Zebra/ISO independence?

Just double-checked it. When I set my zebras to 100% they never change, no matter what ASA, no mater if raw or compressed, they are always the same.

Which makes perfect sense, since they show sensor clipping at hardware level, that has nothing to do with the recording format or metadata (ASA) settings. When the sensor clips it clips.

Super, thanks for checking that -- very helpful. Something must be going on with the camera I've got. Either that, or I've failed to operate the simplest camera out there. I never underestimate my capacity for user error!

If you have a Zebra set to 100% on the BMCC then it will always show sensor clipping.

Some people have seen slight differences between 1600 and 800 (but not 400 and 200) in terms of the way the DR works.

When I've pressed BMD about it, the engineers have told me there is a TINY difference in the way they map the 16 bit linear of the camera into the 12 BIT LOG of DNG @ 1600 ISO. So while there is the same DR, they allocate more bits to the bottom end (shadows). The idea being that any noise reduction later might be cleaner.

What this seems to sometimes mean is that there can appear to be a difference in where something ZEBRAS @100% in highlights, but I think all your seeing is a slight difference in the bit allocation.

If you take a bare lamp to JUST on the point of clipping, you shouldn't see any difference on the zebra between 800 and 1600 though. If there is, I'm going to go out on a limb and say it's wayyyyy smaller than a *stop* of difference.

What is amazing with this camera, and I've true;y yet to see this on other cameras, is that something that is near clipping still can look fine and be recovered. A lot of other cameras will have something up near 90% and they might as well be at 100%/

jb

Thanks for the details John. I spoke to BMD tech support about this yesterday, and you are correct. They confirmed that there is indeed something going on with recorded exposure when ISO is adjusted. Following the "Zebra And Back Off" method, bumping ISO from 800 to 1600 can drive hot parts of the frame back into zebra if they're close enough to clipping. For me it was one or two aperture clicks, a third or a half stop probably. I've done the bare lamp test and the open window test, and it's easily repeatable.

So... if the camera is ZABO'd (ha) at ASA 800, and then bumped up to 1600, it's a good idea to check the zebras again to make sure nothing's over the line. As a new user of the camera, it was confusing to watch an entire window jump from no zebra to completely blown out (overcast day -- the window was basically a giant grey card), and if for no other reason I think this is worth including in the documentation.

Thanks!

For the record, I understand what you're saying.

The zebras, at least before, were not supposed to change in RAW mode if at 100 percent, if you change ISO but I've observed that they do. I can understand that for ProRes, curious if something changed in the firmware as well.

You can easily check this by clipping something at 1600 then switching to 200.

However, I believe that if you simply rate the camera at 800 when shooting RAW, zebras at 100 percent will always tell you what's clipping. I've personally begun to rate the camera at 400 and 800, and meter at 1000 or 1250 for anything extremely lowlit.

EDIT: looks like John responded while I got on about typin'.

With that in mind, it's interesting that there is a change in the RAW when rating at 1600 and that it may be worth simply using 1600 for lowlight. Hmmm~

With that in mind, it's interesting that there is a change in the RAW when rating at 1600 and that it may be worth simply using 1600 for lowlight.

This is good news then for trying to get the best out of a low light situation or at least get more detail or less noise in the shadows when that is important while shooting raw. I had thought it was best to leave the ISO at 800 all the time for raw, but now it's best to judge if you want to protect more highlights (ISO 800) or reveal more in shadows (1600). It may not be a full stop difference as if it was a real film camera, but even a half stop is significant. Still expose to the right to avoid clipping highlights is the general rule, but shift to a higher ISO when you want as much in the shadows as you can get without clipping highlights.

Rick Lang
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Thanks for the in-the-trenches corroboration Kholi. I think they should update the docs with some more details on ISO vs sensor, if only to eliminate confusion for new users.

I just returned the rental, but after a couple days with the cam I generally get where it's coming from exposure-wise. Great image when well lit, but gets grungy fast in the shadows. Given the sensor size this is understandable. We were doing nighttime interiors, and even when the subject was exposed, backgrounds descended into noise and colors faded pretty quickly. We ended up pumping the whole room a couple stops with some tungsten flood bounce, raising key/fill/hair lights accordingly, and bringing everything down in post to get the darker vibe back.

Also, everything looked worse in ProRes, which was notably softer than RAW. Whenever possible I would shoot RAW with this camera, and give it as much light as possible.