General Question

robmandu's avatar

Does type of camera really dictate depth of field?

Asked by robmandu (21285points) August 27th, 2008

I’m reading the Wired article about Red Digital Cinema’s Ultrahigh-Res Camera. The author makes the claim that a digital cine-camera would need an image sensor identical in size and shape to a single frame of 35-mm motion picture film to give filmmakers the control over depth of field, color saturation, tonality, and a half dozen other factors that 35-mm film provides. There’s even a side-bar example.

Here’s the thing. I’ve got a dSLR. Depth of field on that guy is a function of the lens… not the camera’s optical sensor. I gotta think the same is true for video, right?

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22 Answers

lapilofu's avatar

I was under the impression that it was a function of the lens, but I’m no expert.

EmpressPixie's avatar

In film, it is a function of the lens. I cannot imagine that would be any different with digital.

winblowzxp's avatar

Another thing…you can change the depth of field by playing with colors as well.

Scrumpulator's avatar

Yes the Camera is a direct relation to the depth of field, SLR vrs. Fixed lens Digital Camera’s. Fixed lens cameras have a poor focus range. hard to make the foreground blur and the back ground not to, this creates depth of field. With the Fixed lens digital, more of the field is in focus, so the only indicator of depth is the relative size of objects in relation to one another, with the SLR’s you can have a much more flexible choice of your focal matter. you can aim at the sky and focus there, then most of the image will be in focus, if you focus on just something 5 feet away, then everything else behind it will be blurry, just like your eye works. hope this helps you get it, and yes most SLR’s have an image sensor identical in size and shape to a single frame of 35-mm motion picture film. On another note, these can be changed with digital settings to alter the size of the image sensor. So basically, Removable and changeable lens camera’s are the way to go, but as far as money is concerned, to get 3 good lenses, you would need almost 10,000 dollars. I have two lenses, and it is not enough but It set me back 5000 for one of them and 3000 for the other one.

lapilofu's avatar

@scrump: I think the question is, given an SLR/camera with changing lens, isn’t it the lens, not the sensor that determines DOF?

IchtheosaurusRex's avatar

Depth of field is a function of aperture. Small apertures – higher F-stop numbers – give greater depth of field. Large apertures – lower F-stop numbers – give a narrower depth of field. When you’re shooting for effect, you need to compensate for a larger aperture with a faster shutter. Pixie is correct about it making no difference with digital vs. film. However, with a film camera, you need to choose the right film for effect shots.

Scrumpulator's avatar

Didn’t I answer that. Yes. But I also stated that it is important to get an SLR at the same time, especially if you want good depth of field

Scrumpulator's avatar

@Ichth, What you just described is how you stop your picture from being too bright or too dark. the whole F-stop aperture thing is a balance factor for light control. I just got back from taking a bunch of photos, and I used these tools to balance the effect of shooting the sunset and the colors behind it. Just five minutes ago.

lapilofu's avatar

Ichth is right—a larger aperture gives a narrower depth of field. People frequently think of aperture as a light/dark control, but I use mine more frequently to determine my depth of field.

Scrumpulator's avatar

hmm… describe a little more, maybe I am just getting the shots I want on instinct alone, how is it used in the function you are talking about. maybe its egg in my face time, but i want to learn all the same

IchtheosaurusRex's avatar

Here’s a good article about it:

It describes the relationship between aperture and depth of field in detail. That site in general is a great reference for anybody learning how to take pictures.

lapilofu's avatar

I mean, Ichth explained it pretty clearly, but if you turn your aperture to a higher F-stop, a larger range of things will be in focus. If you want a photo with an unfocused background, for instance, you’ll want to turn your F-stop down.

Wikipedia’s article about apertures has some further technical details: “If the admitted rays also pass through a lens, highly collimated rays (narrow aperture) will result in sharpness at the image plane, while uncollimated rays (wide aperture) will result in sharpness for rays with the right focal length only. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise.”

Scrumpulator's avatar

@Ichth, That is a really good article. I just change my lenes to get these effects and now I won’t have to. That explains it more detail, thanks.

Scrumpulator's avatar

The depth of field calculator rocks.

Knotmyday's avatar

@Ichtheosaurus- On the hi-zed! lurve.

Knotmyday's avatar

@rob- I’m not familiar with the inner workings of HD video cameras, but I can tell you that I can get the same depth-of-field effect manipulating zoom and focus (and little else) on the Canon XL2 here at work. I think the writer of the article had a slip ‘twixt the cup and the lip on that particular paragraph.

loki's avatar

the red camera has interchangable lens.
DOF is controlled by f-stop setting.

jballou's avatar

Yes, it is a function of the lens, but no matter how good a lens you have- being able to faithfully reproduce the image it captures is a function of the camera hardware. You can use the same lens on a 7 megapixel camera and a 12 megapixel camera, and the 12 megapixel will probably yield better, more accurate results because the camera is better able to interpret the data its receiving. That’s more then likely what the article was referring to, I would assume.

McHobbes's avatar

The Red Cinecamera’s are designed for digital film-making, not just photos. When it talks about the sensor on a RED ONE camera giving 35mm-film equivalent control over depth of field, they’re talking about the fact that the sensor is much larger than your average video camera, so you have more flexibility with your lenses to adjust the depth of field (among other things) to your liking. With smaller sensors, you have less of a range that you can get away with, because clarity is lost easier when you get to more extreme lens settings.
Does this make sense?

IchtheosaurusRex's avatar

@jballou, megapixels win if all other things are equal, but you get a much better image from a good lens on a 6 megapixel SLR than you do from a shitty 10 megapixel PHD camera.

jballou's avatar

@IchtheosaurusRex – Of course. I wasn’t even considering point-and-shoot cameras. We’re talking about lenses so I would assume we’re talking about cameras that support changeable lenses. :-P

Burner's avatar

While F-stop / Aperture does indeed have direct relation to DOF and how shallow you can make the focus, Sensor size / film size has a direct relation to DOF of your shots.

For instance, a ⅓” or ⅔” has a fairly deep DOF. With these cameras it is often difficult to get the background of images blurry regardless of quality or speed of lens. The RED One has a sensor size that is approximately equal to Super 35 motion picture film, otherwise known as “Academy Standard.” (MPAA)

This film / sensor size allows the shallow DOF that is often synonymous with Feature motion pictures. The Canon 5dMarkII has a sensor size equivalent to 35mm still photography negatives (which is larger than Academy Standard), this allows for even shallower DOF than Academy Standard or the RED One. When shooting at f1.2 on a Canon 5dMarkII, you can focus on a subject’s eyes and have both their nose and ears out of focus. (Such shallow DOF makes it practically impossible for a 1st AC to pull focus)

Another example of smaller sensor allowing more in-focus are small sensor HD cameras such as Flip Video, ContourHD, and Kodak Zi8s. With these type cameras, practically everything is in focus farther than about 18”. (I know many of you will claim it is due to the lenses that are built into these cameras, but it is very much related to their tiny sensor size.

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