FilmmakerIQ on Dual ISO, DR and the BMPCC4K

Following John Hess's excellent tutorials on DR, Exposure and Digital Sensors is this great discussion of the 4K's Dual ISO and how to use dual ISO with this camera

Paul, thanks for posting that. John is a sage. I’ve said previously that you want to use a higher ISO setting on bright scenes if those highlights are important and lower ISO on dark scenes when you want shadow detail. But tests on the URSA Mini 4.6K sensor posted to the forum led us to conclude ISO 400 overall may be better choice than 200 for most scenes.

When I’m able to test the BMPCC4K, I kay conclude ISO 200 is a generally better choice than 100. The video was very good at illustrating how stops above and below middle grey changed with ISO setting. Seeing what happens to the noise floor with ISO 1250 was impressive and confirms the amazement of several folks at how clean 1250 can be.

I wish John had illustrated the charts for settings at ISO 3200 and 6400.


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The problem with that video is that it doesn't consider the ill-effects of adding digital gain. Boosting "native" iso 400 to 1000 on the expectation that it magically provides more highlight capture, because you can reduce the exposure, never considers what would have happened if the iso remained at 400, but the shot was intentionally under-exposed to capture the same highlights, with any necessary gain added in post, rather than in-camera.

True, you can add some gain when you’re shooting highlights, but it’s not a good technique when you’re trying to see into the shadows where noise may kill the shot.


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This is the most important info about the camera I've seen yet. Should be required viewing.

Here's a great explanation on ISO and exposure by Tony Day.

Here's a great explanation on ISO and exposure by Tony Day.

Great explanation and what I observed a while back. ISO is not 'gain' in the traditional meaning where the exposure is changed but simply a midrange curve boost. Best seen in the later part of the video when shooting RAW and the develop setting set to clip. The P4k only has 2 traditional 'gain' settings which relate to how ISO working in other cameras.

Shooting Braw 12:1 with actors in a sunlit office, my actors were more or less in shadow.

I shot both open aperture with low iso, or high iso closing the aperture more...

Having lower iso produced far better results when I worked with the files in post. They were cleaner, and I could recover shadow detail.

Higher iso recorded files had nowhere to go with shadow detail. And those files exposed high had noticeable infrared noise from the BMPCC4K. I didn’t see much noise or change in the highlights. So I am planning to only think about shadows as I expose my shots in the future, and making those adjustments physical- ie lens, lighting, shutter angle.







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Shooting Braw 12:1 with actors in a sunlit office, my actors were more or less in shadow.

I shot both open aperture with low iso, or high iso closing the aperture more...

Having lower iso produced far better results when I worked with the files in post. They were cleaner, and I could recover shadow detail.

Higher iso recorded files had nowhere to go with shadow detail. And those files exposed high had noticeable infrared noise from the BMPCC4K. I didn’t see much noise or change in the highlights. So I am planning to only think about shadows as I expose my shots in the future, and making those adjustments physical- ie lens, lighting, shutter angle.

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Yeah.

Thanks Michael. I’ve encountered the image before. I’m curious what this image means to you. Because it confused me before my first BRAW shoot.

The detail the image didn’t clarify for me before working with BRAW is that the each block of iso values is what seems to matter more shooting braw than individual iso.

Resolve even locks you into either the 100-1000 and under, or 2500 and and up when changing iso values in post. Even at 12:1 it doesn’t seem to matter what iso you are shooting at.

Again, shadow noise is more obvious than highlight detail loss. So shooting in Braw I’d recommend setting the iso at 100 or 1250 and exposing leniently for blacks at that level. Then noting and cutting light based on 100% zebra cut off values for highlights... if anyone has a caveat to add to that I’d love to hear it.


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Caveat I
You can see from the dynamic range chart that exposing for ISO 100 or lower isn’t going to do much for your highlights; you won’t see much graduation so you want to be cautious going that low. When the really important elements of your scene are in the low ranges, you will help using ISO 200 instead of the base ISO 400.

Caveat II
You risk clipping in a single colour channel if you expose with zebras set at 100%. For example your blue might clip but not red and green. The zebra won’t show the area clipping if only one channel clips, but when you’re in the NLE, you’ll see the colour is wrong. Recommend you set it at 95% which Frank Glencairn uses (typically with some controlled lighting) or set it to 90% to be a little safer.

Caveat III
Don’t rely on the histogram and zebras to set exposure. Use False Colour and your experience to determine your exposure even if you intentionally want to favour shadows.


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Thanks Michael. I’ve encountered the image before. I’m curious what this image means to you. Because it confused me before my first BRAW shoot.

The detail the image didn’t clarify for me before working with BRAW is that the each block of iso values is what seems to matter more shooting braw than individual iso.

Resolve even locks you into either the 100-1000 and under, or 2500 and and up when changing iso values in post. Even at 12:1 it doesn’t seem to matter what iso you are shooting at.

Again, shadow noise is more obvious than highlight detail loss. So shooting in Braw I’d recommend setting the iso at 100 or 1250 and exposing leniently for blacks at that level. Then noting and cutting light based on 100% zebra cut off values for highlights... if anyone has a caveat to add to that I’d love to hear it.


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To me, it is something I'd heard people talk about before but never really understood (and I"m still mastering it). In dark scenes (like you describe against a window), you're more concerned with shadow detail (stops under middle gray) than with saving highlights.

Shooting low ISO (100, for example) gives you 11 stops of details in your shadows. These can (theoretically) be lifted without generating a lot of shadow noise (and this is also the part that I'm still mastering - how much can I lift those shadows and still retain detail without introducing noise).

So it's pretty much exactly what you describe - the dual ISO circuits do lock your values in post, but even then you can still raise and lower exposure, you're just more likely to introduce noise if you're bringing up shadows too much.