[simpits-tech] Fresnel Lens

[John Miguez]

Robert,

I am not sure a TV's resolution will be high enough for MSFS.  You might
try connecting a TV to your card and seeing what the picture looks like
to you.  AVSIM's Cockpit forum has several long threads about Fresnel
lens.  If you go there, do a search on Fresnel lens.

John

-----Original Message-----
From: Robert Barringer [mailto:xenobob at hotmail.com] 
Sent: Tuesday, April 27, 2004 10:15 PM
To: simpits-tech at simpits.org
Subject: Re: [simpits-tech] Fresnel Lens

Well, I don't know much about the lens. I know it was originally from a 
Projection TV. There was a man at the dump with a broken one. I asked
him if 
I could have the fresnel lens, and he agreed. I'm afraid all I know
about 
the donor TV system is that it probably ended up in a landfill
somewhere.

Is this a good size lens for use in a simpit? I've never seen anyone
else on 
the internet with a lens this large. Since I'm on a budget, I'm not
going to 
buy a new TV, but I'll look around Goodwill stores and eBay. I'll try to

find a 20" monitor because of the higher resolution.

Oh, and to be honest, my name isn't really Robert, I always use an alias

when I sign up for free e-mail accounts and the like. I've always been
kind 
of paranoid of giving out personal information over the internet.

>From: Rob Hommel <rhommel at tacoma.net>
>Reply-To: Simulator Cockpit tech list <simpits-tech at simpits.org>
>To: Simulator Cockpit tech list <simpits-tech at simpits.org>
>Subject: Re: [simpits-tech] Fresnel Lens
>Date: Tue, 27 Apr 2004 19:45:39 -0700
>
>Robert:
>
>A regular glass cleaner should work fine for cleaning this lens, softly

>remove what ever dust and such as may be removed when dry prior to
using a 
>wet cleaner on the surface. Fresnel lenses should be treat in the same 
>manner as any lens for determination of focal length and imaging a
small 
>amount of experimentation should quickly yield the best distance to get
an 
>objective or virtual image depending upon the manner of use you wish to

>engage your lens.
>
>Some items you should be aware of when using a fresnel lens is the 
>chromatic aberration you will observe near the edges of the lens. This
may 
>result in the appearance of color changes or you may see image
distortion 
>near the edges of the lens. The most perfect imaging will be toward the

>center of the lens. A bit of experimentation using the lens prior to
making 
>he investment of a new television set may save a bit from your
bankbook. As 
>a rough guess, without knowing anything about your lens I would say
that a 
>20 inch should give you a good image enough to fill your fresnel lens.
You 
>may wish to learn a bit more about fresnel lenses by ordering the
Edmund 
>Scientific optics catalog. A brief glance at some of the items that
they 
>sell will yield a bit about what you should expect from your lens.
>
>From the Edmond Scientific catalog
>A Fresnel lens replaces the curved surface of a conventional lens with
a 
>series of concentric grooves, molded into the surface of a thin, 
>lightweight plastic sheet.The grooves act as individual refracting 
>surfaces, very close approximation to a common focal length. Because
the 
>lens is very thin little light is lost by absorbtion. Fresnel lenses
are 
>most often used in light gathering applications, such as condenser
systems 
>or emitter detector setups (lenses should be mounted with the grooves 
>facing the distant light source). Fresnel lenses may also be used as 
>magnifiers or projection lenses; however due to the high level of 
>distortion, it is not recommended.
>
>A further look at the information supplied by this catalog yields the 
>information that the largest lens supplied by them has a focal length
of 30 
>inches. The lens is 35 inches in diameter.
>
>Another good source of information on lenses and optics in general is
the 
>JML Direct Optics catalog. JML supplies Fresnel lenses for TV
projection 
>systems and the Fresnel lenses they sell are designed to be placed at a

>distance of 8 inches from the television projecter
>
>. The focal length of the largest lens they sell is 770 mm from a 203
mm 
>lens.
>
>I highly recommend adding these catalogs to your library optics is not
a 
>difficult science for the lay person to get a basic grasp of and each 
>catalog will give you a very good introduction to optical systems.
>
>Keep 'em Flying
>Rob Hommel
>
>At 06:20 PM 4/27/2004, you wrote:
>>I have a large fresnel lens, about 27.75" by 37". It's gotten kind of 
>>dirty from sitting in the garage and has a few scratches (kind of
large, 
>>but on the edge of the lens so I don't think they'll cause much
trouble). 
>>I am planning on building a Simpit soon, and would like to use this
lens 
>>with it. I don't know anything about fresnel lenses. What type of
display 
>>should I use? This is a very big lens. I'm thinking of getting as big
of a 
>>TV as I can, since my video card has an S-video input. How far away
from 
>>the display should I mount the lens? I'm sure I'll have to work
everything 
>>out myself, but I could use some ideas.
>>Also, what's the best way to clean this thing? It has quite a bit of
dust 
>>and dirt on it, and I don't want to damage it further.
>>
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