Wide angle and telephoto

Discussion in 'Digital Photography' started by Peter Billinghurst, Dec 3, 2003.

  1. Canon advertises x.5 and x2 lenses for the Powershot G3. What does this
    mean? Would it be correct to say that a x.5 lens will double the dimensions
    (both width and height) of the area pictured and the x2 lens would halve the
    dimensions?

    Or to put it another way, what effect do these lenses have on the focal
    length of the lens? I assume that 35mm would become 17.5mm with wide angle
    and 140mm would become 280mm.

    Any advise would be welcome. Thanks

    Peter
     
    Peter Billinghurst, Dec 3, 2003
    #1
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  2. Peter  Billinghurst

    Aardvark Guest

    "Peter Billinghurst" <> wrote in
    message news:bqll5m$n4q$...
    > Canon advertises x.5 and x2 lenses for the Powershot G3. What

    does this
    > mean? Would it be correct to say that a x.5 lens will double

    the dimensions
    > (both width and height) of the area pictured and the x2 lens

    would halve the
    > dimensions?
    >
    > Or to put it another way, what effect do these lenses have on

    the focal
    > length of the lens? I assume that 35mm would become 17.5mm

    with wide angle
    > and 140mm would become 280mm.


    Yes. The x0.5 will halve your focal length ( so your G3 is now a
    17.5-70mm ) and the x2 will double your focal length ( 70-280 ).
    However, at many focal lengths, there will be severe vignetting,
    which means that only SOME focal ranges can be used when the
    converters are attached. The usable focal lengths are usually at
    the wide end for the x0.5, and at the telephoto end for the x2.
     
    Aardvark, Dec 3, 2003
    #2
    1. Advertising

  3. Many thanks - would the first part of my mail concerning dimensions also be
    correct?

    Peter

    "Aardvark" <> wrote in message
    news:3fcdfa70$...
    >
    > "Peter Billinghurst" <> wrote in
    > message news:bqll5m$n4q$...
    > > Canon advertises x.5 and x2 lenses for the Powershot G3. What

    > does this
    > > mean? Would it be correct to say that a x.5 lens will double

    > the dimensions
    > > (both width and height) of the area pictured and the x2 lens

    > would halve the
    > > dimensions?
    > >
    > > Or to put it another way, what effect do these lenses have on

    > the focal
    > > length of the lens? I assume that 35mm would become 17.5mm

    > with wide angle
    > > and 140mm would become 280mm.

    >
    > Yes. The x0.5 will halve your focal length ( so your G3 is now a
    > 17.5-70mm ) and the x2 will double your focal length ( 70-280 ).
    > However, at many focal lengths, there will be severe vignetting,
    > which means that only SOME focal ranges can be used when the
    > converters are attached. The usable focal lengths are usually at
    > the wide end for the x0.5, and at the telephoto end for the x2.
    >
    >
     
    Peter Billinghurst, Dec 3, 2003
    #3
  4. Peter  Billinghurst

    NJH Guest

    "Peter Billinghurst" <> wrote in message
    news:bqll5m$n4q$...
    > Canon advertises x.5 and x2 lenses for the Powershot G3. What does this
    > mean? Would it be correct to say that a x.5 lens will double the

    dimensions
    > (both width and height) of the area pictured and the x2 lens would halve

    the
    > dimensions?


    Yep, if those really are the magnifications of the supplementary lenses. For
    a rectilinear lens, the ratio of focal length to film (or sensor) dimensions
    is the same as the ratio of distance to subject dimensions, as you have
    probably surmised.


    >
    > Or to put it another way, what effect do these lenses have on the focal
    > length of the lens? I assume that 35mm would become 17.5mm with wide

    angle
    > and 140mm would become 280mm.


    That's correct, if the converter lenses really do alter the focal length of
    the prime lens 0.5x and 2x respectively. That's not so difficult for a 2x
    add-on lens, but it's quite a feat for a wide-angle converter to give 0.5x.
    There are many so-called 0.5x converters sold that aren't really that by a
    long shot. If it's a Canon-made lens advertised that way I'd presume it is
    correct, but are you *sure* these advertised converters originate with
    Canon?


    >
    > Any advise would be welcome. Thanks


    I would first of all make sure who made those lenses you're talking about.
    Frankly I would be very surprised if Canon made an 0.5x converter for the
    G3.

    Neil
     
    NJH, Dec 4, 2003
    #4
  5. Many thanks for this - Canon do advertise such a converter on their web
    site. Also several other accessories for the G3.

    I do actually have both converters, but made by an outfit named Digital
    Optics. While the glass seems to be very good, the magnifications or
    conversion factors are nothing like x.5 or x2 as advertised: more like .77
    for the wide angle and 1.2 for the telephoto. I am just checking on the
    facts before complaining!

    Once again thanks



    Peter



    "NJH" <> wrote in message
    news:bAwzb.37429$...
    >
    > "Peter Billinghurst" <> wrote in message
    > news:bqll5m$n4q$...
    > > Canon advertises x.5 and x2 lenses for the Powershot G3. What does this
    > > mean? Would it be correct to say that a x.5 lens will double the

    > dimensions
    > > (both width and height) of the area pictured and the x2 lens would halve

    > the
    > > dimensions?

    >
    > Yep, if those really are the magnifications of the supplementary lenses.

    For
    > a rectilinear lens, the ratio of focal length to film (or sensor)

    dimensions
    > is the same as the ratio of distance to subject dimensions, as you have
    > probably surmised.
    >
    >
    > >
    > > Or to put it another way, what effect do these lenses have on the focal
    > > length of the lens? I assume that 35mm would become 17.5mm with wide

    > angle
    > > and 140mm would become 280mm.

    >
    > That's correct, if the converter lenses really do alter the focal length

    of
    > the prime lens 0.5x and 2x respectively. That's not so difficult for a 2x
    > add-on lens, but it's quite a feat for a wide-angle converter to give

    0.5x.
    > There are many so-called 0.5x converters sold that aren't really that by a
    > long shot. If it's a Canon-made lens advertised that way I'd presume it is
    > correct, but are you *sure* these advertised converters originate with
    > Canon?
    >
    >
    > >
    > > Any advise would be welcome. Thanks

    >
    > I would first of all make sure who made those lenses you're talking about.
    > Frankly I would be very surprised if Canon made an 0.5x converter for the
    > G3.
    >
    > Neil
    >
    >
     
    Peter Billinghurst, Dec 4, 2003
    #5
  6. Peter  Billinghurst

    NJH Guest

    "Peter Billinghurst" <> wrote in message
    news:bqn70f$ru8$...
    > Many thanks for this - Canon do advertise such a converter on their web
    > site. Also several other accessories for the G3.


    Yes, I checked their site and see that under G3 accessories they list both
    wide-angle and tele converters. Unfortunately the site doesn't give the
    magnification of either. But the usual thing from other camera manufacturers
    for a wide-angle converter is 0.8x, and I presume that Canon's is about the
    same. I suspect that is about as much as can be done (as far as getting a
    wider angle goes) with this type of supplementary lens without degrading
    optical performance in one way or another.


    >
    > I do actually have both converters, but made by an outfit named Digital
    > Optics. While the glass seems to be very good, the magnifications or
    > conversion factors are nothing like x.5 or x2 as advertised: more like .77
    > for the wide angle and 1.2 for the telephoto. I am just checking on the
    > facts before complaining!
    >
    > Once again thanks


    You're welcome. I'm not surprised that the w.a. converter doesn't come close
    to the advertised magnification, but it is surprising that the tele
    converter falls so far short. Interesting.

    Neil


    >
    >
    >
    > Peter
    >
    >
    >
    > "NJH" <> wrote in message
    > news:bAwzb.37429$...
    > >
    > > "Peter Billinghurst" <> wrote in message
    > > news:bqll5m$n4q$...
    > > > Canon advertises x.5 and x2 lenses for the Powershot G3. What does

    this
    > > > mean? Would it be correct to say that a x.5 lens will double the

    > > dimensions
    > > > (both width and height) of the area pictured and the x2 lens would

    halve
    > > the
    > > > dimensions?

    > >
    > > Yep, if those really are the magnifications of the supplementary lenses.

    > For
    > > a rectilinear lens, the ratio of focal length to film (or sensor)

    > dimensions
    > > is the same as the ratio of distance to subject dimensions, as you have
    > > probably surmised.
    > >
    > >
    > > >
    > > > Or to put it another way, what effect do these lenses have on the

    focal
    > > > length of the lens? I assume that 35mm would become 17.5mm with wide

    > > angle
    > > > and 140mm would become 280mm.

    > >
    > > That's correct, if the converter lenses really do alter the focal length

    > of
    > > the prime lens 0.5x and 2x respectively. That's not so difficult for a

    2x
    > > add-on lens, but it's quite a feat for a wide-angle converter to give

    > 0.5x.
    > > There are many so-called 0.5x converters sold that aren't really that by

    a
    > > long shot. If it's a Canon-made lens advertised that way I'd presume it

    is
    > > correct, but are you *sure* these advertised converters originate with
    > > Canon?
    > >
    > >
    > > >
    > > > Any advise would be welcome. Thanks

    > >
    > > I would first of all make sure who made those lenses you're talking

    about.
    > > Frankly I would be very surprised if Canon made an 0.5x converter for

    the
    > > G3.
    > >
    > > Neil
    > >
    > >

    >
    >
     
    NJH, Dec 4, 2003
    #6
  7. Yes - come to think, one would hardly expect a conversion right down to
    f17.5 to work very well. I will put in another post to ask whether any one
    has experience of the Canon tele converter.

    Thanks again

    Peter


    "NJH" <> wrote in message
    news:m0Izb.3327$...
    >
    > "Peter Billinghurst" <> wrote in message
    > news:bqn70f$ru8$...
    > > Many thanks for this - Canon do advertise such a converter on their web
    > > site. Also several other accessories for the G3.

    >
    > Yes, I checked their site and see that under G3 accessories they list both
    > wide-angle and tele converters. Unfortunately the site doesn't give the
    > magnification of either. But the usual thing from other camera

    manufacturers
    > for a wide-angle converter is 0.8x, and I presume that Canon's is about

    the
    > same. I suspect that is about as much as can be done (as far as getting a
    > wider angle goes) with this type of supplementary lens without degrading
    > optical performance in one way or another.
    >
    >
    > >
    > > I do actually have both converters, but made by an outfit named Digital
    > > Optics. While the glass seems to be very good, the magnifications or
    > > conversion factors are nothing like x.5 or x2 as advertised: more like

    ..77
    > > for the wide angle and 1.2 for the telephoto. I am just checking on the
    > > facts before complaining!
    > >
    > > Once again thanks

    >
    > You're welcome. I'm not surprised that the w.a. converter doesn't come

    close
    > to the advertised magnification, but it is surprising that the tele
    > converter falls so far short. Interesting.
    >
    > Neil
    >
    >
    > >
    > >
    > >
    > > Peter
    > >
    > >
    > >
    > > "NJH" <> wrote in message
    > > news:bAwzb.37429$...
    > > >
    > > > "Peter Billinghurst" <> wrote in message
    > > > news:bqll5m$n4q$...
    > > > > Canon advertises x.5 and x2 lenses for the Powershot G3. What does

    > this
    > > > > mean? Would it be correct to say that a x.5 lens will double the
    > > > dimensions
    > > > > (both width and height) of the area pictured and the x2 lens would

    > halve
    > > > the
    > > > > dimensions?
    > > >
    > > > Yep, if those really are the magnifications of the supplementary

    lenses.
    > > For
    > > > a rectilinear lens, the ratio of focal length to film (or sensor)

    > > dimensions
    > > > is the same as the ratio of distance to subject dimensions, as you

    have
    > > > probably surmised.
    > > >
    > > >
    > > > >
    > > > > Or to put it another way, what effect do these lenses have on the

    > focal
    > > > > length of the lens? I assume that 35mm would become 17.5mm with

    wide
    > > > angle
    > > > > and 140mm would become 280mm.
    > > >
    > > > That's correct, if the converter lenses really do alter the focal

    length
    > > of
    > > > the prime lens 0.5x and 2x respectively. That's not so difficult for a

    > 2x
    > > > add-on lens, but it's quite a feat for a wide-angle converter to give

    > > 0.5x.
    > > > There are many so-called 0.5x converters sold that aren't really that

    by
    > a
    > > > long shot. If it's a Canon-made lens advertised that way I'd presume

    it
    > is
    > > > correct, but are you *sure* these advertised converters originate with
    > > > Canon?
    > > >
    > > >
    > > > >
    > > > > Any advise would be welcome. Thanks
    > > >
    > > > I would first of all make sure who made those lenses you're talking

    > about.
    > > > Frankly I would be very surprised if Canon made an 0.5x converter for

    > the
    > > > G3.
    > > >
    > > > Neil
    > > >
    > > >

    > >
    > >

    >
    >
     
    Peter Billinghurst, Dec 4, 2003
    #7
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