Archive for September, 2007

DOF Table Stereoscopic Calculations: 200mm Focal Length

Yes, they are matching… This table will show you the calculations for a (maximum) f/64 f-stop, so you can enter a focal length of 200mm and come up with the stereoscopic equivalents:
http://www.dofmaster.com/dofjs.html
Again, verify with the stereoscopic calculator, using the bottom calculation (to calculate a _near_ point), 6.5cm stereo base, 200mm focal length, Max Gap = 1.2mm (of 36mm, or 1/30):
http://www.stereoeye.jp/software/sbcalc_e.html

For example:

Using “35mm camera/film” or “.030 CofC” (same identical results) in the DOF table, and verifying with the stereoscopic calculator:
Hyperfocal Distance will be a constant calculation of 21m, but the actual focus distance of the camera will be a variable.
OFD: 1.2mm of 36mm (1/30) is also a constant, since that’s my target amount of deviation, which is defined by the depth of field calculations _and_ the Circle of Confusion, which is also a constant of .03mm. Notice it is listed in the bottom of the DOF tables, plus you can just use it as the “format option” of .030 at the top of the DOF table:

200mm Focal Length
f/64
Stereo Base: 6.5cm
Far Point: 18.9m
Calculated Near Point: 6.8m
Focus stereo camera at 10m

200mm Focal Length
f/64
Stereo Base: 6.5cm
Far Point: 6.5m
Calculated Near Point: 4m
Focus stereo camera at 5m

And so on…
Okay… I’m done… someone other than myself will have to calculate the focal lengths for more than 200mm… or for stereo 3D pinhole cameras, etc… because I do all this stuff with one piece of paper with one vertical stripe down the center of it, using zero math and zero calculations… this DOF and CofC stuff has all simply been a verification of my theory, which after this point, will never be proved wrong… it will just be further verified…
And again, this is just the same old “1/30th rule” that they came up with over a hundred years ago (or whatever… I’m not a stereoscopic historian, and don’t even intend on playing one in a movie or on TV. ;-) ;-) ;-)

Alrighty, then… I’m going to get my stereo camera in focus…

Stereo (3D) Camera Focus Distance Calculation with a DOF Table

To summarize a couple of recent posts, you can easily calculate the stereoscopic near points for a target amount of deviation (OFD) of 1.2mm of 36mm (1/30th) by using the 50mm Focal Length/35mm Camera “Film” (36mm width) Depth of Field Table, under f-stop f/16 (”Sunny 16 Rule”). Again, the calculator’s Hyperfocal Distance (for stereoscopic calculation) is a constant 5.26m:
http://www.dofmaster.com/doftable.html
If you want an even better calculator, use this one:
http://www.dofmaster.com/dofjs.html
Again, this is for a 65mm (ortho) stereo base, and you can verify the calculation with this stereoscopic calculator:
http://www.stereoeye.jp/software/sbcalc_e.html
Be sure the use the default “Max Gap” of 1.2mm (On Film Deviation), and remember to use the bottom calculation, which calculates the near point (stereo base of 65mm, lens focal length of 50mm, and “far point” are theoretically “known”).

Now, all you have to do to determine where to actually focus your stereo camera is look at the Focus Distance, which is actually called “Subject Distance” in the DOF tables, but that term is irrelevant for stereoscopic calculations, since we are just using it to know where to actually focus your stereo camera so that the near and far points are in clear focus… and that subsequently defines this target amount of deviation (OFD) of 1.2mm of 36mm (1/30th).
Notice the actual focus distance ends up being about 1/3rd of the way from the stereoscopic near point to the far point, which is obviously a good rule of thumb.

DOF Table Near Point Stereo3D Calculations for Other Focal Lengths

Using the same references, you need to change the camera f-stop and
hyperfocal distance (via manual focus) for other focal lengths. I’m
not sure how to calculate the hyperfocal distance for focal lengths
more than 100mm (anyone know?), but focal lengths less than 100mm can
easily be found in the DOF table and stereo calculator. I think many
people might make a mistake by changing their calculated hyperfocal distance for
different far/near points, when it actually should remain constant
for any “given” focal length. For example, here’s the setup for a 25mm
focal length and a 100mm focal length. You’ll have to look up the
calculations in the referenced URLs. Remember to use the _bottom_
calculation in the stereoscopic calculator, i.e. you are wanting to
calculate the distance to the near point (because that’s how it works):

References:
Depth of Field Table:
http://www.dofmaster.com/doftable.html
Stereoscopic calculator:
http://www.stereoeye.jp/software/sbcalc_e.html

25mm FL
35mm Camera/36mm Film Width
f/8
Stereo Base: 6.5cm
On Film Deviation: 1.2mm (1/30th of 36mm)
Far Point Known - Near Point Calculated (_Bottom_ Calculation in the
Stereoscopic Calculator)
Camera Hyperfocal Distance: 2.63m
Circle of confusion: 0.0333mm

100mm FL
35mm Camera/36mm Film Width
f/32
Stereo Base: 6.5cm
On Film Deviation: 1.2mm (1/30th of 36mm)
Far Point Known - Near Point Calculated (_Bottom_ Calculation in the
Stereoscopic Calculator)
Camera Hyperfocal Distance: 10.5m
Circle of confusion: 0.03mm

Near Point Stereoscopic Calculations With a DOF Table

References:
Depth of Field Table:
http://www.dofmaster.com/doftable.html
Stereoscopic calculator:
http://www.stereoeye.jp/software/sbcalc_e.html

50mm FL
35mm Camera/36mm Film Width
f/16
Stereo Base: 6.5cm
On Film Deviation: 1.2mm (1/30th of 36mm)
Far Point Known - Near Point Calculated (_Bottom_ Calculation in the
Stereoscopic Calculator)
Camera Hyperfocal Distance: 5.26m
Circle of confusion: 0.03mm

Far point/DOF Limit: Infinity (99999m)
Near Point/DOF Limit: 2.7m

Far point/DOF Limit: 101m
Near Point/DOF Limit: 2.6m

Far Point/DOF Limit: 30.9m
Near Point/DOF Limit: 2.4m

Far Point/DOF Limit: 16.6m
Near Point/DOF Limit: 2.3m

Far Point/DOF Limit: 10.4m
Near Point/DOF Limit: 2.1m

Far Point/DOF Limit: 6.92m
Near Point/DOF Limit: 1.9m

Far Point/DOF Limit: 4.72m
Near Point/DOF Limit: 1.7m

Far Point/DOF Limit: 3.20m
Near Point/DOF Limit: 1.46m

Far Point/DOF Limit: 2.08m
Near Point/DOF Limit: 1.17m

Far Point/DOF Limit: 1.22m
Near Point/DOF Limit: .84m (or .85m)

Far Point/DOF Limit: .87m
Near Point/DOF Limit: .66m

Far Point/DOF Limit: .55m
Near Point/DOF Limit: .46m

Far Point/DOF Limit: .26m
Near Point/DOF Limit: .24m