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I have a Canon A80 and am now considering a Digital Rebel DSLR. One thing I
am unsure of though is how to determine which telephoto lens I would need
for the DRebel. If I am shooting small birds at a distance of 20 feet what
would I need to ensure the image filled the frame. Can somebody point me
towards a good web site which explains so that I can learn for myself.

Thanks,

Andy

"Andrew Portess" <> wrote in
news:410dfc4b$1_2@127.0.0.1:

> Can somebody point me
> towards a good web site which explains so that I can learn for myself.

Check out the lens reviews at http://www.photodo.com

--
"Live fast. Die young." (Nikki Sixx)

-Richard Cockburn

Andrew Portess wrote:

> I have a Canon A80 and am now considering a Digital Rebel DSLR. One thing I
> am unsure of though is how to determine which telephoto lens I would need
> for the DRebel. If I am shooting small birds at a distance of 20 feet what
> would I need to ensure the image filled the frame. Can somebody point me
> towards a good web site which explains so that I can learn for myself.
>
> Thanks,
>
> Andy
>
>
I like the Sigma 55-200 which starts off where the kit lens ends
(18-55). I just got my EOS Rebel 2 weeks ago and picked up this lens and
love it. It's the Sigma DC 55-200 Digital Series.

Butch

"Andrew Portess" <> wrote in message
news:410dfc4b$1_2@127.0.0.1...
> I have a Canon A80 and am now considering a Digital Rebel DSLR. One thing
I
> am unsure of though is how to determine which telephoto lens I would need
> for the DRebel. If I am shooting small birds at a distance of 20 feet
what
> would I need to ensure the image filled the frame. Can somebody point me
> towards a good web site which explains so that I can learn for myself.
>
> Thanks,
>
> Andy
>
>
How much do you want to spend?

--
Skip Middleton
http://www.shadowcatcherimagery.com

Andrew Portess wrote:

> I have a Canon A80 and am now considering a Digital Rebel DSLR. One thing I
> am unsure of though is how to determine which telephoto lens I would need
> for the DRebel. If I am shooting small birds at a distance of 20 feet what
> would I need to ensure the image filled the frame. Can somebody point me
> towards a good web site which explains so that I can learn for myself.

AT 20 feet, a lens that goes up to 200mm would probably do
you OK..

But.. You'll soon find that isn't enough because you'll find
you're missing the ones at 80ft and further

A 300mm lens would probably do the job. Keep in mind that on a Digital
Rebel, this is actually a 480mm lens due to the 1.6x factor. For an
inexpensive lens, check out the Canon 75-300mm EF USM without IS. B&H Photo
(www.bhphotovideo.com) has this for about $160. If you want IS (image
stabilization), then I recall that it is closer to $400. IS is great if you
want to hand hold the camera rather than use a tripod. I have this lens and
do like it. I do not have IS. What I have found that is in daylight, I up
the ISO to 200 or 400 so that I can use a faster shutter speed. This helps
to resolve camera shake. A tripod is always better, but sometimes I want
the shot and I do not have the tripod with me.

Jeff


"Andrew Portess" <> wrote in message
news:410dfc4b$1_2@127.0.0.1...
> I have a Canon A80 and am now considering a Digital Rebel DSLR. One thing
I
> am unsure of though is how to determine which telephoto lens I would need
> for the DRebel. If I am shooting small birds at a distance of 20 feet
what
> would I need to ensure the image filled the frame. Can somebody point me
> towards a good web site which explains so that I can learn for myself.
>
> Thanks,
>
> Andy
>
>

Andrew Portess wrote:
>
> I have a Canon A80 and am now considering a Digital Rebel DSLR. One
> thing I am unsure of though is how to determine which telephoto lens
> I would need for the DRebel. If I am shooting small birds at a
> distance of 20 feet what would I need to ensure the image filled the
> frame. Can somebody point me towards a good web site which explains
> so that I can learn for myself.

Take the distance you are away from your subject (20 feet), and
divide it by the size of the frame you want to have (measured in
the same units as your distance from the subject, in this case feet).

Multiply this result by the size of the imaging sensor in millimeters
to get a reasonable approximation for the focal length of the lens
you will want.

You mentioned small birds, so let's use a subject size of one foot,
which should give you some margin around the edges of your frame so
you're not completely filling the frame with the bird. You are 20 feet
away. The Digital Rebel's sensor measures about 22.7 millimeters
across.

20 feet / 1 foot = 20.
20 * 22.7 millimeters = 454 millimeters

You will want a focal length around 400 mm if your birds are a foot
or smaller in size and you will be 20 feet away. Each pixel in your
output image will cover about 0.004 inches across at this distance
and focal length.

BJJB

Remember though that the Rebel does not a have a full size CMOS sensor so a
28-300mm lens will actually be like a 42-450mm. 1.5X multiplier.
"BillyJoeJimBob" <> wrote in message
news:...
> Andrew Portess wrote:
> >
> > I have a Canon A80 and am now considering a Digital Rebel DSLR. One
> > thing I am unsure of though is how to determine which telephoto lens
> > I would need for the DRebel. If I am shooting small birds at a
> > distance of 20 feet what would I need to ensure the image filled the
> > frame. Can somebody point me towards a good web site which explains
> > so that I can learn for myself.
>
> Take the distance you are away from your subject (20 feet), and
> divide it by the size of the frame you want to have (measured in
> the same units as your distance from the subject, in this case feet).
>
> Multiply this result by the size of the imaging sensor in millimeters
> to get a reasonable approximation for the focal length of the lens
> you will want.
>
> You mentioned small birds, so let's use a subject size of one foot,
> which should give you some margin around the edges of your frame so
> you're not completely filling the frame with the bird. You are 20 feet
> away. The Digital Rebel's sensor measures about 22.7 millimeters
> across.
>
> 20 feet / 1 foot = 20.
> 20 * 22.7 millimeters = 454 millimeters
>
> You will want a focal length around 400 mm if your birds are a foot
> or smaller in size and you will be 20 feet away. Each pixel in your
> output image will cover about 0.004 inches across at this distance
> and focal length.
>
> BJJB

Petr V. wrote:
>
> Remember though that the Rebel does not a have a full size CMOS
> sensor so a 28-300mm lens will actually be like a 42-450mm. 1.5X
> multiplier.

The sensor size is already taken into account in the computation.
You don't have to worry about multipliers/crop factors at all using
the method I described.

BJJB