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DOF in 3CCD camera


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#1 ljoski johnsen

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Posted 10 September 2006 - 12:28 AM

Hi,

This is my first post here. I have a question.

The other day, someone told me that when he was shooting something last month, he kept aperture wild open to gain less of the DOF using 3CCD camera (XL2). And I was thinking that cannot be possible because XL2's lens doesn't even have the aperture ring. Rather it changes its f-stop inside the camera body electronically, I suppose. If the DOF is relevant to the size of the circle of confusion, it is impossible to gain less of DOF by stopping down electronically in the camera body. I told him that but he never got what I said and still believing that wide open aperture will give him less of DOF. He rented a bunch of ND filters just for that matter.

Am I crazy? Or my pal is just ignorant?

Ljoski Johnsen

Austin, TX
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#2 David Mullen ASC

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Posted 10 September 2006 - 12:41 AM

Lens aperture does control depth of field, and the lens on a Canon XL2 does have an internal aperture (just not a manual f-stop ring unless you get the manual lens), and shooting wide-open reduces depth of field / stopping down the iris increases it. A simple test will show you that.

A DV camera, like any other digital camera, controls exposure with a lens aperture, electronic shutter, and gain, not to mention frame rate & external filters.
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#3 ljoski johnsen

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Posted 10 September 2006 - 12:49 AM

Oh, I see.

So, XL2's exposure ring attached to the side of the camera body actually change the size of the aperture in the lens? So, it does affect the Depth of field. I remeber that when I attached Mini35 onto XL2 the aperture ring was useless as the camera body didn't recognize the mini35 adaptor as a lens. That makes a lot of sense now.
Thank you, David.

Ljoski Johnsen

Austin, TX

Edited by ljoski johnsen, 10 September 2006 - 12:52 AM.

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#4 Joshua Provost

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Posted 15 September 2006 - 05:48 PM

Ljoski,

Aperture does have an effect on depth of field, but going "wide open" can be a problem, since wide open is usually F1.6 or so at full wide zoom, and F2.8 at full telephoto. Also, the small field of view on telephoto gives a much more shallow "look" than full wide open at full wide zoom, even though it's closed down nearly two additional stops.

Check it out for yourself. Set up a scene with an object in the foreground ten feet or more from a background. Put the camera a foot away from the object and frame it up with a wide zoom. Then back up the camera and zoom in the get the same object size. Boom, the background is way out of focus. It's the narrow field of view that does it.

What I do these days is shoot nearly everything at F2.8 for maximum flexibility with the zoom. I light to F2.8 or for exteriors use ND to cut down to F2.8. Where practical, I try to shoot from as far away as possible and zoom in to get my framing. For certain shots, like when you need to show two characters that are at different depths, it's tough to get it framed properly at full zoom, so I comproise and move the camera closer for better flexibility.

Josh
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#5 olan

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Posted 15 September 2006 - 06:52 PM

Oh, I see.

So, XL2's exposure ring attached to the side of the camera body actually change the size of the aperture in the lens? So, it does affect the Depth of field. I remeber that when I attached Mini35 onto XL2 the aperture ring was useless as the camera body didn't recognize the mini35 adaptor as a lens. That makes a lot of sense now.
Thank you, David.

Ljoski Johnsen

Austin, TX



Hi,

When you use a mini35 adapter on a XL2 camera you have to remove the canon lens to put the adapter (using an intermediate lens). But there is no electronic connection between the camera body and the adapter to control the iris witch means that you have to change your f-stop manually on the cine or photo lens ring. That?s why the aperture ring of the canon camera body is useless when using an adapter.
Even if you use an adapter on another camera, like the Sony Z1 for example. You will still be able to use the aperture ring of the camera body to change the f-stop of your in-camera lens but it will not affect the DOF of your frame because you have to focus on a 2D frame that is projected from the cine or photo lens on to the ground glass inside the mini35 adapter. The camera is simply filming the frame that is projected true the lens on the ground glass. It?s the same principle that is use for the telecine.
But if you want to loose DOF when you are using an adapter. You can simply apply the same trick that your friend used with the XL2 but it?s the cine lens that has to be wide open.

Have a nice day,

olan & olivier
the black sheep
director/dp/editor/colorist
brussels. belgium
www.theblacksheep.be
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