Just when you think you've seen it all...

Morgans wrote:

You have one labeled P-38 starting as a Corsair taxies by. I thought,
why is the P-38 starting both engines at the same time? I have never
seen a twin do that; must be hell on a battery. Then I noticed that the
Corsair going by has his prop turning at about the same speed as the
P-38. That is odd. His engine must be running, as nobody is towing
him. Then it occurred to me. The camera must have had a very fast
shutter, and what appeared as the twin starting, is also happening to
the Corsair prop; they are both running at idle, and the camera is
nearly stopping the prop, but rapidly enough that it looks as they are
turning slowly.

When Jay first put that video up, there was extensive discussion about the fact
that the Lightning's engines appear to be turning in the same direction, while
it's known that they didn't. I think you've found the reason. It's possible that
the period in which the Lightning's props seem to be stopped is actually a
period in which they were in perfect synch with the camera.

I don't remember if anyone else proposed your theory during that thread. Someone
might have.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

"Jay Honeck" wrote in message
news:PZhBf.721145$x96.655433@attbi_s72...
You might want to re-label that video. g

Yeah, that's what happens when you take low-res video with a Canon digital
camera. The shutter speed is actually too SLOW, not too fast, and it
messes with the prop rotation.

Nah. A slow shutter speed would result in enough blur to make the motion
obvious.

The real issue is frame rate, when it comes to the apparent motion of the
prop. I didn't look at the videos in question, but NTSC is 30 frames per
sec (okay, technically it is 29.97). If the prop rotation is the right
multiple of that (in blades per second), the prop will look stopped,
regardless of shutter speed.

The camera is actually taking 60 shots per second, since each frame has an
odd field and an even field. So as far as shutter speed goes, the slowest
the shutter speed can be is 1/60th of a second for the above-mentioned NTSC.
That would be slow enough to get some blur in there. But that would
probably overexpose most outdoor shots, even at an f-stop of 22, unless you
also have a filter to cut the light some. In good light, the shutter speed
could be 1/250th of a second or even faster, which would freeze the prop
without much blur at all.

So, to sum up: any frame rate can be a problem, depending on the actual
rotation speed of the prop. Slower shutter speeds can help, by blurring the
image of the prop a bit, but it won't change whether the individual prop
blades appear stationary or not. However, the photographer usually would
need to take special steps to ensure a slow enough shutter speed; the
default autoexposure on a typical consumer video camera probably won't be
slow enough.

Pete

Recently, Jay Honeck posted:

For those who might be feeling a bit jaded, or as if they've "seen it
all before", I submit:


http://www.alexisparkinn.com/photoga...d-bat-suit.wmv

Ay yi yi!

Kinda puts a different spin on "sport pilot", doesn't it?

Neil

Can we all agree that this video (P38 Start Up) isn't CGI? g

The Monk

Yeah, that's what happens when you take low-res video with a Canon digital
camera. The shutter speed is actually too SLOW, not too fast, and it
messes
with the prop rotation.

That's an interesting effect. What still confuses me is that the guy to
the right of the Corsair appears to be walking at a normal pace - that
is, the image seems smooth enough and not visibly erratic or jumpy.

"George Patterson" wrote in message news:n2iBf.31300$RK3.891@trnddc06...
When Jay first put that video up, there was extensive discussion about the fact that the Lightning's engines appear to
be turning in the same direction, while it's known that they didn't.
George Patterson


Actually, the USA sold the P-322 Lightning I (looks a lot like a P-38) to Great Britain where both props turned the same
way...