Green Orb Dresden - How to Demonstrate an "Orb" is Lens Flare
- Thread starter EBE
- Start date
By far the best way of explaining this is to reproduce it. Just go out with your friend on a sunny day, and move the camera around with the sun in shot. You'll see the "orb" move around opposite the sun.
For extra points, put your hand in front of the camera, moving it where the green orb is, and then where the sun is. You'll see the orb in front of your hand, and then when you hide the sun the "orb" (lens flare) will vanish.
For extra points, put your hand in front of the camera, moving it where the green orb is, and then where the sun is. You'll see the orb in front of your hand, and then when you hide the sun the "orb" (lens flare) will vanish.
Mendel
Senior Member.
If you want to work with the video, take a few stills and note that the green orb and the sun are the same distance from the center of the image (in the exact opposite direction) at all times. (If you have video editing capabilities, make a 180⁰ rotated copy (hflip & vflip), and then superimpose that on the original video.)
For an independent orb to achieve this with precision, it would have to always know where the camera is pointing, and that's impossible.
Also, whoever took this video did not see the orb. That's because it was not there.
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MonkeeSage
Senior Member.
I've been meaning to learn how to do that in kdenlive and played around a bit to figure it out. Could probably done better with the composite/opacity and cropping as it was my first attempt at doing this.
Mendel
Senior Member.
my idea was to not crop, which would put the green dot exactly on the sun
but it may be hard to see then?
MonkeeSage
Senior Member.
So more like this so the flares and Suns are basically on the same plane? I just decreased the downward vertical offset of the original clip from from where I originally had it. Does make the sun a bit harder to see.
The effects applied were to duplicate the video track, apply h-flip and v-flip to the duplicated track, apply a composite on the original track with 50% opacity, and a composite on the flipped track of 85%, and offset the original track down vertically. I still haven't figured out how to apply a crop at the end of the whole pipeline hence the "band" at top from where the original track was shifted down and the flipped track is poking out.
Mendel
Senior Member.
That means if you didn't do the vertical offset, the green sun flare would not actually be on the sun?
In that case, my assumption that the optical axis is at the center of the image is wrong, and it is in fact a little offset.
Scaramanga
Senior Member
There is a very simple way of identifying lens flare. It will generally be diagonally opposite the Sun ( or other bright object such as street lamp, etc ) relative to the centre of the image. Thus if the Sun is in the top right of the image, the lens flare will be in the bottom left...for example. Notice how at all times in the OP video...if you draw a line from the Sun to the 'orb' it always passes through the centre of the image. That is a classic symptom of lens flare.
Your friend needs to ask himself....why would the 'orb' just happen to move to the right exactly in time and geometric position with the Sun moving to the left in the frame. That is exactly what internal camera reflections ( lens flare ) actually do !
JMartJr
Senior Member.
Would image stabilization mess with this, though? It seems to me that it converts a smooth pan on my camera into a series of fits and starts, especially when zoomed way out, which if I am envisioning it correctly would mean that the optical center of the image would be "stabilized" along with the rest of it, and would not always be in the center of the image as recorded... if that makes sense.
The offset can come from image stabilization. IN my video above, you see the reflection bounce around a lot more than the sun does.
JMartJr
Senior Member.
I've also seen it in cropped images, too, obviously. Are there other known potential causes?
With cell phones we are dealing with very small sensors, so a small change in the angle of the incoming light can have a significant change. So if any part of the system is not coplanar (or coaxial, for the curved bits), then the light path could result in an offset.
In this sim you can try shifting one end of the Front Glass so it's not coplanar with the sensor. You can do that with the lens too, but you can also move the lens a little off-axis while remaining coplanar, and the reflection moves relative to the image.
https://phydemo.app/ray-optics/simu...NwysBgmqSK5bBoU_iv4WKvNOCrH0ObXqWDjeI2_3ubUAA
More discussion of this sim here:
https://www.metabunk.org/threads/in...do-drone-footage-lens-flare.13702/post-325558
Scaramanga
Senior Member
Well, stabilisation is produced by cropping the 'whole' image which allows the focus to wander across it. It's effectively a smaller rectangle moving about inside a larger one. The downside is the jerking motion you get when the edge of the 'whole' image is exceeded....which I've noticed especially in driving videos. I've actually found zoomed videos to be somewhat more stable...less camera wobble in image...though this may be dependent on camera type and size of masked area. It may simply be that my camera ( a Lumix TZ80 ) has a larger masked area when zoomed. People should use this camera for UFO videos...then we'd get less of the wobble all over the place !
So yes, image stabilisation may affect the exact 'centre' of the image, but it doesn't really affect the general principle that lens flare will be symmetric.
Perhaps a better way of describing lens flare would be to leave out the 'centre' of the image and simply say that lens flare will be symmetric around a point equidistant from the source ( e.g the Sun ) and the flare. That ought to still hold true even for image stabilisation.
Scaramanga
Senior Member
Initially I thought that the sun being over-exposed was hiding any similar bounce from the sun. But then I noticed that the trees exhibit barely any wobble at all.
So I suspect the wobble may be due to two factors....
1) The internal reflections that cause lens flare amplify the apparent flare motion.
2) The flare's biggest wobbles correspond with tiny changes in focus...so I suspect the focus is also having an amplifying effect.
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