daveb867

Right

This is really confusing me.

I am currently dialling in exposure values for SS, f-stop and ISO.

Here's an example for a daylight interior

ISO 100, f-stop 16, Shutter 1 = EV 8
ISO 50, f-stop 16, Shutter 2 = EV 8

Ok so theoretically these should both give the same exposure right??? Same EV Values.

However the one with ISO 100 is far brighter even though no other settings were changed??

Please can someone explain why??

mattclinch

i think i touched on this in another thread.

theoretically they should. but they dont. i dont know why.

its far easier to just use the eV value, unless you have depth of field (?) or are matching exposure in a known photo.

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

daveb867

does the sunny 16 rule apply to interiors and exteriors???

i will use the EV value but wanna understand the other settings also

good for my mental strength

also are there any rules for night shots???

i'm currently using an exposure chart to help me so thats where i'm getting my values from

mattclinch

sunny 16 is just a rule of thumb to get an approximation of a good exposure without having to sit and fiddle and test for ages.

if you want to understand how ISO, SS and f/stop balance and affect each other then i'd do it on a camera, not in MR exposure control.

there are no 'rules' for night shots, only desired setups.

lower the ISO the less grain, but the longer it will take to expose.
higher the f/stop the less depth of field. ie. f/22 keeps everything pin sharp - usually a good bet.
quicker shutter speed for less motion blur.

what would i do for a night shot at night? low ISO, say 50 or 100 to reduce grain. f/22 for sharpness, and set the shutter speed to whatever will expose that iso and f/stop correctly. thats simple 'aperture priority' exposure, where your desire for sharpness (high f/stop) dictates your shutter speed.
but thats a camera.. MR is simply the eV value that exposes it correctly.

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

daveb867

techncially not though. As in the example. If i get two differently exposed images using from the settings i previously mentioned. if i just use the exposure value then when i get to ev8, i will have the exposure that mental ray wants to give me rather than the exposure i want.

if you understand me.

lets say i wanted the brighter of my two setting combos.

iso 100, f 16, ss 1

if use the ev spinner to get to a ev value of 8 then mr gives me values in my dials as iso 100, f8 and ss 4.

which is different again to the setting of 8 that i was happy with.

so in that case are you saying that i just lower the ev value even more and i will eventually get the same resulting image that i had with iso 100, f 16, ss 1

mattclinch

i think you are getting too hung up on the photographic numbers within MR. it appears to me that in MR they basically feed into an formula which gives an 'exposure value'. for EV 8, as you mention, there are multiple combinations of iso, f/stop and ss which should, theoretically, produce the exact same exposure. its not an exact science though, and MR obviously haven't perfected the formula yet. MR seems to pick one of these combinations at random, and whilst varying between these potential combinations should produce 'approximately' identically exposed renders for the same EV, in practice it doesn't.

get a camera. they've had centuries to perfect those

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

daveb867

so what do you use down at HD???

EV

or do you dial in numbers

i can quite happily get nice results its was just confusing me as too how it works. as far as i'm concerned i just adjust values until the image looks how i want it to look, i don't car what the values are or what it is i'm adjusting.

the one i am struggling with is an interior night shot, with photometric lights IES files, and sky portals (with a blackbody shader) acting as area lights in the same scene.

with regards to the settings. in MR if i have a lower f-stop with the render be more blurred than if i use a high f-stop, or does this not differ in MR??? i guess that's why people use VRay and the physical cam in that right??

mattclinch

i personally prefer just using the EV value, but its a personal preference.

as far as im aware, f-stop will not narrow your depth of field (unless perhaps you have MR depth of field activated??)

i'd be interested to hear other peoples take on this function, Zap?, Brian Bradley?, as i wouldn't take my word as gospel!!

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

daveb867

i guess we are just missing this physical camera in mental ray, would be great if there was one that worked like a normal camera and had exposure controls that worked like they should do

any tips on the night interior i mentioned

pfbreton

Here is how it works internally:

the mr Exposure control is based on documentation published by Kodak. It mimics the response curve of cameras by using the "right" weighting of ISO, Fstops and Shutter Speed.

However, if you look at the maths, it end up as a multiplier, which is your EV value.

As an extra color control layer, the other parameters (saturation, midtones, highlights) are applied on top of the calculated EV.

If all your lighting is within physical range (i/e/ correct photometric lighting with correct / typical light intensities), the EV used in the 3D world will match a Photographic workflow - its designed to be in line with the camera response, but to work correctly, your lighting need to be correct too.

Note: since its a 3ds Max exposure control plugin, there is no effect on the DOF and Motion Blur directly. Its purely affecting the color of the calculated pixel.

Hope this helps,