Depth of field

themanwhoknows

themanwhoknows

Member
Im not really sure how to put this question but im basically trying to figure out what the difference is between a film camera and a video camera in terms of their lens and depth of field, it always seems that in a film camera everything seems very flat but in a video camera objects that are closer are bigger. I want to know if their is a way to have this same 'effect' in a video camera?

Any suggestions would be great, thanks.
 
DOF (depth of field) is a product of both the focal length and the aperture. The longer the focal length or the larger the aperture (lower numeric F-Stop) the shallower the DOF.

The difference between a video camera (one with a small sized sensor) and a 35 mm camera is the size of the sensor (or film area). The product of the sensor size and the focal length determines the FOV (filed of view).

In the case of a 35mm camera set to a focal length of 50mm would be considered a "normal" field of view. On a small size imager, the same 50mm focal length would be a telephoto FOV.

The basic conclusion of these pieces of information is that you can not achieve the same DOF for the same FOV between different sensor (or film area) cameras. The one with the larger sensor will have shallower DOF for the same FOV and aperture.

The "best" that you can achieve from (if your goal is shallow DOF) is to use the longest focal length (zoomed in) and largest aperture (minimum F-Stop) possible.
 
khmuse said:
DOF (depth of field) is a product of both the focal length and the aperture. The longer the focal length or the larger the aperture (lower numeric F-Stop) the shallower the DOF.

The difference between a video camera (one with a small sized sensor) and a 35 mm camera is the size of the sensor (or film area). The product of the sensor size and the focal length determines the FOV (filed of view).

In the case of a 35mm camera set to a focal length of 50mm would be considered a "normal" field of view. On a small size imager, the same 50mm focal length would be a telephoto FOV.

The basic conclusion of these pieces of information is that you can not achieve the same DOF for the same FOV between different sensor (or film area) cameras. The one with the larger sensor will have shallower DOF for the same FOV and aperture.

The "best" that you can achieve from (if your goal is shallow DOF) is to use the longest focal length (zoomed in) and largest aperture (minimum F-Stop) possible.
Click to expand...


Great answer. :thumbup:
 
The fomulas for determining the depth of field at a given distance from the camera to the subject depend on three things, the focal length of the lens, the F number being used and the size of the circle of confusion.

The circle of confusion refers to the maximum size that a point can register as an out of focus circle (or blurr) and still produce a image that is "acceptably sharp".

Smaller formats require higher resolution and therefore smaller circles of confusion typically to produce high quality images when compared to images produced on larger formats, resulting in dramatic differences in the depth of field.

The depth of field increases as shorter focal lengths are used to produce the same field of view on the smaller format, achieved by a longer focal length lens on the larger format. Coupled with the need for more resolution at the image plane to cram enough information into the smaller format to produce an acceptably sharp image results in the huge increase in depth of field when using a relatively small video format (compared to 35mm film).

I hope this helps as opposed to adding to the "confusion".

Bill Turner
Century Division
Schneider Optics
 
khmuse said:
The "best" that you can achieve from (if your goal is shallow DOF) is to use the longest focal length (zoomed in) and largest aperture (minimum F-Stop) possible.
Click to expand...
That's not exactly true, kh. Depth-of-field also decreases (becomes shallower) as you focus closer toward the camera (away from infinity).
 
NBCshooter:

Khmuse is right... and you are too.

Three aspects to low depth of field:

Shoot really close. Macro pics have dof of milimeters

Use tele at max.

Wide aperature.

Use all three aspects at same time.
 
Great info everyone.......but.........

no one really addressed the question posed, which had to do with film verses video.

The question really is misguided, because it's not that one format had better DOF than the other. In truth, it's all about the lenses and the amount of light being used.

Most people tend to think film is better for DOF simply because they see better DOF in all the movie we watch (which are shot on film). But the main reason for this is the great DPs that shoot those film and the very expensive cameras and lighting equipment and lenses they use, sometime using lenses that cost more than a Porsche.

As many people know by now, Lucas and Rodriguez have shown time and again that the same thing can be done with video, if it's high quality and has the right lenses. I've seen comparisons between Panavision Gold footage and Genesis video footage and could barely tell the difference.

So the short answer is, its not the format but the lens that matters, combined with light and capture quality.

In fact, most people that are not in the know, if polled when leaving a Lucas or Rodriguez film will think the film was shot on film, not video. Some would argu that's because it'stransfered to film out. Yet many that have seen the films on one of the few digital screens out there attest that it is even better as pure digital.
 
Icarus2005:

I assume when you say "better dof" you mean shallow dof.

Generally, large sensors will give similiar dof (shallow) to film as they tend to be a similiar size. Small sensors 1/3 inch will give deep depth of field.

Lucas and Rodriguez use larger sensor video cameras which give closer dof to film cameras, hence people think their work was shot on film.

If they had used a 1/3 sensor camera like a HVX200 their stuff will look more video like.

In this case expensive porsche costing lenses won't help them out when it comes to shallow dof.
 
The wider the aperture (Letting more light in), the shallower the DOF. The smaller the aperture the greater the DOF.
 
There is a DOF tutorial stickied at the top of this Cinematography forum. That should tell you what you need to know if you care to spend a few minutes reading.
 
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