"Normal" lens for 1.6x crop factor?

Discussion in 'Photography Beginners' Forum' started by fatsheep, Jan 14, 2008.

  1. fatsheep

    fatsheep TPF Noob!

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    DSLR and 35 mm SLR seem to use the same lenses yet DSLR cameras have crop factors (like 1.6x in the rebel's case). So your "normal" 50 mm lens is going to end up being a moderate 80 mm telephoto on a DSLR right (50 * 1.6 = 80)?

    If a "normal" lens ends up being a telephoto, do you have to employ a wide-angle lens to get a "normal"? If you have to go to wide-angle lens to get a "normal" focal length then do you have to go to a fish-eye lens to get wide-angle-like focal length?

    I'm a bit confused here... :confused:
    Explanations are more than welcome. Thanks in advance,

    - sheep
     
  2. Sideburns

    Sideburns TPF Noob!

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    The only problem with a 50mm becoming an 80mm is that it still has the same distortion as the 50mm.

    Say you use a 35mm...that's a bit closer when cropped...but it is wider, and may make the people look fatter. Even though you get the field of view of an almost normal lens.
     
  3. Mav

    Mav TPF Noob!

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    Yep. On 1.5x Nikon DSLRs the 35mm f/2 is what a lot of people use for a "normal" walkaround lens, although it was originally designed as a slight wideangle for 35mm film bodies. The widest angle lens I've seen for Canon 1.6x DSLRs is the EF-S 10-22mm which is equivalent to 16mm on a full-frame body. That's pretty darned wide with about a 100 degree angle of view or thereabouts. 14 or even 12mm on a full frame body will still end up being a lot wider, though. Sigma just came out with a fisheye lens for Nikon/Canon 1.5x/1.6x bodies that will give a 160 degree horizontal field of view and a 180 degree diagonal field of view on Nikons, and just a tad less than that on Canons. But you're correct in your idea that you could also use a full frame 15/16mm fisheye on a crop body, but it won't be as wide as the fisheyes that are designed for crop bodies. Not sure which would be wider, a 15/16mm fisheye on a crop body, or a 10mm rectilinear lens. The angle of view formulas that apply to rectilinear lenses don't apply to fisheyes. I'm sure if you Google around that somebody has tried it and you might be able to figure it out. BTW I think Canon also has a 28mm f/2.8 prime lens that might give a bit more normal view on a 1.6x body, but it's not quite as quick as the 35mm f/2.
     
  4. Ls3D

    Ls3D TPF Noob!

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    In a related thought, does the 1.6 conversion factor apply to cannon's EFS lenses?

    -S
     
  5. Josh66

    Josh66 Been spending a lot of time on here!

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    I've always wondered about that too. Since they know it's going on a crop body, is 18-55 really 18-55, or is it 28-85?
     
  6. Peanuts

    Peanuts TPF Noob!

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    I imagine an 18-55mm is perceived to be a 28-85mm. I can't imagine the confusion they would introduce by stating the 'real' focal length.
     
  7. omardxb

    omardxb TPF Noob!

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    Interesting enquiry and comments, it's true, the 18-55mm is actually a 28-85 lens, but for easiness sake (And marketing purposes probably)
    they still call them 18-55
     
  8. ghpham

    ghpham TPF Noob!

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    hhmm...interesting discussion. The thing that's really confusing to me is the crop factor. Does it really mean "telephoto" or is it because the pictures got cropped, that it actually give you the feel of "telephoto" over the 35mm frame?
     
  9. Mav

    Mav TPF Noob!

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    The focal length of the lens is the focal length of the lens, which never changes. The only thing that changes is the angle of view, which varies depending on the sensor size. A bigger sensor will see wider. Hence to get the same angle of view as 28mm on a full-frame digital or 35mm film, you need an 18mm lens on a 1.6x cropped DSLR to make up for the smaller sensor that doesn't see as wide.
     
  10. jstuedle

    jstuedle No longer a newbie, moving up!

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    They are marked what they are. A 18-55mm lens is a 18-55 focal length no matter the crop factor. The crop factor makes it "look" like a 28-85 as compared to the full frame 35mm film or sensor camera. It's strictly a "field of view" issue. It's no marketing, it is what it is. (no I'm starting to sound like Bill Clinton, gotta work on that) Look at your point and shoot camera. It might have a lens marked 4mm-13.5mm that looks like a 35-115mm lens on a full frame 35mm camera. They just have a similar field of view, but the P&S does in fact have a 4-13.5mm lens.
     
  11. Tighearnach

    Tighearnach TPF Noob!

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    Now im confused!

    An 18-55mm EF-S lens for Canon is 18-55 yes but it is made specifically for a cropped sensor camera therefore it wont work on a full frame camera therefore it is not really 18-55 but 28-88....?????

    Yes? No?
     
  12. Big Mike

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

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    Mav and jstuedle are correct. The focal length listed on the lens is the actual focal length. If it says 18-55mm, then that is the actual focal length.

    Look at the EF 17-40mm lens, for example. It will fit both full frame (or 35mm film) and 'crop factor' cameras. The field of view (FOV) will be different though, depending on the camera it's mounted on. So it's not the lens that's different, it's the camera.

    The same thing applies of EF-S lenses. They aren't any different...18mm is still a very short focal length...but because the camera 'crops' the image, the FOV is narrower than it would be on a full frame camera.

    EF-S lenses are actually different from EF lenses. They will only be used on crop cameras, so they don't need as big of an image circle. Also, the rear element protrudes farther into the camera body, which is the main reason you can't/don't use them on full frame bodies....because the rear element would interfere with the movement of the mirror.

    Just to say it again. The crop factor is a function of the camera...not the lens.
     

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