Depth of focus on different systems?

[Niklas]

Is it true that the depth of focus are different on a DV-camera compared to a 35 mm camera, using the same aperture, shutter speed etc?

[Chance Shirley]

Yes, that's true.

 

I can't explain the science behind it (I'm sure someone here can), but, all other factors being equal, the depth of focus decreases as the size of the film frame/CCD increases.

 

So, MiniDV has more depth of focus than 16mm, 16mm has more than 35mm, and 35mm has more than IMAX.

 

-Chance Shirley

Birmingham, AL

[Guest Daniel J. Ashley-Smith]

Ah, just the message.

 

(Eureka! I now know what depth of field is.... Yeh my understanding of it was completely screwed, I was getting confused with a different effect)

 

Well, I suppose using a smaller format is just like closing the iris down in a way. It can only shoot at a certain perspective. A bit like squinting your eye, smallens the capture area (eye) and it gives you a larger depth of field, enabling you to see more. Ever tried bending your index finger down a creating a small hole, look at something normally that you would have difficulty seeing and then look through the tiny hole. You've effectively made your own iris and by closing it down you've increased the depth of field.

 

Trouble is, with digital you don't always get a wide choice on how much depth of field. Being that it's a smaller capturing device. But if you ask me, people are making to much fuss of this depth of field. I mean, without a large depth of field you get everything or more in focus, I mean, BIG DEAL! The only trouble with greater depth of fields is that they don't let a great deal of light in, but you can compensate for that.

 

I'd say altering the depth of field is merely an arty effect, not sure what all the fuss is about... Adds a bit more excitement to the film I guess... <_<

[Guest Daniel J. Ashley-Smith]

I mean, without a large depth of field you get everything or more in focus

 

Oops,

 

WITH a large depth of field you get everything/more in focus....

[John Sprung]

There are two different concepts here.

 

Depth of field is the region outside the camera nearer and farther than the plane of critical focus where things are reasonably sharp.

 

Depth of focus is sort of the same idea, only it happens *inside* the camera. It's the region fore and aft of the actual film plane where the image is reasonably sharp.

 

Long lenses have little depth of field, and lots of depth of focus. Wide angles have lots of depth of field, and little depth of focus. That's why back focal distance is more critical on wide angles.

 

OK, now, so what does "reasonably sharp" mean? In theoretical optics, a point on the plane of critical focus gets rendered as a point on the film plane, and any point not on the plane of critical focus gets rendered as a circle on the film plane. That circle is called the "circle of confusion" -- wonderful term for it. DOF tables are calculated based on a diameter of 0.002" for the circle of confusion in 35mm, and 0.001" in 16mm. Although that would seem to give an advantage to the larger format, the rest of the math pushes things even farther in the other direction, and the smaller the format, the greater the DOF, all else being equal.

 

 

-- J.S.

[Alvin Pingol]

>>I'd say altering the depth of field is merely an arty effect, not sure what all the

>>fuss is about...

 

Fuss? Photography is an art. DOF plays a large role in how the final image comes out, and since photography is an artform, altering an "arty" effect would create fuss. DOF is a huge part of photography.

 

Think of it this way. Imagine this message board was for people who paint, and see my modified quote:

 

"I'd say altering the type of paint you use is merely an arty effect, not sure what all the fuss is about..."

 

See what I mean? You'd be attacked from all sides - the watercolor guys, the acrylic guys, the oil paint guys, and so forth.

[Landon D. Parks]

If you want less depth, get a Mini35 or a Pro35. Gives you 35mm depth of field on either 1/3" CCD or 2/3" 16:9 CCD's (Pro is for the 2/3" and the Mini is for the 1/3")

[Paul Bruening]

Here's the deal on depth of field. Cinematography is a two dimensional presentation. Cinematographers as well as photographers use little tricks to fool the viewers brain into accepting the 2D illusion as a real life 3D experience. Shallow depth of field is one of those tricks. It gives the viewer a sense of depth that goes deeper than the 2d image. This helps the viewer suspend disbelief and buy into the story. That's what we're all trying to achieve... right?

 

Paul Bruening

[Paul Bruening]

I have an XL1s. The only way I have been able to shorten the depth of feild is to get a manual lens, stop it down to the bottom, and lengthen the lens (zoom out). It works ok on close-ups but not much else.

 

Paul Bruening

[Guest Daniel J. Ashley-Smith]

See what I mean? You'd be attacked from all sides - the watercolor guys, the acrylic guys, the oil paint guys, and so forth.

 

 

Yeh I see what you mean actually... thinking about it..

 

But on the other hand it's not always the effects people watch, it's the story. But yeh your completely right and I can't argue it. I'm just less of an, arty person when it comes to film. Although I do experiment with artistic shots...

 

Ahhh screw it.... :wacko:

[John Sprung]

Cinematographers as well as photographers use little tricks to fool the viewers brain into accepting the 2D illusion as a real life 3D experience. Shallow depth of field is one of those tricks.

The human eye actually has a lot of depth of field. Close one eye and look around. In daylight, everything from an outstretched hand to the horizon will be quite sharp. Then open both eyes and look again. It's the parallax between our two eyes that both gives us depth perception, and confines our attention to a much shallower region where our eyes converge. So, we can accept both large and small DOF as looking reasonably natural.

 

The main importance of DOF is as a storytelling tool. You might want to focus on a foreground actor, then rack to someone behind him. Or you can choose more DOF and hold both of them.

 

 

 

-- J.S.

[Guest Daniel J. Ashley-Smith]

Actually I was thinking about that today. Looking at something close up and then looking at the background in the corner of my eye it semmed to be pretty clear.

I dunow maybe I just have big eyes....

[Alvin Pingol]

I dunow maybe I just have big eyes....

Hehehe... ^_^

 

If I'm not to be mistaken, isn't there some type of device around that allows the use of two lenses simultaneously, so as to reproduce what human vision gives you? I think it was some type of adapter for the Canon XLx cameras or something.

 

I haven't seen any footage or stills with the adapter in use, but I would imagine the results would be somewhat distracting. Everyone is used to seeing that if a pencil is out of focus, it is blurred - not duplicated.

 

Does anyone here know what I'm talking about, or am I just imagining things?

[Phil Rhodes]

Hi,

 

The device exists, I'm not sure how it works or what the recorded material is best used for.

 

At NAB, I saw an interesting no-glasses 3D display which used that tiny prismatic sheeting you get on cereal-box toys where the picture changes, to fire alternate columns of pixels out at different angles. Very effective, but only worked in a very small area - you have to keep your head still.

 

Phil

[Alvin Pingol]

I found an old Forbes article on the 3D lens. Can't seem to find any info on it on the Canon website, though.

 

Guess it's now defunct.

[John Sprung]

Very effective, but only worked in a very small area - you have to keep your head still.

This is a lenticular screen 3D system. The Russians tried this for theatrical projection many years ago. It works fine for a few minutes, but for a feature film it was NG because the entire audience ended up with very stiff necks.

 

 

 

-- J.S.

[John Pytlak RIP]

Kodak has some new technology for 3D displays without glasses:

 

http://www.kodak.com/US/en/corp/researchDe...s/May2004.shtml

 

Kodak Autostereoscopic Display finds applications in Industry, medicine, education - and more

The Kodak Autostereoscopic Display technology is intended for applications that call for prolonged viewing of detailed, three-dimensional images, such as medical evaluations or scientific analysis. Several industries are evaluating Kodak's stereoscopic imaging technology as a tool to study detailed imagery with increased resolution and less eye fatigue.

 

For example, the energy industry relies on detailed analyses of geologic sonar images, and is testing the Kodak Autostereoscopic Display System for data visualization needs. This system's high-resolution displays deliver increased detail in analyses of undersea geology, where oil companies now search for oil and gas deposits. The system may also be used in molecular and chemical modeling, chemical modeling, genomics, and weather forecasting.

 

Other applications for the Kodak Autostereoscopic Display System include:

 

 

Engineering, including computer-aided design, mechanics, and engineering for product design, virtual prototyping, manufacturing, architecture, and landscaping construction.

Medicine, where surgeons and dentists can perform exams with tiny video cameras and view the results with high-resolution stereoscopic detail. Users are also evaluating its value in the emerging remote healthcare business, in which medical professionals evaluate patients via a two-way electronic display.

Entertainment, such as video arcades in theme parks and restaurants.

Virtual trade "e-showrooms," enabling manufacturers to demonstrate new products with an in-depth experience, without bringing actual products to an exhibit hall or conference.

Education, creating near-holographic images for science and technology students to carefully examine objects in close "virtual" detail.

 

The Kodak Autostereoscopic Display System allows people to experience images without the eyestrain or disorientation sometimes encountered with head-worn 3-D glasses, visors, or barrier screens. The prototype display is equivalent to viewing a 36-inch television monitor from less than 3 feet away - with more than five times the resolution of a conventional TV. To get the same field of view from a 21-inch monitor, a user would need to sit closer than 20 inches from the screen. So, users can view the Kodak Display's images for longer periods of time, with less eye fatigue, making it a more productive tool.

[Dominic Case]

But on the other hand it's not always the effects people watch, it's the story.

But the "effects" are how you tell the story. If you just let the camera roll while things happen in front of it, that's one thing. If you draw the viewers' attention to something in the shot, you are actually telling the story.

 

Think of the classic long lens shot of person in a crowd: wide open lens, only one person is in focus, the shot is about that person, alone but surrounded by people: stop down, bring more of the crowd into focus, the shot is about everyone in the crowd.