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Problem With ALEXA PLUS

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David Thiers

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Hello,

First, i’m french so i’m sorry for my bad english !
i got a problem with my Arri Alexa Plus.
I dont know what is the problem but when i shoot with the camera the rendered is so weird.
I upload one rush here :

https://vimeo.com/221716521

Maybe it’s a sensor problem ? Too Old ?

If someone can help me and explain to me what is the problem, it will be so nice.

Thank you for helping.
 
David .. What do you feel is the issue there? .. The strobing effect is from panning to quickly for the shutter angle. Am I missing something else?

Ted
 
Thanks guys. But It does not matter the shutter effect i guess. I try to many different shutter speed and the "strobing effect" is always here. I think he is really too High, no ?
 
A friend tell to me we need to change sensor often. How to know if the sensor got a problem ?
I will post an other video with different shutter speed.
 
?

What bothers you here ?

I don't see any sensor issues.
 
Looks normal to me.

I have to say though, I absolutely love the strobing effect when shooting 180/24p which is how film looks like.
 
You are asking for a miracle from any 24P camera, film or digital cinema with that shot. The pan movement is too fast. My preference would be to lock the camera in position, maybe use a wider lens and let the subject do the moving through a stationary frame. Please take notice of better advice than my comment here.
 
RED has a calculator for the focal length of the lens, the angle of the pan, which then gives you the speed, or duration to move at to not see strobing. Panning too fast on 24p causes the strobing, and it is not a sensor issue, but a 24p format 'issue'. (However, that's an 'issue' that I like as well).

http://www.red.com/tools/panning-speed

The closest camera to the Alexa for the calculator, my guess would be RED Dragon at 6k 16:9 HD.

Hope this helps!
 
One thing to note here is that motion rendition with digital cameras is not the same as film and typically object "stutter" is more harsh because there is no natural motion blur falloff as with film. Compensated to some extent with mechanical shutter solutions and Motion Mount for Red cameras.
 
If you stop on a frame the motion blur should be half the distance of travel to the next frame. If so you you got a 180 deg shutter. A camera shooting with such exposure will strobe when paling at constant speed if something moves faster than about 8 seconds from one edge of frame to the other. Which is pretty slow.
 
I used to have a rule of thumb back when I did a lot of narrative operating. The object of your attention should not take less then 5 seconds to cross the frame or the viewer may have trouble with the strobe effect.
 
Right, what you are talking about is "judder". It's a mathematical motion affect that affects all cameras equally at 24fps.
 
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