0
\$\begingroup\$

I am taking a 60fps 720p video, trying to get sharp frames of a motor rotating.

Setting the shutter speed to 1/4000 and taking a picture (while the motor is rotating) results in the desired sharp image: enter image description here

However, using the same shutter speed and taking a video (again, while the motor is rotating) results in blurry frames: enter image description here

How do I use a very fast shutter speed (1/4000s) when taking a video?

My camera is a Nikon D3500.

\$\endgroup\$

4 Answers 4

1
\$\begingroup\$

With that camera, I believe you can not.

Take a look at this answer: How do fast shutter speeds actually work?

The reason is that above the sync speed, which on your camera should be around 1/250 the shutter speed is done by the mechanical curtain, not the electronics.

I would try to find the maximum shutter speed on the camera using a more measurable experiment. A pendulum.

Make a pendulum of let's say 50cm or 1.5 ft. Define your 60fps and increment your shutter speeds. You could start with 60 or 125.

(I will try this on my similar camera later)

\$\endgroup\$
1
  • \$\begingroup\$ If this is a sync speed issue, why is the still image sharp? \$\endgroup\$ Feb 8 at 17:24
-1
\$\begingroup\$

I am assuming your first case is taking one frame as a still camera shot, and the 2nd case is using video at 60 frames per second.

Each video frame is presumably sharp at 1/4000 second, but video is showing 60 different frames a second, each 1/60 second of motion later. That showing of the motion sounds blurred to me. Pause your video, showing only one frame.

\$\endgroup\$
1
  • \$\begingroup\$ The second image is a single frame from the video... \$\endgroup\$ Jan 7 at 13:56
-1
\$\begingroup\$

The problem is the electronic shutter's actual (readout) speed which is far slower; probably somewhere around 1/60 of a second (I couldn't find the actual spec readily).

Because the sensor readout speed is so much slower, what you are getting is the rolling shutter effect (distortion). The only reason it looks like normal motion blur is because everything besides the motor shaft is stationary, and the movement between sensor line readout (on/off) is minimal.

This video is a good explanation of sensor readout speed vs shutter speed.

Rolling shutter is the reason all high speed cameras use global (or mechanical) shutters.

Edit to add: The only other possible cause would be if the camera was not actually using the 1/4000 SS; but the D3500 manual clearly states that it can.

Manual movie settings: Choose On to allow manual adjustments to shutter speed and ISO sensitivity when the camera is in mode M. Shutter speed can be set to values as fast as 1/4000 s; the slowest speed available varies with the frame rate:

\$\endgroup\$
6
  • 1
    \$\begingroup\$ This is definitely not rolling shutter problem. Global shutter would look exactly the same way. \$\endgroup\$ Jan 7 at 0:25
  • \$\begingroup\$ @EuriPinhollow, how so? \$\endgroup\$ Jan 7 at 4:02
  • \$\begingroup\$ If image is smudged because of low shutter speed you cannot claim the rolling shutter is the problem. Slow shutter roll limits the speed but it's not the direct cause. \$\endgroup\$ Jan 7 at 8:40
  • \$\begingroup\$ I hope it's obvious that provided images would look exactly the same way with global shutter if same speed was used. \$\endgroup\$ Jan 7 at 8:57
  • \$\begingroup\$ @EuriPinhollow, No, it would not look the same with a global shutter. Global shutter would look the same as the first image taken at the same SS with the mechanical shutter. \$\endgroup\$ Jan 7 at 13:54
-2
\$\begingroup\$

I'm seeing this as a frame challenge of how to get a good video of your motor, and not about achieving a 1/4000 s shutter speed

IMHO you are running into some fundamental issues with video frame rate and motor speed. There are several ways to see this limitation.

  1. If you want a shutter speed of 1/4000 s for your video, that means you need to be shooting video at 4000 fps. This is the realm of specialty high speed cameras and will not be achievable with your D3500. (Note - see #3 for the condition of a fast shutter speed in a slow frame rate)

  2. With video at 60 fps, and allowing 10% movement of the motor during a single frame (as an example for ease of calculation, but which is probably way too much motion blur anyway), the maximum speed of the motor would have to be 60 * 60 / 10 = 360 rpm. But electric motors like you have shown will operate at much higher speeds - in the 1000's to 10,000 rpm range.

  3. If you do achieve a 1/4000 s shutter speed at 60 fps, because the motor will still be moving fast in comparison to the frame rate, the video itself could appear to look weird. EG the classic wheels on the wagon in westerns that appear to rotate in reverse even though the wagon is moving forward.

So there are a couple of solutions to your problem:

  1. Get a camera which can shoot video at a very high frame rate

  2. Slow the motor down so that you don't get motion blur with your current camera and 60 fps

Romeo pointed out that I should include shutter angle in my frame rate calculation. Here is an article on why that matters. So technically for a 1/4000 s shutter speed, that would imply only 2000 fps

\$\endgroup\$
3
  • \$\begingroup\$ About point 1: based on 180 degree rule with speed 1/4000 you should make 2000FPS \$\endgroup\$ Jan 7 at 17:53
  • 1
    \$\begingroup\$ @RomeoNinov Probably, but either way 4000 or 2000 fps is more than consumer grade equipment can handle. \$\endgroup\$
    – Peter M
    Jan 7 at 17:58
  • \$\begingroup\$ You can use shutter speeds much faster than the 180* rule would imply, and much lower frame rates. The only thing that causes is unnatural transitions between frames (due to a lack of motion blur). Point 3 is the goal as I understand it... and the spokes appear to go backwards when the frame rate exceeds the speed at which the spokes travel; they record as stationary when the two match, and they rotate forward when the rps/rpm is faster then the fps/fpm. The shutter speed only affects how blurred it appears in each frame. But you can't have a frame rate faster than the shutter speed. \$\endgroup\$ Jan 8 at 20:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.