Re: [CAD_CAM_EDM_DRO] Re: Newbie Intro

skykotech wrote:

>
> Hey Tom, sorry I missed the intro. I sorta limped through the one
> optics course require by my EE major...lol, didn't think it would be
> very usefull at the time. Little did I know I would get into machine
> vision, lasers, etc.
>
> I had a sherline before I got the great deal on this huge mill (long
> story, but it ended up costing me -$300!). I thought about mounting
> a laser to the sherline, but decided the travel and speed is too
> limited (for example, I cut some thin paper at 120IPM...can you even
> move a sherline leadscrew driven table at 120IPM???). I posted a few
> weeks ago about building a universal gantry machine to which a small
> CO2 laser could be mounted (or a router). Most of the people on here
> are deathly afraid of laser beams...or sharks with laser beams? :-)
>
> You probably agree that the CO2 wavelength is one of the safer ones,
> at least compared to eximer and yag, which focus so nicely on the
> retina and pass through most glass and plastics. A little common
> sense and lexan can go a long way in protecting you from the CO2
> wavelength.
>
> On the lens issue. ZnSe is somewhat expensive, and I am the king of
> scrounging, so I am just using what I have collected over the years.
>
> The ZnSe lenses I have now are:
>
> Four 3" F.L. 1" dia plano/convex
> Two 1.75" F.L. 1.1" dia plano/convex
> One 7.0" F.L. 0.625" dia plano convex
> One negative 2" F.L. 0.625" dia
> One negative 5.82" F.L. 0.5" dia
>
> I am not sure about the structure of these last two negative
> lenses...I guess they are plano/concave?
>
> I also have two 2.5" F.L. 1.1" dia Germanium lenses AR coated at 10.6
> which I believe are meniscus.
>
> Any ideas on how to use the negative lenses/positive lenses I have to
> get a better spot with the Synrad J48-1?
>
> By the way, if you need a lens holder machined for your laser I will
> do it for the cost of shipping if you can send me an autocad or rhino
> file. I also have a good supply of 0.062" Indium wire that makes a
> nice cushiony seal for the soft ZnSe material.
>
> Rick

Hello Rick,

I have some of those ebay ZnSe lenses too. 3 inch and 7 inch anyway,
although I would prefer 2 inch.

There are many ways to use multiple air spaced lenses to create an
arbitrary focal length, focal distance and working distance.

Working distance the ususally the clearance between the optical package
and the focal plane. That is the distance that the machinist needs to
keep in mind.

Focal distance is the distance from the focal plane to the nearest glass
surface. For a single thin lens the focal length and focal distance are
the same. For a single thick lens they are slightly different. For
surfaces with large seperations, like air spaced lenses, the focal
distance and the focal length can be totally different.

Focal length is a purely mathematical effect for the optical system. It
can be used in many formulae to predict the end result but is not enough
info to predict how the light passes through the entire system.

I have to scoot out the door soon but I will dig up or make up the
equations that you need. Since you are an EE I will compute the answers
for you but I will give you equations and you can plug in the lenses
that you have and look at various seperations to see what you get for
focal length and focal distance. Working distance depends on how you
package the lenses.

Also, you ask for a better spot. What is better to you may be worse to
me. Do you want smaller or larger? Do you want greater depth of focus or
less? You get the idea here. What do you want to do that you cannot do
with the spot you now have?

As for mounting hardware, I often use 1.0 or 0.5 inch diameter lenses
and ThorLabs optical tubes. These tubes come in 0.5, 1.0, and 2.0 inch
inside diameters. Threaded at both ends for easy extension. I CNC
threadmill to make 1.008 inch 40tpi to mate with ThorLabs tubes. That
allows me to standardize, as much as I can. I also like Edmunds
Scientific singlets and achromatic doublets for visible light beacuse
Edmunds has a variety of focal lengths in 1.0 and 0.5 inch diameters.

Tom Hubin
thubin@...