Re: PMW-320 focus problems
 

Hi Paul, of course when I did all you suggested all was well :). Still testing.

It was misbehaving all right.

Thank you.

Re: PMW-320 focus problems
 

Hi Chris, that does sound very like the way my lens is carrying on.
OK at times and then far from OK.
Did you get it sorted in the end? Was it the lens at fault?

Thanks Chris.

Re: PMW-320 focus problems
 

Thank you Daniel, so what is the best way to go about setting the back focus?

Thank you.

Re: PMW-320 focus problems
 

Sure was the lens. I remember back in the hotel room sitting down with the lens off the camera and having a good look at it when I heard a very slight 'click'. As I rotated the lens nose down nose up an back and forth I could occasionally replicate the clicking sound. When I got back to Sydney I mentioned this to Canon and sure enough they confirmed the noise I detected was indeed the slightest of movements of the suspect element. The element was held in place by a thin screw in retainer ring and this had backed off.

Just remembered a similar incident a year back with one of our Fujinon lenses that has a 16:9/4:3 aspect ratio cross over unit. One day it refused to swing in the ratio converter and it was exactly the same problem. An element screw in retainer backing out enough to block the movement of element in the cross over unit. In this case though the lens element didn't actually move as it had some kind of setting agent applied to it during construction.

So yes it can happen and be rather puzzling when it does.

Chris Young
CYV Productions
Sydney

Re: PMW-320 focus problems
 

If ever you have a walk around inside the gizzards of a damaged or broken lens, especially the modern servo lenses, you will discover some of the most exquisite miniature and precise engineering there is to be found in mass-produced engineering.

In older times, it was apparently routine and desirable for periodic maintenance to be done on lenses.

These days, lenses tend to outlast the cameras they are attached to before receiving attention other than a surface clean. Because of their complexity, precision and inherent reliability, as with modern turbine aircraft engines, a periodic dismantlement and re-assembly for checking purposes may even introduce a fault.

Aside from providing the means to monitor and inspect internal life-limited structures which may fail before their mandated replacement cycle, a philosophy of "if it aint broke, don't fix it" with turbine engines prevails.

Glass and metal are strange bedfellows. They behave differently with changes in temperature. A threaded metal ring retainer for a lens element is apparently best not tightened too firmly. The engineering is so precise that the tension of an over-tightened retention ring not only may risk damaging the element, but distort it ever so slightly but sufficiently for the optical characteristic to be altered.

The downside is that with use, vibration, temperature changes, such retainers, even if thread-locked, may loosen eventually or become polished down at the glass/metal surface as to allow a clearance and movement.

Such events are not necessarily representing a quality issue but unavoidable practical limitations that are sometimes imposed in engineering endeavours. So don't feel too grim about something like this happening. Two years without need for intervention is a good innings.

Please heed the comments of people far better qualified to discuss these things than I.

Re: PMW-320 focus problems
 

Thank you Christopher and Bob for the info and advice.

I'm going to make arrangments to get the lens looked at.

Thanks everyone.