Fran

Am I missing something? Doesn't the difference between ISO 50 and ISO 100 affect the brightness of the scene?

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- Fran
If you must reinvent the wheel, remember that it works best if it is, like, roundish.

daveb867

yes it does, but from what i gather you can compensate for that brightness increase by leaving the f-stop the same and bringing the shutter speed down a notch, like in my example. and what you get is an exposure value of 8 for both sets of numbers. so in reality, regardless of the settings of iso shutter and f-stop, an exposure value of 8, should result in the same exposure regardless of the other settings, but it doesn't. however, i am still learning myself

gotta admit its hard to get your head round. i think someone needs to run a test

jeff??? bri b??? zap??? you know you want to

now that i know that depth of field and motion blur aren't directly affected by these controls, then i guess it all can be controlled by the EV alone regardless of whether the other values work as they should.

i'l try and do a test myself with typical camera values for a typical sunny day and then i'l try and post it on my blog which is still in its early stages

www.3ds-arch-viz.blogspot.com

will try and get that updated after the weekend, as i have a hectic weekend planned. but i shall base my test on the fact that an interior with sunlight coming through the window should have an EV of 8. anyway you'll see the results after the weekend

its really gettin on my nerves now because i don't believe its workin as it should, but thats just my opinion

Fran

Okay, but your settings are identical except for the ISO. Again, unless I'm missing something, the image with ISO 100 will be brighter than with ISO 50.

__________________
- Fran
If you must reinvent the wheel, remember that it works best if it is, like, roundish.

mattclinch

he's trading off the drop in 1 stop of ISO (100 down to 50) with an up step in shutter speed (1 sec to 2 sec).

in theory 1 stop of ISO, shutter speed and f/stop should all be equal amounts of exposure.

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Matt Clinch
Arch Viz Artist @ Hayes Davidson
http://www.hayesdavidson.com

daveb867

matt is correct

fran, the point i'm getting at is regardless of iso shutter and f-stop, if the combination you dial in for those equals an exposure value of 8, then the renders should look the same in terms of exposure. but it doesn't. try it.

dial in a combination that equals a value of 8.

then dial in another combination that equals 8 on the EV and compare the results.

and the end of the day, what MR is saying is that the image is controlled by the exposure value. therefore if the EV is 8, the images should look the same regardless of the combination of numbers dialled in for the ISO, shutter and f-stop

crazy homeless guy

I have been a bit skeptical of how closely the MR exposure represents a real world camera in terms of exposure in general. We should assemble a simple daylight scene for testing. A plane, a couple of boxes, and a daylight system should suffice. And someone should shoot outside on a sunny day, and compare the results.

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travis schmiesing

daveb867

i'm about to do just that but with an interior, i know it's wrong because i was testing today

SandmanNinja

There's a pretty good explanation here:
http://en.wikipedia.org/wiki/Film_speed

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-SandmanNinja
website

MasterZap

Hah

You guys are right, the "camera parameters to EV" calculation is wrong (it uses the ISO backwards). The "EV to camera parameters", however, is correct.

ISO 100, f/16 and shutter 1 should NOT be the same brightness as ISO 50, f/16 and shutter 2, it is shutter 0.5 that is the same.

Remember the "sunny 16" rule: same "shutter speed" as "film speed" for f/16.

So shutter and iso should move in the *same* direction (remember the shutter value is the 1/value measurement) to give "same value".

But the EV is actually calculated wrong for any iso other than 100!

But the EV isn't what is actually used, the "camera parameters" is what is actually used.

Also those wanting the "physical camera" shuold read here

/Z

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mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

daveb867

Ok so in that case, the EV value in MR is well out.

So from what i understand camera values for ISO 100 are caluclated correctly. If i use any other ISO then i need to move the shutter speed in the same direction to get the same exposure.

For example, what you are saying is

Shutter Speed 1/1, f-stop f16, ISO 100 = EV 8.

IS THE SAME AS OR GIVES THE SAME EXPOSURE RESULT ON AN IMAGE AS

Shutter Speed 1/4, f-stop f16, ISO 400 = EV 12

The exposure values are so different yet they look exactly the same when dialled in and rendered. You would expect EV 12 to be much darker than EV 8 right??

But if the camera controls aren't contirbuting to DoF etc, then it would be safe to constantly stick with an ISO 100 and then adjust the other values to suit as this would give us a correct EV value for our desired scene??

ZAP i suggest you do a blog entry to clear this issue up