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  1. #1
    More eagerness than skills.. rzozaya1969's Avatar
    Join Date
    Nov 2005
    Mexico, D.F., Mexico

    Conversion # on standard vs digital lenses...

    I have a Sony A100 with the standard lenses (18-70 / 3.5-5.6).

    The 18-70 refers to how the lenses opens, or something alike in the zoom (1x, 2x.. on P&S cameras). But should I read them the same as for 35mm lenses? Meaning that if in a book they recomend a 40 lens for film, would it be the same for digital?

    The 70 setting (where I have the most zoom), what would be the equivalent in a P&S? 3X?

    I hope it makes sense what I'm asking, even if it's a noobie Q...
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  2. #2
    Member gryphonslair99's Avatar
    Join Date
    Nov 2006

    Re: Conversion # on standard vs digital lenses...

    Yes. No. Maybe.

    An 18-70mm lens is an 18-70mm lens no matter what camera it is on. That is a product of the lens, its construction and focal range.

    It however will not always seem like and 18-70mm lens depending on what you put it on. If you have ever shot 35mm film, you have a concept or knowledge of what a particular focal length will produce on film. When you put that same lens on a digital camera, with the exception of a couple of Canon's full frame pro line cameras, there will be a crop factor to deal with. This crop factor is based on the size of the sensor in your particular camera in relation to the standard size of a 35mm negative. I shoot a Canon 30D and the crop factor is 1.6 or a magnification of 1.6. That would make an 18-70mm lens equivelent to a 29-112mm lens. Nikon DSLR's have a crop factor of 1.5 or a magnification of 1.5. I do not know what the crop factor is for the Sony.

    When a book recomends a particular mm lenght for a particuar style of photography, you will have to figure in the crop factor and choose the lense that comes the closest to the recomendation. Most of those recomendations are usually a range. Portrait range is usually considerd between 80mm and 120mm. Yes you can use shorter or longer lenses, but the standard is basically 80 to 120mm.

    I have never used a P&S so I can not give you any idea as to what times factor a 70mm lense would be. Sorry. Hope this helps

  3. #3
    Captain of the Ship Photo-John's Avatar
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    Aug 2001
    Salt Lake City, Utah, United States

    Re: Conversion # on standard vs digital lenses...

    Quote Originally Posted by gryphonslair99

    I have never used a P&S so I can not give you any idea as to what times factor a 70mm lense would be. Sorry. Hope this helps
    Most compact digitals have a focal length equivalent to 35mm at the wide end. Therefore, a 35-70mm zoom lens would be equivalent to a 2x zoom. But it would be a mistake to compare digital SLR lenses to compact digital camera lenses. The glass is usually much better and you don't want to start looking for the longest zoom ratio. Longer zoom ratios almost always mean poor optics. Therefore, a 2-3x SLR zoom lens is generally about as long as you want to go.

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