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Backfocus Off After Running Four Hours

H

Hans von Sonntag

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This is the phenomenon:

A fortnight ago I shot a commercial in a studio. Camera was powered with DC adaptor all the time running.
After 4 hours 1st AC showed me that the backfocus on the 25mm was off. 1m was now 1.10.

We tested the same thing at my office: Backfocus was off after 3 hours. All Primes showed the same issue.

Yesterday I had another shoot and used my trusty Cooke. Again after 3 hours the back focus was off.

Today at the office we did the same again. After 3 hours: backfocus off.

Seems to me a thermal issue. Does ony experienced the same?

In case someone asks: Yes, all lenses are collimated and the backfocus is spot on when the camera is cold.

Hans
 
Last week i shot a TV commercial. After 8-9 hours of shooting under the sun we went indoors to do some product shots. I inspected the product shots pixel to pixel i can verify that they were super sharp! No backfocus problems there...

P.S the move from outdoors to indoors was 2 minutes.
 
this is a bummer...
interesting to know if it is an isolated problem or a red specific issue...

the owners should chime in
 
Shooting outdoors in Hawai'i's sun for 8 hours has produced zero issue with back focus. I find the RED to be completely different from something like the F900 where BF changes with heat expansion.

However, throwing up a focus chart and checking every lens is the only way to go on each and every shoot day.
 
Hans von Sonntag said:
This is the phenomenon:

A fortnight ago I shot a commercial in a studio. Camera was powered with DC adaptor all the time running.
After 4 hours 1st AC showed me that the backfocus on the 25mm was off. 1m was now 1.10.

We tested the same thing at my office: Backfocus was off after 3 hours. All Primes showed the same issue.

Yesterday I had another shoot and used my trusty Cooke. Again after 3 hours the back focus was off.

Today at the office we did the same again. After 3 hours: backfocus off.

Seems to me a thermal issue. Does ony experienced the same?

In case someone asks: Yes, all lenses are collimated and the backfocus is spot on when the camera is cold.

Hans
Click to expand...



dude! we had the same issue yesterday and we were getting crazy about it!

I was not on the set, but they told me the lenses were giving mistaken distances, and more and more off as time passed. Next day i check the lenses and the camera, i attached those lenses to other cameras also and they were fine. I put some other lenses on the camera and it was fine.

They shot later that same day. Same thing. They start ok and as time passes the marks go crazy. Air temperature stayed the same for the whole day.
Camera heat might change the focal plane distance?
 
It must be batch related or the PL mount hasn't been locked down enough [be it with the collar, flange screws or FFD adjustment]. Every camera I've worked with has been steady as a rock regardless of temperature or run time. I just got out of a 7-hour prep where the camera was on all day... spot on the whole time. I've had the cameras in pretty extreme environments... still, spot on.

I suspect there are strange forces at work here...
 
Brook, i´m pretty sure the mount was tightened. In fact, the guys using the camera were the same crew that have shot The Argentine and Guerilla. ;D

For some time the camera was upside down. Maybe that affects the fans and air circulation...?

Maybe they were shooting at the LOST island, where everything is different...
 
Heheh, I trust your guys, Mac. It sounds like it might be a batch related issue. Or maybe I've just been incomprehensibly lucky [or ignorant] thus far.

Those that have had problems... what are your numbers?
 
Not here

Not here

Adding to the responses, I've been shooting in this hideous heat in LA and then went indoors to air conditioned rooms and after 5 hours in the sun and 4 hours inside, no back focus issues on this body.
j.
 
had the same thing here! thought I was going crazy but indeed I had to change the BF when I should not need to....can't figure out why or how this can happen!
 
obin said:
had the same thing here! thought I was going crazy but indeed I had to change the BF when I should not need to....can't figure out why or how this can happen!
Click to expand...

My bad!

As the orignal poster I should have mentioned that after a month without any response Sean gave me some valuable information, here it is:


"I did send a reply I'm sorry if it didnt reach you. It sounds like you need to tighten down the screws on the collar. If this does not remedy the problem then we may need to bring the camera in to look at that mount.

Sean Ruggeri
Red Bomb Squad
Sent via BlackBerry by AT&T"



Obin, please check your screws of the mount collar. Saying mine were not tight is an euphenmism; they were loose. I never touched the screws because the camera was nicely collimated when we recieved it. Tightening the screws made the mount stable. No backfocus issues any more.

Apart from the digital communication issues we had (I should have phoned them, Sean should have checked how things go on) service is promt and competent.

Hans
 
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