Phil_F_NM
Camera hacker
This is a lens repair writeup for a C mount lens used on 4:3 16mm cameras, and can be used (with vignetting) on M4/3 cameras. I originally posted this on a cinematography forum.
I recently pulled the trigger on one of these potentially trouble prone lenses. It was bought very cheap, with foggy glass and tight focusing, but an aperture which was working, for the most part. This is the H16RX version, but the construction is essentially the same as the non-RX lens, particularly the aperture assembly, which is what I'm writing about repairing.
Last night I set to taking apart the lens to polish the haze off the elements adjacent to the aperture. This is common in old lenses with original lubricants, as over the last 50 or so years, the greases have migrated and outgassed, depositing haze on the elements near the aperture. I've seen this in most older still photo rangefinder lenses, especially Canon and Leica. Anyway, I got the lens down to bits and the aperture block out. I saw the awful "crown" of bent metal which makes up the pivot points in each aperture blade. Getting the lens elements haze free and the focusing helicoid working fine was all good but I still didn't want to have to take this lens apart WHEN, not if, the weak aperture blade pivot points give way.
I have quite a few parts lenses available to me, but no Berthiot 10mm samples. I was on the lookout for replacement blades with better construction. First thing I had to find was a lens that opened the aperture in the same direction as the Berthiot, and had the same number of blades, which is six. Turns out I have three of them, one needed repair. I selected two Bell & Howell Comats, both 25mm f/1.9. One is the first version which is almost like a small golf ball, the other is the later version with the finish that looks like the Angenieux lenses which shipped with Filmos. The third donor lens I have is a Lumax but the aperture blades would require a bit more modification over what I describe below.
Both of the Comats turned out to have aperture blades which are an exact match pivot-to-pivot. Radius, distance and angle are almost exactly the same. The only issue is about .5mm extra on the inside angle of each aperture blade. These blades are easily cut in order to remove the appropriate amount of metal to create a matching blade to the Berthiot original. If this is not done, the lens' rate of closure does not match the aperture scale due to the subtle S bend in one side of the aperture blade. So far I've cut a few blades and using a 20x microscope, I can see that I got the cuts close enough to discourage tearing. The best option would be a rounded corner cut but this is impossible for me in my home workshop.
The carriage for the aperture blades needs to be filed out by about .1mm as well. This is easy as the material is relatively thin brass. Both sides of the carriage, pivot and cam need to be widened with a file until the aperture pivots fit and slide with zero resistance.
Once I get the whole lens back together, I'll have an essentially new Berthiot 10mm RX lens, though I'll have spent five hours of labor on it. The opportunity cost of that time spent on this repair is not offset by the cost of a 10mm Switar RX or Cinegon RX, for me, but might be for most out there. That said, since I work on most of my own gear (aside from my REX4) I figure I'm saving money and enjoying the time I spend improving a lens.
I thought I'd put this out there for all you with Berthiot 10mm f/1.9 lenses which have non-operational apertures due to their cost cutting. It's a fine optic and with some TLC can really be made to work quite nicely for folks who want an inexpensive C mount wide angle.
Phil Forrest
I recently pulled the trigger on one of these potentially trouble prone lenses. It was bought very cheap, with foggy glass and tight focusing, but an aperture which was working, for the most part. This is the H16RX version, but the construction is essentially the same as the non-RX lens, particularly the aperture assembly, which is what I'm writing about repairing.
Last night I set to taking apart the lens to polish the haze off the elements adjacent to the aperture. This is common in old lenses with original lubricants, as over the last 50 or so years, the greases have migrated and outgassed, depositing haze on the elements near the aperture. I've seen this in most older still photo rangefinder lenses, especially Canon and Leica. Anyway, I got the lens down to bits and the aperture block out. I saw the awful "crown" of bent metal which makes up the pivot points in each aperture blade. Getting the lens elements haze free and the focusing helicoid working fine was all good but I still didn't want to have to take this lens apart WHEN, not if, the weak aperture blade pivot points give way.
I have quite a few parts lenses available to me, but no Berthiot 10mm samples. I was on the lookout for replacement blades with better construction. First thing I had to find was a lens that opened the aperture in the same direction as the Berthiot, and had the same number of blades, which is six. Turns out I have three of them, one needed repair. I selected two Bell & Howell Comats, both 25mm f/1.9. One is the first version which is almost like a small golf ball, the other is the later version with the finish that looks like the Angenieux lenses which shipped with Filmos. The third donor lens I have is a Lumax but the aperture blades would require a bit more modification over what I describe below.
Both of the Comats turned out to have aperture blades which are an exact match pivot-to-pivot. Radius, distance and angle are almost exactly the same. The only issue is about .5mm extra on the inside angle of each aperture blade. These blades are easily cut in order to remove the appropriate amount of metal to create a matching blade to the Berthiot original. If this is not done, the lens' rate of closure does not match the aperture scale due to the subtle S bend in one side of the aperture blade. So far I've cut a few blades and using a 20x microscope, I can see that I got the cuts close enough to discourage tearing. The best option would be a rounded corner cut but this is impossible for me in my home workshop.
The carriage for the aperture blades needs to be filed out by about .1mm as well. This is easy as the material is relatively thin brass. Both sides of the carriage, pivot and cam need to be widened with a file until the aperture pivots fit and slide with zero resistance.
Once I get the whole lens back together, I'll have an essentially new Berthiot 10mm RX lens, though I'll have spent five hours of labor on it. The opportunity cost of that time spent on this repair is not offset by the cost of a 10mm Switar RX or Cinegon RX, for me, but might be for most out there. That said, since I work on most of my own gear (aside from my REX4) I figure I'm saving money and enjoying the time I spend improving a lens.
I thought I'd put this out there for all you with Berthiot 10mm f/1.9 lenses which have non-operational apertures due to their cost cutting. It's a fine optic and with some TLC can really be made to work quite nicely for folks who want an inexpensive C mount wide angle.
Phil Forrest
wolfy
Newbie
Hi Phil
I've got the same lens that won't focus, nothing moves when focusing. Do you have a diagram to get this lens apart so I can fix this issue. Any help would be appreciated. Thanks
I've got the same lens that won't focus, nothing moves when focusing. Do you have a diagram to get this lens apart so I can fix this issue. Any help would be appreciated. Thanks
Phil_F_NM
Camera hacker
Unfortunately, I do not have a diagram, nor do I have this lens anymore. Good luck.
Phil
Phil