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Photography Question 
Andrew Laverghetta
BetterPhoto Member Since: 9/13/2004

Lens and Distance Scale

Hi everybody. I have a question about the distance scale on some lenses. How do you use them, and why are they put on some and not others? It doesn't seem to be a big thing to add something that looks like a bunch of numbers and maybe a small piece of plexiglass. I've heard that it helps with manual focusing. What benefit does it have to just looking through the viewfinder and making the subject in focus? Or does it have to do more with things like flash and how far the flash will go by the scale telling you about how far you are focusing?
One more question. I'm looking for a decent zoom telephoto lens for my film camera and hopefully a digital SLR I should be getting soon. I'm looking at a Sigma 100-300 f4.5-6.7 or a Tamron 70(or75)-300 f4.0-5.6. All of these lenses hover somewhere around $130-$150, so that sets them in my price range. I wish I could get a really good f2.8 zoom telephoto, but I don't have the money and I don't need it bad enough. I thought that Tamron is a decent brand, as well as Sigma, but what about these lenses? They would be used mostly for some nature, maybe some outdoor sports, and some portraits. Thanks in advance :)

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12/19/2004 9:57:18 PM

Jon Close
BetterPhoto Member Since: 5/18/2000
  I think the Tamron 70-300 f/4-5.6 LD Macro would be preferred over the Sigma 100-300 f/4.5-6.7.
For a couple of reasons, it is more difficult to include a distance/depth of field scale on autofocus lenses, especially zooms. First, to speed autofocus, the "throw" from closest focus to infinity is much shorter on AF lenses than manual focus, shrinking the focus and DoF scales to be nearly unusable. Manual focus zooms could be easily designed to be par-focal: Focused distance does not change with zoom. But this is more difficult to design in autofocus lenses since the AF motor would be working against the manual zooming, so most AF zooms are vari-focal, so the focus scale becomes more or less approximate.
The distance scale is/was mostly used in combination with a depth of field scale. The DoF scale indicates the range in front and behind the focused subject that will appear in apparent focus at the chosen aperture. It is also easy to set the lens for hyperfocal with the distance/DoF scale.
The focus distance scale can also be used to estimate focus in darkness or in taking candids so that one didn't have to conspicuously raise the camera to eye-level. Autofocus works well in these situations and so the distance scale is not as necessary.
Determining subject distance is useful if you are calculating flash exposure manually. Still nice to know, but not as necessary today with modern auto and TTL-dedicated flashes.

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12/20/2004 7:24:16 AM

Jon Close
BetterPhoto Member Since: 5/18/2000
  ... but NOT as necessary today with modern auto and TTL-dedicated flashes.

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12/20/2004 7:27:32 AM

Scott Pedersen   Your distance scale is supposed to give you an idea of what will be in focus and what will not. Of course that also depends on your apature setting. Your subjet will be in focus of course and so many feet in front and so many behind. You can use this to prefocus your camera. Personally I have never been able to make it work, everything come out blurry.

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12/21/2004 5:44:32 AM

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