Blackmagic Forum

Hi all,

are the BMCC 2.5k and BMPC 4k able to autofocus in an area other than the center of the screen?
(I know continuous AF is not possible, but I am talking of AF before pressing the record button)

Thanks!

It's a fixed center box on the P4K.

On my BMPC 4K, if you touch the screen where you want to focus for one second, the focus is made there and when you press the focus button the next time (on the camera or on the gimbal), the focus is made at the same place. Pressing two time quickly, it focus on the center.

Ahh, hold the screen.

Would you mind telling me which camera version you are using?
On my cam, tapping the screen once brings up the Metadata screen;
Tapping the screen twice zooms in the center;
Pressing focus twice toggles focus peaking on/off
Pressing focus once toggles autofocus.
Pressing and holding on the screen just opens the Metadata screen on release.

Also, di you or someone else ever use an URSA mini handle or another kind of handle to trigger autofocus?

Thanks.

Update: The BMPC 4k works with the Blackmagic URSA Mini Handle. Auto-Iris exposure, Autofocus (albeit very slow, Accurate with Canon Lenses, not so much with Tamron) and Record button all work as expected.

Now, some important info scattered across forum posts, but not clearly stated:

No matter which ISO you select (200,400,800), the output on the SDI out is fixed (Not compensated).
What it means is that you need to take ISO into account when using False colors on an external monitor, and the histogram (Built-in or External).

At ISO 200, the highlights will clip >80 IRE
At ISO 400 the highlights will clip >90 IRE
AT ISO 800 the highlights will clip at 100 IRE

There is no floating line on the internal Histogram. So if you record at ISO 400, for example, you may think that because the signal isn't all the way to the right, your highlights are safe, but those will clip in a quite ugly fashion if your signal is above 90 IRE (Same logic applies to the false colours: It will never hit the Red no matter how bright you expose at ISO 200 and 400). So to be safe, you need to set the Zebra at 80%-ISO 200 and 90%-ISO 400; and use that as the upper limit, if you want to be able to recover your highlights cleanly.

This also means that in reality, the camera doesn't use the full 12 bits at ISO 200 and 400, because the signal is recorded at a lower level in the 12bit container.

You also need to make sure any low-level signal you plan on lifting is recorded above 30 IRE, because the fixed-pattern noise starts appearing below 30 IRE and is clearly visible at 20 IRE and below.

Now, it took me a half day of recording with the cam to notice all of those things. One has to wonder what kind of beta-testing blackmagic used back then, because none of that info is clearly stated anywhere...

Conclusion: If you plan on getting this cam second-hand to record where the lighting is not 100% under your control, you will be better served with a different model. If you record under controlled conditions, the image is very good.

gabriielangel wrote:This also means that in reality, the camera doesn't use the full 12 bits at ISO 200 and 400, because the signal is recorded at a lower level in the 12bit container.

That is an erroneous call based on the display not the data. There's no difference in the sensitivity, dynamic range, or raw data shooting at 200, 400, 800, or 1600. When shooting raw, Blackmagic, Arri, Red, etc., are ISO invariant. Shooting Prores, yes, one is using less of the bucket at lower ISOs.

FYI this was discussed ad infinitum…a decade ago.

Good Luck

Howard Roll wrote:That is an erroneous call based on the display not the data (...) Shooting Prores, yes, one is using less of the bucket at lower ISOs.
(...)
FYI this was discussed ad infinitum…a decade ago.

As you probably know, several people shoot Prores directly or convert Cinema DNG to Prores to facilitate Edits and save a little on storage. It would be a lot more constructive if you provided at least one link where the topic is explained clearly. Even though it has been "discussed ad infinitum… a decade ago.", do a quick search on the forum and you'll see that finding a concise and precise answer is kind of a safari...

Agreed, the internet sucks. Most descriptions of ISO invariance aren’t even correct. That said, you’re gonna have to do your own research or take my word for it. I’m not Jeeves.

Good Luck

gabriielangel wrote:

Howard Roll wrote:That is an erroneous call based on the display not the data (...) Shooting Prores, yes, one is using less of the bucket at lower ISOs.
(...)
FYI this was discussed ad infinitum…a decade ago.

As you probably know, several people shoot Prores directly or convert Cinema DNG to Prores to facilitate Edits and save a little on storage. It would be a lot more constructive if you provided at least one link where the topic is explained clearly. Even though it has been "discussed ad infinitum… a decade ago.", do a quick search on the forum and you'll see that finding a concise and precise answer is kind of a safari...

Slimraw could be a good solution to reduce space of cdng.


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