I...am confused.

Discussion in 'Photography Beginners' Forum' started by OB-LL426, Nov 3, 2008.

  1. OB-LL426

    OB-LL426 TPF Noob!

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    I am rarely confused with photography, but right now, my brain is about to go ka BLOOEY.
    I am confused about focal lengths.

    On my camera, which is a P&S, though a "super-zoom" P&S.
    Its an Olympus SP-550 UZ, with 18x zoom.
    Well, for the focal length of this zoom, it says the farthest out it can zoom, 18x, is 84mm. And the lowest focal length is 4.7mm That is what is confusing me.

    I have been doing quite alot of research on buying a D-SLR, and I know that the normal kit lens, for an entry level SLR, is 18-55mm, which I've also read, is about 3x zoom. Going from 3x zoom at 55mm on an SLR, to 18x zoom at 84mm on a P&S, just...is not working out on my mind.

    Is the focal length numbers between a P&S and a SLR, different? From what I've known, they aren't, but now, I'm starting ot think...are they?

    I reeally need someone to clear this up with me xD. :confused:

    Also, what would a 55-200mm zoom be, compared to the zoom that is automatically on my camera?
     
  2. benhasajeep

    benhasajeep TPF Noob!

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    Yes, focal length is different on P&S than DSLR. Most manufacturers list the 35mm equivallent in their information. Might want to look it up. Reason is sensor size. Just like a 90mm lens on 35mm camera is telephoto, Normal on medium format, and wide angle on 4"x5" film cameras. Same goes for digital sensors. P&S cameras have small sensors. Then you have the larger but not full sized sensors on DSLR, and now you have full frame sensors (same as 35mm film size) and Full sized sensor DSLR. This is why you have what is known as crop factor with the same lens on small sensors on DSLR's.

    Also when they say 18x zoom. It just means that the max is 18x the shortest. Ie 18 x 4.7 = 85mm roughly.

    Just looked up your camera it is the same as a 28mm to 504mm in a full frame 35mm digital or film camera.
     
    Last edited: Nov 3, 2008
  3. doenoe

    doenoe TPF Noob!

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    well, what i think its is that if you multiply 4.7X18, you get 84. So the magnification from 4.7 to 84 is 18......so its an 18X
    So..if im correct the numberX is just some salestalk, because that number depends on your focal-lengths. In your case 18X looks like alot but its isnt really that big of a zoom.
    Just my thoughts, this just makes sense to me........but i could be way off :)

    ps.....maybe it depends on the size of the sensor too?
     
  4. OB-LL426

    OB-LL426 TPF Noob!

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    Ohhh.
    I get it now.

    Thanks guys!

    So, a 55-200mm zoom, for an SLR, would actually be less than what I have, because in 35mm equivalent, my camera is 28mm to 504mm while the 55-200mm is 82.5-300mm. Right?
     
  5. benhasajeep

    benhasajeep TPF Noob!

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    Yes, you must be looking at a DSLR with a 1.5 crop factor. So any lens on that camera you multiply focal length by 1.5 to get the "full frame" equavillant size. So on the 1.5 crop factor to match the range of your current P&S you will need a lens (most likely 2, or more) from 18mm to 336mm (approx) to get the same shots.
     
  6. Dao

    Dao No longer a newbie, moving up!

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    The term "ZOOM" really just means the camera are capable to adjust the focal length of the lens.

    The zoom power (the x factor) means the ratio of the shortest and the longest focal length. It does not actually mean how far your camera can reach optically.

    i.e. If a lens can adjust from 4mm to 8mm, it has 2x zoom power. And a lens that can adjust from 100mm to 200mm is also 2x zoom power.

    4/8 = 100/200



    In the SLR scene, you will see a term called telephone lens. It reference to a lens that has long focal length. A telephone lens has the ability to bring a image of distant object to the image sensor or film and appeared to be magnified.

    If you are looking for a lens that can capture a nice big image of a bird standing on the tree top, you need to look for a telephoto or telephoto zoom (adjustable focal length) lens. The longer the lens focal length, the bigger the magnified image.

    i.e. you will see a more details image of a moon with a 500mm lens than a 200mm lens.

    Hope this help.
     

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