Originally posted by nater So I just bought a used Sigma 50mm Macro 1:1 manual focus lens (with 'A' aperture), and while cosmetically and optically good (apart from some minor bits of dust on the inner elements), the process of manually focussing the lens does not have consistent smoothness or resistance through the range, and since this is my first 1:1 manual focus macro lens, I was wondering if this is normal or not?
Right around 1:2.5 it resistance ramps up quite a bit, stays high until 1:1.3 where it gets a bit higher until 1:1.2 where it starts to drop and is then smooth through 1:1.1 until 1:1 (at which point the lens barrel is fully extended). The reverse trip (compacting the lens back down in size) has resistance variations in the same spots but somewhat less.
And if this isn't normal, is this something that could get worse over time? (i.e. how worried should I be about this?)
Today arrived ths very same sigma macro lens to diagnose/repair for someone.
It suffers from exactly the same problem.
It was easy to repair (if you are a bit technical and have the right equipment)
I will post pictures later, your lens will very likely have the same fault.
George
The pictures :
The lens showed a heliocoid shaped stripe over half its barrel.
The cause seemed to be some material between the focus ring and the lensbarrel.
To remove the focus ring, remove the focus rubber, make a mark (permanent pen or so) how the focus ring is mounted to the focus mechanism.
Then remove the black tape.
You best set the lens at infinity, when the tape is removed, the focus mechanism can go a little beyond 1:1, and an aperture lever will come loose.
To remove the focus ring, you have to remove also the bayonet (3 phillips screws), the aperture ring, and another ring.
Nothing special, but beware of the small metal ball and spring of the aperture click mechanism.
When removed from the lens, I found this :
The felt, originally glued at A, was now compressed at B.
After stretching and glueing :
Something else I noticed are newton rings (actually stripes caused by interference) :
Two lenses must be really close for this.
George