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Wide angle and telephoto

 
 
Peter Billinghurst
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      12-03-2003
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



 
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Aardvark
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Posts: n/a
 
      12-03-2003

"Peter Billinghurst" <(E-Mail Removed)> wrote in
message news:bqll5m$n4q$(E-Mail Removed)...
> 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.


 
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Peter Billinghurst
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Posts: n/a
 
      12-03-2003
Many thanks - would the first part of my mail concerning dimensions also be
correct?

Peter

"Aardvark" <(E-Mail Removed)> wrote in message
news:3fcdfa70$(E-Mail Removed)...
>
> "Peter Billinghurst" <(E-Mail Removed)> wrote in
> message news:bqll5m$n4q$(E-Mail Removed)...
> > 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.
>
>



 
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NJH
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Posts: n/a
 
      12-04-2003

"Peter Billinghurst" <(E-Mail Removed)> wrote in message
news:bqll5m$n4q$(E-Mail Removed)...
> 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


 
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Peter Billinghurst
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Posts: n/a
 
      12-04-2003
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" <(E-Mail Removed)> wrote in message
news:bAwzb.37429$(E-Mail Removed). com...
>
> "Peter Billinghurst" <(E-Mail Removed)> wrote in message
> news:bqll5m$n4q$(E-Mail Removed)...
> > 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
>
>



 
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NJH
Guest
Posts: n/a
 
      12-04-2003

"Peter Billinghurst" <(E-Mail Removed)> wrote in message
news:bqn70f$ru8$(E-Mail Removed)...
> 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" <(E-Mail Removed)> wrote in message
> news:bAwzb.37429$(E-Mail Removed). com...
> >
> > "Peter Billinghurst" <(E-Mail Removed)> wrote in message
> > news:bqll5m$n4q$(E-Mail Removed)...
> > > 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
> >
> >

>
>



 
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Peter Billinghurst
Guest
Posts: n/a
 
      12-04-2003
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" <(E-Mail Removed)> wrote in message
news:m0Izb.3327$(E-Mail Removed) m...
>
> "Peter Billinghurst" <(E-Mail Removed)> wrote in message
> news:bqn70f$ru8$(E-Mail Removed)...
> > 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" <(E-Mail Removed)> wrote in message
> > news:bAwzb.37429$(E-Mail Removed). com...
> > >
> > > "Peter Billinghurst" <(E-Mail Removed)> wrote in message
> > > news:bqll5m$n4q$(E-Mail Removed)...
> > > > 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
> > >
> > >

> >
> >

>
>



 
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