Quick DX/FX question

Discussion in 'Digital Photography' started by fulcrum.1995, Jun 14, 2010.

  1. fulcrum.1995 macrumors member

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    Jun 18, 2009
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    San Jose, California
    #1
    Just a quick question,
    do nikon DX lenses have the 1.5x crop factor included in their focal lengths already?
    for example would a 16-85 3.5-5.6 DX actually be 16-85 on an APS sensor or would it require the 1.5x to be added making it a 24x 130
     
  2. luminosity macrumors 65816

    luminosity

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    #2
    DX lenses will vignette on FX and film cameras, though some are usable for part of their range on those cameras without the vignetting. The 17-55 works from about 26-55mm, covering the entire frame in that range. By contrast, the 18-70 vignettes throughout its range and is not usable on an FX camera in FX mode at any point. You can use it on an FX camera in DX mode, of course.
     
  3. Ruahrc macrumors 65816

    Joined:
    Jun 9, 2009
    #3
    The DX lenses are reporting the actual focal lengths of the optics, just like the FX ones. You have to multiply by 1.5 to see the equivalent FX view.

    So a 16-85 on DX is actually 16-85, but it looks equivalent to 24-130 on FX.

    Remember that focal length is focal length. It's the field of view that changes on DX vs. FX.

    Ruahrc
     
  4. JDDavis macrumors 65816

    JDDavis

    Joined:
    Jan 16, 2009
    #4
    I've always been confused about the same thing. I understand that the field of view is what is different making the effective focal length different. But that's for an FX lens on a DX camera right? The whole point of a DX lens is that it is made for the crop sensor....right? So in reality does that mean that the 18-200 is really physically 12-133 and the crop sensor makes it 18-200 or is the 18-200 optically 18-200 and it's equivalent field of view on my D90 is 27-300? If it's the latter...what's the point of a DX lens.

    Who's on first and what's on second?:D
     
  5. admwright macrumors regular

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    Sep 11, 2008
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    Scotland
    #5
    It is the latter. The point of DX lenses is that they can generally be made smaller and lighter as the image projected by the lens does not need to cover as big an area. This is why they vignette if used on a FX camera.
     
  6. viggen61 macrumors 6502

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    Jul 24, 2002
    Location:
    New Jersey
    #6
    The only difference between an FX and DX lens (or EF and EF-S lens, if you're a Canon junkie), is the size of the image circle that it projects onto the plane of the sensor. FX and EF lenses project a circle large enough to cover a standard 35mm still camera "film" frame of about 36mm x 24mm. The DX and EF-S lenses project a smaller image circle, suitable for their respective maker's "APS-C" sized sensors.

    The focal length of the lens is ALWAYS presented as the actual focal length of the lens, which is the distance from the focal point, where all light paths converge, to the film/sensor plane. So an FX 200mm is the same as a DX 200mm. What is different is the actual internal construction. With Nikon, you can mount a DX lens on an FX body, but you will at the least get some vignetting at the corners, since the image circle can't cover the whole frame. Canon makes it impossible to mount an EF-S lens on an EF (full frame) body.

    The "crop" factor is due to the smaller size of the APS-C sensor. Imagine an image where you have four friends faces, evenly spaced across the image. Think of this as the "full frame" of the image. Now, if you crop in a box with about 40% of the total area, and place it over the center of the above image, you'll only pick up the center two persons in the image. This is what "effective focal length" is all about. Nothing more. So, if you had a D3 (full frame sensor), and a 50mm prime lens, you'd get a picture of all four friends, but with the SAME lens, on a D90 (APS-C sensor), the sensor only "sees" the middle two people, if you don't change your distance from the group.

    This is, in fact, nothing new in photography. It's only "new" in the sense that you now have cameras that approximate the physical size of a 35mm film camera with different size image sensors. In the old days, a 35mm film camera would have a "normal" lens of about 50mm, but if you took photos with medium format (much larger film and image size), your "normal" lens went to around 85 to 95 mm. These differences in focal length approximated the same field of view on each film format.

    The "point" of a DX or EF-S lens is that they can be made smaller, lighter, and probably cheaper than a comparable FX or EF lens. Less glass is needed in a lens that will be projecting a smaller image circle. Since most people with an APS-C sensor camera will stick with an APS-C sensor camera when they upgrade (if they do), there's a market for them.

    Most of the really good lenses, though, will be in full frame format, so they can be used on the full frame digitals, and the film cameras (yes, Nikon and Canon still make film cameras).

    If you have plans, or think you may have plans to ever upgrade to a full-frame sensor camera, it makes sense to buy only the FX or EF lenses.

    :apple::apple:
     
  7. fulcrum.1995 thread starter macrumors member

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    Jun 18, 2009
    Location:
    San Jose, California
    #7
    alrighty
    i think i got it i was worried about having some FX glass in my collection even though as of now i shoot purely DX
    thanks to all of you
     
  8. JDDavis macrumors 65816

    JDDavis

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    Jan 16, 2009
    #8
    +1 Viggen61. Thanks for taking the time to explain.:)
     
  9. aross99 macrumors 68000

    aross99

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    East Lansing, MI
    #9
    Along this same line, when I hear people talking about how great the nifty-50mm prime lenses are for everyday shooting, are they talking about 50mm on a full size sensor?

    It seems like crop sensor cameras should use something more like a 35mm for the same field of view? For example, for a crop sensor camera, the Nikon 35mm AF-S lens would give you a similar field of view to a 50mm prime on a full frame sensor.

    It would seem like a 50mm prime on a crop sensor camera would have the same field of view as a 75mm prime on a full sensor camera.
     
  10. El Cabong macrumors 6502a

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  11. whoseawhat macrumors newbie

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    Apr 14, 2010
    #11
    the lens data is given with the real light physics numbers. so, if you buy a dx 17-50, it actually is 17-50. When you look through it with a dx sensor though, you are not getting a F(x)ull image. So, when you go through the zoom range on your dx camera, you are going 17-50, but seeing something similar to what you would see if you went 27-75 on an fx camera. if you used the same 17-50 lens, you would still be able to crop and get the exact same image you would have gotten on a dx camera (although the pixel density will be different).
     
  12. Arisian macrumors 68000

    Arisian

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    Location:
    China
    #12
    Your assumptions about a 50mm on a crop sensor are correct. However, many people talk about shooting with a prime + "normal" lens, but they are actually shooting at 75 or 80mm (depending on the body).

    Nonetheless, to answer your question of "Great and nifty", check out the link below. For me its getting the f 1.2,1.4,1.8 and just having tack sharp glass. Lots o people shoot it because at 50mm the "normal" mimmicks the perspective & focal length of the human eye.

    I personally, when shooting on a crop sensor, use a 35mm nikkor which is close.

    Hope that helps (link here on 50mm + prime +normal - very helpful)
     
  13. aross99 macrumors 68000

    aross99

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    Dec 17, 2006
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    #13
    Thanks - this explains it perfectly, and as I suspected, to get this "normal" field of view, you should stick with the 50mm on a full frame sensor, and 35mm on a crop sensor.

    It seems like there are alot of people with crop sensor bodies who are shooting with 50mm primes because they are cheap and may not realize that they are not getting that "normal" field of view you would get on a full frame body.

    I have a D5000 with a crop sensor and no auto-focus motor, so I have been looking at the 35mm AF-S as the "normal" lens for my camera...
     
  14. cnolan011 macrumors newbie

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    Jun 17, 2010
    #14
    so then i probably made the right choice of buying this lens Nikon 10-24mm f/3.5-4.5G ED AF-S DX Nikkor
    instead of this lens:
    Nikon 14-24mm f/2.8G ED AF-S Nikkor Wide Angle Zoom

    for a D5000?
     
  15. Arisian macrumors 68000

    Arisian

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    Sep 14, 2007
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    China
    #15
    Absolutely true. Another reason people tend to buy the 50mm on a crop is that the Canon 50mm is truly a beast while the Nikkor is a bit soft in my opinion (I shoot Nikon) - the popularity of the Canon 50mm has crossed brands and ended up being an extremely popular lens for so many good reasons

    that being said, the 35mm Nikkors are beasts and worth a look.

    Glad that article helped!

    Brian
     
  16. flosseR macrumors 6502a

    flosseR

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    #16
    Well that depends.. yes the 10-24 will give you a bigger zoom range and is just marginally smaller field of view on a crop sensor than the 14-24 on a full frame the 14-24 would have been not ULTRAwide on a D5000... also the 14-24 is horrendously expensive, awesome, but expensive. Where the 10-24 is much less so and targeted specifically for DX cameras. Good choice, its a great lens.
     
  17. toxic macrumors 68000

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    Nov 9, 2008
    #17
    just wanted to point out that there's no point avoiding DX lenses just because you have a vague notion that you might want to buy an FX body later. get the lenses that suit the camera you have now, not the one you might have in 5 years. you'll have to buy and/or sell lenses anyway, especially if you have primes.
     
  18. viggen61 macrumors 6502

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    Jul 24, 2002
    Location:
    New Jersey
    #18
    You are correct on all counts, but the main "focus", if you will, with the "nifty 50s" is the very wide aperture, coupled with an almost ridiculously low price tag of around $100. The wide aperture will allow you a much shallower depth of field, allowing you to emphasize the subject to a greater degree than if you were using a zoom with a largest aperture of, say, f/4.5.

    Canon and Nikon also make more pricy 50mm lenses, with wider apertures, and better glass, but for most people the $100 specials work just fine.

    :apple::apple:
     
  19. ManhattanPrjct macrumors 6502

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    Oct 6, 2008
    #19
    The DX lens market also has a lot more competition from 3rd party lens manufacturers.
     
  20. Arisian macrumors 68000

    Arisian

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    #20

    Good point. However there are some advantages to a FX sensor that should make someone look ahead such as low light performance (larger sensor = more light hitting it) and all the things that fx sensors are know for.

    If a person is buying cheap glass, it won't retain it's value... HOWEVER, good glass retains it's value very well and selling it off to go fx is possible.

    I have several fx and dx lenses with 1 fx body and 2 dx bodies that I use for different things. I often times use my 70-200mm on my dx bodies even though its an fx lens just to get that extra reach.

    Im always planning ahead w/ my lenses and was even when I only had dx glass. I owned fx glass before I owned an fx body.

    However, your point is well taken. Buy the lens you need even if its a dx - thanks for bringing that up!
     

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