Odd question regarding compacts

Discussion in 'Digital Photography' started by superted666, Jan 17, 2007.

  1. superted666 Guest

    superted666

    Joined:
    Oct 17, 2005
    #1
    Hey there,

    okay so after looking at the current crop of compacts one thing strikes me.

    Some of the compacts are equiped with incredible lenses capapble of 400m zoom and f2.8. Why are the SLR lenses so much more costly and less range?

    Is it purely down to quality?
     
  2. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #2
    Size of the imaging circle and thus the size of all the elements in the lens.

    A compact has an imaging sensor normally in the 1/2.7" size. DSLRs normally have APS-C sensors, although some Canons have full 35mm film sized sensors. For lenses that are interchangable back to film (or full 35mm sized senors) the imaging size must be that of 35mm film.

    As the area is so much larger all the optics have to scale up as well. As you increase the area of each element in the lens it gets more difficult to make, so the price goes up.

    This larger imaging sensor is what allows DSLRs to have much lower noise (without detail ruining levels of noise reduction) and greater DOF.

    You can read about sensor sizes here.

    Note that this is one reason why DSLR bodies are more expensive than compacts. Larger sensors are more difficult to make resulting in them being more expensive. If you double the sensor area it's much more than twice as expensive to make which is why Canon full-frame cameras are so expensive.
     
  3. superted666 thread starter Guest

    superted666

    Joined:
    Oct 17, 2005
    #3
    Excellent just what i was looking for.

    Just having a look at the link now

    Thanks

    Ed
     
  4. coldrain macrumors regular

    Joined:
    Dec 20, 2006
    #4
    You are partly right, and partly wrong. Yes, the image circle is smaller. But the cameras do NOT have 400mm lenses. And that is the biggest reason for the small lenses. They have 6-72mm lenses (in case of the Canon S3 IS and Sony h2/h5 at least. And their crop factor of 6x translates that to 432mm in 35mm film size equivalent.

    So very simple why the lens is so small... it is only a 6-72mm zoom lens. And the width of the lens can be smaller because the small chip allows for a small image circle.
     
  5. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #5
    That's certainly true as well. It's also a major part of the reason you don't see compacts with 18mm (or wider) 35mm equivalent lenses...
     
  6. ChrisA macrumors G4

    Joined:
    Jan 5, 2006
    Location:
    Redondo Beach, California
    #6
    The surface area of a lens element increase with the square of the diameter, the mass of the lens increases with the cube of the diameter. So when the size of the sensor goes up by 3x the mass of the lens goes up by 27x. Cost to manufacture is proportional to the amount of "stuff" you need to build the lens. Not just the material cost but it takes longer to machine a bigger part and it takes longer to polish and figure a larger glass element.

    Also the optical design is "harder" with an SLR because of the mirror box. The rear element needs to be quite fare from the sensor, this is a big contributor to the cost and size of SLR lenses. The optical design is more complex because of the size of the mirror box.

    Also and maybe the biggest driver of cost is that the quality of SLR lenses is so much better. SLR owners will not put up with the poor to fair optical quality of many P&S cameras.

    And then of cource the SLR lens has a lens mount. the mount is a fairly complex and robust structure and is the lacking on the P&S.

    The SLR lens mmay have other features too like a focus rin, and aperture ring, a powerful focus motor. A micro processot that send data back to the camera body and o on.....
     

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