changing ISO change RAW file ??

I've been told that with RED, changing the ISO settings on camera have no actual effect on the file. It'll change what your monitor looks like, and it'll be recorded as metadata that you chose that particular ISO. But the end result isn't effected at all if you set it to 1600 instead of 400. The sensor is always the same sensitivity, regardless of settings.

By contrast, Canon 5D actually makes the sensor more sensitive when you push the ISO setting higher, so that does in fact change the RAW file.

Anyone know if this is the same situation with BMCC?

With a BMCC recording in RAW mode, changing the ISO setting only changes metadata, not video quality. The RAW video quality is unaffected by changes in ISO.

On all cams, including the BMCC, when recording in a compressed mode (ProRes, DNxHD, h.264, AVCHD, etc.), changing the ISO affects video quality in many ways, especially dynamic range & noise. These effects are "baked into" the compressed video.

Like most cams, the BMCC records its best DR (in ProRes & DNxHD modes) at its "native" ISO setting (which for the BMCC is ISO 800). Raising the ISO tends to make noise more visible, and lowering the ISO tends to crush noise in the shadows. In compressed modes, video quality is best when using ISO 800, and adjust exposure by adjusting the lighting, or aperture, or shutter angle, or use ND filters.

Thanks Peter, that's what I was looking for.

So is it accurate to say that if you're shooting RAW on bmcc, you should basically just pretend that you're shooting on film and the only available stock to you is 800?

Or in other words, if you're shooting RAW, what reason is there to EVER change the ISO settings from 800 (other than to just alter the DISPLAY you're looking at) ??

When shooting BMCC RAW, the ISO setting in metadata is available to post software, for example as a way of indicating the "stock". Some post software use this metadata bit to adjust the brightness of the initial preview.

Since I'm not supposed to post links here to other forums, I hope it's OK if I copy & paste what John Brawley posted recently on the BMCuser.com forum:

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01-04-2013 08:28 PM

The zebra always shows sensor clipping, no matter your ISO or record mode (film / video) or record codec.

The zebra also works in linear space so that's also why it behaves differently to other zebras which tend to work in 709 space or not at all properly (like RED)

The ISO settings only change the way the files is viewed on the back of the screen in DNG recording and if in ProRes, it changes the curve recorded.

Changing the ISO doesn't change your sensor exposure. If something is just clipping at 800 ISO, it will still be just clipping at ISO200. What will change in ProRes or DNx is that the bottom end will crush or lift.

The sensor always shoots at the same ISO. No matter if you agree with BMDs view that it's 800 or not is up to you. But changing the ISO won't change what is happening at the sensor level.

This is why I prefer to use in camera tools like this instead of a light meter at ISO 800 for exposure. I can tell immediately what's clipped and what's not. That's more important to me than where to position the meat of the exposure.

What I do now is look at what's clipping via zebra, then putting the display mode into VIDEO you'll get a good sens of what looks right. When it's super bright, like the recent beach footage I shot, I'll drop the ISO so that The on-camera DISPLAY looks better and is easier to judge by. -- JB

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01-04-2013 08:49 PM

Well here's the thing.

My understanding is that because it's linear the Zebra levels don't relate to IRE.

In other words, 70% isn't 70% of your dynamic range.

So in linear, it's like the opposite of LOG. If there was a 50% value then it would be 1 stop less exposed than what it shows at 100%.

The reason they have chosen this idiosyncratic zebra behaviour is because it kind of overrides all view, monitoring, codec options and will always tell you where that value is no matter how your exposiing, rating and shooting. Which is kind of what the camera does.

Unlike a RED where you can change and influence the way a zebra performs depending on how you rate the ISO, even thoughts always shooting the same base ISO.

That's why I say it's a linear zebra. It's also really only good for showing you clipping or near clipping.

If they were to make it behave like normal zebras you expect, you might end up getting into trouble and judging exposure based of a curve LUT as opposed to what you're doing at the sensor level.

This is also why you can so accurately expose to right. Your absolutely can tell when the sensor is clipping or not.

It's kind of like a really fine highlight zebra.

The old TV rule was to put skin tones at 70% but you're actually putting them a lot higher if you use this rulewi is zebra on the BMCC.

JB.
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I've had my bmcc for a couple weeks now and really love the results I'm getting. When shooting in ProRes do I gain more DR by shooting in "film" rather than "video" and I'm not referring to the display mode. Sorry if this was already addressed.

I've had my bmcc for a couple weeks now and really love the results I'm getting. When shooting in ProRes do I gain more DR by shooting in "film" rather than "video" and I'm not referring to the display mode. Sorry if this was already addressed.

Yes, by recording in FILM mode, you retain more DR than VIDEO mode. Not quite as much as you would in Raw mode - but its the next best setting.

Now I just wish that VIDEO mode would show up through the SDI port. As of right now, it's only FILM.

Now I just wish that VIDEO mode would show up through the SDI port. As of right now, it's only FILM.

And I don't think that can easily be changed I'm afraid.

I do hear some new SMALL and TvLogic monitors have the capability to have LUT's and that might make it easier...

jb

Now I just wish that VIDEO mode would show up through the SDI port. As of right now, it's only FILM.

And I don't think that can easily be changed I'm afraid.

I do hear some new SMALL and TvLogic monitors have the capability to have LUT's and that might make it easier...

jb

I'm not sure I understand. Does that mean that you can't see the image in VIDEO mode through SDI when recording in VIDEO mode (seems strange) or that you can't when shooting in FILM mode but displaying on cam with VIDEO mode (seems difficult to achieve since two feed must come out of the BMCC, or two LUT's) ?

One feature I would really like to see in a next firmware is a way to change the apparent exposure of the image on camera to avoid having a very over-exposed image on the LCD display which can be difficult to shoot with. (kind of the feature in After Effects)

I don't know if it's a LUT or something else as you don't change the contrast or colors but "just" remap/slide downward the signal to be more viewer friendly.

What do you think ?

Sorry if I'm a bit off-topic !

Stef

I've had my bmcc for a couple weeks now and really love the results I'm getting. When shooting in ProRes do I gain more DR by shooting in "film" rather than "video" and I'm not referring to the display mode. Sorry if this was already addressed.

Yes, by recording in FILM mode, you retain more DR than VIDEO mode. Not quite as much as you would in Raw mode - but its the next best setting.

Thanks Tom! Would you happen to know why the BMCC Lut (rec. 709) in DaVinci 9.1 would make all my RAW and ProRes footage look way over saturated? Could it be my display? When adding the Lut to the footage it looks like a 200+ saturation was added. Thanks.

Would you happen to know why the BMCC Lut (rec. 709) in DaVinci 9.1 would make all my RAW and ProRes footage look way over saturated? Could it be my display? When adding the Lut to the footage it looks like a 200+ saturation was added.

How are you applying the LUT? Via node or in the RAW conversion settings. It can also be affected by how your project is set up.

I have tried it via node and raw conversion. I may need to look into my project settings. Any particular settings I may to change?

Maybe you applied the LUT twice, e.g. on both input and display.