To DX or Not To DX...

Discussion in 'Photography Equipment & Products' started by OmlessWanderer, May 17, 2007.

  1. OmlessWanderer

    OmlessWanderer TPF Noob!

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    I've been shopping for lenses to go along with the Nikon D200 I am planning to get and I haven't been able to discover the specific advantages to using a DX lens. I know they're 'designed specifically for digital cameras' but if you want to achieve comparable results between 35mm and APS-sensor digital you still need to multiply the focal length by the given sensor's multiplier, right?

    i.e. an 18mm lens on a Nikon D200 is equivalent to what would be a 27mm lens on a film camera, even if that 18mm lens is a DX lens, correct?

    If yes, then whats the point in having DX lenses? Why not just use standard 35mm lenses that will work fine if you decide to shoot film and might even produce better results on the digital since the majority of fall off associated with resolution and contrast near the edge of the frame(according to the MTF charts) would be off the sensor anyway. Wouldn't that effectively eliminate a whole slough of lens problems that tend to become more apparent near the edges of the frame?

    Is there some caveat I'm not aware of? Can someone explain this to me please? Thanks! :D
     
  2. firemedic0135

    firemedic0135 TPF Noob!

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    I believe, and I may be off a tad,but the dx lenses are supposed to eliminate/greatly reduce the ghosting effect that full frame lenses can create on the aps-c sized sensors.
    Their are alot more experianced photogs here that can provide you with further info and more in depth details.:thumbup:
    I also think that you are still using just the sweet spot of the lens,they have just necked down the rear of the lens.
    and yes you must still apply the 1.5x crop factor when using digital lenses.
     
  3. Don Simon

    Don Simon TPF Noob!

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    Supposedly 'digital-only' lenses (DX and those of other brands) are corrected for various aberrations which might appear with lenses designed for 35mm... I am far from convinced. I have never noticeably suffered from flare, ghosting or other issues using 'film' lenses on my dSLR, and by contrast I have noticed that those lenses perform better on the dSLR than they did with film in terms of edge sharpness (as you suggested).

    So why DX lenses? Well on a more practical level - say you used to use a 28-70mm on 35mm cameras. You want the same field of view on a 1.5x "crop" digital sensor. So you need something like an 18-50mm... where are you going to get an 18-50mm 'full-frame' at a good price? Similarly, say you used to use a 19-35mm lens - for a similar field of view you want what, a 12-24mm? Think how much extra a 12-24mm zoom would cost if it was 'full frame'.

    I think DX or equivalent lenses (ones designed solely for smaller digital sensors) make perfect sense - if you only shoot digital with that sensor size. If you want a real wide-angle you basically have no other choice, and otherwise the smaller image circle should mean smaller and lighter lenses which cost less to produce and to buy. All good. Personally I still shoot 35mm as well, and have no plan to stop in the near future, plus I hope for a larger sensor for my lenses in the future, so I am hesitant about investing in the equivalent of DX lenses - but I will probably do so anyway.
     
  4. fmw

    fmw No longer a newbie, moving up!

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    They just have a smaller image circle. That means that there is no advantage and, in fact, some disadvantage in terms of optical performance. The "crop factor" causes the camera to use only the central sweet spot of a 35mm lens and that's a good thing because the bad parts of a lens optically are normally at the edges of the frame. For long lenses you might as well buy the 35mm models and enjoy that advantage.

    However, if you want wide angle, then DX is the only option because of the "crop factor." I have three DX lenses. Two are wide angles and the third is a very high quality normal zoom that represents a very useful range for me. My longer lenses are all 35mm type.

    I don't often use lenses longer than about 50mm so I'm still hoping for some DX fixed focal length lenses if they ever decide to make them.
     
  5. sabbath999

    sabbath999 No longer a newbie, moving up!

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    Another thing to consider here is the trend in the very highest end cameras, which is larger sensor sizes (that new 10MP 10FPS monster from Canon for example... yes, I have lust in my heart for it)...

    If that trend continues, then DX lenses could go the way of the dinos some day...
     
  6. OmlessWanderer

    OmlessWanderer TPF Noob!

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    The Mark III(the Canon monster) actually has a smaller sensor then the two Canon full frame sensor cameras(The 5D and one other) - It's half way between the APS sensor size and the full frame sensor size, hence the 1.3x multiplier. But the APS lenses are still no good for it, so you're still right. ^_^

    Edit: Doh! I had written a reply to a couple of the other posts but it didn't get saved... It was mostly in response to fmw's comment about the absence of fixed focal length lenses. Now that you pointed that out it seems to me like the most tell-tale factor on the true worth of the APS sensor lenses since we already know that ffl lenses are capable of much higher quality than zoom's.
     

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