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Matt Norwood avatar image
Matt Norwood asked ·

Physical Camera Exposure

Hello.

3ds Max has Physical Camera Exposure Control enabled by default, but is this really the best workflow?

I do get great results with exposure control enabled, but I would like to have more control over my final renders, so would like to start outputting AOVs and editing them in post.

As I understand it, the AOVs do not take the exposure control into account, so the composited AOVs will not look like the beauty image I see in the Rendered Frame Window. This seems odd to me.

I always see lots of tutorials / advice on working with popular render passes - so know it's an industry-standard workflow - but none address exposure control.

So my questions are:

1. Moving forward, is it worth me disabling exposure control entirely and simply use the Intensity / Exposure settings directly on the Arnold lights to compensate?

2. Will doing this be detrimental in other ways?

3. Are there other recommended workarounds, such as leaving the exposure control enabled in 3ds Max, then reapply the omitted EV-number to the AOVs in post?

Thank you very much,
Matt.

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Max Tarpini avatar image
Max Tarpini answered ·

Zeno, it doesn't look Matt has sampling problems so it could be he just lacks some methodology to properly setup his workflow.

Matt, your scenes should use physical values so you should never ever fall into the question, do I increase lights or camera exposure ?

As arnold lights do not use physical input parameters like lumens for example you better setup your camera aperture, exposure time and ISO to something plausible** then increase your light values until your scene has an average illumination. If at that point the overal ligthing is not exactly what you want, you may tweak just a bit your camera.

If you can't reach the illumination you want by a large amount, you have to add environment fill lights ( in real life you may use back panels, reflectors etc). This is important. That's what real photographers do. They don't increase the ISO to 100000 nor they let their lenses stay open for minutes and for sure they won't go in a shop buying a f0.7 aperture lens (only Kubrick did this in the famous candle lit scene in the Barry Lindon film buying it from NASA) ! Also from a rendering pov adding env light helps a lot indirect lighting.

Once this is all consistent you may find also that beaty vs multi-layer compositing is a bit more predictable.

**Something plausible here means that you know the general setup for a camera to shoot for example indoor (ie. f2 and 1/30.. EV=7) vs outdoor (f5.6 1/25.. EV=13) scenes, industrial design (almost no DOF, ie reduce aperture in favor of longer exposure times or higher ISOs) vs casual portrait etc.

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Zeno Pelgrims avatar image
Zeno Pelgrims answered ·

My advice would be to test it, and look at the differences in variance. From a technical standpoint, the camera exposure is just an exponential multiplier or the camera ray weights.

I checked with an extreme case to see if this ray weight multiplier also acts as a control on how much sampling the areas need, but this doesn't seem to be the case.

Both images have a single light, at a very low intensity. The first image is using the exposure slider (weighting on the camera rays) and the second one is pushing up the exposure in post.

The best thing to do would be to adjust the intensity of the lights to reach a certain exposure, as this will influence the sampling and give you optimal variance/speed balance.


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