QUESTION ABOUT LENSES PLEASE

Discussion in 'Photography Beginners' Forum' started by ZIN, Oct 27, 2007.

  1. ZIN

    ZIN TPF Noob!

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    I have been reading and reading to learn about lenses,(hence: mm,f stop,aperture,dof, and such).
    I want to know why a person wouldnt just buy a lens that covers a wider range is it price,function , size?
    you can buy an 18-200 2.8-4.5 or just a 70-200 f 2.8 why wouldnt you just buy the 1st. one?
    then there is a 70-300 wouldnt that be better yet?
    I am confused at all the different numbers .
    I do understand that a macro lens is a very small like 50mm and a low f1.8, but the other lenses got me confused.
     
  2. Keagle

    Keagle TPF Noob!

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    People do buy 18-200mm lenses. If you want an all-in-one lens, and your not doing it professionally or don't need to worry about image quality, price, or size, then there you go. The 70-200mm f/2.8 is faster meaning it has a wider aperture, and in most cases, (Talking about the Canon + Sigma models), have great image and build quality. Most of the 70-300mm zooms, (As far as I'm aware, all of them!), are around f/4-5.6. They also do not have the best contrast, image quality or build quality, and are not as fast meaning they have a narrower aperture.

    A true macro lens is a lens that has 1:1 magnification. The subject will be the same size on the camera's sensor as it is normally.
     
  3. Joxby

    Joxby TPF Noob!

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    Its pretty much about maximum aperture, that is the size of the hole the sensor/film see's through the lens, the bigger the aperture, the more light is available and the faster shutter/lower ccd sensitivity can be used.
    fast shutter = no blur
    low sensitivity = less noise.
    You really cant appreciate the difference in performance between say f/2.8 and f/4.5 unless you shoot in low light regularly, and by low light I mean anything less than a bright sunny day, the difference doesn't seem much, but in light v sensor terms...its a country mile.
    The 18-200 f/2.8-f4.5 max aperture is only f/2.8 at 18mm, once you start to zoom a little that max app reduces gradually till at 200mm its only f/4.5.
    A zoom lens that only quotes 1 max f/stop means that max app is maintained throughout the zoom range, so an 80-200 f/2.8 is f/2.8 from 80mm to 200mm.
    Again, I know it seems 4.5 isn't much worse than 2.8 (they're just numbers) when you consider the full range of apertures available, but believe me it is very significant.
    The 18-200 is a decent do it all lens but by design to cover that range with glass there are certain compromises that have to be made, like max app only at 18mm, theres prolly more distortion than a dedicated 18mm fixed lens, I doubt a pro would use this lens much for a specific task because its a jack of all trades and a master of non, covering this range of 18-200 with one lens is only recent technology, it all depends on what you want to shoot.
    Just take a look at say a Nikkor 300mm f/2.8, its a monster compared with a 70-300 vari app, it has to be this size to maintain f/2.8 at 300mm.
    They're not bored at Nikon HQ, they dont have billions to spend developing big bits of glass for a laugh when any old f/stop will do...this is the difference between consumer equipment and pro gear....well that and a few other quality issues..
    Do you own a lens with a manual f/stop ring ?


    nikkor 300mm f/2.8
    weight 6.3lbs
    filter size is 52mm, but that goes into a drawer half way down the lens because the diameter at the end must be near 100mm.

    nikkor 70-300 f/4-f/5.6
    weight 18 oz......lullz
    filter size 62mm, obviously it fits on the end of the lens

    Can you see the enormous differences between f/2.8 and f/5.6 glass at 300mm.
    Theres an f/2 300mm, and for that .8 over f/2.8, this lens is 10lbs heavier.
    Yeah.....16lbs total:confused:
     
  4. Sideburns

    Sideburns TPF Noob!

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    mostly huge ranges have to do with image quality, and speed.
    If you want the fastest lens, you have to pay for it...
    and usually a huge range covered lens, is not as high quality as something that's dedicated to a small range/a prime.

    I know many people that have all types of lenses...you really just have to know what's right for what.
    You could get away with an 18-200 in a bright light situation, but anything other than ideal, and you have lost your advantage. Plus, if there's motion (like sports), you're even worse off.

    Do you understand the basics of aperture, shutter speed, and ISO? That would probably help.
     
  5. nikonkev

    nikonkev TPF Noob!

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    I would agree with Sideburns. Pick up an introductory photography book with terminology defined (or read/search it online for free (dpreview.com has a good glossary)) and try to grasp the basic concepts of aperture, shutter speed, preferred purposes of lens types, etc. etc.

    That will definitely help with the reasoning. Then of course, there are the absolute technicalities about how it's made and how it performs in all respects (that they show in graphical form etc.), aside from the obvious f-number, etc. that define the lens and "justifies" the price for its quality.
     
  6. ZIN

    ZIN TPF Noob!

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    Thanks everyone it is getting clearer now as I figured size had alot to do with it and boy does it ever... thanks alot.
     

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