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Something I don't get about zoom lenses.

 
 
no_one_cares@whatbusterthinks.com
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      06-07-2011
On Mon, 6 Jun 2011 08:35:43 +0100, "David J Taylor"
<(E-Mail Removed)> wrote:

><(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>[]
>> 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.
 
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no_one_cares@whatbusterthinks.com
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      06-07-2011
On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
<(E-Mail Removed)> wrote:

>On Sun, 05 Jun 2011 19:04:32 -0400, http://www.velocityreviews.com/forums/(E-Mail Removed)
>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...
 
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no_one_cares@whatbusterthinks.com
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      06-08-2011
On Tue, 7 Jun 2011 15:09:22 -0700, Savageduck
<savageduck1@{REMOVESPAM}me.com> wrote:

>On 2011-06-07 14:03:30 -0700, (E-Mail Removed) said:
>
>> On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
>> <(E-Mail Removed)> wrote:
>>
>>> On Sun, 05 Jun 2011 19:04:32 -0400, (E-Mail Removed)
>>> 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.






 
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Whisky-dave
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      06-08-2011
On Jun 8, 11:07*am, Eric Stevens <(E-Mail Removed)> wrote:
> rOn Wed, 08 Jun 2011 04:21:12 -0500, Neil Ellwood
>
>
>
>
>
>
>
>
>
> <(E-Mail Removed)> wrote:
> >On Wed, 08 Jun 2011 10:44:09 +1200, Eric Stevens wrote:

>
> >> On Tue, 07 Jun 2011 17:03:30 -0400, (E-Mail Removed)
> >> wrote:

>
> >>>On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
> >>><(E-Mail Removed)> wrote:

>
> >>>>On Sun, 05 Jun 2011 19:04:32 -0400, (E-Mail Removed)
> >>>>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


 
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Martin Brown
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      06-08-2011
On 08/06/2011 06:22, Savageduck wrote:
> On 2011-06-07 21:19:52 -0700, (E-Mail Removed) 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
 
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M-M
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      06-08-2011
In article <(E-Mail Removed)>,
Eric Stevens <(E-Mail Removed)> 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

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no_one_cares@whatbusterthinks.com
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      06-08-2011
On Tue, 7 Jun 2011 22:22:46 -0700, Savageduck
<savageduck1@{REMOVESPAM}me.com> wrote:

>On 2011-06-07 21:19:52 -0700, (E-Mail Removed) said:
>
>> On Tue, 7 Jun 2011 15:09:22 -0700, Savageduck
>> <savageduck1@{REMOVESPAM}me.com> wrote:
>>
>>> On 2011-06-07 14:03:30 -0700, (E-Mail Removed) said:
>>>
>>>> On Mon, 06 Jun 2011 21:07:26 +1200, Eric Stevens
>>>> <(E-Mail Removed)> wrote:
>>>>
>>>>> On Sun, 05 Jun 2011 19:04:32 -0400, (E-Mail Removed)
>>>>> 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.

 
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M-M
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      06-08-2011
In article <(E-Mail Removed)>,
Eric Stevens <(E-Mail Removed)> 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?

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me
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      06-08-2011
On Wed, 08 Jun 2011 00:19:52 -0400, (E-Mail Removed)
wrote:


>
> 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?



http://www.mystd.de/album/calculator/

http://www.dofmaster.com/digital_coc.html

 
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M-M
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      06-09-2011
In article <(E-Mail Removed)>,
Eric Stevens <(E-Mail Removed)> 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.

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