Re: Canon 17/40 f/4L

Bruce Murphy <pack-(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> "Eric Hocking" <(E-Mail Removed)> writes:
> > " Miro" <(E-Mail Removed)> wrote in message
> > news:3ef4846e$0$26633$(E-Mail Removed) u...
<snip>
> > > So you can actually tell me the difference between a 15mm and a 17mm lens
> >
> > Be happy to. If we're talking about these lenses: Canon 17-40 f4 and the
> > Sigma 15-30 f3.5-4.5, the former has a diagonal field of view of 74deg and
> > the latter 110.5deg. Perhaps a fairer comparison would be the Sigma 17-35
> > f/2.8-4 which has has a 103.7deg diagonal fov.
>
> By what mechanism do you believe these (presumably all rectilinear) lenses
> have different fields of view at 17mm?

The spec sheets supplied by the manufacturers.
http://www.canon.com.au/products/cam...0mm_specs.html
and
http://www.sigma-photo.com/html/lenschart.htm

It is entirely probable that I am misinterpreting or misapplying the
information in an attempt to determine what the linear dimensions of
the "view" is at a distance of 3ft from the focal point. As I said,
they were back of the cigarette packet figgerin's using very basic
trigonometry and an even more basic understanding of the terminology.

Out of curiosity's sake I'd be interested in the methodology that I
should apply.

--
Eric Hocking


Eric Hocking

>
> Out of curiosity's sake I'd be interested in the methodology that I
> should apply.
>

If we are talking about a 10D then let's start with the focal length
multiplier.

Then maybe the actual diagonal OR horizontal angle of view for that focal
length. And we know that doesnt vary.

Then I suppose we can look at the angle of arc for 17mm and 15mm lenses.

After all that is done we can all go back to ignoring this.

(E-Mail Removed) (Eric Hocking) writes:

> Bruce Murphy <pack-(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> > "Eric Hocking" <(E-Mail Removed)> writes:
> > > " Miro" <(E-Mail Removed)> wrote in message
> > > news:3ef4846e$0$26633$(E-Mail Removed) u...
> <snip>
> > > > So you can actually tell me the difference between a 15mm and a 17mm lens
> > >
> > > Be happy to. If we're talking about these lenses: Canon 17-40 f4 and the
> > > Sigma 15-30 f3.5-4.5, the former has a diagonal field of view of 74deg and
> > > the latter 110.5deg. Perhaps a fairer comparison would be the Sigma 17-35
> > > f/2.8-4 which has has a 103.7deg diagonal fov.
> >
> > By what mechanism do you believe these (presumably all rectilinear) lenses
> > have different fields of view at 17mm?
>
> The spec sheets supplied by the manufacturers.
> http://www.canon.com.au/products/cam...0mm_specs.html
> and
> http://www.sigma-photo.com/html/lenschart.htm

Elementary trigometry combined with the magnification law shows us that
the figure on the Sigma website is correct, the Canon one is wrong. Or,
more accurately, mislabelled.

The fields of view for the Canon lens are given for a reduced sensor ala
the D30 et al, whereas the numbers /next/ to them are the dimensions of
a 35mm film frame.

You can check this by looking at the page

http://www.maxwell.com.au/photo/niko...1735_spec.html

Which, becuase Nikon are a much better manufacturer than nasty old
Canon, give the fields of view for both the 35mm frame and for the
reduced sensor size on a D1 series camera.

You might find the numbers are the wide end somewhat familiar.

>
> It is entirely probable that I am misinterpreting or misapplying the
> information in an attempt to determine what the linear dimensions of
> the "view" is at a distance of 3ft from the focal point. As I said,
> they were back of the cigarette packet figgerin's using very basic
> trigonometry and an even more basic understanding of the terminology.

Naivete that manufacturers bother to check their website seems to be about
all you're guilty of in this instance, and a misconception over what
cauuses field of view

> Out of curiosity's sake I'd be interested in the methodology that I
> should apply.

Read the above, and then see how you feel about it.

B>

Eric...
You are asking too much of this group to actually be able to 'prove' one of
the lurkers therories - and that's all most of them are. Every so often
someone will toss in a grain of logical evidence like Brenton did a few
replies back but on the whole... It's all just good fun!
JT

"Eric Hocking" <(E-Mail Removed)> wrote in message >
> Out of curiosity's sake I'd be interested in the methodology that I
> should apply.
>
> --
> Eric Hocking

Andrew Mc <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> In article <(E-Mail Removed) >,
> (E-Mail Removed) says...
> >Bruce Murphy <pack-(E-Mail Removed)> wrote in message
> >news:<(E-Mail Removed)>...
> >> "Eric Hocking" <(E-Mail Removed)> writes:
> >> > " Miro" <(E-Mail Removed)> wrote in message
> >> > news:3ef4846e$0$26633$(E-Mail Removed) u...
> <snip>
> >> > > So you can actually tell me the difference between a 15mm and a 17mm lens
> >> >
> >> > Be happy to. If we're talking about these lenses: Canon 17-40 f4 and the
> >> > Sigma 15-30 f3.5-4.5, the former has a diagonal field of view of 74deg and
> >> > the latter 110.5deg. Perhaps a fairer comparison would be the Sigma 17-35
> >> > f/2.8-4 which has has a 103.7deg diagonal fov.
> >>
> >> By what mechanism do you believe these (presumably all rectilinear) lenses
> >> have different fields of view at 17mm?
> >
> >The spec sheets supplied by the manufacturers.
> >http://www.canon.com.au/products/cam...0mm_specs.html
> >and
> >http://www.sigma-photo.com/html/lenschart.htm
>
> Try here:
> http://www.usa.canon.com/html/eflens...40_4lspec.html

That makes much more sense - thanks. I wonder where the Aussie site
cut/paste their numbers from!?

--
Eric Hocking

"Auspics" <(E-Mail Removed)> wrote in message
news:gnbLa.546$(E-Mail Removed)...
> "Eric Hocking" <(E-Mail Removed)> wrote in message >
> > Out of curiosity's sake I'd be interested in the methodology that I
> > should apply.
> Eric...
> You are asking too much of this group to actually be able to 'prove' one
of
> the lurkers therories - and that's all most of them are. Every so often
> someone will toss in a grain of logical evidence like Brenton did a few
> replies back but on the whole... It's all just good fun!

Old hand at this usenet thing. Read everything in context, follow the leads
and decide who gives information more reliably than others. Basically
usenet is the equivalent of the 19th hole in golf.

--
Eric Hocking
"A closed mouth gathers no feet"
"Ignorance is a renewable resource" P.J.O'Rourke
REPLACE ".com" with ".co.uk" to reply
http//www.twofromoz.freeserve.co.uk

> Old hand at this usenet thing. Read everything in context, follow the
leads
> and decide who gives information more reliably than others. Basically
> usenet is the equivalent of the 19th hole in golf.
>
> --
> Eric Hocking

I thought it more like the water trap.

"Eric Hocking" <(E-Mail Removed)> wrote in message
news:bdstlv$8vo$(E-Mail Removed)...
> " Miro" <(E-Mail Removed)> wrote in message
> news:3f00b23f$0$26633$(E-Mail Removed) u...
> > > Old hand at this usenet thing. Read everything in context, follow the
> > leads
> > > and decide who gives information more reliably than others. Basically
> > > usenet is the equivalent of the 19th hole in golf.
> >
> > I thought it more like the water trap.
>
> I guess that's the difference between us.
>
> I approach aus.photo as somewhere that people with a common interest get
> together to swap war stories, experiences, ask information and have the
> occasional stoush.
>
> Whereas you appear to think it's a frustrating contest where you spend
most
> of your time trying to get out of the hole you've dropped yourself into,
or
> replacing the ball and driving off in a totally different direction.
>

Oh its Guru Eric with the photographic-microdot bindi of enlightenment. We
worship your wisdom.

Miro wrote:

> > I approach aus.photo as somewhere that people with a common interest get
> > together to swap war stories, experiences, ask information and have the
> > occasional stoush.
> >
> > Whereas you appear to think it's a frustrating contest where you spend
> most
> > of your time trying to get out of the hole you've dropped yourself into,
> or
> > replacing the ball and driving off in a totally different direction.
> >
>
> Oh its Guru Eric with the photographic-microdot bindi of enlightenment. We
> worship your wisdom.

Gotta say, Eric makes a hell of a lot more sense than you do Miro.

>
> Gotta say, Eric makes a hell of a lot more sense than you do Miro.
>
>

Birds of a feather ..........