Difference of 18-55mm and 50mm

Discussion in 'Photography Beginners' Forum' started by tenlientl, Oct 3, 2008.

  1. tenlientl

    tenlientl TPF Noob!

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    What is the difference of these two?

    Nikkor 18-55mm F/3.5-5.6 AF-S
    Nikkor 50mm F/ 1.8 AF

    I'm assuming that the 50mm doesn't zoom, therfore has better Focal Point? Is that always true, or just with that lens? What does lower Focal Point really mean?

    I've googled around about Focal Points, but I still can't understand. And there aren't any good basic classes going on around the city atm :(

    Thanks
     
  2. maulrat

    maulrat TPF Noob!

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    f/1.8 makes all the difference in the world!

    That 50mm is a very fast lens. It also pretty good for indoor and low light shooting. And if they are like the Canon versions, the 50mm should also produce a sharper photo.
     
    Last edited: Oct 3, 2008
  3. DavidSR

    DavidSR TPF Noob!

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    I still need a 50mm!!!..I have also heard that primes tend to be sharper than zooms..also great for portrait work!!
     
  4. tenlientl

    tenlientl TPF Noob!

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    Why would you say the 50mm is faster? And why sharper?

    I'm assuming it's sharper because it's focused on one distant than having more than one.

    And f/ 1.8 makes a difference? How so? My lowest is 3.5. When I played around with it, my shots are darker when higher? I've read that I should have a low f/ to blur backgrounds and have my subject that's closer sharper. Is that the only purpose?

    Thanks
     
  5. DavidSR

    DavidSR TPF Noob!

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    What makes the 50mm faster is that it has an aperture of f1.8..the lower the number the bigger the aperture. f1.8 will let A LOT more light come through the lens and hit your sensor. As you noticed at f3.5 your pictures have more light and at higher numbers ex. f16 they come out a lot darker. That's because at f16 your aperture is smaller and lets less light hit the sensor. Oh and what makes it faster is that you can use a faster shutter speed since you have more light entering your lens. This can explain aperture better.

    http://en.wikipedia.org/wiki/Aperture
     
  6. Dao

    Dao No longer a newbie, moving up!

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  7. LWW

    LWW TPF Noob!

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    I'll try to make this easy, but you really need to get a basic photography book from the library and read it.

    Forget f1,8 for a second and let's call it f2 and call your 55mm far zoom 50mm. With a variable maximum aperture such as your 18-55, setting it at 50mm would be slightly faster than the f5.6 number for the full 55mm. We knocked off 1/3 of a full stop on the f1.8 rounding to f2 so all computations will be extremely close and probably the 50 f1.8 would come out slightly better in the math gymnastics we are about to engage in because I doubt backing off 5mm on the zoom will get you 1/3 of a stop.

    First off, you don't have an f3.5 at 50mm ... you have an f5.6 at 50MM.

    Now, what this means is that the f2 lens will be capable of using the same shutter speed at the same ISO in half the light of an identical lens with an f2.8 maximum aperture which will be capable of using the same shutter speed at the same ISO in half the light of an identical lens with an f4 maximum aperture which will be capable of using the same shutter speed at the same ISO in half the light of an identical lens with an f5.6 maximum aperture which is what you have.

    The f2 lens will also have half the depth of field of an identical lens with an f2.8 maximum aperture which will have half the depth of field of an identical lens with an f4 maximum aperture which will have half the depth of field of an identical lens with an f5.6 maximum aperture which is what you have.

    Don't ask me exactly how the math works because it takes some explaining which is why I suggested a good book. Once you read a decent book and play with the camera the math becomes far less intimidating quickly. Please, trust me on this.

    Now, to break this into laymen's terms the advantage of the 50mm lens would be:

    A - You can shoot in 1/8 as much light at the same shutter speed and ISO setting as the 50 f5.6.

    A1 - This allows you to extend the range of your flash.
    A2 - This allows you to shoot more often without flash.
    A2 - This allows you to shoot handheld when your f5.6 would require a tripod or monopod. (Assuming you have the non VR version.)

    B - You can shoot at 8 times as fast a shutter speed at the same ISO under the same light as the f5.6.
    B1 - This obviously allows much better freezes of action.

    C - You can shoot and capture an image with 1/8 the depth of field of the f5.6.
    C1 - This is what gives certain photos that *POP* where the subject is in tack sharp focus while the background is blurred out.

    D - It is a shorter lens.

    E - It is a lighter weight lens.

    F - It is a less expensive lens if you ever had to replace it.

    G - It is sharper and less prone to color fringing because it is a better/simpler optical design.

    I - It qill pincusgion far less as well as have far less barrel distortion

    J - You will also have f2.8 and f4 available as aperture selections, which you don't have now.

    K - You will still have access to f5.6 and smaller apertures when needed, just as you do now.

    Ad vantages of the 18-55 you have now would be:

    A - It zooms with the lens instead of your feet. I could just as well make a case that this is a detriment, because moving as a photographer starts your brain to changing the way you visualize things.

    B - It has 5mm more reach on the long end. This edge is so slight it is hardly worth mentioning.

    LWW
     
  8. sultan

    sultan TPF Noob!

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    I see that you are thoroughly confused.

    Let's start with some definitions:
    Focal point - the object you focus on. All lenses can focus and you don't compare lenses based on this.
    Focal length - related to the field of view. The longer the focal length, the bigger far away things will appear. Zoom lenses (like the 18-55mm) have variable focal lengths. The 50mm prime obviously has a focal length of 50mm with is the essentially the do it all focal length unless you take pictures of birds or need wide angle.
    Aperture - the opening of the lens divided by the focal length - essentially how much light the camera lets in. The lower the f number, the larger the the aperture and the better the lens is. The 50mm lets about 9 times the light in compared to the 18-55 at 50mm, thus it is much better.

    Now, fixed (prime) lenses are usually sharper than zooms, especially cheaper ones like the 18-55. The 50mm f/1.8 can be up to twice as sharp as the 18-55.

    In conclusion, the 18-55 reduces the legwork you need to do because it is a zoom but the 50mm is optically and mechanically far superior.
     
  9. maulrat

    maulrat TPF Noob!

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    wird
     
  10. ANDS!

    ANDS! No longer a newbie, moving up!

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    If you're not getting "sharp" (such a subjective, bandied about term) on that 18-55MM, you're doing it wrong.
     
  11. tenlientl

    tenlientl TPF Noob!

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    Oh. That was a random comparison, sorry.

    I have the 18-105 VR. That's why I said my lowest was 3.5.

    Thanks for the info.
     
  12. Alex_B

    Alex_B No longer a newbie, moving up!

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    primes also often have better colour contrast and better homogeneous image quality over the whole frame in general.
     

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