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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

3D and long lenses

Just to add a broader perspective.

In photogrammetry and Ariel stereo photography long lenses relative to the format size are used to correctly and accurately extract 3d form to build topographic maps. Conversely long lenses can be used on a macro stereo scale to extract or delineate microscopic 3d texture (almost like crumbs) from a flat surface. If you have advanced alignment techniques (and depending on the subject) you can even use long lenses with moderately wide base seperations and convergence (you need good engineering and software for this).

My preference is definitely for wide angle (low distortion lenses) that are able to get close to the subject. In such cases I engineer with the use of Biogon type non retro focal lenses to minimize the effects of radial distortion. When you overlap left and right images, there is a residual Y parallax between corresponding points caused by the differences in radial distortion between left and right. Biogon lenses also allow one to calibrate more accurately for radial distortion so this can be corrected in “post’. It is also possible (again) using photogrammetric techniques to re-sample left and right images into epi-polar pairs so that Y parallaxes from relative swing and tilt can be removed, and there are more advanced techniques that allow one to resample the whole set of parallaxes to preserve fine detail without flattening the overall subject (no cardboarding) and re-jigged to be comfortable on the eye. The latter techniques being rather process intensive, but capable of creating a very rich stereo experience and once built correctly can be used in real time environments.

Rules of thumb are very helpful, and I’m glad folks are discovering the benefit of high quality wide angle work, but at the same time don’t be afraid to experiment with longer lenses to achieve very special and high quality results for and from unusual situations.

Cheers
Eric
 
David Mullen ASC said:
It may be better to just shoot in medium shots, or shoot a master framed through a doorway or window, or reflected in a mirror.
Click to expand...

When you say mirror, do you mean a mirror in the shot that is obviously a mirror or a mirror that isn't seen and is just used for the optical effect (and if so do you flip it in post or just shoot stuff where it isn't as noticeable)
 
Hmmm... so if I want to shoot lion kills on the serengeti in 3D, I think I'm gonna need to mount my 3D cameras on a freakin RC helicopter or something. I wonder if I can acclimate the animals to having a helicopter that sounds like a chainsaw following them around for a year....
 
David, correct me Tom if I am wrong, your question was how to use 300-400 so it is giving natural look of 3D effect as if we were in the exact spot where 300-400mm lenses are bringing you to, closer to the object. From the viewer perspective we are much closer. Shooting crocodile 300 yards away with 28-50mm gives us the same perspective as looking on the crocodile from 300 yards. In this case we should leave intraocular spacing as it is so almost no 3D effect.
However 400mm will bring us closer to the crocodile so it will look like we are 30 yards away.
If crocodile is 6’ long we have to increase intraocular spacing proportionally to the zoom effect of the lenses. In such a case the intraocular spacing has to be increased 10 times to produce the same effect as viewer would be 30 yards away.

Andrew
 
Tom L said:
Hmmm... so if I want to shoot lion kills on the serengeti in 3D, I think I'm gonna need to mount my 3D cameras on a freakin RC helicopter or something. I wonder if I can acclimate the animals to having a helicopter that sounds like a chainsaw following them around for a year....
Click to expand...

Tom, just use zoom lenses and increase intraocular space proportionally to the zoom factor of the lenses.
Make sure that you have open view, any trees much closer to the camera will produce out of place effect like I have seen in Avatar in many scenes.
Objects close to the lion 30-50 yards are actually desirable to enhance the 3D effect.
Objects 10-30 yards away from the camera will produce effect hard to look at.
 
so are you suggesting that intraocular should be 1 yard/36 inches, or 10 yards, for 300 yard away lion with 300/400mm?

1 yard would have its problems but doable - 10 yards is pretty tough.

I have been thinking of making a rail/slider unit which actually would work pretty well with two cameras for adjustable long distance intraocular.
 
I think that a 10-yard interocular would look a bit like the POV of a giant or a normal person looking at a miniature.

Just accept that extreme telephoto shots don't have much of a stereo effect. When I see a 300mm shot of a lion, my brain doesn't think I'm standing only a few feet away, it looks like a distant object being enlarged optically. If I looked at a lion with one eye 10-yards apart from another eye, it's going to look like a miniaturized lion.
 
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David (or anyone), can you post any examples of what this "giant" POV might look like with the interocular distance being several feet or whatever? Is it something like tilt-shift?
 
It would be a cool test, shoot a person (not a lion) at a medium distance on a normal lens in 3D, then back the camera up and put a 300mm on with a 10-yard interocular and see what happens. You'd want to see the test in 3D though on a big screen.

My general belief is, though, that all "immersive" formats, whether 2D Cinerama or IMAX, or 3D, are most effective in creating a "you are there" experience when they use moving cameras and lenses that match human vision/view (which is the debatable part, because do you match our field of vision or how perspective / object size is reproduced?)

This is why you get into the wide-angle vs. medium focal length debate -- Cinerama opted for an extremely wide view, 144 degrees. And IMAX often opts for very wide-angle lenses. But in both cases, the image is projected very large so the sides fall into your peripheral vision, so it's really more like a normal focal length image with extra picture info stuck on the sides.

But no one really thinks that super telephoto images are much like human perspective other than psychologically, the act of concentrating on something in the distance. Certainly the degree of enlargement plus the often shallow focus makes details pop out dramatically for the viewer, but it's still a very graphic "photographic" effect.
 
Interocular distance for zoom lenses is proportional to the zoom factor.
Comes from the equation a2 +b2 = c2 (2 = square)
I didn’t think 10 yards, I was thinking 10 times the distance of normal eyes distance if zoom factor is 10 times.
So if normal human eyes view shot (FOV) is equal 1:1 we need the interocular distance equal to human eyes distance. For zoom effect equal to 10 times shorter distance, we will need 10 times wider spacing for interocular distance.

If a = ½ of eye distance

and

b = distance to the object

So we have direct relation.
If (b) is 10 time longer then (a) have to be 10 times longer
 
Three summed main factors to consider when thinking about long lens + large interocular:

- different background for each eye (even with small DOF)
- different object coverage (larger angle between eyes and object)
- distance to object > no object volume perception > getting flat objects or "cardboarding", the issue which Pedro mentioned

All factors are facts and have consequence of turning 3D experience into "weird" and unrealistic, and are, in my opinion, misuse of 3D.
 
David, would you say that FOV would be the more likely to deliver the "you are there"? I imagine a moving camera going past common objects and think that would be the case. You see what you would see if you were walking there. And what lens would we have to use to accurately reproduce size and perspective? I believe I asked you before and the eyes are more around an 8mm or smaller if I remember correctly, so that's not gonna happen without distortion with a flat sensor. So it is simple, FOV, right?
 
It's never simple. As I said, you have to factor in the size of the projected image and the viewer's distance to the screen. If the image is big enough, then a super wide-angle image has the outer area falling into peripheral vision and you're looking more at the center area, which is more normal in focal length and perspective -- imagine cropping out the center and putting that in a picture frame.

For example, think about a 50mm anamorphic lens in 35mm -- you have the vertical view of a 50mm spherical but the horizontal view of a 25mm. But on a large screen, it's like looking at a 50mm image but with extra picture information added to the sides that you aren't concentrating as much on.

However, show these wide-angle images on a small screen, and they are obviously wide-angle, as evidenced by watching IMAX movies on DVD and noticing just how often they grab that fish-eye lenses out of the case.

Since we can't control how large an image is going to be projected nor how close the viewer is going to sit near the screen, it's not a simple notion of "what matches human vision?" Our field of view is very wide-angle but our perception of object size and distance is more like a middle focal length. That's because we don't have a picture frame cropping reality -- it's a wide-angle vision but a lot of that extra view is falling into our peripheral vision.

Nestor Almendros once said he wan't interested in 360 degree movie formats because adding a frame around reality is what makes it art. That's the basic tension of moviemaking, how we alternate between creating a subjective experience and how we artfully compose and arrange the frame in graphic ways that human beings don't experience in reality.

This comes up when shooting true POV shots in a scene -- I generally always just center-frame the subject in those because a person in reality just looks straight at what they want to look at, they don't "compose" the subject, setting it off to one side while balancing it against another object.
 
Tom L said:
I swiped some RealD glasses from the Avatar screening. Will those babies work with any online images? :smile:
Click to expand...

Tom,

No, those won't work unless you have one of the so called interlaced monitors, but alas, that image Michael posted has very, very convincing 3D effect, even though is shown in the anaglyphic (red & blue) format, which is the oldest and worst of all formats. Michael shot the shark footage with one of his housings, but I am the one that did all the 3D work on it. And let me tell you, since you were being discouraged the other day on another thread that posting 3D is really a very complex endeavor, that was my first ever attempt at posting 3D, and although not the best, the resulting images are 3D, plain and simple. Get yourself a pair of red/blue glasses from 3dglassesonline.com and take a look at that frame. Then send me a PM if you're interested in finding out how feasible it is to start working on 3D, I'll hook you up brotha. As a matter of fact, once you start shooting 3D, I will post your first few projects for you free of charge until you get yourself set up. Don't listen to the naysayers, start playing with 3D, because uncle Cameron is right, it is the way of things to come...
 
Ohhh.. perception is more like middle range... is it because we focus on the very center, around the macula, where we can perceive color? So the lens might be like a 6mm but we crop so much that it "behaves" like a medium?

I never sit too close, always making sure I can see the whole screen easily to take a hard look at everything going on, even if it means sitting at the back of the house where the sound isn't optimal. I never consider being engulfed by the image as you describe. Personally I think that is for video games with three or more monitors. I may be wrong but I like to think that this is the way to work, considering everything equal, TV delivery in mind, and if someone sits that close at the theater... they can sit alone cause I ain't sitting with them for all the gold in Fort Knox. :)

David Mullen ASC said:
That's the basic tension of moviemaking, how we alternate between creating a subjective experience and how we artfully compose and arrange the frame in graphic ways that human beings don't experience in reality.

This comes up when shooting true POV shots in a scene -- I generally always just center-frame the subject in those because a person in reality just looks straight at what they want to look at, they don't "compose" the subject, setting it off to one side while balancing it against another object.
Click to expand...

Yes! And DoF, focal lenghts, camera movement, camera positioning, etc. Thank you David!
 
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