Re: Canon 17/40 f/4L

"Eric Hocking" <(E-Mail Removed)> wrote in message
news:bdctv1$1hp$(E-Mail Removed)...
> " Miro" <(E-Mail Removed)> wrote in message
> news:3ef4846e$0$26633$(E-Mail Removed) u...
> > "Danny Smith" <(E-Mail Removed)> wrote in message
> > news:3ef43b3a.168662033@news...
> > > Of course! I'm so glad you posted this, I just realised I don't need
> > > any of my current zooms!
> > >
> > > You genius, Miro, you've revolutionised photography forever. No
> > > longer will anyone need anything more than a single prime lens!!!
> >
> > 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.
>


You mean to say that the Sigma 17mm has a FOV 103.7 degrees and the Canon
17mm has a FOV of 74 degrees.

Am I reading that correctly ?

And that 7 degrees of arc, 103 degrees versus 110 degrees produces
measurably large changes in composition at a distance of 2 feet (600mm) ?

This I must see ?

I think you should stick to what is possible.




Miro

" Miro" <(E-Mail Removed)> wrote in message
news:3efa0551$0$26638$(E-Mail Removed) u...
> "Eric Hocking" <(E-Mail Removed)> wrote in message
> news:bdctv1$1hp$(E-Mail Removed)...
> > " Miro" <(E-Mail Removed)> wrote in message
> > news:3ef4846e$0$26633$(E-Mail Removed) u...
> > > "Danny Smith" <(E-Mail Removed)> wrote in message
> > > news:3ef43b3a.168662033@news...
> > > > Of course! I'm so glad you posted this, I just realised I don't
need
> > > > any of my current zooms!
> > > >
> > > > You genius, Miro, you've revolutionised photography forever. No
> > > > longer will anyone need anything more than a single prime lens!!!
> > >
> > > 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.
>
> You mean to say that the Sigma 17mm has a FOV 103.7 degrees and the Canon
> 17mm has a FOV of 74 degrees.
>
> Am I reading that correctly ?

Yes, unless I, of course did not. Source:
http://www.sigma-photo.com/html/lenschart.htm
http://www.canon.com.au/products/cam...trawide_zoom_l
enses/ef%2017-40mm_specs.html
>
> And that 7 degrees of arc, 103 degrees versus 110 degrees produces

and 74deg for the Canon, who actually quote the horizontal fov as 84deg

> measurably large changes in composition at a distance of 2 feet (600mm) ?

My simple trig calcs were based on a 3ft separation from the focal point and
the wall.

> This I must see ?
>
> I think you should stick to what is possible.

As I invited in my other post - feel free to correct my simple trig calcs,
it is entirely possible that I hav misapplied the notion of angle of fov to
calculate the linear fov coverage 3ft away from the focal point. But I'd
hazard that my errors are +/- 1in well within a suitable "rule of thumb"
reckoning for this discussion.

What do you calculate as the physical dimensions captured/viewable by these
lenses at 3ft from the photographer?

--
Eric Hocking
"A closed mouth gathers no feet"
"Ignorance is a renewable resource" P.J.O'Rourke
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