# Something I don't get about zoom lenses.

Discussion in 'Digital Photography' started by no_one_cares@whatbusterthinks.com, Jun 3, 2011.

1. ### Guest

I've read that the magnification of a lens is calculated by
dividing it's larger zoom number by it's smaller zoom number.

If true, an 18 - 200mm lens has a magnification (not
considering crop factor) of 11.1...

But a 70 - 200mm lens would only have a maximum magnification
of less than 3 times?

Did I miss something?

If that's true, why would anyone buy a 70 - 200 in preference
to something that can better pull in distant objects?

Obviously, I haven't yet taken a photography course or this
would have been one of the first questions I'd have asked.

Any help is appreciated.

, Jun 3, 2011

2. ### charlesGuest

On Thu, 02 Jun 2011 22:31:49 -0400,
wrote:

> I've read that the magnification of a lens is calculated by
>dividing it's larger zoom number by it's smaller zoom number.
>
> If true, an 18 - 200mm lens has a magnification (not
>considering crop factor) of 11.1...
>
> But a 70 - 200mm lens would only have a maximum magnification
>of less than 3 times?
>
> Did I miss something?
>
> If that's true, why would anyone buy a 70 - 200 in preference
>to something that can better pull in distant objects?
>
> Obviously, I haven't yet taken a photography course or this
>would have been one of the first questions I'd have asked.
>
> Any help is appreciated.

200/70 has nothing to do with magnification, it is the zoom range.
Magnification would be determined by the 200mm or the 70mm, the larger
the focal length number the greater the magnification. Some people
like a greater zoom range, it means fewer changes on lenses, fewer
lens purchases. Some people, like me, believe that lenses with very
great zoom range are not as good optically.

charles, Jun 3, 2011

3. ### TheRealSteveGuest

On Thu, 02 Jun 2011 22:31:49 -0400,
wrote:

> I've read that the magnification of a lens is calculated by
>dividing it's larger zoom number by it's smaller zoom number.
>
> If true, an 18 - 200mm lens has a magnification (not
>considering crop factor) of 11.1...
>
> But a 70 - 200mm lens would only have a maximum magnification
>of less than 3 times?
>
> Did I miss something?
>
> If that's true, why would anyone buy a 70 - 200 in preference
>to something that can better pull in distant objects?
>
> Obviously, I haven't yet taken a photography course or this
>would have been one of the first questions I'd have asked.
>
> Any help is appreciated.

You're confusing zoom range with magnification. Zoom range is easy.
It's just the larger focal length / smaller focal length.

Magnification is a little more complex. For a telescope or binoculars,
it is the focal length / effective exit diameter, which is the
eyepiece focal length. That's all well and good because you are
looking right through the lenses at an object. With a camera, it's a
little different because it's projecting onto a sensor. You can take
the exact same lens and it will have different *effective*
magnification for cameras that have different sensor sizes. This is
true even though the actual magnification of the lens hasn't changed,
and is the focal length / effective exit diameter.

It gets a little more complicated for many zoom lenses with internal
focus that have a small min focus distance. Take the 18-200 as an
example. When you focus close, say less than 10', with the lens zoomed
out to 200mm, it isn't really a 200mm focal length. For close focus,
the lens compensates for the fact that it's length is restricted due
to internal focus by reducing the focal length. That lens can't get
much more than 140mm when the subject is close. At infinity focus, it
does go out to 200mm. So don't believe your zoom ring markings unless
the subject is far away.

I have a quick and dirty calculus for lens magnification which relates
to the "fact" that a 50mm lens on a 35mm camera is considered to be
about 1x magnification. You just take your focal length and divide by
50. Thus, a 200mm focal length would be a 4 power lens if you wanted
to relate it to something like binoculars magnification.

If you're shooting with an aps sensor that has a crop factor of 1.5,
just take whatever you get above and multiply it by 1.5. So on a Nikon
APS sensor, a 300mm lens would be a 1.5 * 300/50 = 9x lens and would
have the same magnification as 9x binocs.

There are more detailed analysis you can get into if you're really
interested. Things like the lens reproduction ratio, which is
dependent on subject distance and therefor ability to focus at
distance X. Just google reproduction ratio and lens focusing formulas
if you really want to get into it.

Steve

TheRealSteve, Jun 3, 2011
4. ### DanPGuest

On Jun 3, 3:31 am, wrote:
>         I've read that the magnification of a lens is calculated by
> dividing it's larger zoom number by it's smaller zoom number.
>
>         If true, an 18 - 200mm lens has a magnification (not
> considering crop factor) of 11.1...

Meaning a picture taken at 200mm compared to one at 18mm is enlarged
11.1 times.
Think of it as zoom range.

>         But a 70 - 200mm lens would only have a maximum magnification
> of less than 3 times?

You get the same magnification/view at 200mm. And lose the wide view
at 18mm.

>         Did I miss something?
>
>         If that's true, why would anyone buy a 70 - 200 in preference
> to something that can better pull in distant objects?

Marketing concentrates on megapixels and zoom range (x10, x30 etc).
These matters least. Look at aperture before anything, sometimes
called the f number, the lower the better.
It means the lens will let a good amount of light in.

I guess you own a good camera with interchangeable lenses. Take some
shots in Av (aperture) mode at various settings.

>         Obviously, I haven't yet taken a photography course or this
> would have been one of the first questions I'd have asked.
>
>         Any help is appreciated.

After getting my camera with the kit 18-55mm lens I have rushed and
bought the 55-250mm. Then I got a 50mm f/1.8 prime (no zoom).
I use the 50mm most and 55-250mm least. I would suggest you get the
50mm prime first as it is the cheapest and a joy to use.

DanP

DanP, Jun 3, 2011
5. ### RichAGuest

On Jun 2, 10:31 pm, wrote:
>         I've read that the magnification of a lens is calculated by
> dividing it's larger zoom number by it's smaller zoom number.
>
>         If true, an 18 - 200mm lens has a magnification (not
> considering crop factor) of 11.1...
>
>         But a 70 - 200mm lens would only have a maximum magnification
> of less than 3 times?
>
>         Did I miss something?
>
>         If that's true, why would anyone buy a 70 - 200 in preference
> to something that can better pull in distant objects?
>
>         Obviously, I haven't yet taken a photography course or this
> would have been one of the first questions I'd have asked.
>
>         Any help is appreciated.

In 35mm terms, you can consider a 50mm lens to be essentially 1:1 and
on an APS sensor to be 1.5:1 or 1.5x magnification. On a 35mm sensor
for every 100mm, you are adding 2x. So a 200mm lens magnification
would be 4x a 300mm lens would be 6x. You simply multiply that
magnification by the sensor crop (1.5x, or whatever) and you have your
effective magnification. A 500mm lens on an APS (1.5 crop) sensor
would be: 500x2 = 10 x 1.5 (the crop) = 15x.
This is all more or less arbitrary, the only important thing being how
one focal length relates to another, 1000mm is 5 times the
magnification of 200mm, etc.

RichA, Jun 3, 2011
6. ### Martin BrownGuest

On 03/06/2011 03:31, wrote:

> I've read that the magnification of a lens is calculated by
> dividing it's larger zoom number by it's smaller zoom number.

I suggest you stop reading that source then. The ratio of longest focal
length to shortest focal length is the zoom *range*.

The magnification of a lens depends on the format of the camera used.
But for a 35mm slide camera is approximately 50mm = 1x, and about 0.7x
that = 35mm for a typical digital SLR. For larger formats the lenses
have longer focal length for a given magnification and for small APS
point and shoots much shorter lengths and smaller sensors.

> If true, an 18 - 200mm lens has a magnification (not
> considering crop factor) of 11.1...

Not magnification zoom range.
>
> But a 70 - 200mm lens would only have a maximum magnification
> of less than 3 times?
>
> Did I miss something?
>
> If that's true, why would anyone buy a 70 - 200 in preference
> to something that can better pull in distant objects?

Because there are extremely well optimised designs for zoom lenses that
over a 3x range work almost as well as a fixed length prime lens.

To get a 10x zoom range some design compromises on either vignetting,
edge/corner sharpeness, barrel distortion and lateral colour have to be
made. These days with software correction of certain aberrations on
digital cameras this compromise is not so bad as it was on film where
you were stuck with whatever image the lens put down.

People still use fixed focal length lenses too (zoom range = 1). Such
lenses can be optimised to be sharper than any zoom (although the
difference between zoom optics and fixed length lenses is much less now
than it was in the past). Zooms used to be pretty dire in the distant
past going soft at long lengths and curvy barrel effects at short.
>
> Obviously, I haven't yet taken a photography course or this
> would have been one of the first questions I'd have asked.
>
> Any help is appreciated.

If you are trekking then weight matters and one 10x zoom instead of a
rucksack full of glass might be quite tempting.

Regards,
Martin Brown

Martin Brown, Jun 4, 2011
7. ### Guest

On Thu, 02 Jun 2011 20:05:00 -0700, charles <>
wrote:

>On Thu, 02 Jun 2011 22:31:49 -0400,
>wrote:
>
>> I've read that the magnification of a lens is calculated by
>>dividing it's larger zoom number by it's smaller zoom number.
>>
>> If true, an 18 - 200mm lens has a magnification (not
>>considering crop factor) of 11.1...
>>
>> But a 70 - 200mm lens would only have a maximum magnification
>>of less than 3 times?
>>
>> Did I miss something?
>>
>> If that's true, why would anyone buy a 70 - 200 in preference
>>to something that can better pull in distant objects?
>>
>> Obviously, I haven't yet taken a photography course or this
>>would have been one of the first questions I'd have asked.
>>
>> Any help is appreciated.

>
>
>200/70 has nothing to do with magnification, it is the zoom range.
>Magnification would be determined by the 200mm or the 70mm, the larger
>the focal length number the greater the magnification.

Thank you.

Now I'm gonna see if I can find the web page that tells people
that the magnification is the lenses' large number divided by it's
small number and thank the author for not knowing what he's talking

I had to wonder, because it didn't make a lot of sense to me
to have various lenses ending at 200mm and a cornucopia of smaller
minimum numbers.

>Some people
>like a greater zoom range, it means fewer changes on lenses, fewer
>lens purchases. Some people, like me, believe that lenses with very
>great zoom range are not as good optically.

, Jun 5, 2011
8. ### Guest

On Thu, 2 Jun 2011 20:14:20 -0700, Savageduck
<savageduck1@{REMOVESPAM}me.com> wrote:

>On 2011-06-02 19:31:49 -0700, said:
>
>> I've read that the magnification of a lens is calculated by
>> dividing it's larger zoom number by it's smaller zoom number.
>>
>> If true, an 18 - 200mm lens has a magnification (not
>> considering crop factor) of 11.1...
>>
>> But a 70 - 200mm lens would only have a maximum magnification
>> of less than 3 times?
>>
>> Did I miss something?
>>
>> If that's true, why would anyone buy a 70 - 200 in preference
>> to something that can better pull in distant objects?
>>
>> Obviously, I haven't yet taken a photography course or this
>> would have been one of the first questions I'd have asked.
>>
>> Any help is appreciated.

>
>You have to talk differences in the lenses beyond zoom range, and also
>
>First, the two types of lenses you have named in your question are an
>18-200mm, an a 70-200mm. Both lenses have a maximum FL of 200mm, both
>have the same telephoto capability to "pull in distant objects."

That's what I didn't get, because I did a search and some
more than one) decided to tell everyone that a lenses' magnification
ability is calculated by dividing the lenses' maximum focal length by
it's minimum.

With an 18-200mm lens, it would work out to a bit more than
11x, if the camera has no "crop factor", and with a 70-200mm, it would
be less than 3 power. It struck me as idiocy that companies would
produce so many lenses with varying minimum focal distances, so I

>
>Most manufacturers versions of 18-200mm lenses are general purpose,
>walk-around, do-it-all lenses, usually with maximum aperture range of
>f/3.5-f/5.6. The larger zoom range is a compromise for image quality,
>usually at the long end of the range, and sometimes at both ends of the
>range. For many it is a compromise they can live with in order to have
>a reasonably wide (18mm) and some reach (200mm) in one lens. The same
>is also true for some of the lenses with even wider zoom ranges such as
>the Sigma 18-250mm, and the Tamron 18-270mm at 15X. All of these are
>usually considered consumer quality lenses which the users are prepared
>to accept image quality compromises due to reasonable cost.
>
>Most 70-200mm lenses are Pro grade lenses, usually with a maximum
>aperture over the entire zoom range of f/2.8, which makes them useful,
>fast lenses for use in difficult lighting situations, including sports,
>weddings, portraits, etc. They are also among the sharpest lenses the
>various manufacturers build since they do not have the compromise of
>the wider range of the 18-200mm.
>The 70-200mm f2.8 will also have a premium price over the 18-200mm.

Oh yes. Once I found out about aperture settings, and checked
out the prices of F3.5 lenses vs. f2.8 lenses on ebay and other sites,
I became well aware of at least that difference.

Thanks for the explanation.

Now, to find the halfwit someone taught to use a computer...

, Jun 6, 2011
9. ### Guest

On Fri, 3 Jun 2011 01:57:44 -0700 (PDT), DanP <>
wrote:

>On Jun 3, 3:31 am, wrote:
>>         I've read that the magnification of a lens is calculated by
>> dividing it's larger zoom number by it's smaller zoom number.
>>
>>         If true, an 18 - 200mm lens has a magnification (not
>> considering crop factor) of 11.1...

>
>Meaning a picture taken at 200mm compared to one at 18mm is enlarged
>11.1 times.
>Think of it as zoom range.
>
>>         But a 70 - 200mm lens would only have a maximum magnification
>> of less than 3 times?

>
>You get the same magnification/view at 200mm. And lose the wide view
>at 18mm.
>
>>         Did I miss something?
>>
>>         If that's true, why would anyone buy a 70 - 200 in preference
>> to something that can better pull in distant objects?

>
>Marketing concentrates on megapixels and zoom range (x10, x30 etc).
>These matters least. Look at aperture before anything, sometimes
>called the f number, the lower the better.
>It means the lens will let a good amount of light in.
>
>I guess you own a good camera with interchangeable lenses. Take some
>shots in Av (aperture) mode at various settings.
>
>>         Obviously, I haven't yet taken a photography course or this
>> would have been one of the first questions I'd have asked.
>>
>>         Any help is appreciated.

>
>After getting my camera with the kit 18-55mm lens I have rushed and
>bought the 55-250mm. Then I got a 50mm f/1.8 prime (no zoom).
>I use the 50mm most and 55-250mm least. I would suggest you get the
>50mm prime first as it is the cheapest and a joy to use.
>
>
>DanP

If I start doing portraits a lot I'll get a prime lens with a
large aperture, but for now I want to be able to bring objects farther
away a bit closer and still have decent performance in low light.

Perhaps NASA will release some optics and electronics combos
that let us take shots in near total darkness with a 40x zoom in a
package you can carry around in your pocket...

, Jun 6, 2011
10. ### David J TaylorGuest

<> wrote in message
news:...
[]
> Perhaps NASA will release some optics and electronics combos
> that let us take shots in near total darkness with a 40x zoom in a
> package you can carry around in your pocket...

... likely you can already do something near to that, given a tripod and
long enough exposure.

David

David J Taylor, Jun 6, 2011
11. ### Guest

On Mon, 6 Jun 2011 08:35:43 +0100, "David J Taylor"
<> wrote:

><> wrote in message
>news:...
>[]
>> Perhaps NASA will release some optics and electronics combos
>> that let us take shots in near total darkness with a 40x zoom in a
>> package you can carry around in your pocket...

>
>.. likely you can already do something near to that, given a tripod and
>long enough exposure.
>
>David

Well, that's true to a degree.

The D3000 is noisy above 400 ISO, but I've taken a long
exposure at night in what I thought was very little light and it
showed a lot of things I was very surprised at.

I also managed to catch some lightning near the end of a 10
second exposure a while back and it was a nice shot.

, Jun 7, 2011
12. ### Guest

On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
<> wrote:

>On Sun, 05 Jun 2011 19:04:32 -0400,
>wrote:
>
> --- snip ----
>
>> Perhaps NASA will release some optics and electronics combos
>>that let us take shots in near total darkness with a 40x zoom in a
>>package you can carry around in your pocket...

>
>What do you think is a 40x zoom? 40 times what?
>
>Regards,
>
>Eric Stevens

I mean where you end up getting the image magnified 40
times...

, Jun 7, 2011
13. ### Guest

On Tue, 7 Jun 2011 15:09:22 -0700, Savageduck
<savageduck1@{REMOVESPAM}me.com> wrote:

>On 2011-06-07 14:03:30 -0700, said:
>
>> On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
>> <> wrote:
>>
>>> On Sun, 05 Jun 2011 19:04:32 -0400,
>>> wrote:
>>>
>>> --- snip ----
>>>
>>>> Perhaps NASA will release some optics and electronics combos
>>>> that let us take shots in near total darkness with a 40x zoom in a
>>>> package you can carry around in your pocket...
>>>
>>> What do you think is a 40x zoom? 40 times what?
>>>
>>> Regards,
>>>
>>> Eric Stevens

>>
>> I mean where you end up getting the image magnified 40
>> times...

>
>You still haven't quite grasped this concept.
>There is a great difference between "zoom range" and "magnification",
>and the sale pitches for many of the consumer grade cameras add to the
>confusion, especially when they add "digital zoom" to the discussion.
>Since we are discussing digital cameras, let's stick to cameras with
>"full frame" sensors (approximating the size of 35mm film) and APC or
>cropped sensors, and optical zoom only.
>
>Zoom range is a ratio between the widest part of the range and the longest.
>For example for the 18-200mm lens you spoke of, is 11.1. For the
>70-200mm, it is 2.85. These are not a magnification factor.
>Magnification for a crop sensor camera, where a 35mm lens might be
>considered "normal", the maximum magnification for both lenses is about
>5.2-5.7x. A 70-300mm lens would be about 8.5-9x at 300mm.
>
>To get 40x magnification on a crop sensor camera you would need a lens
>with a focal length somewhere around 1,400mm.
>That same 40x magnification on a FF camera would require an
>approximately 2,000mm lens.
>If they were available, I don't think you could afford either one.
>Consider that a decent 800mm prime lens would run you somewhere around
>\$6500-\$10,000.

Well I don't think I'll be buying one anytime soon if that's
the case.

So the "magnification" on the lens would not be 200mm divided
by 18 then, if I understand what you're saying.

Is there a formula then by which magnification can be
calculated?

And thanks for the info. This will help when I determine which
of the zooms I can afford will best suit my needs.

, Jun 8, 2011
14. ### Whisky-daveGuest

On Jun 8, 11:07 am, Eric Stevens <> wrote:
> rOn Wed, 08 Jun 2011 04:21:12 -0500, Neil Ellwood
>
>
>
>
>
>
>
>
>
> <> wrote:
> >On Wed, 08 Jun 2011 10:44:09 +1200, Eric Stevens wrote:

>
> >> On Tue, 07 Jun 2011 17:03:30 -0400,
> >> wrote:

>
> >>>On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
> >>><> wrote:

>
> >>>>On Sun, 05 Jun 2011 19:04:32 -0400,
> >>>>wrote:

>
> >>>>   --- snip ----

>
> >>>>>    Perhaps NASA will release some optics and electronics combos
> >>>>>that let us take shots in near total darkness with a 40x zoom in a
> >>>>>package you can carry around in your pocket...

>
> >>>>What do you think is a 40x zoom?  40 times what?

>
> >>>>Regards,

>
> >>>>Eric Stevens

>
> >>>    I mean where you end up getting the image magnified 40
> >>>times...

>
> >> I'm sure you don't really mean that either. Consider that an image of a
> >> 6' man would be 240' high. What a camera!

>
> >> Regards,

>
> >> Eric Stevens

>
> >I do mean it - 40x magnification (up to recently) meant the image on the
> >film/picture plain. This is what is meant by 5x macro when referring to a
> >lens - other lenses have differing sizes of macro.

>
> Describing a macro as 5x is OK. Describing a zoom as 40x is ...
> obscure at least. What do you understand it to mean?

I think the term magnification is what is confusing things.
We could confuse this further by mentioning telescopes, binoculars and
microscopes

Then we could compare magnification with field of view too.

If the OP said what sort of things he wants to shoot then maybe some
examples
of what a specific lens would be best might more useful than these
definitions and calculations.

>
>
>
> >Another context (which was very seldom used) is the ratio between the
> >focal length of the lens and the nominal diagonal of the negative/film
> >(in 35m/m was taken to be around 46m/m).

>
> Regards,
>
> Eric Stevens

Whisky-dave, Jun 8, 2011
15. ### Martin BrownGuest

On 08/06/2011 06:22, Savageduck wrote:
> On 2011-06-07 21:19:52 -0700, said:
>
> The zoom ratio is the ratio between the longest and shortest focal
> length for a given zoom lens. This is not magnification, it is the zoom
> ratio. If a sales person, camera or lens manufacturer represents zoom
> range as magnification they are BSing.
>
> For example an 18-200mm lens has a zoom ratio of 11.11. Somebody might
> try to represent that as "11.11X Zoom." That is not magnification.
> The magnification for that lens on a FF DSLR is 4X. On a crop sensor
> DSLR approximately 6X.
>
>>
>> Is there a formula then by which magnification can be
>> calculated?

>
> Here is a rough guide;
> The usual reference in 35mm photography is a normal lens of 50mm,
> because a lens of that focal length produces 35mm format images which
> approximate the perspective and field of view of the unaided eye. (1X).
> As you increase the focal length from that "normal" number the
> "magnification" will appear to increase with an apparent narrowing of
> the field of view, and shortening of the distance between the camera and
> subject. So a bird 100ft away when viewed through a 50mm lens should
> appear much as it would to the naked eye.
> Zoom out to 200mm and you will have the bird at 100ft appear approx. 4X
> closer. With a 300mm lens approximately 6X closer.
>
> If you are using a crop sensor camera (usually a crop ratio of 1.4-1.5)
> the same 200mm will be an effective 300mm and the 300mm an effective 450mm.

And just to make life arbitrarily more confusing some camera makers have
become totally inconsistent and describe digital camera lenses (crop
DSLRs and P&S cameras) with their lenses "notional" 35mm full frame
equivalent focal length. This makes comparisons much harder even for
people who know what they are looking at.

A workable heuristic definition for effective magnification is given by
focal length of lens divided by 1.5 x sensor diagonal length. It is
crude but close enough to be useful as a rough guide.

As SavageDuck says 50mm f.l. lens on a 35mm format is ~1x

>> And thanks for the info. This will help when I determine which
>> of the zooms I can afford will best suit my needs.

Anything much longer than 300mm on a 35mm camera and you will also need
a decent tripod and/or image stabilisation.

Regards,
Martin Brown

Martin Brown, Jun 8, 2011
16. ### M-MGuest

In article <>,
Eric Stevens <> wrote:

> >>What do you think is a 40x zoom? 40 times what?
> >>
> >>Regards,
> >>
> >>Eric Stevens

> >
> > I mean where you end up getting the image magnified 40
> >times...

>
> I'm sure you don't really mean that either. Consider that an image of
> a 6' man would be 240' high. What a camera!

40X magnification would be 2000mm. Here is ~45X magnification (1500mm x
1.5 crop factor):

http://www.netaxs.com/~mhmyers/d80/DSC_1516w.jpg

--
m-m
Photo Gallery:
http://www.mhmyers.com

M-M, Jun 8, 2011
17. ### Guest

On Tue, 7 Jun 2011 22:22:46 -0700, Savageduck
<savageduck1@{REMOVESPAM}me.com> wrote:

>On 2011-06-07 21:19:52 -0700, said:
>
>> On Tue, 7 Jun 2011 15:09:22 -0700, Savageduck
>> <savageduck1@{REMOVESPAM}me.com> wrote:
>>
>>> On 2011-06-07 14:03:30 -0700, said:
>>>
>>>> On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
>>>> <> wrote:
>>>>
>>>>> On Sun, 05 Jun 2011 19:04:32 -0400,
>>>>> wrote:
>>>>>
>>>>> --- snip ----
>>>>>
>>>>>> Perhaps NASA will release some optics and electronics combos
>>>>>> that let us take shots in near total darkness with a 40x zoom in a
>>>>>> package you can carry around in your pocket...
>>>>>
>>>>> What do you think is a 40x zoom? 40 times what?
>>>>>
>>>>> Regards,
>>>>>
>>>>> Eric Stevens
>>>>
>>>> I mean where you end up getting the image magnified 40
>>>> times...
>>>
>>> You still haven't quite grasped this concept.
>>> There is a great difference between "zoom range" and "magnification",
>>> and the sale pitches for many of the consumer grade cameras add to the
>>> confusion, especially when they add "digital zoom" to the discussion.
>>> Since we are discussing digital cameras, let's stick to cameras with
>>> "full frame" sensors (approximating the size of 35mm film) and APC or
>>> cropped sensors, and optical zoom only.
>>>
>>> Zoom range is a ratio between the widest part of the range and the longest.
>>> For example for the 18-200mm lens you spoke of, is 11.1. For the
>>> 70-200mm, it is 2.85. These are not a magnification factor.
>>> Magnification for a crop sensor camera, where a 35mm lens might be
>>> considered "normal", the maximum magnification for both lenses is about
>>> 5.2-5.7x. A 70-300mm lens would be about 8.5-9x at 300mm.
>>>
>>> To get 40x magnification on a crop sensor camera you would need a lens
>>> with a focal length somewhere around 1,400mm.
>>> That same 40x magnification on a FF camera would require an
>>> approximately 2,000mm lens.
>>> If they were available, I don't think you could afford either one.
>>> Consider that a decent 800mm prime lens would run you somewhere around
>>> \$6500-\$10,000.

>>
>> Well I don't think I'll be buying one anytime soon if that's
>> the case.
>>
>> So the "magnification" on the lens would not be 200mm divided
>> by 18 then, if I understand what you're saying.

>
>Correct.
>The zoom ratio is the ratio between the longest and shortest focal
>length for a given zoom lens. This is not magnification, it is the zoom
>ratio. If a sales person, camera or lens manufacturer represents zoom
>range as magnification they are BSing.
>
>For example an 18-200mm lens has a zoom ratio of 11.11. Somebody might
>try to represent that as "11.11X Zoom." That is not magnification.
>The magnification for that lens on a FF DSLR is 4X. On a crop sensor
>DSLR approximately 6X.
>
>>
>> Is there a formula then by which magnification can be
>> calculated?

>
>Here is a rough guide;
>The usual reference in 35mm photography is a normal lens of 50mm,
>because a lens of that focal length produces 35mm format images which
>approximate the perspective and field of view of the unaided eye. (1X).
>As you increase the focal length from that "normal" number the
>"magnification" will appear to increase with an apparent narrowing of
>the field of view, and shortening of the distance between the camera
>and subject. So a bird 100ft away when viewed through a 50mm lens
>should appear much as it would to the naked eye.
>Zoom out to 200mm and you will have the bird at 100ft appear approx. 4X
>closer. With a 300mm lens approximately 6X closer.
>
>If you are using a crop sensor camera (usually a crop ratio of 1.4-1.5)
>the same 200mm will be an effective 300mm and the 300mm an effective
>450mm.

That clears things up a bit. Thanks.

>
>>
>> And thanks for the info. This will help when I determine which
>> of the zooms I can afford will best suit my needs.

, Jun 8, 2011
18. ### M-MGuest

M-M, Jun 8, 2011
19. ### meGuest

me, Jun 8, 2011
20. ### M-MGuest

In article <>,
Eric Stevens <> wrote:

> >> >40X magnification would be 2000mm. Here is ~45X magnification (1500mm x
> >> >1.5 crop factor):
> >> >
> >> >http://www.netaxs.com/~mhmyers/d80/DSC_1516w.jpg
> >>
> >> Whatever it is you have calculated, it is not magnification.

> >
> >
> >Ok then, what is it?

>
> I'm not quite sure. I don't understand what it is you think you are
> doing.

If 50mm is 1x magnification then 1500mm is 30x and then add in the 1.5x
crop factor.

The lens states it is 1500mm.

--
m-m
Photo Gallery:
http://www.mhmyers.com

M-M, Jun 9, 2011