Re: Canon 17/40 f/4L

>
> The Sigma 17mm gives an horizontal 38in fov - 11ins better than the Canon.
>
> Again the above is back of the envelope calcs - anyone feel free to
correct
> them, but it's good enough for government work in my book.
>

One minute you quote diagonal then you quote horizontal ....... lay off the
shiraz hey.




Miro

"Eric Hocking" <(E-Mail Removed)> wrote in message
news:bdd4bv$7b2$(E-Mail Removed)...
> " Miro" <(E-Mail Removed)> wrote in message
> news:3efa05aa$0$26639$(E-Mail Removed) u...
> > > The Sigma 17mm gives an horizontal 38in fov - 11ins better than the
> Canon.
> > >
> > > Again the above is back of the envelope calcs - anyone feel free to
> > correct
> > > them, but it's good enough for government work in my book.
> >
> > One minute you quote diagonal then you quote horizontal ....... lay off
> the
> > shiraz hey.
>
> It's called simple trigonometry - do the math for yourself.

Oh, and you should know me by now, Miro. I'm an engineer and like dicking
with numbers.

P.S. Why the ad hominem? I responded in what I felt was quite a reasonable
manner to your request "So you can actually tell me the difference between a
15mm and a 17mm lens"
P.P.S. The last person on usenet to call me a drunk was a kook that invaded
sci.skeptic a few years back. Not the sort of company you want to keep
shirley?

--
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

> P.S. Why the ad hominem? I responded in what I felt was quite a
reasonable
> manner to your request "So you can actually tell me the difference between
a
> 15mm and a 17mm lens"

Well time and space bends in your hands. Two 17mm lenses have alternate
angles of view.

Maybe sigma quotes diagonal and Canon quotes horizontal angles. Im afraid
this is where engineering is no substitute for common sense.

I will stick with the kook. At least his calculations are plausible.

" Miro" <(E-Mail Removed)> wrote in message news:<3efac2f8$0$26638$(E-Mail Removed). au>...
> > P.S. Why the ad hominem? I responded in what I felt was quite a
> reasonable
> > manner to your request "So you can actually tell me the difference between
> a
> > 15mm and a 17mm lens"
>
> Well time and space bends in your hands. Two 17mm lenses have alternate
> angles of view.

You *did* read the spec sheets then?

> Maybe sigma quotes diagonal and Canon quotes horizontal angles. Im afraid
> this is where engineering is no substitute for common sense.

Sigma quotes diagonal, and Canon both. You *did* read the spec
sheets, before you made this comment, didn't you.

> I will stick with the kook. At least his calculations are plausible.

I'm always ready to be enlightened and had already admitted that the
calc'ns could be in error. So how *does* one determine physical area
covered by angle of view from these numbers?

--
Eric Hocking

"Eric Hocking" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> " Miro" <(E-Mail Removed)> wrote in message
news:<3efac385$0$26637$(E-Mail Removed). au>...
> > By the way, not all people who enjoy wine are drunks. I simply think one
> > should attempt these calculations before a large meal.
>
> I'd be interested to see how I *should* have calculated this - there
> was certainly enough handwaving in my posts to indicate that they were
> done on-the-fly with the most cursory overview of the concept.

Think about it Eric, 7 degrees of arc and maybe 2 or 3 feet in it. Even I
think that is bordering on not being different.

Maybe the lesson from all this is that focal length determines angle of view
by definition. Just what is the focal length is the question.

"Eric Hocking" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> " Miro" <(E-Mail Removed)> wrote in message
news:<3efac2f8$0$26638$(E-Mail Removed). au>...
> > > P.S. Why the ad hominem? I responded in what I felt was quite a
> > reasonable
> > > manner to your request "So you can actually tell me the difference
between
> > a
> > > 15mm and a 17mm lens"
> >
> > Well time and space bends in your hands. Two 17mm lenses have alternate
> > angles of view.
>
> You *did* read the spec sheets then?
>
> > Maybe sigma quotes diagonal and Canon quotes horizontal angles. Im
afraid
> > this is where engineering is no substitute for common sense.
>
> Sigma quotes diagonal, and Canon both. You *did* read the spec
> sheets, before you made this comment, didn't you.
>
> > I will stick with the kook. At least his calculations are plausible.
>
> I'm always ready to be enlightened and had already admitted that the
> calc'ns could be in error. So how *does* one determine physical area
> covered by angle of view from these numbers?
>
> --
> Eric Hocking


I must agree with Miro that common sense must prevail and that possibly
Canon have misquoted or we are misunderstanding something.

The horizontal field of view (by very simple trigonometry) of
84° - 34° (36mm) "canon"

cannot *ever *be greater than the diagonal FOV of
74° - 29° (43.2mm) "canon"

in a rectangle (no matter how much it is distorted by the optics).

What are those lengths given in mm for?

I, too, studied engineering but my recollection of studying optics etc fails
me. But by simple trigonometry as you quote, the diagonal should be the
longest line (is that the 43.2mm as opposed to 36mm bit..dunno).

The angle from a given point in the centre should be greater in the
direction of the longest line from that point to the extremities of that
line.

I am not an expert in neither photography nor optics, but without sitting
down to work out the angles using *simple* trig as you did, a 17mm lens is a
about ~17mm lens it doesn't matter who has made it. I think canon has
misquoted as there should not be a 29°+ difference in the FOV.

As Miro said, I think its only common sense, but I stand to be corrected
also, as I really do not know the numbers of photography and optics.

BillP

> As Miro said, I think its only common sense, but I stand to be corrected
> also, as I really do not know the numbers of photography and optics.
>
> BillP
>
>

Now that you have agreed with me you are an outcast. Now quickly disagree
with me before anyone thinks you are in a Miro consipiracy.

http://www.canon.com.au/products/cam...0mm_specs.html

The spec sheet on this canon web site are WRONG... it is a trying error.
A clear case of don't believe everything that you read.... use your
common sense.

The 17-40 Diagonal angle of view quoted is using a 1.6x conversion for a
DSLR body with a 1.6 x crop.

(17 mm x 1.6= 27.2mm) if you look at the spec sheets (I have a canon
EOS system manual in front of me now) you will see that a 28 mm lens has
a diagonal angle of view of 75 Degrees diagonal... hence the misquote in
the above web site.

And then the site quotes the correct horizontal angel of view for a 17
mm lens based on a full frame SLR (84 degrees)

Clearly the hypotenuse of a right angle triangle (diagonal distance
across the screen through the middle) MUST be longer that any of the two
subtending side (horizontal and vertical).. this is year 7 maths (or for
Miro... MATH) A^2= B^2 + C^2 where a is the hypotenuse b and c are the
subtending sides.

This is a clear case of someone at canon's web page office stuffing up
and not realising it yet.
Basically a 17 mm lens has the same 35 mm FOV as any other 17 mm lens...
regardless of brand.

Brenton

PS Of course.. this ridiculous argument can continue... bit at least get
the facts right.

> Now that you have agreed with me you are an outcast. Now quickly disagree
> with me before anyone thinks you are in a Miro consipiracy.
>
>

Ok. I disagree with you Miro.

I am not an outcast!!!

Phew, that was close. Thanks.

BillP

Brenton <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> http://www.canon.com.au/products/cam...0mm_specs.html
>
> The spec sheet on this canon web site are WRONG... it is a trying error.

was that delifferate? ^^^^^^

> A clear case of don't believe everything that you read.... use your
> common sense.
>
> The 17-40 Diagonal angle of view quoted is using a 1.6x conversion for a
> DSLR body with a 1.6 x crop.
>
> (17 mm x 1.6= 27.2mm) if you look at the spec sheets (I have a canon
> EOS system manual in front of me now) you will see that a 28 mm lens has
> a diagonal angle of view of 75 Degrees diagonal... hence the misquote in
> the above web site.
>
> And then the site quotes the correct horizontal angel of view for a 17
> mm lens based on a full frame SLR (84 degrees)
>
> Clearly the hypotenuse of a right angle triangle (diagonal distance
> across the screen through the middle) MUST be longer that any of the two
> subtending side (horizontal and vertical).. this is year 7 maths (or for
> Miro... MATH) A^2= B^2 + C^2 where a is the hypotenuse b and c are the
> subtending sides.

Have to admit that I could not reconcile the horizontal angle of view
with the quoted diagonal one quoted on the Canon site so only worked
with the quoted diagonal angles.

> This is a clear case of someone at canon's web page office stuffing up
> and not realising it yet.
> Basically a 17 mm lens has the same 35 mm FOV as any other 17 mm lens...
> regardless of brand.

The quoted data had me quite thrown - that's why I attempted the math.
Jeez what's the world coming to when you can't believe everything you
read on a webpage?!

> Brenton
>
> PS Of course.. this ridiculous argument can continue... bit at least get
> the facts right.

Hey - this is usenet, fact have absolutely no precedence over opinion,
you should know that!

--
Eric Hocking