be fine for a full body shot.

    That's the point. You have to be so close to fill the frame that you end up with crap results.

    If the only alternative (other than using a more appropriate lens) is to stand far away and crop most of the picture out...well, that's just not really a good option.
     

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