Originally posted by Just1MoreDave One possible cause of the blades not closing fully is the adapter.
That's it, mystery solved! It's the adapter, not the lens. Thanks for pointing that out.
In case this could help someone else, here are the details:
The original P/K => Adaptall adapter that came with the lens is equipped with a spring loaded aperture lever:
Moving the lever causes this tab (located on the lens side of the adapter) to go up and down:
The tab from the photo above pushes another spring loaded lever located inside the lens. This causes the aperture to open/close:
It's a precise mechanism so every mm counts. The big_is Adaptall => EOS adapter has no spring loaded anything:
It's just a piece of metal that exerts a constant pressure on the lever inside the lens. This alone should keep the aperture closed at the set value. Don't know if that's a design flaw or they couldn't make the flange any higher without running into some kind of trouble. All I know by now is that the pressure coming from the adapter dimensions alone is not enough to make the aperture fully close, hence the aperture effective range of f/2.5-f/13.
In a spare time I'll do some experiments stacking masking tape on the adapter and checking if that changes anything. The lever inside the lens goes up and down a bit as you turn the aperture ring. The first permanent solution that occurred to me was a tiny leaf spring in the right place on the adapter... but it may as well be that the masking tape will become my permanent solution
Originally posted by Just1MoreDave Or, the focus ring issue could be related and something isn't tight inside. I had a 52BB and it fidn't change the aperture diameter when focused.
OK, so the extension tube issue was my lack of knowledge and the aperture not fully closing is caused by the adapter. I'm glad I started this thread
The only issue left is the focus ring causing the aperture diameter to change.
I did another video showing what effect this issue has on light (filmed the live view screen on my camera since it's more readable than filming VF) :
It doesn't make the lens unusable but it's a bit annoying. Two more things I've noticed:
- when you turn the lens upside down, sometimes one of the blades seems to fall off a bit. Not by much but it's different from all the others. After moving the aperture ring it gets back in line.
- when you manipulate the lens a delicate sound can be heard, like if some tiny piece was rolling inside. Difficult to guess from the sound alone but it could very well be a tiny screw or spring
Does it help with the diagnosis or nothing will be certain until opening the lens?
Originally posted by Just1MoreDave Macro lenses are unusual construction because of the long focus. Taking one apart might be a bit more involved than an ordinary lens.
After I've done some reading I imagine it can be indeed. Well, as I wrote before, for now I'd like to know what the illness is. This doesn't necessarily mean I'll start playing the doctor right away
In the meantime I'll just try not to pay too much attention to the focus ring/aperture issue, practice my MF skills and enjoy this great lens.
The first attempt on my cat's whiskers