Incident illumination

[wporter]

For a quick trial, try a rattle from an aerosol paint can; here in the U.S., they are often clear marbles of about 1 cm. They do have some bubbles.

[MichaelG.]

Edmunds has 8mm ball lenses for $35. ...

.
That’s where my stroke of genius [or lunacy] comes in, Bram ... I have a few of these:
https://www.manchesterminerals.co.uk/ac ... ml#SID=105
... bought on a ‘Magpie’ whim, when Manchester Minerals had a retail shop nearby.

They are 3/4 balls, with the flat surface mirrored [aluminised] to give a reflected image of the viewer
... very effective, very attractive, and I have no idea how they can be made to sell at that price.

Optically, they are excellent and [used ‘sideways’] it looks like they will work in this application.
< cue joyous fanfare ! >

MichaelG.

[MichaelG.]

On an initial quick read** through it didnt seem to me that the ball lens was a big claim ?
More to do with the mobility of the direction of the (converging) light, or lights if more than one are [s]required[/s] to be experimented with.

I put converging in brackets cos they dont seem to be specifically requiring that as part of the novel claim, the emphasis is more on the novelty of being able to conveniently adjust the direction, 360*. The convergence is mentioned 'en passant' and not quantitatively ?? So there is scope for experiment not only with a filament, aka led, at the conjugate focus of the ball from the specimen , but somewhere else at up to infinity of lens ? ha, that should occupy a few more months of lockdown !

** and then would you adam&eve it - the lights went out, a power cut in southern England in 2020 !pah.

.
I think you are correct there ^^^
There is no patentable novelty in using the optics of a ball lens ... it’s just like the water-filled globes that were used with candles.

Glad to see from your footnote that you are in England
... I was about to ask.

MichaelG.

[Mraster2]

They are 3/4 balls, with the flat surface mirrored [aluminised]
and [used ‘sideways’]

Might it be undone with sodium hydroxide perhaps ?
Then you would have a planosuperconvex lens ? !

[MichaelG.]

They are 3/4 balls, with the flat surface mirrored [aluminised]
and [used ‘sideways’]

Might it be undone with sodium hydroxide perhaps ?
Then you would have a planosuperconvex lens ? !

It can be removed by careful abrasion with a very fine diamond hone [ Eze-Lap]
The resulting lens is interesting; but unlikely to be useful for this application, unless perhaps you place a flat LED in direct contact with the plano surface.
I believe the configuration in the patent is intended to put the lamp filament at 2f, which gives a ‘life size’ spot of light at a similar distance on the output side.

MichaelG.
.

UPDATE 08-Jul-2020 ... Please ignore that closing sentence for now.

[Mraster2]

It can be removed by careful abrasion
intended to put the lamp filament at 2f,

Yes, thought of grinding but may involve too much polishing, depending.
Wouldnt caustic soda be easier, the surface must be reasonably optical already for it to be a mirror.

Yes I presumed 2f also, can you not do that with a fat plano ?

You are right about the cost, I was nearly tempted, shame about the p&p (that was well buried!) they should be on ebay, would save all the form filling

[MichaelG.]

Yes ... stripping with caustic soda is probably preferable to removal by abrasion [but the resulting surface was good enough for what I was doing at the time]

The nominal ‘3/4 ball’ is, I believe, technically known as an ‘aplanatic ball lens’ and is usefully described here:
http://doriclenses.com/optical-componen ... enses.html

The Effective focal length (EFL) and Working distance (WD) of these lenses are dependent on the selected wavelength, glass material, parent ball diameter, central thickness and can be easily calculated.

For the full ball EFL= n x D / 4 x (n-1) and WD = EFL x (2-n) / n
where n is the index of refraction of the selected glass and wavelength.

The thickness of the hemispherical lens is D/2.
The thickness of the aplanatic lens derived from a ball is D/2+D/2n.

Note: I’m playing-about with these things, and have a lot to still to learn.

MichaelG.

[Mraster2]

http://doriclenses.com/optical-componen ... enses.html

and have a lot to still to learn.

Thanks for the link,
fascinating stuff. I had no idea that balls were in such widespread use, other than in seances and futurology !