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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

OLPF change affecting back focus?

R

Richard Bradbury

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I've been regularly using a RedOne with a serial number around 500 for a couple of months now, and I've had no back focus problems with it. I had it checked out on a collimator at the beginning and it was spot on, and it's still spot on despite all it's been through.

More recently I've done a couple of jobs with a camera with a serial number around 1000. It seems to have back focus issues. Taking it to the same lens service house has revealed that it needs its back focus to be adjusted for each individual lens in a set of, for example, superspeeds.

Then I discovered that another company who have two cameras - one serial number below 500 and one above 1000 - have discovered exactly the same thing. The older camera holds back focus perfectly, but the newer one has the same issues of needing adjustment for individual lenses.

My contact at the lens service house suggested that the only possibility as far as he could think of was that a different optical low pass filter was introduced into the camera between numbers 500 and 1000, and it's affecting the back focus differently. He thought he could see a difference in the filters on the collimator, but wouldn't swear to it.

Has anyone else had an experience of this kind? Is it possible that a different olpf is being used in newer cameras?
 
Richard, there have been some recent discussions to that effect here:

http://www.reduser.net/forum/showthread.php?p=215342#post215342

Whether it has to do with the OLPF or the thermal qualities of the different metals used in the camera's construction would be next to impossible for an end user to determine with absolute certainty.

What is certain, however, is that there seems to be a difference between early models and late models when it comes to back focus calibration requirements, as you're indicating here. Something which I find a bit puzzling, so I'll be following this thread with interest.
 
Uh? Adjust back focus for each lens!!! :umm: There is no way on a feature shoot (or any other really) that you can spend time adjusting the back focus each time you change a lens.

Reading the other threads it must be thermal if it happens over time.

I can understand back focus adjustment is a required facility for adapting Nikons and other non-standard lenses, another neccesity of being all things to all people. But as far as the PL mount goes - no film camera allows for back focus adjustment other than on an optical bench, in a workshop, by the rental house. They calibrate it - you leave it. I'd want my PL mount locked and I'd expect it to stay that way.

Is this really an issue or just isolated incidents on a few cameras?

Stuart G.
 
It is an issue. The alternative to adjusting bf for individual lenses is to individually mark up lenses, which is probably the way most focus pullers will have to work. Obviously zooms are more of a problem...
 
But is it an issue common to all 1000+ cameras or just a few?

I get the re-marking; all lenses are usually tested and calibrated before a shoot and (sometimes) adjusted / re-marked - standard practice and not a problem. But I was refering to the thread link above where users reported the back focus drifting when in use for 3 hours or more.

Stuart G.
 
It would be nice to hear something from red on this.
 
We are looking into it - but I am racking my brain to think of any mechanical differences between a camera in the 500's and and one in the 1000's. And I got nothing.

Regardless, we are researching it.

BC
 
Deferences between lenses is due to the lens shimming and not due to the mount.

If changing 4 times lens A in same temp conditions does it have consistent results? If not... we have a problem.

I can't imagine how this could happen. The mounts -500 and +1000 would be really too different to have non consistent results.

Hope you don't use PL adapters on your lens test.

???

Pat
 
This is exactly why we suspected it's not an issue with the mounts but rather with the OLPF.

Lenses do produce consistent results in the same temperature (I've not experienced the possible temperature problems discussed in the post linked to above). The problem is that one back focus setting is not good for a variety of lenses on +1000 cameras.

No, we didn't use PL adapters.
 
655 is spot on with S4 set and Optimo. When changing to Nikon mount it requires no adjustment and all lenses are spot on as well. I'm not touching my back focus until I have a reason to. Although we check it with charts.
 
This sounds more like a lens issue than a mount issue. If the camera is set right, it should always be right.
 
Even if it's the same set of lenses being tested on two different cameras?
On camera A bf is set for control lens and holds for all other lenses.
On camera B bf is set for control lens but needs adjustment for all other lenses.
I don't understand it either.
 
This sounds like it may be a mechanical thing. If the pl mount is just the tineist bit loose, or there is a chip left over from machining, under the mount, it colud rock or move just enough to screw stuff up, and be almost imperceptable to the eye or feel.

Try this, take the pl mount off, clean everything with with a micro fiber cloth, make sure none of the bolts, or holes are stripped, I don't know if there are helicoils in the body or if it's just tapped aluminum, but if there are helicoils make sure there is no play there. Put everything back together and see if it's the same.

For it to be consistantly inconsistant really makes it sound mechanical.

Good Luck,

Nick
 
It could be an issue with the mount on camera B I suppose. But it's been checked by people who really know what they're doing.

But the reason I posted is that I discovered that another owner of two cameras (<500 and >1000) had the same problem. So I wondered if something had changed in the manufacturing between those numbers...
 
Sounds like camB wasn't set perfectly. That would cause the other lenses to shift varying amounts. But they would always shift in the same direction.
 
I don't doubt that it has been checked out by qualified people, I don't think you could find the problem (if it is mechanical) unless you remounted the mount, and even then, you may not be able to tell what was causing it.

I just don't see any other way for there to be a problem. If the sensor is 52mm away from the flange, and the lenses are good, then something is moving.

Cheers,

Nick
 
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