Home  1: Introduction and research  2: Basic parts and materials 
3: Initial test box  4: Framework mockup  5: Designing lens and aperture mount 
6: Designing camera back and film holder  7: Design tweaks  8: Film holder construction 
9: Camera back construction  10: Camera aperture failure  11: Camera aperture success 
12: Camera back framework  13: Camera shutter  14: Ground glass 
15: Camera front framework  16: Bellow test  17: Remade bellow 


CHAPTER 11: CAMERA APERTURE SUCCESS


I was almost impressed by myself the last time right before I realized that my setup did not work, and I was very near admitting defeat for a second there, but with some tweaks to my design it went on to work perfectly. And here we have it, the aperture unit in all its glory. The next part to build will be the shutter, which will feature a similar design but with a few additions making it slightly trickier to build (maybe). The only thing that is missing on this peice right now are a scale with F stop numbers below the control dial on the top, I will add all that in the last step when I have all the parts working properly mechanically.

aperture front

Camera aperture front.

aperture back

Camera aperture back.


Below you can see the inside of this contraption. If you compare it with the previous design youŽll see the small changes IŽve done. One of the bigger problems on the old design was the fact that the forces applied to turn the blades was coming from a really akward direction, that is from the outside of the blades towards its pivot point, indirectly pushing it in the intended direction. And because of the imperfections in my handywork some of the blades got stuck and as the turning force was increased the blades started to bulge making things even worse. What I did was moving the outer pins on the blades to the outer ring, basically inverting the construction at that end, then by opening up a "rectangular" hole in the blades the pin was allowed to slide up and downwards in the blade instead of the outer ring. This also effectivly inverted the forces applied to the blades which is now pushing them around its pivot, the secondary force from the first design now became the primary. As I assembled all the parts I noticed one strange thing, the diaphragm that was created was oval in shape, this puzzled me and I ripped everything apart and put it together again, basically just shuffling the blades around. Now I had an almost perfect circle exept for one blade that was off in its angle, and after some measuring and repositioning of the "drive" pin about one millimeter that blade was correctly aligned and all problems seemed to be gone, exactly what caused the diaphragm to become oval in the first case I really donŽt understand, and I dont really care :) It turned out really good and above my expecectations I have to admit.

aperture construction

Aperture construction.


Below you can see the aperture fully open and fully closed. At maximum aperture I will get f2,1 with the 100 mm lens, and fully closed I get f33. I can close if slightly further but then the shape of the hole gets less appealing. There is one thing that I will need to compensate for in the end. As I tested this thing on top of a grid I noticed that the diaphragm opening created is slightly off center. When using smaller apertures this might not be a problem, but as i get above f20 it might. What I need to do is shift this unit about 2 millimeters to the right behind the lens to get the hole centered, but that wonŽt be a problem at all. All I need to do are making the slots in the front holder slightly wider than the units that will go into them, then I can easily shift the units sideways and insert padding on the sides, jamming them into their optimal position.

aperture diaphragm

Aperture opened and closed.

Continue to chapter 12: Camera back framework


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