# Confused by the shutter speed set up

It’s not setup like a camera. I want a 1/48th sec shutter speed for my 24 FPS frame rate, but the setup makes no sense. You don’t measure shutter speed with a decimal system. Do we seriously have to do fraction to decimal conversions to get our shutter speeds? It won’t even take “0.02083.” It will only accept “0.02.” Am I misunderstanding something here?

Shutter time is expressed in frames. (That’s what the tooltip says for both BI and Cycles.) So (1/48) * 24 = 24/48 = 0.5 frame.

0.02 means 1/1200th sec at 24 FPS. You won’t get much motion blur with that…

Yeah, I don’t understand that. How is it expressed in frames? A frame has nothing to do with shutter speed. Shutter speed and frame rate are totally separate things, so this defies how cameras function.

0.02 means 1/1200th sec at 24 FPS. You won’t get much motion blur with that…

How did you get 1/1200? Two decimal places is a 100th, so .02 is 2/100ths, which would be 1/50th…I think…

God, I hate math. I just wish this was set up like a regular camera’s shutter speed dial.

Frames can also be used as unit of time. At 24 FPS (Frame Per Second), a frame lasts 1/24 sec. So, you can write an equation where shutter time equals the frame time multiplied by an unknown.

Shutter_Time = Frame_Time * number_of_frames

<=> number_of_frames = Shutter_Time / Frame_Time

Now, Frame_Time = (1/FPS). We do a simple substitution.

=> number_of_frames = Shutter_Time / (1/FPS)

<=> number_of_frames = Shutter_Time * FPS

That’s the formula for the value to give to Blender.

If Shutter_Time is the unknown. we just need to resolve the equation:

=> Shutter_Time = number_of_frames / FPS

Now, Shutter_Time = (1/value). We do another substitution.

=> 1/value = number_of_frame / FPS

<=> value = 1 / (number_of_frame / FPS)

<=> value = FPS / number_of_frame

In your case: value = 24/0.02 = 1200.

Class dismissed!

Now, excuse me, I must go into my head and put the math teacher back into his cage.

Setting the shutter speed to 1 means the exposure is the same length as the frame. Setting the shutter speed to .5 means the exposure is half the length of the frame. You’re right, an option to set it to a fraction of a second would be useful, but I don’t think I’ve ever added CGI to a scene knowing what shutter speed the video footage was shot at. Even if I shoot it myself I don’t really remember that kind of info.

Myself, I tend to leave it at .5 .

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Here is my test. Cube was animated to move .1 blender unit per frame. Movement was converted into Linear Extrapolation, so movement is constant to infinite before and after frame1.

First image shows render at frame one with no Motion Blur. Second render was done with Sample of 5 and Shutter set to 5. Shutter of 5 means over 5 frame animation. This setting shows that 5 sample was taken and rendered over 5 frames. Point here is that blurred object center is not at the object center at that frame. It is ahead of the object. In fact object at that frame is not rendered at all!