Blackmagic Forum

Hi,

I've gone through the 5 stages of denial, anger, bargaining, depression and finally acceptance which helped me to change my order from EF to a BMCC MFT.

This version is able to shoot with faster lenses e.g. Voigtlander 17mm or 25mm at f0.95 or SLR Magic 12mm f1.6 etc. I wonder for productions for use both in a studio and outside, are there any disadvantages or difficulties when using these faster lenses as compared to shooting at e.g. f4, or with slower lenses for example?

Thanks for any insights,

Jules

Couple of lens-independent problems with opening right up.

• Some lenses get soft at their maximum aperture.
• Depth of field is so thin that it's difficult to maintain focus on moving objects or subjects
• Chromatic aberrations appear. Often the two sides of the focal plane will have opposite colour fringing (for example, my Zeiss 35mm F1.4 has purple on the close side and green on the far side).
• Vignetting can go as extreme as a 2-3 stops around the edge.

Off the top of my head.

Nick raises a few good points.

Conversely, you'll often find that fast lenses perform better at more 'normal' apertures.

Most lenses operate at their best for Cinema at an aperture between f2.8 and f5.6

So if you have a 50mm f1.4 lens and a 50mm f2.8 lens, I'd always go for the f1.4 as it will likely be sharper at f2.8. Just because I own an f1.4, doesn't mean I'll often use it wide open.

Its worth bearing in mind that the two lower and higher stops - e.g. f1.4, f1.6 and f20, f22 will not be lens' best for any issues it may have. You'll often find that you get some abberation, vignetting etc on cheaper lenses at these apertures.

Roger Deakins likes to shoot all his interiors at f2.8 and his exteriors between f4 and f5.6 where he can.

Luke Armstrong wrote:Nick raises a few good points.
Roger Deakins likes to shoot all his interiors at f2.8 and his exteriors between f4 and f5.6 where he can.

What about for green screen work? I have an actor in front of another actor, I'd want them both to be in precise focus right? That would mean a deeper DOF. I noticed that Avatar was shot, obviously using a lot of green screen work, but on a 2/3 sensor camera. That would automatically have a deep DOF.

HOw would I control depth of field to be deeper?

Nick Bedford wrote:Chromatic aberrations appear. Often the two sides of the focal plane will have opposite colour fringing (for example, my Zeiss 35mm F1.4 has purple on the close side and green on the far side).

I know this existed but didn't know it varied across aperture setting, interesting. I have read software can correct this. Is this done automatically or would I have to adjust shot for short? Is this something DaVinci Resolve fixes and easily? Actually for chroma keying I'd want this earlier in the pipeline. Maybe in the editor it is best to do the correction?

Thanks for any help,
Jules

Jules Bushell wrote:What about for green screen work? I have an actor in front of another actor, I'd want them both to be in precise focus right? That would mean a deeper DOF. I noticed that Avatar was shot, obviously using a lot of green screen work, but on a 2/3 sensor camera. That would automatically have a deep DOF.

HOw would I control depth of field to be deeper?

That's up to you. Its not necessary - most DP's shoot greenscreen the way they want the final shot to be. If you want a wide deep focus shot you shoot it deep focus with a high aperture. If you want a long lensed shallow dof you shoot it that way with a low aperture. So long as your subject is in focus it doesn't matter. This has been the case for the movies I have worked on.

If you want a deep depth of field - stop down. There is no rule that says you shouldn't. Anything greater than f5.6 will be reducing the depth of field quite dramatically. You'll need a lot more light.

I'm not sure what 'Avatar' was shot on. But I understand the sequel is being shot on Red Epic for the live action parts.

Luke Armstrong wrote:I'm not sure what 'Avatar' was shot on. But I understand the sequel is being shot on Red Epic for the live action parts.

Sony F23, Sony HDC-1500, Sony HDC-F950... afaik at first they used two F950 on their 3D rig, later on switched to two HDC-1500...

So no full frame there, completely shot on 2/3" sensors

I would say that 'Avatar' is probably the exception rather than the rule.

With Avatar, the 2/3 sensor is a boon because it's in 3D, not specifically because it's greenscreen.

All lenses get softer wide open, most lenses vignette wide open, and all lenses have sweet spot where it is the sharpest and looks the best optically. This is usually 2-3 stops from open, so generally the faster the better, that means your sweet spot will also be faster.

Nick Smith wrote:With Avatar, the 2/3 sensor is a boon because it's in 3D, not specifically because it's greenscreen.

I guess when shooting for 3D where it takes priority over normal 2D, having really shallow DOF would seem more forced upon to the viewer. Is that what you meant?

Also, would anyone know if shooting for 3D using two BMCCs be practical/possible considering there is no gen-lock?

Jules

Jules Bushell wrote:

Nick Smith wrote:With Avatar, the 2/3 sensor is a boon because it's in 3D, not specifically because it's greenscreen.

I guess when shooting for 3D where it takes priority over normal 2D, having really shallow DOF would seem more forced upon to the viewer. Is that what you meant?

Also, would anyone know if shooting for 3D using two BMCCs be practical/possible considering there is no gen-lock?

Jules

I have seen numerous 3D shorts shot with 2 canon DSLR's sans GenLock. So anything is possible if you put your mind to it

cmckinlay wrote:I have seen numerous 3D shorts shot with 2 canon DSLR's sans GenLock. So anything is possible if you put your mind to it

I did a Google and apparently should be able to sync the cameras with LANC but then it mentions the cameras will drift out of sync (like any camera I guess). I'm not sure why they would ever drift, being 100% electronic and no mechanical tape transport etc. Of course no one's had the luxury to test this on 2 BMCCs. On various threads people just give up without genlock so I guess it isn't possible to get professional grade 3D footage on the BMCC without it?

I'll ask this on another thread as it's a bit off-topic.


Cheers,
Jules