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#23665 - 10/05/12 07:50 AM nightswimmer
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
Caught last night by my motion camera. Reminds me of the undulating fins along the siders of cuttlefish. I think I know what it was, but I'll allow you to speculate...

http://vftp.net/virtual1/temp/MFIF/flyby.mov

cuttlefish:

http://www.youtube.com/watch?v=5qwt_BM7wec
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#23669 - 10/05/12 09:48 AM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
OK, I'll bite. I think it's an inanimate object, and more specifically some kind of leaf, dried into a spiral. It's blown by the wind past your cam in 4 frames and less than half a second. Careful viewing shows that the spiral rotates, but I think that too is caused by the wind. Interestingly, in QuickTime Player I get some pixel artifacts that look like bubbles in front of the object... tongue
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#23676 - 10/05/12 07:11 PM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
I'm fairly sure I know what it is, and it's not vegetable. but I'm still soliciting ideas, I'm looking to see if anyone else is thinking the same thing as I am.
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#23678 - 10/05/12 08:46 PM Re: nightswimmer [Re: Virtual1]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Hard to tell from three low-res frames, but I'm thinking "flying squirrel."
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#23681 - 10/06/12 04:48 AM Re: nightswimmer [Re: tacit]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
the resolution isn't as big of an issue as the exposure time
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#23682 - 10/06/12 07:24 AM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Since your clue is exposure, that suggests that what looks like a rippling scuttlefish-like mantle is in fact caused by motion blur. In addition, I suspect there may be prolonged, quasi-multiple exposure in play as well. If true, that would make the actual object (much) smaller than it appears to be on the clip. The 400msec clip contains 4 frames, making for 100msec/frame. Motion blur means speeds in excess of that, but not knowing viewing angle and distance to object makes it hard to translate that in actual speed.

Anyway, tacit's guess the flying squirrel glides pretty much like a wingsuit pilot (except it's the other way around, of course), but the point is whether the edge of a squirrel's patagium or its steering paws move this fast during a glide. Although that's perhaps possible, I happen to think it's not likely, a.o. based on this slo-mo video clip. The clip also shows the fairly static braking tail of the squirrel, which seems absent in the mystery clip.

So, if it's an 'animal' instead of flying debris, I figure winged insects are a better guess, and one that meets various requirements posed by the clip. But exactly which insect (other than a probably two-winged species) I can't tell, sorry.
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#23684 - 10/06/12 08:12 AM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
First I should say that that trying to figure out speed based on fps is probably going to be a waste of time since you don't know distance from camera nor frames per second. But that said, I believe it to be a bat. We get a lot of them flying around here between dusk and dawn, and I think that one is just motion blur, they're pretty quick. That's the second time I've caught such a thing on camera, and they both looked very similar.
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#23686 - 10/06/12 08:30 AM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Originally Posted By: Virtual1
First I should say that that trying to figure out speed based on fps is probably going to be a waste of time since you don't know distance from camera nor frames per second. But that said, I believe it to be a bat.

Interesting on both counts, but I happen to disagree with your conclusion. While I concurred with the problem the unknown distance poses for calculating speed, I'd like to point out that the clip offers other measuring options. To wit:

1. The 'quasi' object in the mystery clip moves at least at about the speed of its apparent length per frame or 100msec. If its trajectory is not perpendicular to the camera direction, the object's speed is higher.

2. There are what looks like 3 up and 2-3 down (wing) movements visible per frame, based on the changeover points between up-stroke and down-stroke. Because the vertical wing speed is zero at these transition points, they appear more clearly at the top and bottom of the object (see frame #2).

3. If (2) is correct, that would suggest that the animal is 2-3 times smaller than it's apparent length, and that one up or down stroke of the wing takes about 15-20msec (100msec/5-6 strokes), or 50-65Hz. A full wing beat (one up + one down stroke) would then take 30-40 msec, or 25-33Hz, easily within range of insects (approx. 5-1000 Hz).

4. As bat wing beat frequency tends to range between 5 and 10Hz (200-100msec/beat), this appears to exclude a bat as the mystery object. Finally, given the relative size of the object within the frames, the smaller the actual size of the object, the smaller its distance to the camera must have been.

Comment? tongue
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#23688 - 10/06/12 08:54 AM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
found it, I had been looking for another video of this same phantom that I got awhile ago and finally located it. Yes I think it is an insect. but what?

http://vftp.net/virtual1/temp/MFIF/flyby2.mp4
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#23693 - 10/06/12 09:41 AM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Nice catch! Indeed, that second clip clinches it. I had briefly been thinking of a moth or small butterfly, but I quickly realized that their wing beat frequency would then likely be lower and the periodic deviation from steady horizontal movement greater than the up and down oscillation seen in the 2nd clip. I'm afraid we need an entomologist to offer better suggestions.
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#23694 - 10/06/12 10:15 AM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
looks like a flying stick, or three dragonflies taped together huh?

Interesting to see how it bobs through the air though, most insects fly in fairly straight lines, the bobbing is part of what was suggesting bat to me earlier.

Now I don't think the length was exaggerated by exposure time, I'm starting to think that's how long it really is.
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#23695 - 10/06/12 11:30 AM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Originally Posted By: Virtual1
Now I don't think the length was exaggerated by exposure time, I'm starting to think that's how long it really is.

That may be true for the second clip (although it's much harder to see there because of the smaller relative size of the object), but I doubt that's the case in the first, for the reasons I outlined above. After all, it's quite possible that the two clips show two different species of insect.

PS, I looked again at single movie frames of the second clip, and (like the first clip) here too is clear evidence of 'multiple exposures' per frame along the object's trajectory due to the long exposure time. The vertical size of the object also appears larger than it actually is due to both motion blur and overexposure of a well lit object as seen by a camera with a large aperture setting.

Do you happen to know the real frame rate, aperture (equivalent) and particularly the actual exposure time per frame of that motion camera?

PS2 the apparent length of the object varies in different frames, and with it the number of presumed wing beats. This strongly suggests variations in object speed, and hence that the animal's real length is only a fraction of its apparent length.


Edited by alternaut (10/06/12 12:23 PM)
Edit Reason: Added details.
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#23696 - 10/06/12 02:51 PM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
Looking at the 2nd shot, the source video is 20 fps and the object is in view for a total of 19 frames. Crossing a distance of about 8 feet.

8 ft / 19 frames
20 frames / 1 sec
3600 sec / hr
1 mile / 5280 ft

gives an estimated speed of 5.7 mph

(I knew that class exercise in elementary math class would come in handy eventually!)

I've watched a lot of videos made by this camera under similar conditions and I can't find any examples of motion blur, it seems to have a very fast shutter speed. So I am inclined to think that the object really is as long as it appears to be in the video.

It's also fairly maneuverable. It comes in just on the far end of the left legs, goes wide around the feeders, and then banks sharply to the right to come in inside the right legs before leaving frame.


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#23697 - 10/06/12 05:20 PM Re: nightswimmer [Re: Virtual1]
roger Offline


Registered: 08/04/09
Loc: Vermont
nice use of an old swingset!
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#23698 - 10/06/12 06:22 PM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Originally Posted By: Virtual1
- Looking at the 2nd shot, the source video is 20 fps and the object is in view for a total of 19 frames. Crossing a distance of about 8 feet. ... gives an estimated speed of 5.7 mph

- I can't find any examples of motion blur, it seems to have a very fast shutter speed.

Both MediaInfo and iMovie give 68 frames at 30 fps for the 2nd clip, 28 of which (12 through 39) show the object, for a total duration of about 28/68 x 2.272 sec = 0.94 sec. That equals about 1/30 sec max per frame. But just based on the estimated length of the trajectory as derived from the size of the tube frame in the image and the time taken to traverse it, my number (5.83 mph) agrees well with your speed estimate.

However, the actual shutter speed (~ exposure time per frame) is critical. The object only 'moves' in 18 of the 28 frames it's visible, during which time it covers about 8 feet. That makes its apparent size a bit over 5 inch long (8 ft/18), and that seems to be about right compared to the (~ 2 inch?) tubing diameter of the swing set frame. If we take the minimally 3 full wing beats into account that appear to be visible in my interpretation of the object, the actual length would be at most something like 1.7 inch.

At a speed of about 5.7 mph (or about 100 inch/sec) the object moves for a distance of its apparent 5 inch length during an exposure time of about 1/20 sec. If its size is actually less than 5 inch, its apparent length should decrease at exposure times smaller than 1/20 sec. If, as I postulated, its actual length is indeed about 1/3 of that apparent 5 inch, the latter length should decrease to 1.7 inch at an exposure time of 1/60 sec, and remain stable at even shorter exposure times.

The maximum exposure time at 30 fps is 33.3 msec (1/30), or 50 msec (1/20 sec) at 20 fps. The actual exposure times will be less than these maximum values, say 1/40 sec or less at 30fps. If true, it means that you're probably right after all: at 1/40 sec the apparent length should be about half the 5 inch calculated above.

I'm sorry, but now I really need that drink you just earned... smirk
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#23701 - 10/07/12 08:21 AM Re: nightswimmer [Re: alternaut]
alternaut Offline

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Registered: 08/04/09
Waking up this morning I realized that I must have been intoxicated by the thought of that drink alone last night, because there's at least one serious flaw in the reasoning of my previous post. Anybody (who hasn't gotten a headache by now)?

In case you need more clues than just your Sunday morning cuppa, how about this:
If a 5 inch long object moves a distance of 5 inch parallel to sensor or film during (single frame) exposure, what is its apparent length on the exposed frame?
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#23703 - 10/07/12 11:48 AM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
sorry alt you are watching the transcoded clip, not the original material. your calculations are based on the whims of quicktime's video codec. My measurements above were made with the source material, which were very large and covered considerable time, guessing you didn't want to try to download those. Don't use the videos I posted for frame analysis.
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#23705 - 10/07/12 12:55 PM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
As it happens, the difference doesn't matter much anyway, since the critical shutter speed value is quite a bit smaller than the maximum value calculated from the metadata I saw. Same thing for the apparent size and speed of the object: they pretty much fit your numbers. But I sure would like to know what critter we've been looking at. tongue It still seems prudent to me not to get hung up on a stick... smirk
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#23708 - 10/07/12 02:47 PM Re: nightswimmer [Re: alternaut]
MacManiac Online
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Registered: 08/04/09
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.....and my wife thinks I'm too geeky......

Great thread!!!!!
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#23709 - 10/07/12 03:51 PM Re: nightswimmer [Re: MacManiac]
artie505 Online


Registered: 08/04/09
Second the "Great thread!!!"

This may be really simplistic and defy the math, but even allowing for elongation/blurring due to motion, the profile and body shape sure look bat-like, and the erratic, bat-like flight pattern supports a bat hypothesis.
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#26160 - 06/29/13 01:29 PM Re: nightswimmer [Re: Virtual1]
alternaut Offline

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Registered: 08/04/09
Earlier this week I came across this intriguing picture from the latest installment of InFocus' Animals in the News. The image is a long exposure of seagulls flying in the sky over Rome on May 2, 2013 (Gabriel Bouys/AFP/Getty Images), and it immediately reminded me of your clips above.

Why bring this up after all this time, apart from the overall image impact? Well, we already agreed that the mystery object must have been a (rather small) winged animal, and—if nothing else—some similarity in flight path and -shape seen in this picture appears to confirm that. It also shows what a long exposure does to a flying bird, and we can compare the resulting image with that of our mystery object. Does it help in identifying that object, for instance to determine whether it was scuttlefish-like winged versus more 'regularly' winged, or how-many-winged if the latter etc.?

But most importantly, did you ever find out exactly what it was by direct observation?
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#26161 - 06/29/13 03:06 PM Re: nightswimmer [Re: alternaut]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
not yet. The image reminds me a bit of a cuttlefish with its wavy side fins. but I don't think there's anything out of water that does that.
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#26165 - 07/01/13 02:53 PM Re: nightswimmer [Re: Virtual1]
joemikeb Offline
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Registered: 08/04/09
Loc: Fort Worth, Texas
Believe it or not, my just installed security camera captured an almost identical image to your cuttlefish. You can see a still from the movie here . I puzzled over it until the next night when the camera captured this image. I was still puzzled until I downloaded the second image and captured a single frame. Don't ask what kind of bird this is, I am still working on that. I have turned off the IR lighting and tweaked the other settings so maybe I will be able to actually see what species it is. Of course there is the possibility that it is the IR lighting that was attracting it in the first place, but we shall see what we shall see.
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#26176 - 07/03/13 11:58 AM Re: nightswimmer [Re: joemikeb]
joemikeb Offline
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Registered: 08/04/09
Loc: Fort Worth, Texas
It is interesting to me that since I disabled the IR nightlight the "cuttlefish" or bird has not reappeared and triggered the video cam.

I am speculating either the IR light was attracting insects and thus the nighthawk (or as we call it in Texas "bullbat") or without the IR light the camera is not sensing enough motion to trigger a recording.
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#26178 - 07/03/13 02:49 PM Re: nightswimmer [Re: joemikeb]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
I was wondering if it might be a hummingbird that just has wings moving too fast for the frame rate of the camera... but I don't think any species of hummingbird is active at night?
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