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Zoom Clarification

 
 
Ed Mullikin
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      11-25-2006
A point of confusion: For example, what does zoom 6.7X mean? Is that the
multiplier if one uses the smallest to the largest image a camera can
record? What is the reference? A friend of mine asked me and I'm not
certain that I told her correctly.


 
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David J Taylor
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      11-25-2006
Ed Mullikin wrote:
> A point of confusion: For example, what does zoom 6.7X mean? Is that
> the multiplier if one uses the smallest to the largest image a camera
> can record? What is the reference? A friend of mine asked me and
> I'm not certain that I told her correctly.


It's usually the ratio of the maximum focal length to the minimum. So a
25 - 100mm zoom lens might be described as a 4:1 zoom. The area covered
would have a 16:1 ratio. This is /not/ the same as the "magnification" of
binoculars.

David


 
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Ed Mullikin
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      11-25-2006
That makes sense. My Sony DSC-F828 then can optically zoom 7.1 (from 28 to
200mm). According to the instruction book I can also get into "Digital Zoom"
and "Precision Digital Zoom" which serves to confuse me and I've not really
needed to use it. Thank you.

"David J Taylor" <(E-Mail Removed)-this-bit.nor-this-part.uk>
wrote in message news:OAZ9h.6705$(E-Mail Removed) k...
> Ed Mullikin wrote:
>> A point of confusion: For example, what does zoom 6.7X mean? Is that
>> the multiplier if one uses the smallest to the largest image a camera
>> can record? What is the reference? A friend of mine asked me and
>> I'm not certain that I told her correctly.

>
> It's usually the ratio of the maximum focal length to the minimum. So a
> 25 - 100mm zoom lens might be described as a 4:1 zoom. The area covered
> would have a 16:1 ratio. This is /not/ the same as the "magnification" of
> binoculars.
>
> David
>



 
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David Ruether
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      11-25-2006



"Ed Mullikin" <(E-Mail Removed)> wrote in message news:UWZ9h.3167$%(E-Mail Removed)...
> "David J Taylor" <(E-Mail Removed)-this-bit.nor-this-part.uk> wrote in message
> news:OAZ9h.6705$(E-Mail Removed) k...
>> Ed Mullikin wrote:


>>> A point of confusion: For example, what does zoom 6.7X mean? Is that
>>> the multiplier if one uses the smallest to the largest image a camera
>>> can record? What is the reference? A friend of mine asked me and
>>> I'm not certain that I told her correctly.


>> It's usually the ratio of the maximum focal length to the minimum. So a 25 - 100mm zoom lens might be described as a 4:1 zoom.
>> The area covered would have a 16:1 ratio. This is /not/ the same as the "magnification" of binoculars.
>> David


> That makes sense. My Sony DSC-F828 then can optically zoom 7.1 (from 28 to 200mm). According to the instruction book I can also
> get into "Digital Zoom" and "Precision Digital Zoom" which serves to confuse me and I've not really needed to use it. Thank you.


"Digital zoom" involves increasing the appearance of magnification by
cropping the image area used of the sensor. As you might expect, this
reduction of the sensor area used reduces the pixel count and therefore
results in an image that is less sharp and more "pixelated". Most choose
not to use digital zoom once the results are seen (except possibly in
moderation, for small prints).
--
David Ruether
http://www.velocityreviews.com/forums/(E-Mail Removed)
(E-Mail Removed)
http://www.ferrario.com/ruether


 
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Prometheus
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      11-25-2006
In article <0I_9h.31817$(E-Mail Removed)>, David Ruether
<(E-Mail Removed)> writes
-----------------cut-------------------
>"Digital zoom" involves increasing the appearance of magnification by
>cropping the image area used of the sensor. As you might expect, this
>reduction of the sensor area used reduces the pixel count and therefore
>results in an image that is less sharp and more "pixelated". Most choose
>not to use digital zoom once the results are seen (except possibly in
>moderation, for small prints).


Or desperation, since I can do no worse on my PC I seldom use it.


--
Ian G8ILZ
 
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Joseph Meehan
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      11-25-2006
Ed Mullikin wrote:
> A point of confusion: For example, what does zoom 6.7X mean? Is that
> the multiplier if one uses the smallest to the largest image a camera
> can record? What is the reference? A friend of mine asked me and
> I'm not certain that I told her correctly.


A 20 - 80mm lens and a 100 - 400 mm lens are both 4X zoom. A 20-400
would be a 20X zoom.

That is all it means. On a full size 35 mm or full size sensor that
20-80 would be a nice wide to slightly long lens. On a typical 1.6 crop
factor digital camera it would be a nice mid range zoom. The 100 - 400
would be a nice mid range zoom on a 8x10 view camera (assuming it would
cover the area.)

Don't bother with any "electronic" zoom numbers. Only optical zoom
means anything.

--
Joseph Meehan

Dia 's Muire duit



 
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Dr. Joel M. Hoffman
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      11-26-2006
>A point of confusion: For example, what does zoom 6.7X mean? Is that the
>multiplier if one uses the smallest to the largest image a camera can
>record? What is the reference? A friend of mine asked me and I'm not
>certain that I told her correctly.


It's the ratio between the highest zoom and the lowest zoom. For
example, a 35mm-105mm lens has 3x zoom. Many people mistakenly think
that this zoom number directly represents how much closer you can get
to a subject. It does not.

But almost all P&S cameras start around 35mm (equiv.), so a 3x zoom
will end up around 105mm, a 5x zoom around 150mm, etc.

"Normal" is about 50mm (equiv.), so a 5x zoom (probably about 35mm to
165mm) will probably bring you about 3x closer to the subject.

-Joel

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