Ross, Ketch and Pedro, when do you guys expect the delivery of the Deep Atom rig?
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07-19-2011, 04:13 AM
Ross, Ketch and Pedro, when do you guys expect the delivery of the Deep Atom rig?
08-08-2011, 12:43 PM
I no longer expect it...
I am no longer getting the DEEP ATOM for health related issues which I posted here: a SHUTTERED DREAM
08-12-2011, 04:43 PM
Hey, Pedro, we are dying to see the charts shot underwater through the flat port shot with Ruby. Can you post some 1:1 corner crops?Originally Posted by Pedro Guimaraes
10-16-2011, 12:56 AM
OK Guys,
Finally I found a minute to shoot some tests through a flat port.
Attached here are 1:1 crops at 45° off optical axis (90° angle of view), which is probably the most representative angle for underwater.
The shot in air was made from 30% closer distance to account for water magnification factor.
Shot with Tokina 11-16mm at f/2.8 (which for flat port is the best and only gets worse as you step down), not that the lens choice seem to matter much in this case....
04-16-2012, 09:22 PM
Hi all,
I'm at NAB with the 3Ality team (who are endlessly supportive and wickedly smart) and DEEP PULSAR / ATOM on display in their booth. On the left is the housing base with ATOM rig. On the right the main housing shell with Transvideo monitor housing. What you can't see behind the monitor is the underwater FIZ controller (which will be complimented by an IO/Convergence controller).
J-
IMG_2422.jpg
04-16-2012, 11:29 PM
Way to go John I am so excited that my Deep Atom is shipping in a couple of weeks!!!! The test footage looks so incredibly sharp edge to edge I am very impressed.
04-16-2012, 11:37 PM
What some people regard as "sharp" may not be sharp to others or not sharp at all. Can you post it? I can not fathom how can you possibly obtain sharp images through a flat port other than macro/closup. It is just physically impossible due to chromatic aberrations. This is illustrated in my post above.
Wide angle shot of a zone chart or SFR chart would be great.
04-17-2012, 05:45 PM
Well, for all people that do like maths then...
The refractive index of air is 1.000.
The refractive index of water is approximately 1.33. However, this index varies in with the color (wave length) of the light. The refractive index of water is 1.343 for the 400 nm wave length (blue), and 1.334 for 550nm ‘green) and 1.330 for 700nm red spectrum.
The refractive index of water also depends on the water density, including factors such as the salinity, the temperature and the pressure. If we look at the refraction of a ray of composite white light as it leaves the air/water interface, we see that the deviation of the red, orange, yellow, green, and blue components of the white light will vary as a function of the color, the blue rays being more refracted than the reds, with the spectrum spread between them. This is the phenomenon known as light dispersion.
This dispersion has great importance in optical performance: the apparent distance of a subject that is linked to the refractive index because there is up to 1% variation between the blue and the red.
It is in the variations in the enlargement factor that this phenomenon is most sensitive.
Let's consider the enlargement refraction for indices of n1= 1.33 (red spectrum) and n2 = 1.34 (blue spectrum) for incident angles of 20° and 45°.
The magnification factors for 20° angle of incidence are m(r) = 1.403 for red and m(b) = 1.417 for blue spectrum.
The magnification factors for 45° angle of incidence are m(r) = 2.766 for red and m(b) = 2.964 for blue spectrum.
Accordingly, for 20° angle of incidence the difference between blue and red images at the edge of the 5k frame will be about 24 pixels.
Accordingly, for 45° angle of incidence the difference between blue and red images at the edge of the 5k frame will be about 80 pixels.
After converting to horizontal resolution it becomes clear that such optical ystem will not even resolve a fraction of standard definition in the corners.
The corner resolution in case of a 20° angle of incidence will be equivalent to less than that of standard definition.
The corner resolution in case of a 45° angle of incidence will be equivalent of roughly 1/5 of standard definition.
Flat ports also create severe "pin-cussion" distortion. But, they are also responsible for the variation in aperture.The real aperture will vary according to the point in the frame, This explains the phenomenon, mostly seen with wide-angle lenses, of the images being lighter in the centre than at the edges.
Additional aberrations degrading the image quality when photographing underwater with a flat port are astigmatism and coma. They originate in the differences in the path taken by rays coming from the subject in a plane including the optical axis, compared with rays situated on a plane which does not include the optical axis: so the image of a cross which is not situated on the optical axis will be situated on two different image planes (implying two different focus points), one where the horizontal branch of the cross is sharp, the other where the vertical (radial) branch is sharp. This defect is more pronaunced as the aperture is opened.
All of the optical defects associated with a flat port can be seen by a diver through a mask, as it is effectively a flat port. But because the eye’s field of view is relatively narrow and the line of sight usually perpendicular to the plane of the mask these defects do not appear very obvious.
However, when recorded and projected on a cinema screen, those flaws will be clearly visible by the audience. Most of them are difficult or impossible to correct in post.
I believe that it is a mistake to use a flat port in a cinema grade underwater housing.
Regarding convergence
Convergence control behind a flat port will only create further, this time asymetrical, chromatic aberrations and geometrical distortions. For this reason convergence control in underwater housings is typically done with image plane, not the lens. However, converging in camera was common because acquisition format was HD and distribution format was IMAX and further loss of resolution to converge in post was not acceptable. I see no practical reason to converge in camera when filming underwater when recording 5k. Having said that, our 3Deep housing has convergence control if that's what required. One that does not deteriorate image quality because it is not affected by the limitations caused by a flat port described above.
Last edited by Pawel Achtel; 04-17-2012 at 09:51 PM. Reason: corrected calculations as refractive index changes with angle of incidence
04-17-2012, 09:58 PM
I just corrected the calculations adjusting for the variation in refractive indeces for red and blue as a function of angle of incidence. The results are much more dramatic showing that even modest 20 degree angle of incidence (40 degree viewing angle) will not reach quality of standard definition in the corners just as a result of chromatic aberrations alone. On top of that there will be compounding effects of distortions, coma, and astigmatism as well as aperture variation.
It is beyond my comprehension how anyone can call such optical system "sharp edge to edge".
04-18-2012, 03:33 AM
Pawel perhaps there is a place for both systems...3Deep sounds like it will be good for all those big wide establishing shots but not so good for close ups and medium shots. As you can't really control interaxial and convergence 3Deep will have it's limitations. On the other hand Deep Atom has the ability to control IO and convergence and actually control depth, place the screen plain presicely and produce the 3D effect comfortably for an audience.
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