[Tfug] ... and, yet another, optics question! ;-)

[johngalt1]

----- Original Message ----- 
From: "Bexley Hall" <bexley401>
To: "Tucson Free Unix Group" <tfug at tfug.org>
Sent: Friday, August 22, 2008 9:52 AM
Subject: Re: [Tfug] ... and, yet another, optics question! 
;-)


> Hi, Jeremy,
>
> Come to my rescue, yet again??  :>
>
> --- On Thu, 8/21/08, Jeremy D Rogers <jdrogers> wrote:
>
>> Diopters is the optical power of the lens in inverse 
>> meters. Being
>> near sighted, my glasses are -3 diopters, so they have a 
>> focal length
>> of -1/3 meters or -30 cm. That would not help you.
>
> Are you playing fast-and-loose with terms or strictly 
> pedantic?
> I.e., "optical power"... so, is a "2X magnifying glass" (2 
> power?)
> a "-2.00"?
>
> Or, am *I* playing fast-and-loose?  :-/
>
>> Glasses for far sighted people (reading glasses) are
>> positive power which is what you want.
>
> Yes, which is why the thought struck me that I could just
> buy some El Cheapo (reading) glasses and steal the 
> lenses...
> But, how do I convert/compare diopters to "2X, 4X, 7X, 
> etc."
> encountered on magnifying glasses?
>
>> A magnifying glass works by increasing the optical power 
>> of your eye
>> or equivalently shortening the total focal length of the 
>> eye/lens
>> system. Since I am near sighted, my glasses have a 
>> negative
>> power.. so all I have to do is take off my glasses and 
>> put the
>> object closer -- no pocket magnifier needed. :-)
>
> OK, I'm far sighted so don't normally need glasses for 
> close in
> work.  *But*, reading the little tiny writing on surface 
> mount
> components, etc. is now beyond me.  :<  Even bringing the 
> item
> "up close" ... I just end up feeling like I am looking
> cross-eyed!  :<
>
>> So what you want to look for is
>> higher power or more diopters and you want them to be
>> positive (which all reading glasses are).
>
>> The magnifying power that you get from a
>> given lens depends on your eye's near point though.
>
> OK, what's a "near point"?
>
>> The only drawback
>> to using a lens from a pair of glasses is that the lens 
>> is
>> usually curved, so give a focal length, the thickness 
>> might be more
>> than a lens made to be a magnifying glass. On the other 
>> hand,
>> sometimes glasses use a higher index glass or plastic 
>> that requires
>> less curvature to achieve the same focal length which 
>> would make
>> it thinner. Probably your best bet is to play around with 
>> the
>> pair of glasses in the store and see if it works for you 
>> better
>> than what you have.
>>
>> One other thing you might look for is a loupe. This is 
>> what jewelers
>> and such use, and it isn't flat, but it gives more like 
>> 10x and still
>> is easy to carry around.
>
> I had such a thing (clipped onto my eyeglasses) when 
> younger.
> But, realized I rarely needed it back then so...  :<
> (I also used to have a nice *metal* shoe horn that I never
> needed but sorely mis now!)
>
> The problem I have found with most things (like *worn* 
> reading
> glasses is that I end up with the lens close to my eye 
> and.or
> the "target" close to my face.
>
> Ideally, I want to be able to hold something (lens) in my 
> hand
> at a comfortable distance with my head far back from both.
> For exemple, I may be trying to solder a component on a 
> circuit
> board -- I don't want my face so close that I can feel the 
> heat
> (and fumes!) from the soldering iron.

Is the scope of the application changing here? Do you want 
to find a magnifying device you can carry around *and* use 
to see when soldering a component on a board?

You don't want to snort them all day, but solder flux fumes 
smell good on occasion. :-p

> And, I think (?) to get any decent magnification, I would 
> have
> to have a large (diameter) lens so both eyes could see 
> through it
> if it was close to my face -- hence a smaller diameter 
> lens would work
> if it was close to the "target" (i.e., both eyes could 
> converge on
> the lens more easily).

When I worked in electonics manufacture they used "Luxo 
lamps" for larger assmebly. This was a 4-5 inch approx 
diameter glass lens in the middle of a circular fluorescent 
lamp. For smaller stuff, (surface mount devices, etc) 2-10x 
binocular microscopes were used.

The bonus here, is these items distance your face from the 
work to be done (and the fumes). After the fumes hit the 
magnifying thing between the work and your face, a small fan 
can be placed to disperse or exhaust the fumes. This can 
mitigate the fan sinking your soldering iron heat.

For the Luxo lamp, the working part of the whole assembly 
was 8-9 inches in diameter so a fan might not be necessary. 
Usually the lens was positioned at an angle so fumes would 
hit the assembly and get plowed out of the way.

Another bonus is these magnifiers are table mounted, so you 
don't need three hands.

You might find these sorts of things at Southwest Liqudators 
or UofA Surplus.





>
>
>
>
> _______________________________________________
> Tucson Free Unix Group - tfug at tfug.org
> Subscription Options:
> http://www.tfug.org/mailman/listinfo/tfug_tfug.org
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.138 / Virus Database: 270.6.7/1628 - Release 
> Date: 8/22/2008 6:32 PM
>
>