Re: lens 'recipes'

Charles Manoras wrote:
"Phil Hobbs" wrote

snip

3. Measure the focal length of the lens (crack doublets apart for
measurement purposes, assuming you have several identical ones--use a
knife and a soggy hammer, and wear safety glasses).

You crack me up! :-)

What's a soggy hammer? You mean a mallet?
I love the safety glasses part. You forgot the cold chisel I assume.

You actually separated a doublet using your method without chipping
the individual lenses? If so congratulations on your dexterity and luck!

The method to separate a doublet is to immerse it in a solvent and
let it soak overnight, or as long as it takes (which may be several days).

Sometimes the separation is impossible.
Especially with modern UV curing cements or bonding agents.

Sometimes the separation proceeds half way and then stops.
Then good luck on being able to reuse the doublet.

The sovent depends upon the cement that was used.

For old lenses "Canada Balsam" was used in which case hot water may do the
trick. Raise the temperature slowly as the doublet may shatter.

If using a solvent put the container in a fume hood.
Solvents have often disagreable features (toxicity, flameability etc.)

Most of the ones I've done have been non-precious. I wouldn't try taking apart an antique that way, but mass-produced lenses are cheap--I'd much rather buy a couple of spares and crack one apart than wait a day. If it gets gouged up--oh, well. Even shards have the right radius of curvature for measurement, but I've never shattered one.

A soggy hammer is a soft-faced hammer, typically made of hard but not very bouncy rubber, that is used for auto body work and other such jobs. Snap-On sells "dead hammers" that are pretty good for this too, but a bit too small. Lead-faced hammers are (a) hard to find these days, and (b) not soft enough for splitting lenses. The nasty plastic-faced ones are useless--too light and too hard. You don't use a chisel, you use a sharp knife--extra big XActo blades are okay, if a bit thin, but the little ones are useless. I have a heavy folding knife that I usually use for this. The knife blade sits on the edge of the glue bond line, so the lenses start coming apart before any serious damage occurs. It really works--try it some time.

Hammers are great for lots of optical things, surprisingly enough. I often use ball-peen hammers to take off photodiode windows. You just grab the photodiode leads in a vice (with the bottom of the can sitting on the jaws), and gently tap the window with the ball. The glass turns to powder, which comes out very neatly when you take the diode out of the vice and tap it against the side. Amusingly, the key thing is that you have to use a *sufficiently big* hammer--you want the ball to be caught by the edges of the can before it grinds the glass dust into the silicon. I've used a three-pound hammer on germanium quad cells.

This trick is far superior to filing the can or cutting it in a lathe--faster, cleaner, and higher-yielding, though not every hermetically-sealed diode is well enough passivated for open-air use.

I also align gas lasers with a pry bar, but that's another story. ;)

Cheers,

Phil Hobbs
.

Relevant Pages
Quantcast