Ok, I have noticed on my Rokkor 58 1.2 that on at least two occasions the focus would seem to get stuck and lock up. The strange thing is that on those occurrences, I would just turn it back and forth a little and it would seem to free itself. After that, it would then work silky smooth throughout the entire range. Does anyone have any idea what could be going on and/or how to fix this?

Did this happen at minimum focus?

If yes it can be that the barrel has extended beyond the range of the helical. There are two locks (I don't know what to call them) that hold the helical and barrel together. If you extend too far they get stuck between the helical and barrel. Your lens may be adjusted so it is right at the edge of this range when at mfd.

Rodney

rgallie wrote:
Did this happen at minimum focus?

If yes it can be that the barrel has extended beyond the range of the helical. There are two locks (I don't know what to call them) that hold the helical and barrel together. If you extend too far they get stuck between the helical and barrel. Your lens may be adjusted so it is right at the edge of this range when at mfd.

Rodney

Thanks. I believe the last time it occurred the lens was not at minimum focus but somewhere in the middle of the range. Once when it occurred, I was working on the rear mount with the lens front face down on the table. I wonder if its possible that too much downward pressure might have caused the helical to somehow get stuck.

Let's hope it is not one of those aperture detent ball bearing stuck down in the helical.

HansenTsang wrote:
Let's hope it is not one of those aperture detent ball bearing stuck down in the helical.

No, I don't remember loosing one. I guess I will just have to wait for it to occur again and see if I can discover some sort of pattern.

Perhaps a metal shaving then? Seems like something is in the helical, or it is going bad.

pdmphoto wrote:
Perhaps a metal shaving then? Seems like something is in the helical, or it is going bad.

Well, I guess if it continues, I will have to tare it apart and see whats going on. The lens does not appear that it has seen much use so I don't think its going bad from use.

Those helicoid assemblies will act up if you look at them funny. They require clean room cleanliness. After a clean and relube, its common for roughness, but it smooths out with time. You know, it has to find it's groove.

Metal filings will lock it up big time.

JimBuchanan wrote:
Those helicoid assemblies will act up if you look at them funny. They require clean room cleanliness. After a clean and relube, its common for roughness, but it smooths out with time. You know, it has to find it's groove.

Metal filings will lock it up big time.

Well, that probably explains things then as this particular lens had a lot of dust in it when I bought it.