View Full Version : What is this B&L Projection Lens and reflection question...

11-Sep-2010, 09:46
Might anyone have experience with the B&L Lens on the left...and deciphering reflections....

I have the two, and the one on the right (to me) is typical of the B&L projection type lens....it's a Triplet, the complete interior assembly comes out, has the single up front, and two lenses air spaced in the rear....

The one on the left has me stumped....it only has two threaded cells front and back....also B&L but with brass, sn 1416xxx...

I've been trying to figure out the reflections, but have no clue with figuring cells or types from the reflection....

The front lens I see three reflections - one main mirrored reflection on front surface and a second slightly smaller, then one much smaller....

The back lens I see one main large mirror reflection from surface then, another medium sized reflection, and two small reflections....

Do you count the main mirrored reflection, or just look at the smaller ones?

Is this lens a triplet as well? beyond triplets and petzvals, were other types of projection lenses made?

Edit - The one on the right reads 12 in. E.F. - but the other only reads 10 in. (without the EF)

Thanks in advance,

Louis Pacilla
11-Sep-2010, 12:16
Hi Dan

Maybe this is a question you have answered in your post.

Why not disassemble the lens? At least as far as possible. If you have not done this before it's very easy. That way you'll know just what u have.

When it comes to air spaced lenses( Triples,Petzvals, Gauss, ) . I almost always take the lens apart . It's always a good idea to make sure the cells are in right positions. (Quit often they are not)Then I properly clean the cells if needed & reassemble correctly .
Now you'll Know What the optical design is . Oh Yea, your lens will be clean with all cells in proper positions .

BTW-Just my two cents your lens is either a triplet or petzval design about 95% sure. I made the percentage up . :)

In most cases ,the only time I rely on reflection is when I'm working with 3-5 glued lens Cells with no air spacing or simply can not remove the cells from mounting.
For instances an unmarked lens could be Dagor type design or a Protar .

Hope that helps


11-Sep-2010, 12:40
Thanks Louis,

With this lens, it only has front and rear groups...nothing else...

It doesn't appear to break down further....for that reason, I was trying to rely on the reflections to determine type....

Building a board for it at the moment - but would like to have some idea as far as the lens construction....

This photo is of the lens with the groups removed....

(The front with the 10 in. mark has the hood attached to it)

Thanks again,

Jim Galli
11-Sep-2010, 12:53
The brass one is a petzval, and a very good one at that. Score!

11-Sep-2010, 13:01
Thanks Jim,

If you don't mind me asking....

Do you know that from experience with the lens, or from the description of reflections from above....Curious...

The reflections have me completely confused...

Thanks again,
Dan King

Jim Galli
11-Sep-2010, 13:06
Experience. I didn't pay much attention to the reflection bit. But here goes. you should see strong vss weak reflections. Weak reflections are from cemented pairs. strong from air glass interface. So on the front 2 strongs and a weak are correct. It is a cemented pair. From the rear, 4 strongs is correct. Different sizes et al doesn't matter. 4 strongs is 4 air glass interfaces. Hold a penlight both near and far to figure out where the best view is. Sometimes on 'strong' will be so large it isn't seen until the pen light gets farther away.

11-Sep-2010, 13:12
Thanks again Jim....

I really appreciate the response....

Now if the paint on the new board will dry....I'll find out if this thing will cover 5x7....and see what it'll do.... :)