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Difference between two Alexa Mini Cameras


xax@...
 

Dear CML Group,

we are having a problem on set shooting with two Alexa Mini Cameras,

both are on the same lens, same settings (WB, CDL, etc), same stop, same LUT, everything is the same, but one camera unfortunately looks completely different than the other!

In the Image, on the left side, we have the A Cam on top and the B Cam at the bottom.



I then tried to create a LUT to match the two cameras, as can be seen on the bottom right, which matches the B cam to A cam.

It works in this one lighting situation, but in others, it falls apart.

This is the first time we are having such a big difference between two Alexa's and are quite puzzled by it to be honest. We are getting another replacement body next week, but in the meantime I am very eager to find out what the reason could be. It would help for future 2 Camera shows, in regards of what to look for (serial numbers?) and how to remedy that problem.

Thanks for any advice pointing to a solution,

all the best,

Xiaosu Han
cinematographer, 
currently based and shooting with FFP2 masks in Vienna, Europe
www.stilfabrik.at


Art Adams
 

Could you send me higher-res images? I can pass this on to someone internally for a look.

 

-Art

 

_______________________________________________________
Art 
Adams
Cinema Lens Specialist
ARRI Inc.
3700 Vanowen Street
BurbankCA 91505
www.arri.com 

 
aadams@...

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Andrew Hunter
 

Hey Xiaosu,

That sounds like one of your bodies needs to go back to Arri for recalibration.

For any long format work with multiple cameras, I shoot a side by side to verify matching for color and exposure in prep. If they don't, we swap the body. 

I've seen some mini bodies have 3/4 of a stop difference. Rare but we noticed it for the current season of Kim's Convenience. 

Sincerely,
Andrew Hunter
A cam 1st AC - Kim's Convenience S5
Toronto, Canada

On Thu., Oct. 1, 2020, 10:55 , <xax@...> wrote:
Dear CML Group,

we are having a problem on set shooting with two Alexa Mini Cameras,

both are on the same lens, same settings (WB, CDL, etc), same stop, same LUT, everything is the same, but one camera unfortunately looks completely different than the other!

In the Image, on the left side, we have the A Cam on top and the B Cam at the bottom.



I then tried to create a LUT to match the two cameras, as can be seen on the bottom right, which matches the B cam to A cam.

It works in this one lighting situation, but in others, it falls apart.

This is the first time we are having such a big difference between two Alexa's and are quite puzzled by it to be honest. We are getting another replacement body next week, but in the meantime I am very eager to find out what the reason could be. It would help for future 2 Camera shows, in regards of what to look for (serial numbers?) and how to remedy that problem.

Thanks for any advice pointing to a solution,

all the best,

Xiaosu Han
cinematographer, 
currently based and shooting with FFP2 masks in Vienna, Europe
www.stilfabrik.at


John Sheeren
 

Xiaosu:

     Does each camera have it’s own monitor?  The monitors may not be matching. Try A/B’ing the cameras on one monitor or better yet, put both camera pictures up side-by-side on the same monitor. Try switching the camera input top to bottom and bottom to top. See if the problem follows the BNC input.
     Are you using the internal ND’s. The ND’s may not be matching. 
     Are you using the same firmware build in both cameras?  Make sure both cameras have the latest firmware and are matching. 

Hope this helps,

John


John Sheeren
Film/HD
713-385-7595
Johnsheeren@...

On Thursday, October 1, 2020, 9:58 AM, xax@... wrote:

Dear CML Group,

we are having a problem on set shooting with two Alexa Mini Cameras,

both are on the same lens, same settings (WB, CDL, etc), same stop, same LUT, everything is the same, but one camera unfortunately looks completely different than the other!

In the Image, on the left side, we have the A Cam on top and the B Cam at the bottom.



I then tried to create a LUT to match the two cameras, as can be seen on the bottom right, which matches the B cam to A cam.

It works in this one lighting situation, but in others, it falls apart.

This is the first time we are having such a big difference between two Alexa's and are quite puzzled by it to be honest. We are getting another replacement body next week, but in the meantime I am very eager to find out what the reason could be. It would help for future 2 Camera shows, in regards of what to look for (serial numbers?) and how to remedy that problem.

Thanks for any advice pointing to a solution,

all the best,

Xiaosu Han
cinematographer, 
currently based and shooting with FFP2 masks in Vienna, Europe
www.stilfabrik.at


Leonard Levy
 

I know this sounds  very basic, but I assume you have switched lenses to make sure that's not the problem right?
--
Leonard Levy, DP
San Rafael, CA


xax@...
 

I just saw that the picture is indeed very low-res,
 
here's a higher res version:
 
https://www.dropbox.com/s/k32a708gkbtbgnk/5322cd29-4263-4321-aa15-c06fec27b089.jpeg
 
John, they are on the same firmware, and the results shown here are straight from the LogC -> LUT converted files from camera where everything has been set the same on both cameras, so a monitor mismatch can be excluded.
 
Indeed the test was done on an internal ND6 on both cameras, we will check if that could be the issue.
 
Thanks Andrew for your message, looks like that in the future, we will have to do this for longer form 2 camera shows.
 
Leonard, this has been done on the exact same lens and stop, which we put on the A camera first, then on the B cam.
 
Art, I am in contact with Jan Heugel at ARRI already, he's trying to help me too. 
 

Aurelien, we set both cameras at the same kelvin, but it's a good idea to try to WB both cameras. But then we would have to do it everytime we change the lighting/scene...

 
Thanks everybody for their help so far,
 
we are getting a 3rd camera next week too, and will compare that to those two. I'll keep everyone updated!
 
all the best,
 
Xiaosu Han,
cinematographer based in Austria, Vienna.
shooting a two camera BBC show at the moment with mismatched cameras
www.stilfabrik.at
 


xax@...
 
Edited

We've not got a third camera body in and did some more testing. It matches one of the cameras better than the other. We've swapped out the camera body which looked the least like the others and will continue like this. Our third focus puller that day told us that he had Alexas before that were almost 800 Kelvin apart from what they looked like.

Here are the files:

https://www.dropbox.com/sh/gupbvedtcth13ci/AADm4v8ANCUMUOKuRvU1BoEza?dl=0

In the future we will do more rigid side by side tests when running two full cameras for the entirety of a long shoot,

thanks everybody,

all the best,

Xiaosu Han,
cinematographer, Vienna - Austria
www.stilfabrik.at