[Sidefx-houdini-list] Camera model

Colin Doncaster colin.doncaster at gmail.com
Tue Nov 27 11:36:39 EST 2012


Agreed.  What I'm trying to determine is what exactly do you mean by what you see through the lens ( BTW, if you're shooting a film with a live camera what you see in the lens isn't always what ends up on the cell/censor )? There is, of course, a very real association between focal length and fstop ( or T stop in motion picture cameras, though that is more lens specific ) for determining depth of field ( film back also comes into play ). ISO was brought up which I'm having a little more trouble swallowing and understand that it contributes to depth of field based on being able to stop up or down more due to film speed but this is more about the medium than the lens.  

Since we're talking about f-stops and defocusing would you want the lens simulation to also include softer renders when the aperture is fully open vs. tack sharp when closed etc.?  I believe someone mentioned Maxwell which also renders chromic aberration - is there also any merit in relying on Lens manufacture's MTF charts  ( these aren't as accessible when dealing with motion picture primes as each lens varies a little, hence the need for serial numbers etc. ), where is the line drawn?

I'm not trying to play devils advocate, maybe just preempting some questions SideFX might ask/need to ask when implementing. 

Cheers

On 2012-11-27, at 10:25 AM, jason slabber <jason.slabber at gmail.com> wrote:

> for me, it's more about getting closer to what we see through lenses, so
> taking pictures rather then rendering them.. :)
> it's no way the final step, comp still needs to be big part in the process,
> we just need to spend less time trying to make renders look "real" in comp
> and more time crafting the frame.
> 
> j
> 
> 
> 
> On Tue, Nov 27, 2012 at 5:15 PM, Jordi Bares Dominguez <jordibares at gmail.com
>> wrote:
> 
>> below
>> 
>> On 27 Nov 2012, at 14:44, Pablo Giménez <pablogipi at gmail.com> wrote:
>> 
>>> 2012/11/27 Colin Doncaster <colin.doncaster at gmail.com>
>>> 
>>>> Hi Jordi,
>>>> 
>>>> I understand the outcome of setting these parameters but what do you
>> mean
>>>> by "set your environment in the most correct way"?
>>>> 
>>>> Also, are referring to a camera shader ( or similar ) that provides more
>>>> than a standard pin hole camera or are you just looking to balance the
>>>> amount of light exposed against the film back based on the described
>>>> settings?
>> 
>> That is what I meant, everything needs to be physically correct, otherwise
>> in fact is counterproductive.
>> 
>>>> 
>>>> This of course assumes that you're using energy conserving shaders and
>>>> your shaders, textures, lights etc. are all being managed correctly
>> also.
>>>> 
>>>> Lastly, would doing this in the renderer be the best place?  Ultimately
>> I
>>>> would assume you could reproduce a similar control over exposure in
>> comp,
>>>> and maybe a few new options to mplay to control the exposure based on
>> iso,
>>>> shutter speed and aperture?  Just some thoughts, to me having to
>> re-render
>>>> every time the ISO changes feels like a lot of work.
>>>> 
>>> Well I think this is the main reason because such a realistic camera
>> model
>>> hasn't been implemented yet in Mantra.
>>> I think most SESI clients do this in comp.
>>> Anyway getting a more realistic lighting simulation tool is always
>> welcome
>>> and is the way to go with PBR.
>>> 
>> 
>> Two things I aim towards;
>> 
>> A ) technical - 3Dmotion blur plus depth of field should to be rendered
>> together
>> B)  artistic - focus is a storytelling tool and should be in the hands of
>> the lighting TD, which in fact takes you to point A
>> 
>> 
>> I know in the film pipelines this  may not be ideal for many studios and I
>> understand why, but this approach brings a lot of benefits, not free though.
>> 
>> ;-)
>> jb
>> 
>> 
>>>> 
>>>> Cheers
>>>> 
>>>> On 2012-11-25, at 4:19 PM, Jordi Bares Dominguez <jordibares at gmail.com>
>>>> wrote:
>>>> 
>>>>> After a few months off the lists now I am back and wanted to start by
>>>> requesting SideFX through this list an feature on the camera model.
>>>>> 
>>>>> Seems to me after exploring various options that the camera is not
>> fully
>>>> modelled and exposure controls are not there yet, meaning, I would like
>> to
>>>> deal with ISO speed, shutter speed and aperture and set my environment
>> in
>>>> the most correct possible way.
>>>>> 
>>>>> I have been using this with Mental Ray over the course of the last 4
>>>> years in various degrees and although at first may seem unnecessary in
>> my
>>>> experience brings a lot of value and would like to throw the idea to the
>>>> community to discuss it and may be even have a workaround/method/trick
>> to
>>>> the system.
>>>>> 
>>>>> Actually looking at the implementation from Next Limit in Maxwell
>> plugin
>>>> for Houdini I am looking after something like that… I feel this should
>> be
>>>> part of the core package so there you go…
>>>>> 
>>>>> thanks in advance
>>>>> jb
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>>> 
>>> 
>>> 
>>> --
>>> Un saludo
>>> Best Regards
>>> Pablo Giménez
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