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Depth of field lever accessory

On cinema cameras e.g. from Blackmagic Design or RED, is there any accessory that someone can purchase to make adjusting depth of field easier? I mean, instead of rotating the circular dial on the lens at the front of the camera, maybe there could be a lever which can be attached to the camera rig where one moves it horizontally or vertically with two fingers to adjust for depth of field. The center position can be neutral. A concept of such lever is in the below picture:

http://www.butkus.org/chinon/chinon/ceii-metrotone/body09.jpg

This lever will make it so convinient especially when the cameras have super long lenses and especially if there is a moving camera shot that has a change of depth of field in the shot. Instead of the camera operator having to stretch/extend their hand all the way to the lens at the front to rotate the lens dial to change depth of field, while having the added task of moving the camera, the separate add-on accessory depth of field lever solution can make things better by being present, perhaps on the camera rig at the back of the camera, or somewhere on the tripod, where it is within easy and convinient reach for the camera operator.

So, does any such depth of field lever exist?


edit - I just realized that I should have posted this under Cameras and Lenses
 
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Do you mean to change the focal point/focus?

You could use something like this:

http://store.redrockmicro.com/Catalog/microRemote-Accessories/remote-fingerwheel-controller.html

That looks like a nice tool and is something which I am referring to.

To change the focal point/change the focus means to also change the depth of field - am I correct?

Also, do you know what such tool can be found in professional Arri film camera or Arri digital camera rigs which is used in feature film in the film industry to easily change focus (depth of field)?
 
Changing the point of focus and changing the depth of field are two different things.

Depth of field is affected by the aperture and the focal length of the lens. The more telephoto the lens, the shallower the depth of field. Similarly, the wider the aperture, the shallower the depth of field.

To get a shallower depth of field, you need to zoom in, or use a longer lens, and/or open the aperture.

To change the point of focus, you would use a follow focus. High-end camera rigs usually include a traditional mechanical follow focus, though some will use a wireless follow focus which consists of a motor that attaches to the lens and a hand controller that allows you ro change the focus. That's what the RedRockMicro product is based around.
 
Changing the point of focus and changing the depth of field are two different things.

Depth of field is affected by the aperture and the focal length of the lens. The more telephoto the lens, the shallower the depth of field. Similarly, the wider the aperture, the shallower the depth of field.

To get a shallower depth of field, you need to zoom in, or use a longer lens, and/or open the aperture.

To change the point of focus, you would use a follow focus. High-end camera rigs usually include a traditional mechanical follow focus, though some will use a wireless follow focus which consists of a motor that attaches to the lens and a hand controller that allows you ro change the focus. That's what the RedRockMicro product is based around.

Thanks but when the point of focus is changed, the corresponding depth of field alters as well, right? What I am trying to ask is - will changing the point of focus ever result in the depth of field remaining the same?
 
Yes to your first question and no to your second. Are you really just talking about changing the depth-of-field of a shot and nothing else?

There are three things that affect depth-of-field: focal length, distance to subject (or focus point) and aperture. Now in practice, aperture is really the only control that tends to get used, because the first two cancel each other out. Let me explain, let's say you want a medium shot of an actor and you want a very shallow depth-of-field. You could go with a telephoto lens (right, longer lens= less depth-of field) however, you'd have to put the camera really far back to get the medium shot and then you'd be increasing your depth-of-field (because the farther your focus point=great depth-of-field). Conversely, you could move the camera closer, but then you'd have to use a wider lens. So in practice, aperture is what we use to control dof.

That being said, if you wanted to adjust ONLY the depth-of-field of a shot you would have to change the aperture, but then your exposure would change unless you could somehow compensate for that (by changing exposure time or ISO). I suppose hypothetically, if you had a camera with a very nuanced auto exposure you could change the aperture and have the camera adjust the ISO. I doubt however that that would ever work as there would undoubtedly be exposure variation as the camera tries to compensate.
 
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