Camera Focal Length

[Ben Beckett]

Hi

Maya's cameras clearly have a defined Focal Length Tab.

Where in Soft is this because sitting with the Driector yesterday soft really did it self no favours, I was telling him how it a great app is but he now not having any of it.

On the camera prop's menu there is the Focal Length but its in (mm)

, can it be switch, and why mm's.

Thanks

Ben

[Leonard Koch]

I would think because mm is the standard in focal lengths.
Lenses' focallengths and also sensor sizes - which also play a role in how much the camera sees - are always given in mm.

[Jens Lindgren]

Camera Focal Length is always in mm. It's a global standard.

Just check the Enable box and set the Film Aperture to something realistic, for example I always use the aperture of the Arri Alexa camera (23.76/25.4 = 0.9354 inches).

After that you could just set the lens with the Focal Length.

 

/Jens

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Jens Lindgren

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Lead Technical Director

Magoo 3D Studios

[Morten Bartholdy]

Hi Ben

 

I may be missing your point here, but afaik focal length is expressed in mm wheereas backplanes ie. the Film Aperture (chip size in digital cameras) is expressed in inches - both as in Soft. We use this all the time and use Red and Alexa data to get it right when matching CGI to real footage, and are having no problems with it.

 

What exactly did you or the director want to do?

 

cheers

Morten

[Jens Lindgren]

Yeah the Film Aperture should really be in mm in Softimage... Don't get why it's in inches.

 

/Jens

[Ben Beckett]

Sorry maybe I have confussed I mean the standard numbers such as 40mm 35mm 22mm lenz, When he said lets try a 40mm lenz how does that equate in soft

Thanks

[Jens Lindgren]

On the Projection Plane tab:

Enable it, set Film Aperture X to 0.9354 (the value of a Arri Alexa camera), chose whatever lens in mm in the Focal Length field.

 

/Jens

[Ben Beckett]

Thanks that brill to know, thankyou everyone

[Rob Wuijster]

not really getting it.

If you set the proper settings for the backplane, the focal length lens settings are as they are.
There's no 'equate in soft' setting for lenses, all 3D apps follow real world mechanics.

Rob

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[Ben Beckett]

Well there is no confussion in Maya as such, it just seem very odd in soft. It maybe base on real world settings, but for a dum nut like me some times maya seem to have it nailed.

[Martin]

You need to enable Projection Plane and specify the Film Aperture.

You may need to convert mms to inches because SI only uses inches for Film Aperture.

You could also create a custom property like this: 

http://www.softimageblog.com/archives/65

This addon is a little old so you may need to modify it to support newer standards.

It works even with the default film aperture locked and automatically converts the orientation to the vertical/horizontal equivalent.

SI should have something like that by default.

M.Yara

[Ben Beckett]

NIce thanks, this is what am saying.

[Martin]

Oh I forgot to tell you, this addon has a custom option that you can easily edit, but it won't remember your custom settings unless you create a preset file and load it every time.

I don't know if you can code, but even if you don't know Python or scripting in general, you can add a new preset quite easily.

Just open the RealLens.py with a text editor and in " dCameraTypes " add your camera specs in millimeters. Just keep the format (quotes, brackets, comma , at the end if it isn't the last preset, etc)

Ex:

"Arri Alexa HD": [23.760, 13.365]

And you'll have a new option for this camera

Now, the cool thing with this addon is that you specify your camera specs in the custom property and it will do the math for you and calculate the SI camera values no matter what Film Aperture you have in your SI camera.

The not so cool thing is that it doesn't change your SI camera Film Aperture, but it calculates instead the equivalent Focal Length with your current Film Aperture.

The image result should be the same though.

cheers,

M.Yara

[Raffaele Fragapane]

The director might need to read into the fundamentals of his job.

In first place the focal length doesn't mean much without knowing how big the film back is and where it is.

40mm on a m4/3 (or any small sensor) is a fairly long lens, like shallow depth portrait long. On an Epic it's actually closer to a 37mm on a 35's film back, and on a 35's film back it's a natural lens.

Assuming that, like many, he assumes the 35mm film standard (not to be confused with a 35mm focal length), you should set your film back to a 35mm full frame sensor settings, and then whatever focal length will match his expectations.
If he refers to lenses he shot plates with, he needs to let you know what they were shot with.

Shooting with a GH3, a m4/3 black magic, a 5D MIII, a Phantom or an Epic all respond from wildly to slightly differently to focal lengths.

The settings in Soft make perfect sense, and the ones in Maya don't differ really, just some of the camera settings are actually stashed away or slightly odd.
It's time to study the basics of photography/camera work if you think the ones in Soft don't make sense. The only difference is Maya might have defaults and things hidden away that for the one sequence happened to be lucky, but the two apps don't differ.

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[Chris Covelli]

I suppose this would be a good place to ask......something Ive always wondered.  I understand the controls on the Projection Plane tab well enough, but on the Primitive tab, under the Pict and Pixel Ratio sliders theres one called Feild of View, which seems adjust the lens distortion similar to the focal length, but on a 1-180 degree scale.  Whats this one for and how is it supposed to be used in conjunction with the focal length controls?

Thanks!

Chris Covelli
http://www.polygonpusherinc.com/
http://exocortex.com/products/species

TurboSquid Models

[Chris Covelli]

Oh nvm, I just realized they are directly linked together, changing one also changes the other.  Makes sense now.

Chris Covelli
http://www.polygonpusherinc.com/
http://exocortex.com/products/species

TurboSquid Models

[Jens Lindgren]

From my experience directors and DOPs always assumes a lens is on a moving picture film camera in the Super 35 format, not a 35mm stills camera.

I know it's very confusing that they almost have the same name, but the film back size is very different.

On a 35mm stills camera (Nikon D4/D800 and Canon 1D, 5D), the Film Aperture width is 36mm (yes 36 and not 35).

The Super 35 film format used for movies has a Film Aperture width of 24.89mm. This format is very rare now in the digital age but the Red and Alexa follows the Super 35 standard pretty closely with the Alexa at 23.76mm and the Red Epic at 27.7mm.

The Nikon DX format and Canon APS-C cameras also has a size very close to Super 35. In fact, the majority of DOPs I've met actually use Nikon DX cameras, probably because they can just shoot stills on location scouts and tech recces and know they can use the same focal length when shooting with the Red or Alexa.

 

Bottom line... if a director or a DOP talks about a 40mm lens, it's probably safe to assume a Film Back (Film Aperture) of around 24mm (Super 35), but if you're in doubt, just ask him/her.

Personally, I always set Softimage to use the Alexa size of 23.76mm because 90% of all the work we do with live action is shot on the Alexa. Of course I change the Film Aperture if it's shot on anything else.

It's also worth noting that depending on the resolution/format being recorded on Alexa and Epic, they use different amount of pixels on the sensor and thereby changing the size of the Film Back as well.

 

Hopes this clears it up further.

 

/Jens

[Martin]

I wrote something about fov in my blog that may help to understand the FOV and Aperture relation.

It is in japanese but the graphics are enough to understand the basic relation.

http://myara.blog.fc2.com/blog-entry-167.html

I'm not an expert so if there is something wrong, please let me know