Formula for degrees of movement for smooth timelapse

Aaron Priest

Active time-lapser
I was recently asked at a workshop if there was a good formula or rule of thumb for estimating how many frames one should take for a pan to still get smooth video. I wagered that 0.2% of your image width is probably acceptable, but I'm not certain if that's a solid estimate or not. I have to do more experimenting. Assuming it is a good number, here is a formula for calculating the number of frames for a given pan or rotation:

pan/rotation ÷ (horizontal field of view x acceptable %)

In the case of a 14mm lens on a full frame sensor and a 90° pan it would be 90° ÷ (104.1° HFOV x 0.2%) = 432 images. A 50mm lens would require 1139 images, 200mm would need a whopping 4386 images, and so on to get the same 0.2% movement between frames for a 90° pan. You can look up horizontal field of view for any focal length and camera sensor combination in apps like PhotoPills.

Play around with this if you get the chance and let me know what percentage of your image width you find to be acceptable for smooth video. Maybe we can get it added to the timelapse calculator of PhotoPills.

Aaron Priest

Active time-lapser
I would guess that rotator is probably constant movement and not shoot-move-shoot (or SMS)? It also appears to move at 6°/min (or a full 360° in 1 hour). I'm not sure the formula for ensuring sharp shutter speeds with such a continuous pan, but closer subjects and longer focal lengths would certainly require shorter shutter speeds without SMS.


New time-lapser
Hi Aaron,
I just was wondering what was the right pan rotation speed ...
Actually my approach was a little bit different, I analysed the rendering of some sequences shooted with 50mm and 85mm focal lenses considering also the intervales.
I tried to define the range of percentage of horizontal field of view to have a good result for landscapes.
My feeling is that the ideal range is 20% ( slow ) to 70% ( quick ). rotation / hour
Then the smooth is linked to the intervalle.
Trying to have the same formula that you propose I got a maximum of roughly 0,08% ( 4s intervalle with 70% of 40° for 50mm lense )
So it's a different approach...

Aaron Priest

Active time-lapser
I've discovered a slide is more forgiving than a pan. My formula above was for a pan. Just to clarify for future discussion, as I forgot to mention that.

My formula was assuming SMS, not continuous, where your shutter speed and interval didn't matter, just how many frames you took per degrees of rotation. Your scenario is going to be more challenging in that you have to stay under a maximum shutter speed to get enough frames per minute as your rotation speed is constant. You'll also get motion blur from moving while shooting with close objects and longer focal lengths, which my formula didn't take into account either.

360°/hr = 0.1°/sec. 20% of that would be .02°/sec and 70% of that would be .07°/sec. A 90° pan therefore would take 75 minutes at 20% and 21.43 minutes at 70%. 50mm on a full frame camera has a HFOV of 39.5°, and 85mm is 23.85°. Assuming 0.2% image width for movement gives you 432 images for a 90° pan with a 50mm lens. You'd have to take 432 images in 75 minutes at 20% speed which means a maximum interval of 10.42 seconds, and a shutter speed a little less than that for buffer. For a worst case scenario, an 85mm lens at 70% speed would be dramatically shorter shutter speeds as you'd have to take 1887 images in 21.43 minutes, or an interval of .68 sec max where most intervalometers won't allow less than 1 second. Slowing it down to 45% works as your interval becomes 1.06 seconds, you'd just need fast shutter speeds under 1 second for buffer time, which you'd probably need anyway at longer focal lengths with continuous movement for a sharp foreground (depending on subject distance).

Hope all that makes sense? LOL

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