Velocity Reviews > Something I don't get about zoom lenses.

# Something I don't get about zoom lenses.

Whisky-dave
Guest
Posts: n/a

 06-09-2011
On Jun 9, 1:49*pm, M-M <(E-Mail Removed)> wrote:
> 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.

I would think that is because it is 1500mm focal length.
I'm guessing that if I took a picture with this lens at the same
distance as I would with the
50mm then the ratio would be 30X
i.e if I took a picture of a coin at distance Y then it would look 30
times bigger through
the 1500mm than it would do through the 50mm, but that isn't real
magnification.

I would have thought this would be obvious from the moon shots on your
website.

M-M
Guest
Posts: n/a

 06-10-2011
In article
<(E-Mail Removed)>,
Whisky-dave <(E-Mail Removed)> wrote:

> I would think that is because it is 1500mm focal length.
> I'm guessing that if I took a picture with this lens at the same
> distance as I would with the
> 50mm then the ratio would be 30X
> i.e if I took a picture of a coin at distance Y then it would look 30
> times bigger through
> the 1500mm than it would do through the 50mm, but that isn't real
> magnification.
>
> I would have thought this would be obvious from the moon shots on your
> website.

The moon shots were not taken with that setup. They were taken through
the eyepiece of the telescope, with the magnification probably at 40-75X
through a camera that had its zoom at approx 2x more.

The birds were taken through an adapter that replaced the zoom eyepiece
of the telescope and is a true 1500mm lens.

Here is a photo of the setup for the moon shots:
http://www.netaxs.com/~mhmyers/camera/DSC_0897.jpg

Here is a photo of the setup for the bird shots:
http://www.netaxs.com/~mhmyers/camera/DSCN0170.jpg

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

Whisky-dave
Guest
Posts: n/a

 06-10-2011
On Jun 10, 3:35*am, M-M <(E-Mail Removed)> wrote:
> In article
> <(E-Mail Removed)>,
>
> *Whisky-dave <(E-Mail Removed)> wrote:
> > I would think that is because it is 1500mm focal length.
> > I'm guessing that if I took a picture with this lens at the same
> > distance as I would with the
> > 50mm then the ratio would be 30X
> > i.e if I took a picture of a coin at distance Y then it would look 30
> > times bigger through
> > the 1500mm than it would do through the 50mm, but that isn't real
> > magnification.

>
> > I would have thought this would be obvious from the moon shots on your
> > website.

>
> The moon shots were not taken with that setup. They were taken through
> the eyepiece of the telescope, with the magnification probably at 40-75X

So are you saying it magnified the moon by say 40X.
The moons diameter is about 2,000 miles ..
I';m sure you're not saying that the moons image on the sensor
would measure 40X2,000 = 80,000 miles.

> through a camera that had its zoom at approx 2x more.

So it's now 160,000 mile sin diameter as measured from the focal
plane.

>
> The birds were taken through an adapter that replaced the zoom eyepiece
> of the telescope and is a true 1500mm lens.

So what was the magnification or that set up, was the bird bigger than
the moon ?

>
> Here is a photo of the setup for the moon shots:http://www.netaxs.com/~mhmyers/camera/DSC_0897.jpg
>
> Here is a photo of the setup for the bird shots:http://www.netaxs.com/~mhmyers/camera/DSCN0170.jpg

It's quite a nice setup and something I'd like to do sometime, but I'd
avoid the term magnification because
photography magnification and Astral magnification as through
telescopes is different you might want to consider using field of view
in degrees rather than magnification as your yard/metre stick.
>
> --
> m-m
> Photo Gallery:http://www.mhmyers.com

Martin Brown
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Posts: n/a

 06-10-2011
On 10/06/2011 13:57, Whisky-dave wrote:
> On Jun 10, 3:35 am, M-M<(E-Mail Removed)> wrote:
>> In article
>> <(E-Mail Removed)>,
>>
>> Whisky-dave<(E-Mail Removed)> wrote:

>>> the 1500mm than it would do through the 50mm, but that isn't real
>>> magnification.

>>
>>> I would have thought this would be obvious from the moon shots on your
>>> website.

>>
>> The moon shots were not taken with that setup. They were taken through
>> the eyepiece of the telescope, with the magnification probably at 40-75X

>
> So are you saying it magnified the moon by say 40X.
> The moons diameter is about 2,000 miles ..
> I';m sure you're not saying that the moons image on the sensor
> would measure 40X2,000 = 80,000 miles.

It is normal when talking about magnification to mean *angular*
magnification. And the meaning of telescope is literally to look at far
away objects and make them seem nearer. It doesn't make any practical
difference whether the lens makes the moon appear as an 80,000 mile one
at 250,000 miles or a 2,000 mile one at 6,250 miles both make it appear
40x bigger in angular size than it did through the 50mm lens.
>
>
>> through a camera that had its zoom at approx 2x more.

>
> So it's now 160,000 mile sin diameter as measured from the focal
> plane.

I take it English is not your first language then?
>
>>
>> The birds were taken through an adapter that replaced the zoom eyepiece
>> of the telescope and is a true 1500mm lens.

>
> So what was the magnification or that set up, was the bird bigger than
> the moon ?
>
>>
>> Here is a photo of the setup for the moon shots:http://www.netaxs.com/~mhmyers/camera/DSC_0897.jpg
>>
>> Here is a photo of the setup for the bird shots:http://www.netaxs.com/~mhmyers/camera/DSCN0170.jpg

>
> It's quite a nice setup and something I'd like to do sometime, but I'd
> avoid the term magnification because
> photography magnification and Astral magnification as through
> telescopes is different you might want to consider using field of view
> in degrees rather than magnification as your yard/metre stick.

The usual means of describing it is as a plate scale in degrees per mm
to avoid any ambiguity. But if you take the nominal plate scale of a
50mm lens as your reference point for 35mm cameras than the nominal

Regards,
Martin Brown

John Turco
Guest
Posts: n/a

 06-30-2011
David J Taylor 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

With the exception of the "carry around in your pocket" part of the
equation, no?

--
Cordially,
John Turco <(E-Mail Removed)>

Marie's Musings <http://fairiesandtails.blogspot.com>

John Turco
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Posts: n/a

 06-30-2011
Martin Brown wrote:
>
> > On 10/06/2011 13:57, Whisky-dave wrote:

<heavily edited for brevity>

> > So it's now 160,000 mile sin diameter as measured from the focal
> > plane.

>
> I take it English is not your first language then?

<edited>

I believe that your oft-inebriated British countryman ("Whisky-dave)",
may be a "cockney" -- which could explain his strange dialect (apart
from his renowned tipsiness, of course).

--
Cordially,
John Turco <(E-Mail Removed)>

Marie's Musings <http://fairiesandtails.blogspot.com>

David J Taylor
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Posts: n/a

 06-30-2011

"John Turco" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> David J Taylor 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

>
>
> With the exception of the "carry around in your pocket" part of the
> equation, no?
>
> --
> Cordially,
> John Turco <(E-Mail Removed)>

I've certainly seen extending tripods you can carry round in your pocket,
or you could use a gorillapad....

Cheers,
David

David J Taylor
Guest
Posts: n/a

 06-30-2011
"John Turco" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> David J Taylor 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

>
>
> With the exception of the "carry around in your pocket" part of the
> equation, no?
>
> --
> Cordially,
> John Turco <(E-Mail Removed)>

"Is that a tripod in your pocket or are you just pleased to see me?"

... or words to that effect ..

Whisky-dave
Guest
Posts: n/a

 07-01-2011
On Jun 30, 7:38*am, John Turco <(E-Mail Removed)> wrote:
> David J Taylor 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

>
> With the exception of the "carry around in your pocket" part of the
> equation, no?

I dunno, "is that a tripod in your pocket or are you just plesead to
see me"
I wish my girlfriends wouldn't keep asking that question

Whisky-dave
Guest
Posts: n/a

 07-01-2011
On Jun 30, 7:39*am, John Turco <(E-Mail Removed)> wrote:
> Martin Brown wrote:
>
> > > On 10/06/2011 13:57, Whisky-dave wrote:

>
> <heavily edited for brevity>
>
> > > So it's now 160,000 mile sin diameter as measured from the focal
> > > plane.

>
> > I take it English is not your first language then?

>
> <edited>
>
> I believe that your oft-inebriated British countryman ("Whisky-dave)",
> may be a "cockney" -- which could explain his strange dialect (apart
> from his renowned tipsiness, of course).
>

Maybe keeping the original quote in I could have helped.
What is this renowed tipsee ness, I'bvve not heard anything of this.