How fast to create after images

[mr friendly guy]

Ok, this is a common enough trope in fantasy and comic book mediums. Someone moves so fast that they create after images.

My question is, how would you begin to calculate how fast someone needs to move to create an after image. Assume for this purpose distance is known.

[Jub]

After images aren't a real thing and if they were it would be less about speed and more about leaving a bright flash at set distances. Jets, race cars, rockets, satellites, close or far none of these things leave such an effect and they move pretty quick. If they started to move faster they'd blur as the light they emit would be spread and stretched (to our frame of reference) and at some point they couldn't be seen except from the front or back.

A teleporting hero that teleports at a few jumps a second leaving a moderately bright flash after each hop is a far better candidate to create this effect.

[mr friendly guy]

I actually did some reading, and a better way of looking at this problem is duplicate images. To achieve this, an object would have to move, pause and then move again. For example, the object when changing direction could pause long enough to be perceived and then move again at a speed that is too fast to perceive, and then pause again, giving the impression of 2 images.

According to a quick search it seems some airforce pilots can perceive things at 1/220 of a second or 4.5 ms, although they most probably can't get a good look at it, they might be able to get a sense something had changed. To move faster than a human can perceive, it would have to cover the distance (ie the human's view) in less time than 1/220 of a second. The site I read suggest 1/250 of a second to cover whatever distance required.

So now I have the time, we can calculate the speed based on whatever distance the scenario requires.

[Jub]

You also have to show that the heroes you're thinking of do this when moving at super speed. I doubt that they do as it gives them no advantage outside of specific cass where they want a distraction but even then there isn't much reason to make more than one or two.

[LadyTevar]

I know that they've shown both Superman and the Flash pulling this trick. Now -- how do they move that fast without wind kicking up and giving it away?

[Elheru Aran]

I know that they've shown both Superman and the Flash pulling this trick. Now -- how do they move that fast without wind kicking up and giving it away?

With the Flash: Speed Force. With Superman... No good explanation ever given.

[Elheru Aran]

Ghetto Edit to elaborate on the above now I'm on a computer (was on a cell phone last night):

For those who don't know, the Speed Force is a... frankly, magical is the word, field or force that Speedsters (a specific type of superhero in the DCU) are unconsciously connected to. Some more than others, naturally, and it didn't come out until the 90s when Wally West became the Flash. Barry wasn't involved with it until the very end when he died in the Crisis on Infinite Earths, but that was actually him disappearing into the Speed Force. It's more or less what let Wally do some of the straight-up ludicrous feats he pulled off during his time as Flash, such as clearing an entire... North Korean? town of people in the micro-second between fusion and detonation of a nuclear bomb. 50+ K people (IIRC?) run to safety in something like a yottasecond or whatever. That's a couple of people picked up, run several miles away, dropped, rinse and repeat... needless to say he was going far faster than the speed of light, as in he could've run from Earth to Centauri in *minutes* at that kind of speed.

Anyway. Yeah. That's not even the craziest thing (though it's WAY up there) that he did. Out-running entropy itself and travelling through time to the end of the entire multiverse... and BACK... is probably the craziest. If it wasn't for Superman-worship, Wally-Flash would be pretty much the most powerful hero in the DC universe. Granted he doesn't have super-strength, but still.

So that's how Flash doesn't screw up stuff when he runs. How about Superman? We don't know. He's not a Speedster, he's just very fast. Some people theorize that he unconsciously taps into the Speed Force at some level (vaguely plausible but come on, next they'll be talking about Super-Math). Other people think there's simply some... intrinsic property of Superman, same as prevents him from crushing people who he catches falling from heights or breaking large objects in half when he lifts them in the middle, picking up airliners by the tail and it doesn't break. Things like that. The tactile-telekinesis they were big into in the 90s, I guess.

Usually for other non-Speedster heroes who do super-speed feats (and there aren't that many of them) without corresponding physical effects, either it's futuristic technological trickery at work, or some bullshit explanation like 'uhhh they have some kind of field around them that slows everything down I don't know shut up your face is stupid'.

[mr friendly guy]

You also have to show that the heroes you're thinking of do this when moving at super speed. I doubt that they do as it gives them no advantage outside of specific cass where they want a distraction but even then there isn't much reason to make more than one or two.

Yeah, I am thinking its mainly a case of creating some type of distraction or intimidation.

The only other way I can create duplicate images, is if they do a Picard Manoeuvre type thing, where they literally move faster than light without violating casuality and appear and then the light from their previous image catches up.