ND Filters For Dummies

[Ty Pilot]

I agree with @vindibona1 - an ND filter is used to create motion blur which; allows one to see the difference between foreground, midground and background when there is motion. This parallax adds depth to a scene. Here is a screen shot I did flying between two trees, notice the difference in blur of the two trees as opposed to the trees just behind them in the mid ground and the clouds in the background.



And here is that clip in real time.

 

[RussOnTheRoad]

I'll try to give it a go to explain.

When you are far away from a subject, like up in the sky away from the ground, that which is far away moves very slowly in the frame and is perceived as "natural" almost regardless of shutter speed. But when you are close to a subject, as you might be a few feet off the ground, the changes in the subject matter change very quickly. In cinema video, subjects/object that are in close proximity to the moving camera, need some blur to the "look" to look natural. So when you're further from those subjects/objects the human perception doesn't need the blurring to look natural. So while you can still use your ND filter and 2x fps shutter speed ratio at distance, it only matters if you're passing close to things where the blur is required for a more natural perceived experience.

I'm sure someone can explain it better than I've done.

Actually, I think the explanation you provided was quite good. I might draw a fine point, though.

When I first read your comment about the effectiveness of ND filters I wondered how it could be possible they worked better under some circumstances. Being a piece of darkened glass, nothing more, I wondered how could its performance possibly change? I see now that while an ND filter always does the same thing--reducing the transmission of light--consistently, reliably, you really weren't talking about that as much as you were the circumstances under which controlling motion blur is more important and has more of an effect on video quality. In other words, what I understand your meaning to be is that when the subject matter is further from the camera motion blur may become less important and therefore the need to control it is diminished. So, while ND filters become less important from the point of view of motion blur when the subject matter is distant their effect on light transmission is unchanged. It's not really the effect of ND filters that we are talking about then as much as that of motion blur, and the contribution to controlling motion blur that ND filters may provide. Make sense?

To borrow your words, I think someone else might better be able to explain what I'm trying to say LOL.

 

[MAvic_South_Oz]

@vindibona1 did fine explaining that altitude aspect of motion blur issue.

There is a second aspect as important and that is speed of flying.
The faster you fly the more important the 180o rule of frame rate to shutter speed is.
Again at 120m / 400’ even in sports mode and steady flying/ turning might be ok, but at half that height it’s going to start looking more ‘jittery’.

 

[vindibona1]

@vindibona1 did fine explaining that altitude aspect of motion blur issue.

There is a second aspect as important and that is speed of flying.
The faster you fly the more important the 180o rule of frame rate to shutter speed is.
Again at 120m / 400’ even in sports mode and steady flying/ turning might be ok, but at half that height it’s going to start looking more ‘jittery’.

Good call. Something to think about that I hadn't.