How far can you stop down with the brevis?

D

davide

Well-known member
How far can you stop down with the brevis on something like a 50mm 1.4 lens before seeing grain? And does anyone know how much DOF they get at this f-stop? When using the brevis can I go by the markings on the lens to figure out how wide the DOF, or will the brevis change that so the that the DOF is wider at a given f/stop?

I'd like to use an adapter for my next project so that there's a gentle fall-off into out out of focus backgrounds, but I don't want to be rackfocusing between faces in a dialogue sequence. Whenever I saw that done in the Shield or Infernal Affairs II it took me out of the action. So I'm wondering how far I can stop down on a standard 50mm lens with the brevis without getting grain and how wide of a DOF that'll give me.
 
f/5.6 with a 1/48th shutter is as far as I personally go on primes. For some reason I can get down to f/8 on my zooms without grain showing.
 
First I would presume you mean the CF1 series of screens on the Brevis.
No further than 5.6 for sure. I haven't tested carefully, but personally i would test before going above f4 just to be sure if you plan to blow up.

William have you looked at the 5.6 images on a big monitor to be sure?

Marco should have a good idea since he's been shooting features with it.

You will get the deepest DOF with the Brevis, and I presume (only presume) that's because there might be the least additional loss of DOF due to the adapter screen itself.

As for whether you can trust the lens markings - are you referring to any DOF markings your lens barrel may have or trusting charts? In either case I haven't read any careful tests of that here though I'd like to hear from people who have.

Because of the lack of linearity in the Brevis response to the iris change its an open question how it will track DOF. My guess though is that if anything you will have more DOF than the markings or charts. From 1.4 to 2.8 I saw no change in DOF (along with exposure) at all, though Dennis said he did.

Hope that's helpful - lots of guessing though.

Lenny levy
 
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Yes forgot to mention all my data is with the CF1L. As for testing, this piece I did used the Brevis on everything. I have watched on a 42" plasma, 57" rear projection, and 120" projection and haven't seen anything objectionable sans a couple shots. On those, I was f/8 on my zooms shooting 60i @ 1/120. I see it because I know exactly where it is. I doubt is even 1% of my audience sees it.

I don't really trust the Brevis to act exactly as if I was using a SLR still or an actual film camera. You need to strap one on and go shoot to find all it's little quarks. It is a great piece of kit though, and it lives on my DVX.
 
Thanks guys. When I mentioned DOF markings I meant those on the lens. When I stop my 50mm 1.4 down to f/5.6 I get about a foot of DOF. Is that about what you guys are getting with the CF1? It'd be awesome if there were more, like a foot and a half or two feet.

davide
 
Don't trust those markings while on a Brevis ( or any of these adapters is my guess.) You probably have more DOF but there is no guide other than your own research.

William - that's great to know and I agree with how you are using the lenses - figure them out according to their own behavior.

_ Lenny

Lenny
 
It's pretty safe to stop down to f/5.6 but as always shutter speed and the HVX's aperture make a difference. Also some lenses may not be entirely accurate and might be slower at f/5.6 than they should be. I would recommend to use Focus Assist and zoom into a bright white area (properly exposed of course) and check f/4.0-f/8.0 to see where the static grain starts to appear.


Marco

P.S. The CF1's depth of field at f/5.6 is much like f/11 on the other adapters so deep focus isn't so hard.

P.P.S. It's pretty much pointless to stop down on CF2 or CF3 because grain will immediately show.
 
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