View Full Version : Having a go at the B&L Plastic Iris problem

Steven Tribe
7-Mar-2016, 03:42
Just after the turn of the Century, B&L made a couple of models which used early plastic leaves for their professional lenses. I don't know the range of models, but it included the Portrait Unar- modified by B&L to allow softness adjustment - and the A series Portrait Petzvals with considerable movement in the rear cell. Both are very impressive lens with a cool design of the sliders. As far as I know, they didn't continue these models for very long. The system at the back looks fairly straightforward - a angle cut slot in an inner 1/6th barrel engages the rear slider and looks to be without problems even after a 100 years. The iris system in front looks far more complicated and it is impossible to work out the system by inspection.

A fellow LFPF contributor has the large size 16" 3A Portrait version and his plastic blades had been totally removed by a previous owner, but still present in a brown envelope. Needless to say, there not enough complete blades to make a complete repair. He sent me the complete barrel, minus lens cells and the original blades

This is a story of an attempt to repair with replacement blades and document exactly how the iris works.

Steven Tribe
7-Mar-2016, 04:01
First of all I have to say that a rational user of this type of lens would be far better off converting the lens to Waterhouse slots and stops. The maximum aperture would go up to 5" giving a maximum of F3.2 instead of current F4. This would take far less time and would give a permanent solution, whilst a repair of the existing system can only be temporary (decades?) as the design has built in problems - quite apart from known plastic problem. This is especialy true if the pinion drive is missing because this locks the inner barrel in position. Adjusting the Aperture with an absent drive entails that the chrome barrel is held tight! Perhaps there is another user who would like to have a go? I know there are many sick Portrait A users out there.

Steven Tribe
7-Mar-2016, 07:22
The plastic irises used by B&L are made of Celluloid. I can't speak about the other plastic used in various shutters from the same period. The first plastic, celluloid, was discovered from experiments with reduced collodion used in wp photography!
Celluloid has the ability to keep it's flat form very well - and therefore very suitable for packed leaves in an iris. The contact friction - surface to surface - is very low. In addition, it can coloured black in production instead of being painted. It is reasonably flexible but snaps under extremes, rather than taking on a permanent bends.

The pins are blackened bronze. They have small 1mm turned ends which are long enough to go through the celluloid blades (0.3mm thick) and be turned down to stay on. The pressing was just enough to make a retaining rim, but not enough to restrict movement of the pins in the leaves. This is precision manufacturing which would be hard to duplicate.

The first idea was to manufacture bronze leaves to replace the missing and U/S blades. Appearance might be bit odd and perhaps a combination would lead to unforeseen problems. The decision was to make a complete new set in bronze. In a perfect world, I would have made a mechanical join between the pins and the leaves allowing the blades to turn in leaves. But this is quite beyond my skills. Fixed pins means increased friction. Bronze/bronze friction on the leaves instead of celluloid/celluloid is likely to increase the pressure needed at the lever too.

Phosphor Bronze was chosen as providing low friction surfaces and a good of deal pf "spring" effect. I choose 0.2mm thickness (celluloid is 0.3mm) giving a little play for joining solder. I know that automatically controled laser cutting has been used successfully to make iris sets but I thought that a one-off job would be OK with hand cut leaves.

The B&L has 21 leaves which needed two sheets of phos/bronze. The "least waste" arrangement was found by trial and error, using the remaining original blades. Cutting the concave edges was by using nail scissors.

Struan Gray
7-Mar-2016, 07:39
Wishing there was a 'like' button :-)

One traditional material for these kinds of things in scientific instrumentation is beryllium copper sheet, which once heat treated is very stiff for a given thickness. You make the shape while it's soft, and then heat treat. There are safety issues working it by hand though.

7-Mar-2016, 07:59
McMaster Carr also has black Derlin and ABS plastics and Self-Lubricating MDS-Filled Nylon in .01" size. Either might also be suitable if the bronze wrinkles on you.

Steven Tribe
7-Mar-2016, 09:14
I admit that a modern plastic solution would have better if the problem with attachment of pins could be solved. There are health issues with both phosphor/bronze and tin/lead/silver as well!

The bronze leaves did curl a little during cutting. Heating up to about dull red and hammering did remove most of this and the spring was retained in the metal.

I have done some rather horrible drawings of the way the iris is mounted in the barrel. The adjustment lever moves an internal barrel. The other side of this internal barrel there is a thin lengthwise slot in which the actuating rod on the turning ring fits.
This iris nearest the front is held in place by a black painted ring pressed in. Once this is out, the upper iris ring can be withdrawn by lifting up the edge opposite the section where the actuating rod is. It can't be seen, but there is a mark on the top to show where it is.

el french
7-Mar-2016, 11:30
Were the original pins in the Celluloid peened in order to hold them in place? If so, it may not be that hard to reproduce the leaves.

Steven Tribe
7-Mar-2016, 14:03
Yes, but another problem with the original set, apart from damaged leaves, is that some pins are loose and others are missing.

After heat treatment, the bronze leaves have now lost their attractive appearance and are very mottled. Chemical blackening, with nitric acid saturated with copper, is no longer an option in Denmark - but perhaps a light dusting with mat black lacquer will do the trick.

The drilling for holes has to done to quite tight tolerances. The cutting of the leaves doesn't have to be that precise. The first time I assembled the iris, I found that as many as 5 leaves came out of their slots during the full aperture range movement.
An autopsy showed the distance between the pin pairs was slightly off (1-2mm).

I found a soft alloy bar of unknown material (but including zinc) which took up the solder. I cut all 42 "pins" in 1cm lengths. Bored holes of the right length in old plaster board, placed the pins into hole and pushed the blade holes down onto the captured pin so the pin was flush with the top surface. It is easier to ensure that the pin/blade are perfectly at 90 degrees this way with over long pins. Soldering is not too difficult and the plaster surface ensures that the difficult to remove clumps of solder do not form underneath. Obviously some finishing of the surfaces is needed and the pin shortened using cuttings (pincers) rather than saw. The joins need testing now - much better at this stage than having problems halfway through mounting.

The bottom ring is the usual type with 21 equidistant holes. In a perfect world, I would have removed the bottom ring and assembled the iris outside of the barrel. But:

1. I cannot see how this ring is attached to the barrel and, even if I could take it out and attach the blades and top ring, there would not be enough room to insert the actuating rod into the small hole because of the extra width.
2. The actuating rod can be removed (screw thread) but there is just no way to install it again through the barrel.

The movement of each blade is checked in holes. In movement, the rounded edges can rub against the barrel. Installing the first 10 or so takes just a minute. Then it gets more and more tricky as the holes are invisible and the leaf is pushed under increasing numbers of already installed leaves. This is 5" barrel, but it is still a problem for normal sized hands to have room down there. And hands make it dark and restrict vision. I loaned a small mirror from my wife (under protest) and glued this midway on a short piece of wood. Using a small pocket torch, I was able to see, to some degree, what was going on. It is not possible to catch sight of the holes very often, so I marked up the exact position of the holes on the inside edge.

Jim C.
7-Mar-2016, 15:44
Nice write up Steven, that bottom aperture pivot ring ( as I call it ) is possibly a force fit, slip fit with a shellac or lacquer used as a glue
or worse case soldered in. Of the limited lenses I have from that era force fit and slip fit with a "glue" seems the norm.

It had to have been assembled so there is a way to disassemble. :)

Jim C.
7-Mar-2016, 15:49
One thing I forgot to mention is you might be able to tool black to blacken the blades,

I've used this with limited success with some brass waterhouse stops ( probably because I didn't buy the sealer ) -


It's the ABC blackener for non ferrous metals.

This may be available in Denmark, as far as I can tell from the MSDS it's selenium based blackener.

Sean Mac
7-Mar-2016, 16:57
Steven unwraps another mystery!:)

As good as a new Sherlock Holmes story.

The recipes for taking the shine off bronze go back a long way. I'm sure I've seen at least one involving the correct phase of the moon.

Thanks for this and the Hermagis thread. You have made projection petzvals look much more interesting.:)

7-Mar-2016, 21:17
Micro hardware available here, may give some ideas for the pins.

Steven Tribe
8-Mar-2016, 01:02
...... that bottom aperture pivot ring ( as I call it ) is possibly a force fit, slip fit with a shellac or lacquer used as a glue
or worse case soldered in. Of the limited lenses I have from that era force fit and slip fit with a "glue" seems the norm.

It had to have been assembled so there is a way to disassemble. :)

I must admit that this account is partly reconstructured reflecting my thoughts at the time I was doing the operation described! I am quite sure now that is a friction fit and I thought at the time that was the most likely assembly method.
This fixed iris ring has a cut out slot, mirroring the F control, very close to the top edge. This was already deformed when I opened it up. Removing this ring would require pressure from underneath which could easily deform this part even more - or even break it off. This could lead to problems in use. There are some things you doesn't want to risk with someone else's property!

About assembly. I am certain that the two tiny screws holding the external lever body have to be removed before the intermediate barrel taken out. The only way I think this can be done is to remove the remaining part of the iris and turn the internal barrel through about 180 degrees to see first one screw head and then the other through a small hole! An endoscope would be useful.

Steven Tribe
8-Mar-2016, 01:21
One thing I forgot to mention is you might be able to tool black to blacken the blades,

I've used this with limited success with some brass waterhouse stops ( probably because I didn't buy the sealer ) -


It's the ABC blackener for non ferrous metals.

This may be available in Denmark, as far as I can tell from the MSDS it's selenium based blackener.

This reads like a very good solution which matches the original method for blackening with dipping rather than painting. I see "1 quart bottles" and "not available for air transport" though!
The bronze sheet material has the technical description of PB 102. It was much more suitable than similar brass sheeting I have used on previous iris repairs/replacements.

Steven Tribe
8-Mar-2016, 01:39
Micro hardware available here, may give some ideas for the pins.

I did, in fact, use rivet stems which were 1.65mm in diameter. A copper solution would make a compression fit possible. A fun site!

Steven Tribe
8-Mar-2016, 03:28
Now the really difficult parts!

Getting the last pins into the bottom holes becomes more difficult for the final leaves. There very little to see and the pin has to be directly over the hole to fall down in place. I was reduced to making some microtools from paper clips which didn't fill up to much to allow for some restricted visibility. Guiding marks are very necessary. If there is some non-flatness in a few of the already installed leaves, they may lift out of their holes (why do I know this!).

Then, when all leaves are seated, the top iris ring, with the actuation lever, needs to inserted. This is a totally blind job at the start. The long lengthwise slot in the totally hidden intermediate ring needs to be located exactly at at the extreme open External F4 position. The external chrome barrel needs to be turned in the brass sleeve (at least when the position is not locked due to absent tangential gear) unit the hole (which is really just a section of a slot) can be seen using the mirror reflection.

The ring is inserted at an angle, just resting on the first few pins sticking up at both sides. I inserted a tiny wedge at the other side of the ring between it and the barrel to ease the pressure on these pins.Working out from each side, I used the "tools" to move the nearest pins to the right position. These will only go into the body when a number of pins have positioned correctly. The ring at wedge site is gradually lowered as the progression continues. Eventually, this wedge can be removed without risk of the lever coming out of the hole. Many of the pins did not need movement to be in the right place.
When in place, the ring should sit about 0.5mm under the fixed ring at the edge. The locking ring rests on this edge, allowing the working part of the iris to turn without contact.
The locking ring appears quite loose compared to when it was removed so I added some solder around the edges to ensure a good compression fit.

Carsten Wolff
10-Mar-2016, 04:35
Blades are normally not a problem; I'd just get them laser-cut from thin stainless steel, or brass and, depending on optical design, not even worry about blackening them. If anyone knows where to get small rivet pins however (e.g. 1.5mm diam.)... that would be of current interest; got a nice early Russian portrait lens, which may be worth having a few dropped leaves replaced, although I tend to use if at f3.5 anyway.

Randy Moe
10-Mar-2016, 09:52
Following your adventure with interest. Noticed you desire a Bore Scope. There are now many affordable models available. This is just an example.


14-Mar-2016, 20:55
Wow, I just might buy one of those endoscopes. I had no idea they were so cheap now! These kinds of repairs are fascinating. I keep thinking the day will come when it will be fairly easy to make a 3D scan and then use a 3D printer to make parts for all sorts of antique cameras. I have a 1914 Kodak Special No.2 with an Optimo No.1 shutter that uses celluloid leaves. I've been babying it and shooting at 1/100s or less.

Kent in SD

Steven Tribe
15-Mar-2016, 01:02
The completed B&L has now been dispatched!

Not a complete success!

- the new leaves fit well and form a near perfect circle at all settings.

- blackening of the iris blades is less than perfect. I think this due to the surface of the heat treated bronze being rather mottled to start with. If I did it again, I wouldn't use any sort of coating.

- even though the individual blades have the right length, there are one or two which have a tendancy to exit the movement slots and not automatically return the slot. Caution is needed when the maximum displacement position is reached.

- The fancy turn lever for the iris on the barrel requires an unacceptible high torque for the first 1 cm reduction of the iris diameter. Unacceptible, both in terms of the frail construction and the distortion of the thin barrels. The first movements can be securly achieved by counter rotating the chrome and sleeve barrels which has the same effect as the movement of the F lever. I think this first movement is difficult because the friction area is so close to the barrel. When at a distance, the lever can provide a better torque. I think this is probably a standard problem with this B&L design. The lens I worked on had the complete tangential attachment removed which is a prerequisite for being able to use the "alternative barrel twist" method I have described, so it may have been a problem with the original blades as well. When doing this barrel twisting, the positions of both the F and Softness levers are moved in relation to their scales and range of movements, but it is quite easy to get them back - so the barrel track is seen in the middle of the focus drive cut-out.

So a half success, perhaps. Having done this, I would advise others not to do it. A WHS solution would be both simpler, much quicker to do and far more resistant to future wear and tear. And give that exciting bit of extra speed.The existing lever slot in the barrel would have to be extended by about 5mm at each end (chain saw round file?) and then a thin saw cut through the remain 2 barrels. The only disadvantage is that the front focus, if still present, becomes unuseable. The WHS stop system would be an advantage where the focussing gear has already been removed as the Waterhouse in position will lock the barrels together.

By contrast, the Soft Focus adjustment looks well-built!

Randy Moe
15-Mar-2016, 02:12
Good show. We, 100 years past, have appreciation for machinery that was state of the art and fiddlely.