Exposing properly with Dual ISO cameras

[kye]

Just saw this video and thought it would be useful for those with Dual ISO cameras like BMPCC4K, GH5S, etc..

Includes how Dual ISO works, impacts on DR, and how to expose - really great content from John Hess.

 

[AlexTrinder96]

Brilliant stuff! I think Blackmagic should include this video with every camera they sell. Seriously. 

 

Cheers @kye

[kye]

I'd recommend the other videos from John on that same channel too.  Thorough, well researched, clearly explained, and is one of the very few film-making channels that remembers that there were films before the year 2000.

[leslie]

well that was quite interesting and informative i think i'll be watching that again

[KnightsFan]

This is a great video. Very clear, concise, and informative, as are the few other videos by Hess that I've watched.

I think it would be much better if, instead of giving a single ISO value, the camera just displayed that DR bar graph that simply shows where middle grey is measured, and the number of stops over and under that are retained. It's a shame we're stuck using ISO ratings to describe exposure, even after technology has moved beyond film stocks.

[UncleBobsPhotography]

It seems like setting ISO to 400 or 3200 and ETTR would be the easiest way to get the same results as using "high ISO for bright scenes" and "low ISO for dark scenes".

[Anaconda_]

Yes, but since your iris and shutter determine the look of your footage, by strictly using 400 and 3200, you're essentially locking your iris, shutter and ISOs, which will give you very little freedom in how to adjust your exposure - either NDs or lights. Then if you don't have a controlled environment, you're limited to NDs only. I much prefer to use the ISO to help me expose, rather then limit my shots more than they need to be.

[webrunner5]

Speaking about ISO.

https://www.redsharknews.com/technology/item/1966-understanding-iso-in-digital-cameras,-it-s-not-what-you-think-it-is

11 minutes ago, Anaconda_ said:

Yes, but since your iris and shutter determine the look of your footage, by strictly using 400 and 3200, you're essentially locking your iris, shutter and ISOs, which will give you very little freedom in how to adjust your exposure - either NDs or lights. Then if you don't have a controlled environment, you're limited to NDs only. I much prefer to use the ISO to help me expose, rather then limit my shots more than they need to be.

Yeah from what I have seen from this camera there is not much freedom to just pick any ISO you want or need. When it works it works, but that is not a dependable solution for lots of situations. Having to use ND filters a lot of the time is not ideal. But I guess it is just the price yo have to pay for more of a Cine camera over a true Hybrid.

[Anaconda_]

That’s not true. 

You can use iso 100 to 800 perfectly fine. Skip 1000 and go from 1250 up. You (I) only consider the noise etc. once you hit 6400 or more. 

400 and 3200 are of course ideal, but it’s far from a hard limit one should never deviate from. 

Like he says in the video , as long as you understand the benefits and pitfalls of the settings, you can make educated and informed decisions on a scene by scene basis. 

Limiting yourself to 400 and 3200 can of course work, but it’s not a rule I would follow unquestionably. 

[KnightsFan]

1 hour ago, Anaconda_ said:

Yes, but since your iris and shutter determine the look of your footage, by strictly using 400 and 3200, you're essentially locking your iris, shutter and ISOs, which will give you very little freedom in how to adjust your exposure - either NDs or lights. Then if you don't have a controlled environment, you're limited to NDs only. I much prefer to use the ISO to help me expose, rather then limit my shots more than they need to be.

Any setting below 1250, and the data recorded is the same. Changing ISO from 100-1000 only changes the curve that determines where "middle grey" is mapped within the range from noise floor to saturation. In other words, from ISO 100-1000... iris, shutter speed, NDs, and lighting are the only ways to change the data that is recorded. Adjusting ISO within that gain range doesn't actually adjust "exposure" anyway.

(Of course I'm assuming we're talking about Raw or Log on the P4K.)

2 hours ago, UncleBobsPhotography said:

It seems like setting ISO to 400 or 3200 and ETTR would be the easiest way to get the same results as using "high ISO for bright scenes" and "low ISO for dark scenes".

That's one way to do it. I think Hess's video is most useful for exposing with a light meter, because "high ISO for bright" and "low ISO for dark" is 100% relative to properly exposing for middle grey. If you are at ISO 400 and your grey card is one stop under, Hess's method implies adding TWO stops of light and then changing to ISO 200. Which is essentially the same as adding your two stops of light, staying at ISO 400, and then dropping down a stop in post.

Your method chooses an ISO based on the ratio of over exposure latitude vs. under exposure latitude, and then you adjust iris/shutter/ND/lights for exposure, because those are the only things that actually affect the data recorded (apart from the 400 vs. 3200 gain switch)

[Anaconda_]

7 hours ago, KnightsFan said:

Any setting below 1250, and the data recorded is the same. Changing ISO from 100-1000 only changes the curve that determines where "middle grey" is mapped within the range from noise floor to saturation. In other words, from ISO 100-1000... iris, shutter speed, NDs, and lighting are the only ways to change the data that is recorded. Adjusting ISO within that gain range doesn't actually adjust "exposure" anyway.

(Of course I'm assuming we're talking about Raw or Log on the P4K.)

Well this whole discussion goes out the window if you're talking about RAW. Like you say, as long as you're in the right ISO bracket, you're good in that case, sticking to 400 or 3200 is irrelevant. I was assuming we're talking about filming in ProRes and wanting to expose right in camera, in which case ISO plays a big part.

[KnightsFan]

37 minutes ago, Anaconda_ said:

Well this whole discussion goes out the window if you're talking about RAW. Like you say, as long as you're in the right ISO bracket, you're good in that case, sticking to 400 or 3200 is irrelevant. I was assuming we're talking about filming in ProRes and wanting to expose right in camera, in which case ISO plays a big part.

For sure! Even when shooting raw it is worthwhile to visualize the shot as it will be graded, even if it is just metadata. I guess i was mainly talking in the framework of hess' argument.

[mercer]

I thought ISO worked the same in the P4K as it does with the Pocket/Micro... you’re taking a DR/noise hit when you stray away from the native ISO? I believe that is why the OG Pocket originally used ASA instead of ISO.

10 hours ago, Anaconda_ said:

Yes, but since your iris and shutter determine the look of your footage, by strictly using 400 and 3200, you're essentially locking your iris, shutter and ISOs, which will give you very little freedom in how to adjust your exposure - either NDs or lights. Then if you don't have a controlled environment, you're limited to NDs only. I much prefer to use the ISO to help me expose, rather then limit my shots more than they need to be.

Obviously, you can use ISO to expose, but aperture, NDs and light has kinda been the go to method for exposing on cinema cameras since forever.

In the P4Ks case, the Dual ISO feature was so exciting at the announcement because the OG Pocket only had a single ISO that was usable... 800. And since the P4K’s native ISOs are 400 and 3200, the camera instantly became a goodlight and lowlight camera where you could use less ND filtration and less light than the Pocket needed.

With that being said, times change and if you’re not noticing that much of a hit in noise/DR/saturation, then that’s good news!

[zerocool22]

Captain hook from BM shared this on bmcuser.

"Native" ISO is what we determine is the best compromise of noise and dynamic range distribution (over/under). It doesn't necessarily mean the most dynamic range, the most even distribution, or least noise. It's more our 'recommended starting point'.

[Kisaha]

1 hour ago, zerocool22 said:

Captain hook from BM shared this on bmcuser.

"Native" ISO is what we determine is the best compromise of noise and dynamic range distribution (over/under). It doesn't necessarily mean the most dynamic range, the most even distribution, or least noise. It's more our 'recommended starting point'.

that is not very scientific though, and doesn't explain much!

[zerocool22]

48 minutes ago, Kisaha said:

that is not very scientific though, and doesn't explain much!

Well yeah, but at least for me it means "Dont stick to the native iso's and try some stuff out if needed." 

[thephoenix]

the thing is, if you follow his advice, that you would shoot 1200iso in daylight and 400 at night.

so why constructors spend time and money building dual iso cameras ? as most of us need high iso to shoot at night and low to shoot in daylight.

people doing photography are used to zone system, at least the one that shot print film.

you just need to set the exposure for the result you want more than for standards exposures.

with film we used to expose as wanted and we processed the films with order in order to complete the process

[Shirozina]

Good advice for anyone who uses middle grey as an exposure method but using middle grey as and exposure method may not be good advice.....

[Shirozina]

The P4k does some strange things when you change ISO ( or perhaps perfectly logical things?). At 100 ISO the IRE % on my Ninja V scopes max out at 80% i.e no matter how bright the content of the frame the levels won't to push past 80%. This increases gradually up to 100% at 400 ISO. If you ETTR with the zebras anywhere between 100 and 1000 ISO the highlights remain the same and all that changes is the brightness of the shadows and midtones. If all the camera is doing is internally applying 'digital gain' when you change ISO then this is quite logical and between 400 and 1000 ISO you just use ISO like a 'brightness' adjustment which lifts the shadows and midtones but preserves the highlights.

[mercer]

10 minutes ago, Shirozina said:

The P4k does some strange things when you change ISO ( or perhaps perfectly logical things?). At 100 ISO the IRE % on my Ninja V scopes max out at 80% i.e no matter how bright the content of the frame the levels won't to push past 80%. This increases gradually up to 100% at 400 ISO. If you ETTR with the zebras anywhere between 100 and 1000 ISO the highlights remain the same and all that changes is the brightness of the shadows and midtones. If all the camera is doing is internally applying 'digital gain' when you change ISO then this is quite logical and between 400 and 1000 ISO you just use ISO like a 'brightness' adjustment which lifts the shadows and midtones but preserves the highlights.

How’s the rolloff seem on the scopes at 100 iso?