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Deep Focus & The Connection between Aperture and Quality


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#1 Benjamin G

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Posted 28 February 2012 - 04:35 PM

I'm prepping to shoot an indie feature in 3D. Produce and Direct actually, I am hiring a cinematographer for this one. I don't like shallow depth of field in 3D, I find the unfocused areas are much harder to look at if they do catch your attention. So I'm trying to take a page from the book of Greg Toland, and shoot it like he shot Citizen Kane. With pretty much everything in focus and use composition to focus the audiences eye.

Now I understand the basics of depth of field and the circle of confusion. I understand that longer lenses have shallower depth of field than wide lenses. That the aperture being open leads to a more shallow depth of field, and that the opposite is true for a greater depth of field.


What other things make a big difference to depth of field?

I remember reading in a cinematography book at some point that a lens is at it's sharpest when shooting at around an aperture of 4. Is this true? If so. what techniques could be used to give greater depth of field with the aperture relatively low like that?

I know Greg Toland experimented with many lenses and also coatings on lenses to achieve the look he got. Is there a specific set of lenses that is best for deep focus?

Any answers to those questions would be great, as would any other thoughts you have on the topic.
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#2 Jock Blakley

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Posted 28 February 2012 - 11:33 PM

Toland also used compositing for some of the shots - there were many optically-printed mattes, for example. The shot where Kane bursts into the Susan Alexander's room after her suicide attempt was even performed in-camera; with the foreground shot in focus against a dark background the camera was then backwound and the shot reshot with the foreground blacked-out.

This is necessary because you will eventually run out of depth of field, and you'll do it quickly unless you have a lot of light.

Remember that simply using wide-lenses is not necessarily the best solution - as you reduce focal length you increase depth of field, yes, but you also change perspective and visually move the background further from the viewer, which will in turn diminish the apparent importance of that background - problematic if you want to block across the whole depth of the shot.

As to the "sweet spot" of any given lens: it is generally considered to be three or four stops down from maximum aperture - usually around f/5.6 or f/8 - though of course some lenses are specially optimised to be different and so may not adhere to this 'rule'.

As you would probably know many lenses are more-than-acceptably sharp when opened up more than that, but 99% of the time you will get the best performance out of a lens when in that ballpark.

Stopping down more actually reduces sharpness though a phenomenon known as diffraction, where the diaphragm actually scatters the light coming through the lens. The exact point where this becomes a serious issue varies based on lens and film size, but I generally don't like to stop down below f/16 unless I'm shooting 60 mm or larger.

Which is another thing actually - DOF changes with film or sensor size. The smaller the recording area, the wider the DOF.
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#3 Marcus Joseph

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Posted 29 February 2012 - 05:59 AM

Another consideration against stopping down is once you get past around f/11 the contrast also increases.
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#4 Benjamin G

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Posted 01 March 2012 - 03:47 AM

Thanks for the replies. I had forgotten about the effect of sensor size on depth of field. I've been using a 35mm adaptor for so long I forgot how huge a difference it was without it. For this feature I will be shooting with Epic's most likely, unless I can get my hands on a pair of Alexa's.

I agree about not wanting to shoot the whole thing with wide lenses, and that's why I'm curious about what other factors can be used so I'm not stuck with a limited lens selection. Compositing is definitely something I will need to do for a few of the shots in the script but I'm hoping to avoid it when possible since it will be harder to cheat perspectives in 3D.

If I were fo use lenses like the Cooke Panchro/i which are relatively slow at T2.8 and stopped them down 3-4 to get the best out of the lens (and add deeper depth) would you think that would give me a good start at what I'm looking for? Keeping in mind, the script all takes place in one house so the greatest distance would probably be 50 feet.

As for the comment on increased contrast could you explain that a little more? I was always under the impression that blacker blacks and whiter whites were a good thing. Or do you mean it lessens the dynamic range in a sense?
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#5 Marcus Joseph

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Posted 01 March 2012 - 11:05 AM

As for the comment on increased contrast could you explain that a little more? I was always under the impression that blacker blacks and whiter whites were a good thing. Or do you mean it lessens the dynamic range in a sense?

If it's the kind of look you're after then it can be a good thing, but in most productions you want to keep the contrast for the grade, cause it's harder to take away contrast than it is to add. Specifically shooting with higher end cameras.

It was something that Russell Boyd once said in a lecture I attended and it kind of stuck with me about how he avoids going over f/11 cause of the contrast increase. I'm sure someone else here could explain it in more depth though.
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