Alpha Aperture

Discussion in 'Photography Equipment & Products' started by sdgmusic, Apr 14, 2007.

  1. sdgmusic

    sdgmusic TPF Noob!

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    I just got a Sony Alpha with the 18mm-70mm f3.5-5.6 Lens. Why is it that my aperture will only open as open as 5.6 when 3.5 is clearly an option in the title of the lens name? am I missing something, I read the whole manual, and nothing works....help please
     
  2. fmw

    fmw No longer a newbie, moving up!

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    It is a variable aperture zoom. The maximum aperture varies with the focal length. The higher the focal length, the slower the maximum aperture.

    The reason is fairly technical and complicated to discuss here but I'll give you the basics. The least expensive way to design a zoom lens is to have the physical length of the light path expand and contract internally as it is zoomed. Fewer lens elements are required to design one this way. The down side to this type of design is the result you asked about. The lens gets slower as the focal length increases due simply to the laws of optics. These are the same laws of optics that cause every lens to become slightly slower as it is focused more closely.

    Better zoom lenses move the element groups back and forth within the body of the lens to change focal length without actually changing the physical length of the light path. These lenses maintain a constant aperture throughout the zoom range. The downside of this type of design is that it requires more elements and is more expensive to manufacture. These lenses are also heavier and larger because of the additional elements and element groups and that could be a downside to some people. They are also heavier because the better lenses usually have metal components inside to handle the element movements instead of plastic like the cheaper zooms.

    While f3.5 is clearly an option on your lens, it is an option only at the shortest focal length of the zoom range. At the long end of the range, f5.6 is the maximum aperture and the maximum aperture will vary across the zoom range between these two f numbers. I'm not familiar with the Sony product line, but I would assume there is an upgrade zoom lens in the line that will give you a larger and constant maximum aperture.
     
  3. Don Simon

    Don Simon TPF Noob!

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    /\ What he said :)

    The implications of this, as you've probably discovered, are that you have a very slow lens once you get to the telephoto end... and, just as you won't get the best results shooting at f/3.5, so the same applies with f/5.6 when that is the max aperture... you will probably want to stop down at least a couple of f-stops, which obviously might present a problem with a max aperture of f/5.6 if you're shooting with low available light. If you find the lens is not flexible enough, you could consider getting a constant aperture zoom - for example an f/4 (which would perform better at f/4 than the kit zoom), f/2.8 (obviously faster but more expensive), or one or more primes (could be very affordable or very expensive depending on the focal length and speed required).
     
  4. sdgmusic

    sdgmusic TPF Noob!

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    Well for the portrait stuff I just picked up a Minolta Maxxum 50mm f1.4 for $120 US including shipping. Good Deal?
     
  5. Don Simon

    Don Simon TPF Noob!

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    That's not a good deal. That's an amazing deal! They sell new for over $300! Quite an achievement to get it at that price, even used. :thumbup:
     
  6. sdgmusic

    sdgmusic TPF Noob!

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    sorry f1.7, still a good deal?
     
  7. Zatodragon

    Zatodragon TPF Noob!

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    not too bad, i picked mine min up for 82 bucks after shipping, but they shipped me a MD lens the first time.
     
  8. Frequent Traveler

    Frequent Traveler TPF Noob!

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    Ya know Sean, i nearly had to curse your name due to an overwhelming sense of injustice i experienced regarding you obtaining such a sweet deal on a F1.4. Nearly. :)

    Thankfully, you cleared that up for me and you may now feel free to curse me for the undisclosed price i got mine for.... ;-)

    As to the price you paid for your F1.7, hard to say these days - comparatively speaking, BUT rest assured for $120, yep you have a magnificent lens.

    Tried it yet?

    frank
     
  9. zioneffect564

    zioneffect564 TPF Noob!

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    There are a couple..There's a tamron and sigma 24-70 f/2.8 and then there's the zeiss 16-80 but for that you're going to pay the 24-70 arent too bad they're around $400-450
     
  10. sdgmusic

    sdgmusic TPF Noob!

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    no haven't tried it yet, getting it next week
     
  11. Mad_Gnome

    Mad_Gnome TPF Noob!

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    For a constant aperture short zoom, I'd recommend the Sigma 24-70mm f/2.8 EX DG. I've got one, and it quickly became my primary lens. It's a bit on the loud side, but rugged, and it performs extremely well.
     
  12. Frequent Traveler

    Frequent Traveler TPF Noob!

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    I find when i'm not being a lazy-butt and actually use my 50mm a it was meant to be used, i somehow become a photographer again. Not that rules are the "rule", but i begin to see more compositionally and become willing to use my foot-zoom more often.

    This may be because 50mm is the focal length (despite the crop - i know...) i primarily use on my film cam's (except for specific portraiture where i prefer my Rokkor-X 135mm F3.5).

    Can you post up some examples sometime? You're really going to have fun!!!

    frank
     

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