Anyone able to make a biconvex lens for a camera application?

[Pete Hanlin]

A gentleman brought in a rather ancient camera today. Seems it has a view finder that looks down into the camera. Only problem is, he has to physically pick the lens out of the holder and increase the distance about 1/4" to obtain a clear view.

Figuring I needed to decrease the focal length of the lens, I increased the converging power until he said "that's perfect!" Consequently, I need a lens that is +1.50 stronger than the one currently in the camera's viewfinder. It is the form of the
lens that may prove troublesome, however...

The lens currently has a power of +12.50 diopters. I need to increase it to +14.00. The lens is 27mm (I'll need a 28mm lens, to properly edge it, however) in diameter and has an ocular curve of +2.50 and a base curve of +12.50.

Oddly enough, if I compare the lens clock readings to the actual power of the lens, the result is that the index of the lens must be around 1.44, hmmmm. I'm guessing that my clock readings must be slightly off and the lens is actually CR-39 (however, he bought the camera used over 20 years ago... the lens is decidedly not glass).

Anyone out there able to make a lens to the specifications I've provided???

Thanks,
Pete
PS- The gentleman is leaving the country on Oct. 1st, and would ideally like to take his revamped camera with him...

[Jeff Trail]

Pete,

It's done if ya want it :) I put it on a 12 base CR39, it bounces between a +13.87 and +14 ...and is 30 mm ...oh well close as I wanted to get.. it was starting to eat into my alloy and block...
This is the type of things someone like me loves to tinker with.. plus I got to spend an hour extra here at the lab.. and an hour here is an hour I don't have to put up with "LifeTime" and the latest male bashing movie at home
I'll send an E-M with the bad news ($) if ya take it.. if not, that's ok, I'll just add it to my stock...I was interested in what the CT would end up being anyway..sometimes my tinkering gets the best of me :)
BTW you might want to consider sending it out for an AR coat if you have time..


Jeff" Just call me lightning" Trail

[Shwing]

Jeff, I have decided (for both of us, sorry) that we are of the same ilk. When I was in the lab, nothing was impossible, at least until I had tried it...(the fire wasn't too bad...)

Same holds true today, (granted, with some wisdom) and I still love to try, change, adapt, modify.

One of my favorite quotes is:

"Is it a groove you are in, or a rut??"

Well? Can you (the generic You) see over the edge??

If not, it's a rut. Just this last week I moved or improved about 3 things in my optical (no pun intended, AND, the name is already taken...)

Not because the way things were was improper, it's just better now.

Is it a groove, or a rut?

Ask yourself (the generic yourselves) rut or groove?

Shwing;-}

P.S. back to that crazy name game, I have one for you.

Dude came in, we conversed, and I asked his name.

He stated it 4 times before I caught it....

Last name: Loblaw


First name: Bob

I then apologised for crying while laughing...

True story.

[Dave Nelson]

Some handheld mags have biconvex configurations much as described, with a curve differential to correct spherical abberations. Although it appears the problem is solved, I wonder if coil has a suitable lens?

[Shwing]

Another thought (gasp!).

A true salesperson would recommend (strongly) a Digital camera...

You know, get with the 'groove' of optics....


Ya, o.k., it's a stretch.

Shwing'-}

[chip anderson]

go to www.edmundscientific they have an optical products catalogue that you will not believe. Unfortunately you have to be smarter than I to know what you want. But they have very sort of focusing/alignement devise you could ever want. Catalogue is free. They also have a lot of other scientific catalogues with lots of good stuff. If I had infinite time, money and knowledge I would probably go broke buying their stuff and stuff from Bass ProShops.