What is Zoom or Magnifaction for a telephoto?

ggumpshots · Nov 27, 2004

How is Zoom different from Magnification?
A 28 200 mm lens has a zoom of 200/28 ie 7.14,

DOESNT THIS MEAN MAGNIFICATION OF 7.14,........ obviously not according to the manufacturer.........?????????

The max magnification is 1: 4 according to The Tamron brochure I have in front of me

Zoom and magnifcation must be differenrt things but I can see what the difference Help!

DavidMillier · Nov 27, 2004

The 28-200 range has a zoom ratio of 7:1 which means the magnification at 200mm is 7x what it is at 28mm and consequently the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is exactly the same size as the subject itself e.g. if you shoot a shot of say a thimble that is 2cm tall, the image on film/sensor will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the image on film/sensor will be 12.5mm tall not 2cm.

Hope this helps.

Dave Millier

ggumpshots said:
How is Zoom different from Magnification?
A 28 200 mm lens has a zoom of 200/28 ie 7.14,

DOESNT THIS MEAN MAGNIFICATION OF 7.14,........ obviously not
according to the manufacturer.........?????????
The max magnification is 1: 4 according to The Tamron brochure I
have in front of me
Zoom and magnifcation must be differenrt things but I can see what
the difference Help!

Barrie Davis · Nov 27, 2004

DMillier said:
The 28-200 range has a zoom ratio of 7:1 which means the
magnification at 200mm is 7x what it is at 28mm and consequently
the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is
exactly the same size as the subject itself e.g. if you shoot a
shot of say a thimble that is 2cm tall, the image on film/sensor
will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the
image on film/sensor will be 12.5mm tall not 2cm.

Hope this helps.

Dave Millier

What Dave says here is perfectly true, but I think the emphasis is a bit wrong ... ;-)

The lens you mention has a macro facility extending to a maximum image size on the sensor of 1/4 the size of the thing you are photographing....

Make no bones about it, that is a VERY adequate macro performance, particularly from a lens that is ALSO a reasonable Wide Angle (28) AND a reasonable tele (200) AND everything in between!

The 1:4 lens would permit you to fill the frame with something 4x the size of the sensor. Since the sensor itself is pretty small, that is still a high degree of 'enlargement'. You could easily fill the frame with a single medium flower head, for instance. Bear in mind, you can print it at high quality 15" across, maybe.

Furthermore, 1:1 reproduction (same size) is less useful with the smaller sensors of digital cameras, simply because it is hard to find pleasing subjects small enough to fit within that area (when they are reproduced same size as they are in life). A medium/large sized postage stamp would be the kind of size you are looking at, because the sensor you are shooting on to is about that size.

Conclusions....

If you are heavily into macro photography, then get a special macro lens; for convenience in use, choose one around the 100mm f/length.

If you are not heavily into macro, but would like to do it now and then, the lens you describe would cover your needs very well, I think.

Regards,
Baz

Frits Thomsen · Nov 27, 2004

Barrie Davis said:
DMillier said:

The 28-200 range has a zoom ratio of 7:1 which means the
magnification at 200mm is 7x what it is at 28mm and consequently
the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is
exactly the same size as the subject itself e.g. if you shoot a
shot of say a thimble that is 2cm tall, the image on film/sensor
will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the
image on film/sensor will be 12.5mm tall not 2cm.

Click to expand...

why is it 12.5 ? why not 20mm/4= 5mm???

and a nother question, isn´t these magnification ratios from the manufacturer, related to 35mm frames, i.e. will the magnification not change if my sensor have a crop- factor ?? F.ex. if my sensor is only 10mm high then the object mensioned above would be pictured in 2:1 or am I completely wrong ???
Thanks in advance
Frits Thomsen
http://www.pbase.com/yoicz

Barrie Davis · Nov 27, 2004

Hello Fritz,

Some of the inormation you have been given IS incorrect. See below.

Frits Thomsen said:
Barrie Davis said:

DMillier said:

The 28-200 range has a zoom ratio of 7:1 which means the
magnification at 200mm is 7x what it is at 28mm and consequently
the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is
exactly the same size as the subject itself e.g. if you shoot a
shot of say a thimble that is 2cm tall, the image on film/sensor
will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the
image on film/sensor will be 12.5mm tall not 2cm.

Click to expand...

Click to expand...

why is it 12.5 ? why not 20mm/4= 5mm???

You are right -- at 1:4 "reproduction ratio" (also called "magnification") an item 2 cm tall will be projected on to the sensor at 5mm tall --1/4 of it's 'life size'. Dave made a mistake here, and I made a mistake when I didn't notice it! Thanks for putting us both straight!

Frits Thomsen said:
and a nother question, isn´t these magnification ratios from the
manufacturer, related to 35mm frames, i.e. will the magnification
not change if my sensor have a crop- factor ?? F.ex. if my sensor
is only 10mm high then the object mensioned above would be pictured
in 2:1 or am I completely wrong ???

Yes, you are wrong ;-) Here's why......

The actual magnification ratio of the image is separate to the size of the sensor it is being recorded by, which is what I was trying to explain in my first post.

So an image which is being recorded at 1:1 ratio (life size) is always "life sized" on the sensor. How much of the image falls on the sensor, and how much falls off the edges, will depend on the size of the sensor itself.

At the 1:1 ratio it is obviously impossible to record the WHOLE of a subject which happens to be bigger than the sensor!!

This the point I was trying to make about stamps, and the reason 1:4 image ratio (which DOES, as you say, make smaller images on the sensor) is more useful than at first appears --- reason being, the sensor ITSELF is smaller and therefore quite adequately filled by an image which isn't so large as 1:1. Something less will do, most of the time.

If you think we should maybe forget about ratios, and concentrate on the minimum size of small object that can be photographed filling the frame(with any one sensor, used with any one lens) then I think you are right!!

Trouble is, with many sensor sizes to choose from, (instead of just one film frame of 35mm size) the ratio of reproduction (m) has to be known, so that we can work out the size of the image. And the size of the sensor has to be known, so that we can work out HOW MUCH of that image will fill it, and whether any will "spill over", or not.

Is that any clearer now?

If not, don't beat yourself to death over it. Lots of very bright people get in a muddle about this.

Regards,
Baz

DavidMillier · Nov 28, 2004

When I wrote 12.5mm I'd has a glass or two of wine and got myself confused between inches and metric.

2 INCHES/4 is 1/2inch or 12.5mm.

I blame it on my age - I was at school when the UK went metric and we were taught both systems - a sure recipe for muddle!

Actually, a well known comedian on british TV pointed out recently that a lot of people here use the Farenheit and centigrade scales simultaneously using the F scale for hot and C for cold

e.g. A hot day might be described as a scorching 90F degrees and a chilly night be -1C degrees...

Frits Thomsen said:
Barrie Davis said:

DMillier said:

The 28-200 range has a zoom ratio of 7:1 which means the
magnification at 200mm is 7x what it is at 28mm and consequently
the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is
exactly the same size as the subject itself e.g. if you shoot a
shot of say a thimble that is 2cm tall, the image on film/sensor
will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the
image on film/sensor will be 12.5mm tall not 2cm.

Click to expand...

Click to expand...

why is it 12.5 ? why not 20mm/4= 5mm???
and a nother question, isn´t these magnification ratios from the
manufacturer, related to 35mm frames, i.e. will the magnification
not change if my sensor have a crop- factor ?? F.ex. if my sensor
is only 10mm high then the object mensioned above would be pictured
in 2:1 or am I completely wrong ???
Thanks in advance
Frits Thomsen
http://www.pbase.com/yoicz

chuxter · Nov 28, 2004

ggumpshots said:
How is Zoom different from Magnification?
A 28 200 mm lens has a zoom of 200/28 ie 7.14,

DOESNT THIS MEAN MAGNIFICATION OF 7.14,........ obviously not
according to the manufacturer.........?????????
The max magnification is 1: 4 according to The Tamron brochure I
have in front of me
Zoom and magnifcation must be differenrt things but I can see what
the difference Help!

All this is old 35mm camera stuff. By convention, a focal length of 50mm is considered "normal", thus a picture taken with a 50mm lens is not magnified (mag ratio = 1:1). 200mm is 4 times as magnified as 50mm, thus the 1:4 ratio. BTW, at 28mm, the mag ratio would be 1.78:1. Note that 1.78 * 4 = 7.14.

--
Charlie Davis
CATS #25
'I brake for pixels...'

Leon Wittwer · Nov 28, 2004

--
Leon
http://homepage.mac.com/leonwittwer/landscapes.htm

Barrie Davis · Nov 28, 2004

Just check my recent posting history. Just lately I have seem to have been more of a hindrance than I help!!

DMillier said:
When I wrote 12.5mm I'd has a glass or two of wine and got myself
confused between inches and metric.

My wife has the same delusion -- I have told her that that's > [---------] a foot!!! ;-)

DavidMillier said:
2 INCHES/4 is 1/2inch or 12.5mm.

I blame it on my age - I was at school when the UK went metric and
we were taught both systems - a sure recipe for muddle!

I wouldn't care, but our American friends don't even have full size gallons. Oh, it's an 8 pint gallon allright, or so I believe, but they are 16 floz pints instead of the full 20.

I bought some special developer from the US many years ago.(Diafine?) The can said mix up to "one quart" -- so I did, a 40 fluid once quart as used in UK. All my negs came out very thin and under-souped.........

DavidMillier said:
Actually, a well known comedian on british TV pointed out recently
that a lot of people here use the Farenheit and centigrade scales
simultaneously using the F scale for hot and C for cold..

DavidMillier said:
e.g. A hot day might be described as a scorching 90F degrees and a
chilly night be -1C degrees...

Yes, I remember seeing that -- he is right, too. Who was it?
---------------------------------------------------------------------

Remember, don't believe anything you read on the web, especially this.

Regards,
Baz

Frits Thomsen · Nov 28, 2004

Barrie Davis said:
Some of the inormation you have been given IS incorrect. See below.

Frits Thomsen said:

Barrie Davis said:

DMillier said:

The 28-200 range has a zoom ratio of 7:1 which means the
magnification at 200mm is 7x what it is at 28mm and consequently
the field of view at 200mm is 1/7th of what is at 28mm.

I suspect the 1:4 figure refers to the macro capability.

True macro means that the image recorded of a close up subject is
exactly the same size as the subject itself e.g. if you shoot a
shot of say a thimble that is 2cm tall, the image on film/sensor
will also be 2cm tall.

It sounds as if the tamron doesn't do true 1:1 macro. At 1:4, the
image on film/sensor will be 12.5mm tall not 2cm.

Click to expand...

Click to expand...

why is it 12.5 ? why not 20mm/4= 5mm???

Click to expand...

You are right -- at 1:4 "reproduction ratio" (also called
"magnification") an item 2 cm tall will be projected on to the
sensor at 5mm tall --1/4 of it's 'life size'. Dave made a mistake
here, and I made a mistake when I didn't notice it! Thanks for
putting us both straight!

Barrie Davis said:

and a nother question, isn´t these magnification ratios from the
manufacturer, related to 35mm frames, i.e. will the magnification
not change if my sensor have a crop- factor ?? F.ex. if my sensor
is only 10mm high then the object mensioned above would be pictured
in 2:1 or am I completely wrong ???

Click to expand...

Yes, you are wrong ;-) Here's why......

The actual magnification ratio of the image is separate to the size
of the sensor it is being recorded by, which is what I was trying
to explain in my first post.

So an image which is being recorded at 1:1 ratio (life size) is
always "life sized" on the sensor. How much of the image falls on
the sensor, and how much falls off the edges, will depend on the
size of the sensor itself.
At the 1:1 ratio it is obviously impossible to record the WHOLE of
a subject which happens to be bigger than the sensor!!

This the point I was trying to make about stamps, and the reason
1:4 image ratio (which DOES, as you say, make smaller images on the
sensor) is more useful than at first appears --- reason being, the
sensor ITSELF is smaller and therefore quite adequately filled by
an image which isn't so large as 1:1. Something less will do, most
of the time.

If you think we should maybe forget about ratios, and concentrate
on the minimum size of small object that can be photographed
filling the frame(with any one sensor, used with any one lens) then
I think you are right!!

Trouble is, with many sensor sizes to choose from, (instead of just
one film frame of 35mm size) the ratio of reproduction (m) has to
be known, so that we can work out the size of the image. And the
size of the sensor has to be known, so that we can work out HOW
MUCH of that image will fill it, and whether any will "spill over",
or not.

Is that any clearer now?

If not, don't beat yourself to death over it. Lots of very bright
people get in a muddle about this.

Regards,
Baz

Thank you very much for the explanation.

I think I got it now 1:1 or 1:4 , or whatever, is an actual measure of the object , and then I just have to figure out , to what degree a certain object will fill my particular sensor; so this 20 mm object will create an 20 mm image (at 1:1) whether(?? spelling) or not my sensor is big enough to " hold"it , right ??
--
Frits Thomsen
http://www.pbase.com/yoicz

Barrie Davis · Nov 28, 2004

But your post is incorrect, at least by all the understanding that I have.

chuxter said:
All this is old 35mm camera stuff. By convention, a focal length of
50mm is considered "normal", thus a picture taken with a 50mm lens
is not magnified (mag ratio = 1:1).

Not so, I'm afraid.

The convention that makes a "normal lens" a "normal" one, is its Field of View (FoV), it being reckoned to approximate that of the human field of vision when the f/length equals the image diagonal. With a 35mm camera, that happens when the f/length is at or around 50mm.

It has NOTHING whatsoever to do with image size, (or 1:1 ratios). Please allow me to assure you of that.

[As it happens, the approximation in Field of View that the 'normal' lens offers is very approximate INDEED! Due to dramatic differences between how the eye sees, and how camera lenses render images, no REAL correlation exists in FoV terms, and hardly any other terms, either!]

chuxter said:
200mm is 4 times as magnified
as 50mm,

That's correct, no quibbles!

chuxter said:
thus the 1:4 ratio.

No. That is just a coincidence in this case.

The 1:4 is an indication of the magnification ratio obtained when this lens is focused as close as it goes when using its macro capability. In this case the lens can manage a 1:4 ratio on the sensor. Put another way, the image is 1/4 the size of the subjects real life dimension. (This point has been made further up thread.)

chuxter said:
BTW, at 28mm, the mag ratio would be
1.78:1. Note that 1.78 * 4 = 7.14.

These figures may add up, but the information is spurious because it is based on a flawed concept.

The 200mm is 7.14 times as long as the 28, but that is ALL it is.

This is a different issue. I attempt an explanation below....

There is a current fashion for expressing the long end of a lens f/length range as a function of the short end f/length. This yields a single figure, as in "3x zoom" or "7x zoom" etc......

These figures may be slick and easily promoted, which seems to be their purpose, but they don't MEAN anything useful until the short end is known. We need to know "three times WHAT?" -- and that is the question left hanging by a single figure. In this case we DO know the short end, also the long end, so the "x" power of the lens is entirely superfluous.

Please accept these comments in good part.

I make as many mistakes as the next man, and am probably prone to even more misconceptions. However, on this matter I am sure of my ground.

Thank you.

Regards,
Baz

Barrie Davis · Nov 28, 2004

Frits Thomsen said:
Thank you very much for the explanation.
I think I got it now 1:1 or 1:4 , or whatever, is an actual
measure of the object , and then I just have to figure out , to
what degree a certain object will fill my particular sensor; so
this 20 mm object will create an 20 mm image (at 1:1) whether(??
spelling) or not my sensor is big enough to " hold"it , right ??

Absolutely right, Fritz !!

Thank you for re-stating my point so that I can see you got it. That sort of feedback is much appreciated.

However, (and not wishing to confuse you all over again) it isn't quite the end of the story.....

Because the magnification in dimensional terms is fixed by the lens, does NOT mean it is fixed by the sensor.

As we have seen, the reproduction ratio produces different "amounts of subject on the sensor" (for the same ratio,1:1 say) when DIFFERENT sizes of sensor are used -- possibly smaller ones. So your original point about "cropping factors" in macro is a valid one, just as it is in any other sort of photography.

Let me take you through an example, s-l-o-w-l-y.....

Take a macro lens set to 1:1 and lined up to be sharp....(OK?)

used on a sensor "too small" by a factor of 50%, say...(still OK?)

Well.....

it yields an image that is framed precisely as IF a LARGER sensor was used..

but used with a lens that yielded a 2:1 ratio at ITS closest focusing distance.

When reading, bear in mind that 2:1 is twice life size (2x the size of the actual subject, not just 'same' size)

So you can get the EFFECT of 2:1 magnification, from a lens limited by its construction to a mere 1:1 repro ratio, just by the act of cropping. The same kind of 'gain' you can get when cropping any image.

Do you understand? (Hope so!) To sum up.....

The smaller sensor can be seen as either "getting LESS on the sensor" or "providing GREATER magnification" of the subject, since both these things are EFFECTIVELY the same.

Furthermore, they are the SAME regardless of how big the image scale, is when compared with the subject scale.

Phew! I do hope I didn't muddy the water by making this point now. :-(

Either way...

Best Wishes and Regards,
Baz

ggumpshots · Nov 28, 2004

Hi Barie,

Its getting a little hairy getting all this information for something I thought was going to be simple.
Barrie wrote

In this case we DO know the short end, also the long end, so the "x" power of the lens is entirely superfluous.

Can you give a numerical example . I thought maybe 28 and 200 were the short and long end, whatever that is????????

I am getting the hang of Magnification but what is zoom

ggumpshots said:
How is Zoom different from Magnification?
A 28 200 mm lens has a zoom of 200/28 ie 7.14,

DOESNT THIS MEAN MAGNIFICATION OF 7.14,........ obviously not
according to the manufacturer.........?????????
The max magnification is 1: 4 according to The Tamron brochure I
have in front of me
Zoom and magnifcation must be differenrt things but I can see what
the difference Help!

Craig Gillette · Nov 29, 2004

ggumpshots said:
Hi Barie,
Its getting a little hairy getting all this information for
something I thought was going to be simple.

It really is pretty simple. Try not to mix up the same terms used with other types of devices because conventions differ. This site will help:
http://hypertextbook.com/facts/2002/MiriamJanove.shtml

Magnification: In simple terms, this really is about how much closer the item seems compared to using the unaided eye. Example: you'll see binoculars advertised as a 2x binocular, like in those rather dainty opera glasses or a 7x pair of field glasses. If there is no magnification, it's the same perspective as looking with the unaided eye. If you look through a paper towel tube, there is no magnification and it might be called 1x on some types of scopes. (Where a "wide-angle" makes it seem that you are seeing from further back even if you haven't actually moved back and it's a fractional value like .9x)

Zoom range: This is the ratio of the short to long focal length of a zoom lens. For example, a 30mm to 90mm is a 3x zoom (3 times). Likewise a 50mm to 150mm zoom is 3x. So the 28 to 200 is indeed a 7.14x zoom.

Focal length: The focal length of a camera lens is the distance between the center of the lens and the film when an in-focus image is formed of an object very far away. There is a chart on the site noted above that shows how different film sizes (and likewise sensor sizes) change the angles of view/perspective of the same focal length lens. In a practical camera sense, as sensors or film sizes get smaller, shorter focal lengths are used to get the same magnifications. For a 35mm camera, a 50mm (or so) lens appears to have no magnification, a 6x7cm film size takes a 90mm lens to have "no" magnification, etc.

What that means is that zoom range doesn't connect to magnification without knowing what focal length is at 1x. And that varies with the sensor or film size. Most people perceive that a 50mm or so lens has no magnification when used with 35mm cameras. While that may move around some, it's easy to work with. That means a 100mm lens is 2x magnification, a 200mm lens gives 4x magnification, etc., in terms of what most people see using a 35mm camera. So in the case of a 28-200mm lens on a 35mm camera, you go from a wide angle .56x to a 4x magnification. If most people picked up a pair of 4x binoculars, the image of the subject would look to be the same size as the image at the 200mm setting.

FWIW, This site will give you some added discussion of binoculars and related terminology. A 7x32 binocular means a 7x binocular with a 32mm objective lens - and it doesn't tell us the focal length.
http://opticsplanet.com/info/how_to_buy_binoculars.shtml

chuxter · Nov 29, 2004

ggumpshots said:
Its getting a little hairy getting all this information for
something I thought was going to be simple.

Jut ignore them. They are talking about something other than what you asked about. My post was the answer you needed and wanted. It was simple.

--
Charlie Davis
CATS #25
'I brake for pixels...'

ggumpshots · Nov 29, 2004

Thanks for the explanation in good detail .
Is zoom the ability to bring somethin 7 times closer if its a 7 times zoom.
Doesnt this mean the image is magnified 7 times?

What is my zoom ability and Magnification on a D70, my first slr and an owner for 2 days.

I now undestand magnificaton but what about zoom , ie the ratio of the short focal lenght to the long focal length.
Tamron 28 200 and d70 has a 1.5 factor?

Craig Gillette said:
ggumpshots said:

Hi Barie,
Its getting a little hairy getting all this information for
something I thought was going to be simple.

Click to expand...

It really is pretty simple. Try not to mix up the same terms used
with other types of devices because conventions differ. This site
will help:
http://hypertextbook.com/facts/2002/MiriamJanove.shtml

Magnification: In simple terms, this really is about how much
closer the item seems compared to using the unaided eye. Example:
you'll see binoculars advertised as a 2x binocular, like in those
rather dainty opera glasses or a 7x pair of field glasses. If
there is no magnification, it's the same perspective as looking
with the unaided eye. If you look through a paper towel tube,
there is no magnification and it might be called 1x on some types
of scopes. (Where a "wide-angle" makes it seem that you are seeing
from further back even if you haven't actually moved back and it's
a fractional value like .9x)

Zoom range: This is the ratio of the short to long focal length of
a zoom lens. For example, a 30mm to 90mm is a 3x zoom (3 times).
Likewise a 50mm to 150mm zoom is 3x. So the 28 to 200 is indeed a
7.14x zoom.

Focal length: The focal length of a camera lens is the distance
between the center of the lens and the film when an in-focus image
is formed of an object very far away. There is a chart on the site
noted above that shows how different film sizes (and likewise
sensor sizes) change the angles of view/perspective of the same
focal length lens. In a practical camera sense, as sensors or film
sizes get smaller, shorter focal lengths are used to get the same
magnifications. For a 35mm camera, a 50mm (or so) lens appears to
have no magnification, a 6x7cm film size takes a 90mm lens to have
"no" magnification, etc.

What that means is that zoom range doesn't connect to magnification
without knowing what focal length is at 1x. And that varies with
the sensor or film size. Most people perceive that a 50mm or so
lens has no magnification when used with 35mm cameras. While that
may move around some, it's easy to work with. That means a 100mm
lens is 2x magnification, a 200mm lens gives 4x magnification,
etc., in terms of what most people see using a 35mm camera. So in
the case of a 28-200mm lens on a 35mm camera, you go from a wide
angle .56x to a 4x magnification. If most people picked up a pair
of 4x binoculars, the image of the subject would look to be the
same size as the image at the 200mm setting.

FWIW, This site will give you some added discussion of binoculars
and related terminology. A 7x32 binocular means a 7x binocular
with a 32mm objective lens - and it doesn't tell us the focal
length.
http://opticsplanet.com/info/how_to_buy_binoculars.shtml

david70 · Nov 29, 2004

ggumpshots said:
What is my zoom ability and Magnification on a D70, my first slr
and an owner for 2 days.
I now undestand magnificaton but what about zoom , ie the ratio of
the short focal lenght to the long focal length.
Tamron 28 200 and d70 has a 1.5 factor?

The Chuxter post is the correct answer. The Tamron lens on the D70 with the smaller sensor applies a "cropping factor" to the image. In essence, you are getting the center 2/3 of what a 35mm camera will record on film using the same lens. Conversely, the lens on a D70 has the effective angle of view similar to a 42mm to 300mm zoom. 300mm has the magnificaiton factor of 6x (300/50). It is that simple.
dpc
http://www.bytephoto.com/photopost/showgallery.php?ppuser=2233

Craig Gillette · Nov 29, 2004

ggumpshots said:
Thanks for the explanation in good detail .
Is zoom the ability to bring somethin 7 times closer if its a 7
times zoom.
Doesnt this mean the image is magnified 7 times?

Yes. But you need to remember that the 7x magnification in a zoom is relative to the original magnification. If you start with a wide angle, the starting point is smaller (like starting farther away). If the zoom starts at a telephoto length, the starting point is already larger (like closer).

ggumpshots said:
What is my zoom ability and Magnification on a D70, my first slr
and an owner for 2 days.

That's going to be dependent on the lenses you use. There are a wide variety of lenses available from very wide to extreme telephotos. The zooms run anywhere from 2x on up to 10x and performance is very much a "you get what you pay for" proposition. A cheap lens of the same focal length/zoom range is unlikely to approach the finest available lenses of the same length/zoom.

ggumpshots said:
I now undestand magnificaton but what about zoom , ie the ratio of
the short focal lenght to the long focal length.
Tamron 28 200 and d70 has a 1.5 factor?

If the zoom is used on a D70, it's going to look like a 42mm to 300mm lens would look on a 35mm film camera: very close to 1x to 6x magnification

ggumpshots said:
Craig Gillette said:

ggumpshots said:

Hi Barie,
Its getting a little hairy getting all this information for
something I thought was going to be simple.

Click to expand...

It really is pretty simple. Try not to mix up the same terms used
with other types of devices because conventions differ. This site
will help:
http://hypertextbook.com/facts/2002/MiriamJanove.shtml

Magnification: In simple terms, this really is about how much
closer the item seems compared to using the unaided eye. Example:
you'll see binoculars advertised as a 2x binocular, like in those
rather dainty opera glasses or a 7x pair of field glasses. If
there is no magnification, it's the same perspective as looking
with the unaided eye. If you look through a paper towel tube,
there is no magnification and it might be called 1x on some types
of scopes. (Where a "wide-angle" makes it seem that you are seeing
from further back even if you haven't actually moved back and it's
a fractional value like .9x)

Zoom range: This is the ratio of the short to long focal length of
a zoom lens. For example, a 30mm to 90mm is a 3x zoom (3 times).
Likewise a 50mm to 150mm zoom is 3x. So the 28 to 200 is indeed a
7.14x zoom.

Focal length: The focal length of a camera lens is the distance
between the center of the lens and the film when an in-focus image
is formed of an object very far away. There is a chart on the site
noted above that shows how different film sizes (and likewise
sensor sizes) change the angles of view/perspective of the same
focal length lens. In a practical camera sense, as sensors or film
sizes get smaller, shorter focal lengths are used to get the same
magnifications. For a 35mm camera, a 50mm (or so) lens appears to
have no magnification, a 6x7cm film size takes a 90mm lens to have
"no" magnification, etc.

What that means is that zoom range doesn't connect to magnification
without knowing what focal length is at 1x. And that varies with
the sensor or film size. Most people perceive that a 50mm or so
lens has no magnification when used with 35mm cameras. While that
may move around some, it's easy to work with. That means a 100mm
lens is 2x magnification, a 200mm lens gives 4x magnification,
etc., in terms of what most people see using a 35mm camera. So in
the case of a 28-200mm lens on a 35mm camera, you go from a wide
angle .56x to a 4x magnification. If most people picked up a pair
of 4x binoculars, the image of the subject would look to be the
same size as the image at the 200mm setting.

FWIW, This site will give you some added discussion of binoculars
and related terminology. A 7x32 binocular means a 7x binocular
with a 32mm objective lens - and it doesn't tell us the focal
length.
http://opticsplanet.com/info/how_to_buy_binoculars.shtml

Click to expand...

ggumpshots · Nov 30, 2004

chuxter said:
ggumpshots said:

Its getting a little hairy getting all this information for
something I thought was going to be simple.

Click to expand...

Jut ignore them. They are talking about something other than what
you asked about. My post was the answer you needed and wanted. It
was simple.

--
Charlie Davis
CATS #25
'I brake for pixels...'

Hi Charlie,

The Tamron lens 28 200 means, I have 4 times maginification relative to the human eye view of 50mm as I now understand it.

The D70 has a 1.5 magnifaction factor associated with it , bringing the magnificaton to around 6
Is it correct to say I have the equivilent of a 6 times zoom on my D70?

Is it correct to say zoom, is relative to the short and long focal length, whilst
magnification is realtive to the human eye view?

If I am wrong can you give a numerical example to clarify

chuxter · Nov 30, 2004

ggumpshots said:
Hi Charlie,
The Tamron lens 28 200 means, I have 4 times maginification
relative to the human eye view of 50mm as I now understand it.

The D70 has a 1.5 magnifaction factor associated with it , bringing
the magnificaton to around 6
Is it correct to say I have the equivilent of a 6 times zoom on
my D70?

Is it correct to say zoom, is relative to the short and long focal
length, whilst
magnification is realtive to the human eye view?

If I am wrong can you give a numerical example to clarify

I think you have it now. But let me offer this advice: With any camera, start by first converting the lens to 35mm equivalent. In the case of your D70 and 28mm-200mm Tamron lens, multiply the focal lengths by 1.5. This gives 42mm-300mm. Then compare the extremes to the 50mm "normal", giving a magnification range of 0.84 to 6.

"Zoom" is just a marketing word that means "variable focal length", so the "zoom range" in simply the range of focal lengths. It's often expressed as a ratio. Note that the zoom range does not compare with magnification range...they are apples and oranges. It's quite possible to have a zoom lens that only covers mag ratios below 1:1 (called a wide angle zoom). Equally possible to have a zoom lens that only covers mag ratios above 1:1 (called a telephoto zoom).

Enjoy your camera. Take pictures!

--
Charlie Davis
CATS #25
'I brake for pixels...'

What is Zoom or Magnifaction for a telephoto?

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