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Optics of door security viewer
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Jane
science forum beginner


Joined: 08 Jul 2006
Posts: 3

PostPosted: Sat Jul 08, 2006 9:54 am    Post subject: Optics of door security viewer Reply with quote

What is the optical arrangement of lenses in a door security viewer and
what sort of powers might they be?

These teo are the sort of thing I mean:
http://www.c-p-p.co.uk/product/asp/ProdID/2045/CtgID/1032/af/page.htm
http://www.imagewonders.com/

I want to make my own viewer to watch birds immediately outside my
window! The viewer would go through my curtains.

Binoculars do not focus down enough to the 0.5 to 1.0 meters I need.

I have no idea of optics but I reckon I could probably build some sort
of lens arrangement if only I knew what arrangement I was aiming for.
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2
science forum beginner


Joined: 15 Mar 2006
Posts: 33

PostPosted: Sat Jul 08, 2006 3:57 pm    Post subject: Re: Optics of door security viewer Reply with quote

"Jane" <jane@invalid.com> wrote in message
news:Xns97FA6EF2754421A7D4@127.0.0.1...

Quote:
I have no idea of optics but I reckon I could probably build some sort
of lens arrangement if only I knew what arrangement I was aiming for.

For gosh sake, just buy one. They are cheap enough.
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tadchem
science forum Guru


Joined: 03 May 2005
Posts: 1348

PostPosted: Sat Jul 08, 2006 6:55 pm    Post subject: Re: Optics of door security viewer Reply with quote

Jane wrote:
Quote:
What is the optical arrangement of lenses in a door security viewer and
what sort of powers might they be?

These teo are the sort of thing I mean:
http://www.c-p-p.co.uk/product/asp/ProdID/2045/CtgID/1032/af/page.htm
http://www.imagewonders.com/

It is a simple Galilean telescope. It uses lenses instead of mirrors.

The lenses have been selected to give a wide-angled view instead of a
magnified image.

They work like a wide-angled lens on a camera.
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John C. Polasek
science forum Guru


Joined: 30 Apr 2005
Posts: 321

PostPosted: Sun Jul 09, 2006 5:39 pm    Post subject: Re: Optics of door security viewer Reply with quote

On 8 Jul 2006 11:55:39 -0700, "tadchem" <tadchem@comcast.net> wrote:

Quote:

Jane wrote:
What is the optical arrangement of lenses in a door security viewer and
what sort of powers might they be?

These teo are the sort of thing I mean:
http://www.c-p-p.co.uk/product/asp/ProdID/2045/CtgID/1032/af/page.htm
http://www.imagewonders.com/

It is a simple Galilean telescope. It uses lenses instead of mirrors.

The lenses have been selected to give a wide-angled view instead of a
magnified image.

They work like a wide-angled lens on a camera.

Look backwards through an opera glass and you'll get the same effect
with inverse (de)magnification.
The door has a positive longer FL lens inside, and a negative, shorter
FL lens outside. The angle is multiplied by the ratio of focal
lengths.
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Jane
science forum beginner


Joined: 08 Jul 2006
Posts: 3

PostPosted: Sun Jul 09, 2006 10:28 pm    Post subject: Re: Optics of door security viewer Reply with quote

On 08 Jul 2006, 2<nhoj@droffats.ten> wrote:

Quote:

"Jane" <jane@invalid.com> wrote in message
news:Xns97FA6EF2754421A7D4@127.0.0.1...

I have no idea of optics but I reckon I could probably build some
sort of lens arrangement if only I knew what arrangement I was
aiming for.

For gosh sake, just buy one. They are cheap enough.


The overall length of one which fits a door will be far too small. I
want to build one because I have to.
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Jane
science forum beginner


Joined: 08 Jul 2006
Posts: 3

PostPosted: Sun Jul 09, 2006 10:29 pm    Post subject: Re: Optics of door security viewer Reply with quote

Quote:
Jane wrote:
What is the optical arrangement of lenses in a door security
viewer and what sort of powers might they be?



Quote:

It is a simple Galilean telescope. It uses lenses instead of
mirrors.

The lenses have been selected to give a wide-angled view instead of
a magnified image.

They work like a wide-angled lens on a camera.


On 09 Jul 2006, John C. Polasek<jpolasek@cfl.rr.com> wrote:
Quote:

Look backwards through an opera glass and you'll get the same
effect with inverse (de)magnification. The door has a positive
longer FL lens inside, and a negative, shorter FL lens outside.
The angle is multiplied by the ratio of focal lengths.

That's it. Thank you!
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2
science forum beginner


Joined: 15 Mar 2006
Posts: 33

PostPosted: Sun Jul 09, 2006 10:58 pm    Post subject: Re: Optics of door security viewer Reply with quote

"John C. Polasek" <jpolasek@cfl.rr.com> wrote

Quote:
Look backwards through an opera glass and you'll get the same effect
with inverse (de)magnification.

Not really. The door lens is a "fisheye" type. It has a very wide view while
the reversed opera glass does not have a particularly wide view.
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2
science forum beginner


Joined: 15 Mar 2006
Posts: 33

PostPosted: Sun Jul 09, 2006 10:58 pm    Post subject: Re: Optics of door security viewer Reply with quote

"Jane" <jane@invalid.com> wrote in message
news:Xns97FBEEFBE3A581A7D4@127.0.0.1...

Quote:
Look backwards through an opera glass and you'll get the same
effect with inverse (de)magnification. The door has a positive
longer FL lens inside, and a negative, shorter FL lens outside.
The angle is multiplied by the ratio of focal lengths.

That's it. Thank you!

Won't work the same at all.
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John C. Polasek
science forum Guru


Joined: 30 Apr 2005
Posts: 321

PostPosted: Mon Jul 10, 2006 12:15 am    Post subject: Re: Optics of door security viewer Reply with quote

On Sun, 09 Jul 2006 23:28:07 +0100, Jane <jane@invalid.com> wrote:

Quote:
On 08 Jul 2006, 2<nhoj@droffats.ten> wrote:


"Jane" <jane@invalid.com> wrote in message
news:Xns97FA6EF2754421A7D4@127.0.0.1...

I have no idea of optics but I reckon I could probably build some
sort of lens arrangement if only I knew what arrangement I was
aiming for.

For gosh sake, just buy one. They are cheap enough.


The overall length of one which fits a door will be far too small. I
want to build one because I have to.
It works like I said, but it is important to have a low f-number on

the negative lens(big lens, short FL) so it doesn't vignette your
view.
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2
science forum beginner


Joined: 15 Mar 2006
Posts: 33

PostPosted: Mon Jul 10, 2006 3:35 am    Post subject: Re: Optics of door security viewer Reply with quote

"John C. Polasek" <jpolasek@cfl.rr.com> wrote

Quote:
It works like I said, but it is important to have a low f-number on
the negative lens(big lens, short FL) so it doesn't vignette your
view.

Why don't you give a specific recommendation? Are you suggesting the OP
purchase a fisheye lens for a camera? That's nutz! She does not need the
acutance and corrections of a spendy camera lens. The rest, for example
utility glass, don't specify what F of the lens.
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Jeff179
science forum addict


Joined: 09 Nov 2005
Posts: 59

PostPosted: Tue Jul 11, 2006 3:00 am    Post subject: Re: Optics of door security viewer Reply with quote

2 wrote:
Quote:
"John C. Polasek" <jpolasek@cfl.rr.com> wrote


It works like I said, but it is important to have a low f-number on
the negative lens(big lens, short FL) so it doesn't vignette your
view.


Why don't you give a specific recommendation?

Who knows what she wants and where she wants to shop. Edmiunds
Scientific springs to mind though.

Are you suggesting the OP
Quote:
purchase a fisheye lens for a camera? That's nutz! She does not need the
acutance and corrections of a spendy camera lens. The rest, for example
utility glass, don't specify what F of the lens.

F = focal length / Lens Diameter

Google for more info. Newsgroups are best used after the OP has googled
around a bit first. You are more likely to better know how to ask a
better question and more likely to get a more informed answered.

Jeff
Quote:


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Google

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