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Deep dof with fast lenses


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#1 Jed Shepherd

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Posted 18 January 2011 - 04:42 AM

If a shot had to use natural light, meaning the lens had to be wide open but shallow dof is not required what could be done to correct this? Apart from raising iso on digital medium cameras, is it possible to have a reasonable iso, wide open aperture on a large sensor while keeping deep depth of field?
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#2 Stuart Brereton

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Posted 18 January 2011 - 06:30 AM

No. The only way to increase the DoF is to use a deeper stop. This means you would either have to use a higher ASA or augment the natural light to a higher level.
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#3 Chris Millar

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Posted 18 January 2011 - 06:50 AM

Wide angle lens - get closer

;)
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#4 Adrian Sierkowski

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Posted 18 January 2011 - 08:50 AM

Chris, that wouldn't work; if you got closer on a wider lens you'd be focusing closer thus reducing DoF....
you
'r only real option would be to back away, the further you are from your subject the more DoF you'd've had.
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#5 Stuart Brereton

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Posted 18 January 2011 - 10:23 AM

Wide angle lens - get closer



Chris, that wouldn't work; if you got closer on a wider lens you'd be focusing closer thus reducing DoF....
you
'r only real option would be to back away, the further you are from your subject the more DoF you'd've had.



Actually neither. If the field of view remains the same, at the same stop, on the same size imager then both would have the same DoF. The only way to change DoF is by varying the stop.
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#6 Adrian Sierkowski

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Posted 18 January 2011 - 10:28 AM

Sorry Stuart, I didn't phrase myself properly, I meant "reducing the Dof [normally associated with wider lenses]" And "move away," implied keeping the same lens on, not changing over to a longer lens for the same FoV.
This is why I have 2 cups of coffee in the morning.. 1 only get's 1/2 of the sentence.
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#7 Stuart Brereton

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Posted 18 January 2011 - 11:26 AM

Ok, sure, if you leave the same lens on and move back, the resulting longer focal distance with have greater DoF, but that doesn't help if you then cannot get the shot you want. If you need a Medium shot, then it doesn't matter whether you are close on a wide lens or backed off on a long lens - DoF remains the same and the only way to change that is to alter your stop.

If the shot absolutely cannot be lit and must be at a low ASA and therefore requires shooting wide open, I would suggest shooting on a wider lens. It won't give you any more DoF, but because objects in the background are smaller in frame, they appear sharper.
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#8 Chris Millar

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Posted 18 January 2011 - 04:29 PM

If the shot absolutely cannot be lit and must be at a low ASA and therefore requires shooting wide open, I would suggest shooting on a wider lens. It won't give you any more DoF, but because objects in the background are smaller in frame, they appear sharper.


;)

When I said get closer I didn't specify 'all things being equal' (which it wouldn't be anyway). Character blocking could be changed if need be...
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#9 Stuart Brereton

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Posted 18 January 2011 - 05:15 PM

The original question was about achieving deep depth of field in a shot that needed to be shot wide open, at a low ASA, and on a large sensor camera. You can change the blocking all you like, but you cannot change the laws of optical physics. This has been covered so many times before, and considering that we're in the student section of the forums, perhaps we should try to be accurate.....
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#10 Jed Shepherd

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Posted 18 January 2011 - 07:09 PM

Thanks for the replies. My question was just something i was wondering about. I normally light everything unless natural light is strong and can be bounced etc. I just see so many dslr videos where people open their lenses as wide as possible which results in focus being lost with the slightest movement. Just thought i would see if anyone had ever worked out some solution to my original question. I couldnt think up anything logical apart from lighting the shot.
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#11 Paulo Eduardo Uchoa

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Posted 18 January 2011 - 08:54 PM

Perhaps the best thing to do is use a camera with a smaller sensor. Because here is what I can see that will work against you

1. You are using natural light, so you need to close the aperture down and increase the ASA - Here you face adding noise (depending on the ASA) which you may disike.
2. Using a wide lens may affect how you frame the shot, once you start getting the camera closer you'll be right back with your DOF problem.

So like I said get a camera with a smaller sensor which has a deeper DOF so it will give you what you want.

DSLR's aren't KING to every single project.
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#12 Jed Shepherd

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Posted 19 January 2011 - 01:50 AM

Never even said dslrs were ok. Was just using them as an example because of the millions of videos on the internet filmed on them in comparrison to any other new age hd digital cinema camera. But dslr's arent too bad. But i would much prefer to shoot on red or film etc if i could.
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#13 Paulo Eduardo Uchoa

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Posted 19 January 2011 - 01:33 PM

Never even said dslrs were ok. Was just using them as an example because of the millions of videos on the internet filmed on them in comparrison to any other new age hd digital cinema camera. But dslr's arent too bad. But i would much prefer to shoot on red or film etc if i could.



RED and 35mm film are large sensors just like the DSLR, so you would still have the same issues.
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#14 Michael Kubaszak

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Posted 19 January 2011 - 08:09 PM

RED and 35mm film are large sensors just like the DSLR, so you would still have the same issues.



For the most part, HDSLR's don't use Cine lenses.
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#15 Jed Shepherd

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Posted 20 January 2011 - 07:21 AM

RED and 35mm film are large sensors just like the DSLR, so you would still have the same issues.

I know they have large sensors. Saying to swap to a smaller sensor doesnt seem like a good solution. The reply above mine about cine lenses makes sense. My question was just stupid really. Using natural light only when its dark seems useless. But i guess darkness might help some focus issues. Maybe...
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#16 Stuart Brereton

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Posted 06 February 2011 - 11:32 AM

For the most part, HDSLR's don't use Cine lenses.



A 50mm lens is a 50mm lens. It makes no difference if it is a PL mounted Cine lens or a stills lens, it will have the same DoF characteristics.
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#17 Chris Keth

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Posted 06 February 2011 - 01:18 PM

Just light the scene. I don't see why it's so hard to grasp that movies need to be lit to look good in 99.99% of locations. If you can't light it to a decent stop, I hope you're smart enough to spend the money to hire a good focus puller. He/she may be able to give you enough of it sharp to cut the scene.

Edited by Chris Keth, 06 February 2011 - 01:18 PM.

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#18 K Borowski

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Posted 06 February 2011 - 02:43 PM

Ditto what Chris said.

They managed to get great DOF, exposure shooting everything on stocks 3-1/3 stops slower in the '60s. WHy could they light to 50T film with, in general, slower primes and slower zooms?

And their lights weren't cheaper. They were hotter, had shorter lifespans. The film wasn't the most expensive part of production, even back then with 35mm color neg costing I think 3-4 times as much as it does today.



It was and is the lights and talent that operates the camera sets up the lights that gives you good-looking results, not what model DSLR you have or a Platinum with Carl Zeiss glass.

I've heard an aweful lot of positive things said about DSLRs. Not just in cinematography, but in still photography I had and still do find the quality of the images they produce to be abyssmal. The same garbage that they had to deal with in the '50s with video cameras we STILL have to deal with 60 years later?

Surely this must be some kind of sad joke!


Does anyone know, BTW, if the Starz cancelled series "Gravity" was shot on a DSLR?



Personally, if this were my problem, and I couldn't find the light (I'd be shooting S16 or better, of course), I'd try to cheat with lower framerates. Obviously this isn't' doable with dialogue, stunts.

Despite the trend to want to shoot everything wide-open, I tend to try to stop down 2-1/2 stops to the sweet spot of a lens whenever I'm shooting.
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#19 Jed Shepherd

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Posted 09 February 2011 - 08:58 PM

Just light the scene. I don't see why it's so hard to grasp that movies need to be lit to look good in 99.99% of locations. If you can't light it to a decent stop, I hope you're smart enough to spend the money to hire a good focus puller. He/she may be able to give you enough of it sharp to cut the scene.

Guess i should clarify. I am not trying to find a way of not using light. It was just a random question that popped into my head. Im all for lighting scenes.
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