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General Lens ZOOM question....

 
 
advid
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      06-25-2004
.... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
using for mainly birds/wildlife....

We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
for close ups of birds etc...

I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
near as close as the Canon at 300mm.... Even with the 1.4 on it's only
just about the same as the Canon wothout the 1.4 on - why should there
be such a difference ????

Surely 300mm is 300mm no matter what make of lens..... ?
 
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leo
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      06-25-2004
"advid" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> ... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
> using for mainly birds/wildlife....
>
> We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
> for close ups of birds etc...
>
> I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
> near as close as the Canon at 300mm.... Even with the 1.4 on it's only
> just about the same as the Canon wothout the 1.4 on - why should there
> be such a difference ????
>
> Surely 300mm is 300mm no matter what make of lens..... ?



I can't answer you what makes the difference bettween lenses. I just sold my
Canon 75-300 IS lens ($400) and replaced it with 300mm f/4 IS prime lens
($1100). I compare the picture quality of the same images I took at 300mm.
The advantage of a good prime lens is not only the sharpness but the color
and contrast are much, much better.


 
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Jeff Durham
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      06-25-2004
That is an interesting observation. I too thought 300 was 300 per my
observations. I had a ~270mm telephoto on an old 35mm. I compared what I
saw with my Rebel using 270mm factoring in the 1.6X conversion number for
35mm and the picture information was darn near identical. That old lens was
more than twice the size so I was really curious if they would be the same.
I also compared my Kodak P&S digital to my Rebel and found similar results.

Maybe some of the experts in this group can explain what you are seeing.

Jeff


"advid" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> ... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
> using for mainly birds/wildlife....
>
> We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
> for close ups of birds etc...
>
> I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
> near as close as the Canon at 300mm.... Even with the 1.4 on it's only
> just about the same as the Canon wothout the 1.4 on - why should there
> be such a difference ????
>
> Surely 300mm is 300mm no matter what make of lens..... ?



 
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leo
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Posts: n/a
 
      06-25-2004
"Jeff Durham" <(E-Mail Removed)> wrote in message
news:gAXCc.158680$(E-Mail Removed).. .
> That is an interesting observation. I too thought 300 was 300 per my
> observations. I had a ~270mm telephoto on an old 35mm. I compared what I
> saw with my Rebel using 270mm factoring in the 1.6X conversion number for
> 35mm and the picture information was darn near identical. That old lens

was
> more than twice the size so I was really curious if they would be the

same.
> I also compared my Kodak P&S digital to my Rebel and found similar

results.
>
> Maybe some of the experts in this group can explain what you are seeing.
>
> Jeff
>
>
> "advid" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
> > ... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
> > using for mainly birds/wildlife....
> >
> > We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
> > for close ups of birds etc...
> >
> > I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
> > near as close as the Canon at 300mm.... Even with the 1.4 on it's only
> > just about the same as the Canon wothout the 1.4 on - why should there
> > be such a difference ????
> >
> > Surely 300mm is 300mm no matter what make of lens..... ?


I misread the question. The focal length are not exactly the same. My new
300mm f/4 IS is slightly longer than the 75-300mm IS at 300mm. Only very
slightly though. If the difference is huge, somebody's cheating...


 
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George
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      06-25-2004
As you may have guessed, there is some "rounding" (by marketing) of the
actual focal length on virtually all lenses. I believe the industry allows
about 5%...I don't believe that it is a deliberate attempt to mislead, more
likely a convenience (to the customer) for comparison and remembering the
lens. Sounds like your Tamron is rounded "up" on the high end while your
Canon may be rounded "down" a bit. But, I wouldn't expect it to be so
noticeable unless your subject to camera distance is changing as well and
one lens focuses closer as well (from your comments, that would likely be
the Canon).

"advid" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> ... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
> using for mainly birds/wildlife....
>
> We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
> for close ups of birds etc...
>
> I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
> near as close as the Canon at 300mm.... Even with the 1.4 on it's only
> just about the same as the Canon wothout the 1.4 on - why should there
> be such a difference ????
>
> Surely 300mm is 300mm no matter what make of lens..... ?



 
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Tony Spadaro
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      06-26-2004
In general there is a 10% fudge factor on lenses. (ie anything between
270 and 330 would be a 300, but believe me now one ever called a 325mm lens
300. It could be that for these "super" zooms, a lot of the range has more
to do with advertising than fact. I would say that if you need a 1.4 TC to
get 300mms out of it, it's a good lens to send back.

--
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"advid" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> ... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
> using for mainly birds/wildlife....
>
> We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
> for close ups of birds etc...
>
> I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
> near as close as the Canon at 300mm.... Even with the 1.4 on it's only
> just about the same as the Canon wothout the 1.4 on - why should there
> be such a difference ????
>
> Surely 300mm is 300mm no matter what make of lens..... ?



 
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Giorgio Preddio
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      06-26-2004
"Tony Spadaro" <(E-Mail Removed)> wrote in message news:<Iv5Dc.74672$(E-Mail Removed) .com>...

> In general there is a 10% fudge factor on lenses. (ie anything between
> 270 and 330 would be a 300, but believe me now one ever called a 325mm lens
> 300. It could be that for these "super" zooms, a lot of the range has more
> to do with advertising than fact. I would say that if you need a 1.4 TC to
> get 300mms out of it, it's a good lens to send back.


> > Surely 300mm is 300mm no matter what make of lens..... ?


You will find that the Sigma lenses are the most accurate in terms of
focal length accuracy. I conducted some very thorough testing in this
area last year. My photography students learned quite a bit from the
study. Unfortunately, my sponsors prevented me from publishing the
results due to corporate politics.
 
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Randall Ainsworth
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      06-26-2004
In article <(E-Mail Removed) >, Giorgio
Preddio <giorgio@****shitpussy****.com> wrote:

> You will find that the Sigma lenses are the most accurate in terms of
> focal length accuracy. I conducted some very thorough testing in this
> area last year. My photography students learned quite a bit from the
> study. Unfortunately, my sponsors prevented me from publishing the
> results due to corporate politics.


Put down the crack pipe, George.
 
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JPS@no.komm
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Posts: n/a
 
      06-26-2004
In message <(E-Mail Removed) >,
giorgio@****shitpussy****.com (Giorgio Preddio) wrote:

>My photography students learned quite a bit


Did you ask the toddlers if they really wanted the lessons?
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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Dave Martindale
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      06-26-2004
http://www.velocityreviews.com/forums/(E-Mail Removed) (advid) writes:

>Surely 300mm is 300mm no matter what make of lens..... ?


It is. At most one of the lenses is marked accurately.
Why not measure the actual lens focal length yourself?

All you need is a pair of objects with clear edges a measured distance
apart. Shoot them from a long way away so both are visible, and the
distance between them is (say) 1/10 to 1/4 of the image width. Then
look at the digital image and determine the distance between the two
objects in pixels.

The distance in pixels multiplied by the pixel pitch of your camera's
sensor tells you the image distance between the two objects. You
already measured the distance between the real objects. Now measure the
distance from the front of the camera lens to the real objects. Given
these three pieces of information, plug them into one of the standard
lens formulas and solve for the lens focal length.

Done carefully, this is very accurate. The focal length of a lens is
*defined* by its on-axis magnification.

Dave
 
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