how about a DOF tutorial??

The millimeters are in fact the same. But the field of view is very different. Smaller sensors only see through a smaller portion of a lens.

Think about a 35mm slide. That's how big a 35mm piece of film is (obviously, because it *is* a 35mm piece of film). Now cut out the center 5mm x 3mm portion. That's about how much a 1/3" CCD would see, using the same lens. It's a smaller sensor, so it sees a smaller patch. The lens would project the same-size image under all circumstances, but the sensor can only see so much due to its physical size.

If you projected the full 35mm frame onto a projection screen, you'd see a certain field of view. If you then magnified that central 5mm x 3mm portion so that it fills the same screen, obviously it'll look like you used a much-more-telephoto lens. That's because the little sensor only sees that small central portion.

Which is why, when using a smaller sensor camera, you have to use wider-angle lenses in order to get a usable field of view. A 35mm movie camera would use maybe 20-200mm, and for the same field of view a 1/3" video camera has to use 5mm-50mm. And that's why the depth of field is so deep on the 1/3" video camera -- because you're using much wider-angle lenses to get the same field of view.
 
Brilliant! That makes sense. Its all about field of view and image aquasition and not the lense per se. It is all propoartionate to the means of which you are recording your image. There is a physical limitation imposed by the imager. In order for a 1/3 CCD camera to have the same FOV as a 35 Film Camera, assuming they are at the same postion, it must have a shorter lense, because the image from the 35mm camera lense would be too large for the CCD and would not give the same FOV.

Does that sound right?

Thanks!
 
I would just like to say that the image size in a slide is bigger than the one in a 35 mm feature film. That's because the image in the slide is set horizontally and in the feature film it's set vertically.

I don't know whether this may be useful or not...

Best regards
 
In some cases, the larger image size that pulling the film horizontally vs vertically is desireable. Such as in the movie Vertigo, where they shot in "VistaVision". It gave them a shallower depth of field second only to 65mm and IMAX.
 
I hope this hasn't been covered, because that would mean I haven't understood everything that's been covered in the many previous pages.

Basically because of the smaller ccd size in video cameras getting a shallow depth of field is more difficult, and I believe I understand how to use the HVX to push the backgrounds of my dialogue scenes out of focus so the audience is watching my characters. This helps because my shots will be composed and locked off.

I also want to shoot action scenes but with Barry's thread of the dire importance of focusing in HD I've got the fear that my actors will be flying in and out of focus. Also I'll need to steady-cam many of these shots and my same focus fears appear. With the small ccd making an f stop above 8 a detriment, is there an effective way of focusing shots that will be moving and not locked off? Like an infinity / back-focus technique?
 
The highest resolution commercially available digital camera back is Phase One 45.

Some details: "What else is known about this remarkable device? The chip size is the same as that in the previous P25 and other "full-frame" 645 backs. It's almost full-frame. A magnification factor of 1.1X over film is seen. Image size is 7216 x 5412 pixels." Thus it is 39 Mpixel and about 55x40 mm in size.

The pizel size is so small, that new lenses have been designed for it, as normal view camera lenses were not sharp enough. The image quallity equals 4x5 film with those lenses.

More: http://www.luminous-landscape.com/reviews/cameras/phase-one-0705.shtml
http://www.luminous-landscape.com/reviews/cameras/digital-view.shtml
 
Came across this a diagram explaining Depth of Field in a Kodak 35mm guidebook. I liked it because it was visually explaining bunch of different things in a simple way. I redrew it and posted it here. Hope it helps. I recreated it directly from Kodak.
depthoffield.jpg
 
Aejaz said:
Shallow depth of field:

2. LESS LIGHT

Deeper depth of field:

2. MORE LIGHT
Click to expand...

A very important thing to remember when you are thinking about the look of the shot.
 
DoF

DoF

Dept of Field is determined by three factors:

1. Focal Length
The longer the Lens the shallower the DoF
(Focal Length means dimention of Lens in milimiters... for example 50mm Lens means that Focal Length is 50mm (this is a distance from an optical center within lens and a Film Plane)

2. Focus Distance
The bigger the distance from subject the bigger the DoF

3. Iris/F-Stop/Aperture
Large F-stop - Small Aperture Opening - Large DoF
Small F-stop - Big Aperture Opening - Shallow DoF

Cinematography Workshops Hollywood
 
Okay all I want to throw this into the ring because I generally agree with what is being said here with one exception and that is that the focal length of a lens has any bearing on the DOF of a shot. I typically subscribe to the school of thought that while somtimes it contributes to the "apparent" DOF the effective DOF is unaltered by the focal length of a lens. Walter Graff does a much better job of explaining this than I can but take a look and tell me what you think. I was really surprised to hear Barry quote the contrary here and would be interested in further understanding his reasoning on this.

http://www.bluesky-web.com/dofmyth.htm

In what is considered the bible of cinematography, "A Hands-On Manual for Cinematographers", David Samuelson states at the conclusion of his section on depth of field : "Depth of field remains the same, regardless of lens focal length, so long as the image size (and f-stop) is the same. There is no point in changing to a shorter focal length lens and moving closer, because if the image size remains the same so will the depth of field." (Focal Press, London, second edition, 1998, p.218)
 
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Yeah, but -- that's a technogeek explanation that (while technically accurate) completely disagrees with the observable evidence. The APPEARANCE of shallower depth of field is absolutely influenced by the focal length of the lens. Change your camera position so that you have equivalent framing, and you'll see the appearance of much shallower DOF in the telephoto shot.
 
What really kills me about that explanation is that DOF is all about appearance. Apparent DOF is the only DOF. The definition of focus is when things appear sharp. If things appear to be in focus, they are. With wider lenses, more things appear to be in focus, just like in notthere's diagram.
 
ProfessorU said:
What really kills me about that explanation is that DOF is all about appearance. Apparent DOF is the only DOF. The definition of focus is when things appear sharp. If things appear to be in focus, they are. With wider lenses, more things appear to be in focus, just like in notthere's diagram.
Click to expand...
There's technically accurate, and there's "for all intents and purposes" accurate. What you're describing is, of course, that the look is obvious. I'm just throwing a bone to the "technically accurate" group out there, by allowing that yes indeed technically the level of focus is the same. But does it matter? Because when you look at the shots, the appearance of DOF is drastically different and, as you say, isn't that what we're after?
 
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