This is the tale of a large Suter Portrait Petzval (no.4, 24cm and F.3.2). Absolutely in perfect condition except for the missing iris blades - all 24 of them. I have done iris blade replacement before and it is not really a quick fix. Just cutting out 24 blades and keeping the blades with zero distortion is very difficult. Then you have to drill 48 holes in the perfect position, prepare 48 pins of the right length and diameter and then fit these to the holes permanently, without adding to the thickness of the blades at the join.
Many of these big Petzvals have this many blades - we think of this as ensuring complete roundness of the aperture. But I think the main reason is that makers did not want to mess with their models with known speed. Suter, for example, had the WHS version of the no.4 as F3.2. For 10% extra you could get the iris version - with the same speed. To be able to do this, you would have use a lot of iris blades that were narrow rather than fewer, which being a good deal wider, would reduce the maximum speed.
So the many narrow blades are a problem and with makers like B & L, the composite material used for blades adds to the difficulties. I have had the misfortune to work on one of B&L's , otherwise superb, Petzvals. I got the mechanics to work, but replacement with bronze instead of the original blade material, meant the friction in the extreme positions was just too much. A WHS conversion would have been simpler and with a garanteed better result in function - if not in cosmetic appearance!
A repair was not possible with this Suter 🇨🇭 as they had introduced a separate iris section in the middle of the barrel which bulged out giving diameter for the two iris rings and giving extra space for the iris blades. Even when the front and rear parts of the barrel are removed, there is no clearance for removing the holed/slotted iris rings. They are going to be in there forever! So the idea was to use these two iris plates as a basis for guiding/holding/light trapping for the Waterhouse stops. The two plates could be pushed to one side allowing entry of slots through the cut-out through which the long gone iris lever used to travel.
Bookmarks