View Full Version : What have I got and why wont it focus?

3-Jun-2008, 17:34
I've had this beauty lying around for years but just last week had my machinist buddy make a mounting flange so I could try it out.

The result is it wont focus at any bellows extension. It seems to want to focus at a near range rather than far, but will not even come close even at minimum bellows draw.

The only identifying feature is the engraved numeral "1" visible in the photo. There are no marks on the cells, either outside or in and no other wording anywhere on the barrel. It obviously is from the age of Waterhouse stops, but that's my only other clue. It does seem to be a Petzval design since both sets of cells appear to be identical (see Photo).

Two questions. Any idea who the manufacturer might be (the engraving style seems to match my Dallmeyer #A)? And, why wont it focus?

I tried it out mounted on my Ansco 8x10, if that makes any difference.

My only thought is that at some point in time, a previous owner switched one or both sets of cells or took them apart and got an element or two out of place. However, there is nothing in their appearance that would indicate that.

I'm confused.

Please help.



3-Jun-2008, 17:43
a quick way to find the rough focal length is to stand in a dark room and open the blinds to a bright window. Hold the lens out a foot or so from the far wall (or a white sheet of paper or something) then just move the lens in and out until it focuses. You'll quickly find out if the lens will focus, and roughly how far out it needs to be extended. If it doesn't focus, I suppose maybe there is an element missing, or one is backwards, out of order or miss aligned?

Mark Sawyer
3-Jun-2008, 17:59
What Daniel said... It's almost certainly a Petzval or Rapid Rectilinear/Aplanat, and the lens layouts are pretty easy to find through google or Yahoo. But in your second image, both the elements seem to have a convex element facing outward, which is correct. That in itself would insure that a RR is correct, (even if you reversed the front and rear, you'd still get a pretty clear image). If it's a Petzval, the interior lens could be reversed. That's all I can think of...

3-Jun-2008, 18:41
Mark and Daniel....Thanks for the replies. The one thing I didn't say was that the elements can't be interchanged. The threads are different for front and rear sections. I'll try the window idea tomorrow, but I did try the lens off the board with the camera while moving the lenses back and forth inside the body with still no ability to focus on the ground glass.

Wish I were more of a n optical physics guy.

Jim Galli
3-Jun-2008, 18:42
Looks like one of the little Darlot elements that would have been combined with 3 more just like it to make 4 little cabinets on a single full plate sheet. I always start by holding a piece of ground glass in one hand and holding the lens out in front of it with the other. In a fairly dark spot, look at a curlycue flourescent bulb or some other bright object in the next room. My bet is that it's a petzval of about 65 - 80mm focal length. Another way to do it is to unscrew the lens from your Nikon and hover that one out front until you see a focus snap in.

Here's (http://tonopahpictures.0catch.com/Wee_Petzvals/Wee_Petzval_96mm.html) a page of images done with a very similar lens. Shown on 2 1/2 X 4, click on them to see full circle images on 4X5.

Brian Bullen
3-Jun-2008, 19:00
I have a lens somewhat similar to yours and here is a link to a little write up I did about it. http://brianbullen.blogspot.com/2007_11_01_archive.html
One thing I'd check is to make sure the elements are all in their proper place. There should be a way to unscrew them to check the configuration. One thing I noticed about my lens is that even though the front and back mounts are different sizes the elements are the same diameter and can be changed front to back.

3-Jun-2008, 19:03
I also have the same lens, everything looks like yours but the engraved number. Mine reads Darlot on the two thick glass lenses. About 6 inch focus. Mine also was assembled as a "backwards" petzval (Cemented lens in the rear), but can barely be configured with the cemented in front. It seems to work both ways, and I need to experiment more. I was very surprised and pleased with this little lens. Two wetplates taken with it here:

I'm not sure, but it sounds like you have not taken the actual glass lenses out of their metal assemblies. Unscrew the metal ring on the inside of each threaded part. Do that with a gentle turn on a rubber mousepad or such. The glass(es) will drop out. If a petzval, you should be able to hold three glass lenses in your hand (one is actually a cemented double). The two separatable ones need a little metal spacer to keep them slightly apart. The convex mates with the concave, and then these two have to also face the correct way. Google a graphic and it'll become clear....no pun.

3-Jun-2008, 19:22

Such great responses!!!! Thanks to all and please keep 'em coming. I need all the knowledge I can get. I'll try the light bulb on ground glass to see it it focuses at all. Otherwise, I'm guessing that elements are out of place and I'll see if I can find some kind of schematic.

These old lenses are more fun than color TV (to quote a favorite movie).

Mark Sawyer
3-Jun-2008, 20:38
Same principle, but I just go into a fairly dark room with a window to the outside, and point the lens out the window while varying the distance between the lens and a white wall behind it to see where it focuses.