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Getting a deep dof with a 35mm adapter.


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#1 Karl Katz

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Posted 07 December 2007 - 01:49 AM

Sounds stupid, I know. We are going to be filming a short using the hvx and the new sgpro rev3. I feel the image yeilded by the 35mm adapter is aesthetically much nicer than straight through. Only thing is I don't want the whole film with blurred out backgrounds. Is it a matter of focusing at hyperfocal distance? How do they get a deep dof on 35mm cameras?
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#2 Michael Nash

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Posted 07 December 2007 - 02:08 AM

Depth of field, as always, is controlled by three (or four) things; aperture, focal length, and distance to subject. There's no trickery beyond that. That "fourth" thing is the circle of confusion, which in a nutshell means the resolution of the format you're using.

In the case of relay lens adapters the circle of confusion is increased a bit by the groundglass, in other words the image is made softer overall compared to the optics of the taking lens or the camera's lens. You also lose a bit of contrast.

If you want deep focus with 35mm optics you use the combination of highest aperture, shortest focal length, and farthest distance to subject that you can manage for the setup. This isn't always so easy with 35mm adapters.

If you want to take advantage of the deep focus offered by 1/3" chip cameras but still want some of the softening and lowered contrast of an adapter, you can try different diffusion filters like Ultracons and low-cons.

But I have to admit, getting deep focus with a 35mm adapter is really going 'round your a$$ to get to your elbow. Take a good look at what you like about the "look" of these 35mm adapters -- is it influenced by the shallow depth of field? Have you seen a deep-focused image from one of these, or are you just imagining what it might look like? If you have seen it, what did that image look like? Was it just washed-out and softened compared to the camera's "clean" image? Unless there's some other particular characteristic you like of the lenses you're using...
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#3 Jonathan Bowerbank

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Posted 07 December 2007 - 02:20 AM

The downside of this is, if you go with a standard to longer lens, you're going to have the light the hell out of it to get that deep focus.

Keep in mind that with the adapter you're probably losing up to 2 stops, and if you're closing down the 35mm lens to let's say T.8 your ASA is going to be extremely slow.

IMHO, the aesthetic of achieving that film look by using 35mm lenses on an adapter is completely lost if you're not taking advantage of the shallow depth of field.
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#4 Karl Katz

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Posted 07 December 2007 - 02:50 AM

Thanks for the quick reply. I should have explained myself better. I'm using the adapter specifically for the short dof. My problem is I'm worried if i shoot straight through for other shots it won't match the distinct look the sgpro gives. I don't want any distractions to the audience caused by mismatching footage. I understand dof and its problems, that's why I was wondering if there was a simple way around it like focus or how they obtain with 35mm cameras. Thanks.
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#5 Jonathan Bowerbank

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Posted 07 December 2007 - 04:20 AM

So they match, the easiest way of achieving that in camera is probably through just using a wider lens for the deep focus shots.

On a recent shoot, we switched from using a Pro35 adapter to a Canon zoom to gain our two stops back for some night exteriors. To soften the image a bit and get it closer to that ground glass look, we adjusted the Master Detail level from -5 to -15 and adjusted the shutter from 1/48 to 1/36.

I couldn't quite tell in camera whether the shutter angle made much of a difference, but in tests we could definitely see the difference when we adjusted the master detail level. It just brought back some of that softness in the highlights that comes as a result of the ground glass when shooting with an adapter.
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