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Thread: Digital lenses

  1. #1
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    Default Digital lenses

    sorry for asking such a newbie question, but what's the diff for digital lenses and normal lenses? i know using normal lenses on DSLRs give it a 1.5x magnification. right? (so eg. for nikon, sorry i know nuts bout canon, a non-DX 18-70mm on DSLR = effective 27-105mm. correct me if i'm wrong)

    so a DX lens, say, the new 18-200mm on a DSLR will give effective range of 18-200mm issit? is that what DX means? then if u use on SLR what range it become?

    thanks.

  2. #2

    Default Re: Digital lenses

    It's not the lenses that determines the crop factor, it is the image sensor inside the camera body.

    The effect is to show less of an image (compared to 35mm frame), there is no actual magnification. It is only the field-of-view that changes.

    Digital lenses like the DX or EF-s (for Cannon) are designed only for the smaller sensors in most DSLR's, i.e. they produce a smaller image circle (the light projected from the back of the lens onto the sensor) then regular lenses. Both digital and normal lenses can be used on any DSLR, but the digital lenses can only be used for the specific sensor size (or smaller) they were built for...

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    Default Re: Digital lenses

    When a 'nomal' lens is used on a APS DSLR, only the centre portion is used because the sensor is smaller than film size.

    so, since the edges are not used, people make 'smaller' lenses for APS DSLR. e.g. DX lens for Nikon.

    if these lenses are used on film or full-frame SLR/DSLR, the corners of the picture will be 'cut-off'.

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    Default Re: Digital lenses

    Quote Originally Posted by jonnie84
    sorry for asking such a newbie question, but what's the diff for digital lenses and normal lenses? i know using normal lenses on DSLRs give it a 1.5x magnification. right? (so eg. for nikon, sorry i know nuts bout canon, a non-DX 18-70mm on DSLR = effective 27-105mm. correct me if i'm wrong)

    so a DX lens, say, the new 18-200mm on a DSLR will give effective range of 18-200mm issit? is that what DX means? then if u use on SLR what range it become?

    thanks.
    u still got to multiply by the "magnification/crop factor". e.g. Sigma's DC lenses would be multiplied by 1.5x on Nikon DSLRs and 1.6x on the non 1 or non 5 series Canon DSLRs.

    The focal lengths are actual physical properties (just like weight of the lens or filter size - whether a lens is digital or not, a 500g lens with 72mm filter size is still a 500g lens with 72mm filter size). The "multipled focal lengths" equivalent is just a proxy for the field of view. Why people use "multiplied focal lengths" as a proxy is probably because it is easier to visualise than degrees (e.g. 28mm equivalent is a proxy for 75 degrees diagonal angle of view). This creates some confusion though
    Last edited by mpenza; 14th March 2006 at 06:25 PM.

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    Default Re: Digital lenses

    A 100mm lens on normal SLR or full frame DSLR will give 100mm.

    A 100mm lens on DSLR will give 130mm or 150mm or 160mm, depending on the crop-factor (not 'magnification' factor) of 1.3x, 1.5x, 1.6x.

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    Default Re: Digital lenses

    Another example, 17mm lens:
    on full frame (17mm equivalent angle of view) - 104 degrees diagonal angle of view
    on 1.3x DSLR (22mm equivalent angle of view) - ~90 degrees diagonal angle of view
    on 1.6x DSLR (27mm equivalent angle of view) - ~78 degrees diagonal angle of view

    Same lens, different angle of view on cameras with different sensor sizes. People use the "mm" equivalent as an easier way of visualising the angle of view.

  7. #7

    Default Re: Digital lenses

    i dun think this is what he is asking. he is asking if the focal length of a 18-200 DX lens is different from a 18-200 non-DX.
    the answer is no.
    the focal length a DX lens shows does not account for the crop factor of the camera. so a DX 18-200 is actually still a 27-300 lens.(with 1.5 crop)
    Last edited by satay16; 14th March 2006 at 06:34 PM.

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    Default Re: Digital lenses

    thanks guys, i'm getting a clearer picture. so the focal length of DX or non-DX is the same, and whether u use DX or non-DX on DSLR, the focal length is also the same. the "magnification" is due to the crop factor of the camera, which means it differs camera from camera. <-- so far am i correct?

    so i gather from your replies that the DX lens merely focusses the light into a smaller frame, so that it fits the sensor. right? so in that sense, if using the same shutter speed and aperture, ISO all those, using a non-DX lens at 50mm(for example) to take a picture, compared to another, using same shutter speed, aperture, ISO, focal length, etc, but use DX lens to take the same picture. the difference will be the one take with DX lens will be brighter?

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    Default Re: Digital lenses


  10. #10

    Default Re: Digital lenses

    Quote Originally Posted by jonnie84
    the difference will be the one take with DX lens will be brighter?
    erm.... wrong.

  11. #11

    Default Re: Digital lenses

    Quote Originally Posted by satay16
    erm.... wrong.

    actually i would be a bit confused too..

    for example, on a zoom lens that would usually peak at f8 on film/fullframe to get optimal sharpness corner to corner, on a 'lesser' digital sensor, wouldnt the odd corners be in manner of speaking 'cropped off', taking in the so said 'meatiest' portion closest to centre, say the 'cropped' image taken by the smaller digital sensor be sharp all over pretty much by what..f5.6/6.3?

    wouldnt that be interpreted as er.. brighter..or is it faster..or is it...???

    pls dont execute me!!!

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    Default Re: Digital lenses

    Quote Originally Posted by satay16
    erm.... wrong.
    ok.. then what's the difference between 2 photos taken all at same settings(ISO, shutter speed, aperture, focal length, same position, same lighting, etc), on the same DSLR camera, but only difference is that 1 with DX lens and the other with non-DX lens?

    i'm assuming got difference la, cos if no difference then what for they go make new lens rite?

  13. #13
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    Default Re: Digital lenses

    Quote Originally Posted by ortega
    thanks for the link. browsed through the page, but page 10 doesnt answer my questions. page 2, however, does shed some light on my queries.

    i quote from page 2:
    These are special lenses designed so that the image circle matches the smaller size of the image sensor of most digital SLR cameras. Their specialized design gives these lenses the ideal properties for digital cameras. The compact and lightweight construction is an added bonus!
    wat are the ideal properties?

    i quote from page 3:
    Reduction of the image circle diameter makes it possible to reduce the size and the weight of the lens, and contributes widely to the handling characteristics at the time of taking pictures.
    so the main difference is really the weight and size of the lens? photo-wise, watz the diff?

  14. #14

    Default Re: Digital lenses

    Quote Originally Posted by jonnie84
    ok.. then what's the difference between 2 photos taken all at same settings(ISO, shutter speed, aperture, focal length, same position, same lighting, etc), on the same DSLR camera, but only difference is that 1 with DX lens and the other with non-DX lens?

    i'm assuming got difference la, cos if no difference then what for they go make new lens rite?
    not sure if you noticed this, but there is no EFS lens with the same focal lengths as its full frame counterpart.

    EFS is really purely for the sake of lighter and cheaper lens. quailty wise........i would say the current EFS series are below average, but who knows, nxt time, when full frame goes obsolete, canon would start producing L series EFS.
    Last edited by satay16; 17th March 2006 at 03:26 PM.

  15. #15

    Default Re: Digital lenses

    Quote Originally Posted by jonnie84
    ok.. then what's the difference between 2 photos taken all at same settings(ISO, shutter speed, aperture, focal length, same position, same lighting, etc), on the same DSLR camera, but only difference is that 1 with DX lens and the other with non-DX lens?

    i'm assuming got difference la, cos if no difference then what for they go make new lens rite?
    For a wide angle lens, you will know that if you use it on a DX body, your angle of view will be reduced because it is cropped. So, in order to get back the angle, you will need an even wider angle lens. However, if you notice, all the full frame ultra-wideangle lenses are terribly expensive because the optics need to cover a larger image area. DX lenses doesn't need to cover such a big area and so are easier and cheaper to design, especially for the ultra-wideangles.

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    Default Re: Digital lenses

    i see i see... yup thanks guys!

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