Why fixed standard zoom?

Discussion in 'Beyond the Basics' started by sincere, Aug 29, 2007.

  1. sincere

    sincere TPF Noob!

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    I see how - for instance - people swear on the 50mm when it comes to portrait but why use a fixed standard zoom and not one where you can change the length on desire? Whats the purpose of a fixed standard zoom then and why use it when you can have more flexibility wit hthe others?
     
  2. EOS_JD

    EOS_JD TPF Noob!

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    Firstly the 50mm is NOT a zoom.... It's a prime lens. Prime lenses are fixed focal length lenses.

    The prime lenses generally have a much wider apertures and are more useful in low light. Also they are generally sharper than zooms.

    The fastest zoom in the Canon range is f2.8. Now look again at the primes. The fastest in the current Canon range is f1.2 which lets in 2.5 times the amount of light that the fastest zoom does. Also the depth of field is so much smaller with these lenses (when used wide open) you can make almost any background very out of focus!

    They have their uses and the 50 f1.8 (which lets on 1.333x more light than the fastest zoom is very good for shooting in lower light, is sharp, is very cheap (canon's cheapest lens) and is a nice focal length for portraits.

    When you need to "zoom" with a prime, you use your feet as the zoom. ;)
     
  3. sincere

    sincere TPF Noob!

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    Prime is what i meant, didnt know how to explain it better. Thanks. is there any solution to have the quality and sharpness with a zoom lense?
     
  4. EOS_JD

    EOS_JD TPF Noob!

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    Canon's L zooms are as close to prime quality as you will get. But they cost plenty!! Primes are cheaper to manufacture and have less glass.

    Compare the fastest shutter speeds you get with your 50mm f1.4 (wide open at f1.4) compared to your 18-55 set at 50mm and wide open (probably f5.6). I'd guess the shutter speed will be around 16x faster with the f1.4. there is a 4 stop difference in aperture with the prime you have. f1.4 - f2 - f2.8 - f4 - f5.6. Take the lenses indoors or use in low light and this can be the difference in getting a shot and not getting a shot.
     
  5. EOS_JD

    EOS_JD TPF Noob!

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    A great starting point would be to read Bryan Petersen's "Understanding Exposure". A great read that really helped me when starting out.
     
  6. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Pay top dollar. There are very good quality zoom lenses...but you would be hard pressed to find one for less than $500 and they go up from there. Although, the top quality prime lenses are still better in many aspects.

    Consider that when a lens is being designed, there must be compromises in order to allow for the zoom. A prime lens, on the other hand, can be optimized for only one focal length.
     
  7. Rick Waldroup

    Rick Waldroup No longer a newbie, moving up!

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    Mike is right. I only own 3 zooms, of which only one ever sees any heavy use. The really fast, top quality zooms are usually big and heavy and cost a lot more than primes.

    I use my primes all the time. Especially my 180 2.8

    It is half the weight of the Nikon 80-200 zoom and smaller and more compact. And to me it is just as sharp as the zoom, if not sharper.
     
  8. S2K1

    S2K1 TPF Noob!

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    I find this to be the best way to describe to people why primes are sharper(in general).
     
  9. gordon77

    gordon77 TPF Noob!

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    i also have a question reguarding prime lenses, there is alot of positive feed back on the 50mm f1.8, but that is 80mm on a digital. i thought a 'prime' lens meant 50mm because thats what your eyes see, or does prime just mean fixed focal length?
     
  10. S2K1

    S2K1 TPF Noob!

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    There's your answer.
     
  11. Alex_B

    Alex_B No longer a newbie, moving up!

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    i have a 300mm prime lens ...

    but you are right that 50mm on an aps-c sensor is longer than on full frame. so it does give a slight telephoto effect regarding overall image impression
     
  12. WDodd

    WDodd TPF Noob!

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    Prime and fixed can be used interchangeably.

    50mm is about what the eye sees when used on a 35mm camera. However because of crop factor of the smaller sensor in most digital SLRs it will have a 35mm equivalent of 80mm.

    That being said the lens is still 50mm. That is just a measurement of the distance from the image sensor or film plane to the optical center of the lens or nodal point in case you were wondering. :thumbup::)
     

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