Need a specialty lens for a camera application... Jeff?

[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 added various powers 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...

[Darris Chambless]

Hello Pete,

You need to call Edmund Industrial Optics at 1-800-363-1992. They also have a web page at www.edmundoptics.com. (http://www.edmundoptics.com.)

If you can decipher what type of camera it is I might be able to check my camera collection and see if I have a lens for that type of camera in the power your patient needs. It sounds like the viewer on a Brownie, but I've never heard of this particular problem. I'm not sure of the exact type of plastic that the lenses were made of but you are correct that it isn't glass. These lenses tended to get very foggy with age and would turn yellow. And then little green guys would jump out and yell boogie, boogie, boogie while taunting you with a large Berginshire billet and unless you sing the Tangy Taffey theme song in D minor you couldn't get rid of them...or something like that. I think :-)

Sorry, I got bored writing viable information only :-)

Darris C.

[Jeff Trail]

Pete,

Making the lens is not a problem :-) .. just made a pair of +15's for Barry S. on here on a 12 base :)

If it isn't glass, chances are it's an acrylic base material, pretty popular around that time trying to find a "cheap" way to get around using glass.. but about the only way to check is to chip it, or burn the edge..
The bad part is that when grinding a bi-convex it is very hard to get the EXACT power .. I think in that +15 I came up with a +15.12..
To make sure you get an exact job you may want to take that lens and make a very precise pattern so the lab has something to go by.. also what is the edge thickness of the old lens.. and what type of mounting? ..
Doing it is the easy part.. making sure it will work (thickness, etc. ) will be the tricky part...

I think you might be better off going with a 1.55 instead of a CR39.. the trade off of some chromatic aberation (not to bad in a 1.55) would be better then that higher bi-convex surface, also the 1.55 or 1.56 can be found in a 12 curve.. that's upto to you though..the difference would be you go from that +2'sh ocular down to almost a plano surface ocular :)

Jeff "some of the stuff I get into..sheesh" Trail

[Ed_Optician]

You might try something like an old trial case lens....if you are lucky you may find one of the right power in some old dusty box in the back room or basement of an old optometric practic should have a +14 probably biconvex and glass to boot curves may not be precisely matching the old one but it will work well I am sure

I once hand edged a +1.00 glass lens down to fit the eyepiece of a customers ancient Konica Autoreflex T couldnt get eyepiece correction diopters anywhere so I made one for hem

[Chris Ryser]

Edmund Scientific has all sort of odd lenses by the thousands. Look up the link on my website,,,,,,,,,,,,,,, http://optochemicals.com/web_ratings.htm ,

[k12311997]

maybee the patient needs to be wearing reading glasses???

[Judy Canty]

Y'all did notice this was an almost 6-year old thread?.

[k12311997]

Y'all did notice this was an almost 6-year old thread?.

looks down at feet in meek voice replys " uh no"

[npdr]

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..

Is this a Hasselblad or a Rolleiflex?

[HarryChiling]

Y'all did notice this was an almost 6-year old thread?.
That's funny, this board just made my day.

[Michael Walach]

It is 6 years old thred:hammer: !
However, if anyone needs any special lens to make, try QUEST LAB. We do it all :cheers: .
www.questopticallab.com (http://www.questopticallab.com)

Michael Walach