[LargeFormat] Re: fresnels

[Skip Roessel]

As each little ring is cut with a slightly different angle to approximate the
rear surface of a condenser lens, making the master mould of a fresnel is not
too feasible in the home shop.  You need to visit your good friends at Edmund
Optics (www.edmundoptics.com) and pick one out.  I got a 16x20 fresnel for my
7x17 banquet camera and mounted it over the existing glass on my Korona with
velcro.  Works great, image is as bright as can be, if you're lined up while
viewing it.  'Course if you move to one side everything disappears.

They're all plastic, can be cut with a table saw, and are mounted outside the
ground glass, farthest from taking lens, so the GG depth remains true to the
film plane in the film holders. They scratch easily, though.  Anyone know where
I can get that non-scratch coating they put on plastic eyeglasses now?  I put
car wax on mine... better than nothing.

Big fresnels are also found in overhead projectors, now crowding eBay for $30.
Here's one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2302924199&category=25322

If you buy one at auction, see if the seller will pop out the lens and send it
to you alone, scrap the rest rather than shipping a 30-pound machine to you.
skip

skiproessel@mindspring.com

Vincent Dobson wrote:

> It is strange this thread started just as I am now in the process of
> building a facility for CXXXXX Vision they are renting space from xyz co.
> xyz co did the inventing and R&D to develop machinery that injects optical
> plastic in molds to manufacture eyeglass lens. CV manufacturers and markets
> the machines to the labs.
> Interesting process, but, expensive to develop, however once developed, the
> per unit cost is drastically reduced as compared to the labor intensive
> method of taking a hockey puck size disk of plastic (or glass) and grinding
> down to a particular prescription.
>
> small world.
>
> Vince Dobson
> Visions In Nature
> www.VisionsInNature.com
>
> -----Original Message-----
> From: largeformat-admin@f32.net [mailto:largeformat-admin@f32.net]On
> Behalf Of Les Newcomer
> Sent: Tuesday, January 21, 2003 4:50 PM
> To: largeformat@f32.net
> Subject: Re: [LargeFormat] a gritty day
>
> And that would be just to make the mould to inject the optical plastic!
>
> I think this thread started with ground glass for Speed Graphics and if
> you want to use one for a  Speed you have to be a little careful where you
> put it.
>
> Most Anniversaries and Some Pacemaker Speeds did use fresnel or "Ektalite
> Field lenses" as Graflex called them.  The ground glass on a Speed is
> loaded from the back, and if you installed a fresnel where there wasn't
> one, you'll shift the ground glass out of position the thickness of the
> fresnel.
>
> On Tuesday, January 21, 2003, at 01:28 PM, Vincent Dobson wrote:
>
> > hmm, The material the man is made of is from various keys on~~~~~~~~~
> > oops,
> > I guess you mean the fresnels?  The ones I have are made from a very hard
> > plastic, but this would not be a do it yourself project.  It takes a very
> > precision and expensive machine - think optical grade lathe and cost mid
> > 5
> > to 6 figures I think.
> >
> >
> >
> > Vince Dobson
> > Visions In Nature
> > www.VisionsInNature.com
> >
> >
> >
> > -----Original Message-----
> > From: largeformat-admin@f32.net [mailto:largeformat-admin@f32.net]On
> > Behalf Of philip.lambert
> > Sent: Tuesday, January 21, 2003 4:18 PM
> > To: largeformat@f32.net
> > Subject: Re: [LargeFormat] a gritty day
> >
> >
> >
> > ---
> > From: "Vincent Dobson" <manitec@bellsouth.net>
> > To: <largeformat@f32.net>
> > Sent: Tuesday, January 21, 2003 7:52 PM
> > Subject: RE: [LargeFormat] a gritty day
> >
> >
> >> Very precise circular strokes. :)~~/~~~~!<
> >
> >
> > Pardon me  -Is that a diagram or an oriental language?  And from what
> > material
> > do you make them?  PL
> >
> >
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