Perspective, and Focal Length

[fango]

i need to look into real world cameras more, but i read in one of syomka's post that an angle of view higer than 36 and your eye starts registering distortions. so i guess model with an angle of view of 36.

[ceql]

opps! I didn't see ur post, so I started another [much more in-depth] one in the modeling forum...

http://www.cgtalk.com/showthread.php?threadid=40871

Thank you for your reply fango :)
I too remember syomka mentioning 36 degrees, but initially wasn't entirely sure if I had remembered properly... but I've found the thread and it's confirmed that he did say 36 ;)

[beaker]

Your eye is around a focal length of 65-70. I have no idea why maya's default camera is set to such a wide angle of 35.

[beaker]

Maya's cameras work just like real world camera's do. Go pick up an SLR camera book or borrow a physical one from a friend.

[ceql]

Thanks Beaker, I've quoted your reply in my other thread (in the general modeling forum) ;)

[edit: I've also made a complilation of all the various numbers I've collection on the subject in that thread too... lol I must have too much time atm :)]

http://www.cgtalk.com/showthread.php?&threadid=40871

[Lunatique]

I just model with the camera all the way out to telephoto(highest setting) so I don't get any distortion at all. I learned this from being a photographer. It reallyworks. :)

[ceql]

Thnx Lunatique!!

does this mean you use around about a 31 Degree Angle of View / 65 Focal Length? :)

[mattwood]

For the most natural perspective setting you should try to match the horizonatal field of view of your camera to the distance and size of your monitor. For example, my 21" monitor, seems to fill about 30 degrees of my vision when I'm sat comfortably, so when modelling full-screen a 30 degree camera would match that. But, if I'm modelling in a little window only half as big as the screen then really I should be using a 15 degree camera.

That's the science of it anyway. That might not actually help at all in practice.

[Lunatique]

I just replied to the other thread. I explained everything there:

http://www.cgtalk.com/showthread.php?s=&postid=379465#post379465

[ceql]

Thnx for your insights... lol I'm still confused as to what to use for modeling, but it's very interesting hearing people's opinions :D

[Plasticbag]

HI all

I would like to ask how to set that 'telepro' lens that was mentioned in the software?

Thank goodness i found this thread..the viewoport FOV setting has been troubling me abit too lately..

Heres my findings.: In Lightwave they use 24 degrees, from the LW literature it says that thats closest to what the human eye see ( not sure but its great for adjusting proportions and stuff).

I have tried this setting in Max and was able to make something decent compared to the '45 they default it to.

[mark_wilkins]

It's hard to find a focal length that has a reasonable relationship to the human eye. Your eye has a field of view of over 180 degrees, but most of your visual acuity is in a narrow region in the center, with a broad swath in between that's pretty good.

Unlike a camera, your eye takes in a scene by darting around a wide range of angles and allowing you to form an impression of what you're seeing. At any given time your eye may focus on a detail but that doesn't necessarily correspond to your impression of the scene before you.

So, all in all, it doesn't make a whole lot of sense to say that a particular focal length matches the human eye.

However, you CAN find a combination of focal length, image plane size, and viewing distance that create an accurate field of view.

-- Mark

[ceql]

Plasticbag:

Yeah, Mark Wilkins is very correct...

Looking back at this thread, what I was really looking for was 'What is the FOV was best for modelling [Heads]?'...
(Which I think is what you're really after too, right? :))

initially, I mistakenly assumed that the solution was to find a FOV setting to simulate what the eye sees... however, as Mark Wilkins just explained, I found that cameras don't function exactly the same way as eyes :p

so, I restated the question in a new thread: http://www.cgtalk.com/showthread.php?&threadid=40871

One of the concerns was whether to;

a) use a default FOV (usually something like 45 or 60) and compensate around the distorting by editing your model so that it looked good from that specific FOV (but downside being that it could look ackward in other FOV's or in orthographic views), or

b) use a setting with less perspective, and lower FOV... ie. a zoom/telephoto lens (but downside being that it would look ackward when you were close with a *default* FOV of like 60 or 45)



I think that it was concluded by the end of the thread, was that for modelling heads a using a telephoto setting was best. (b)
[A telephoto lens is just a zoom lens, and has a FOV ~ 30 or lower]

When you get further away from something, perspective distortion decreases, and so when photographers shoot heads, they use a zoom lens and photograph from a distance (instead of getting up real close with a normal lens) to avoid perspective distortion.

Modelling in telephoto means that:

-Heads will look good up close when viewed from a telephoto/zoom lens (just like in real life photography!).

- Heads will also look good from virtually any lens (even wide lens) when further away from the camera (for full-body shots, etc), as perspective distortion naturally decreases as objects get further away anyway.

- Heads will look ackward with a wider angle lens when taken up close, as you're not really meant to do that in the first place :p

I'm pretty convinced that Modelling heads with zoom lens / less distortion is better, instead of modelling with a default program FOV and trying to compensate around the distortion by editing the model ;)





Lookie at these pics of the nvidia fairy model, created by Steven Giesler:

http://users.bigpond.net.au/sequel/gieslerfov.jpg

1st pic: Head looks great, no perspective distortion. It's how it was suppossed to look, and the pic originally came from a full-body shot, and so the camera was of course a distance away from the head. (or you could just use a zoom lens from a similar distance to get a non-distortion photo of just the head if you wanted)

2nd pic: This comes from a nvidia presentation and they haven't used a suitable FOV to display his model, and so you can see some nasty distortion. (granted the purpose of the presentation was just to tweek cg shaders :p)


So, therefore, imho I think Giesler must optimise his models with lower FOV/zoom lens so that it looks good without any distortion, and naturally looks a bit ackward when you use a wrong FOV/too-wide-a-lens up close. Giesler (http://stevengiesler.com) is a master modeller, so if he does it, it must be a good thing! :D




note that there isn't a one-solution-FOV setting for everything, as photographers use different lens for different situations, like they typically won't need to use a zoom lens to capture a full-body shots, etc. :)

In Maya, you can select your camera and then in the Attribute editor you can change the Angle of View or focal length :) I use a FOV of around 20 myself anywayz... but in the end what you use is your own prefference, and I'm assuming we're taking about heads, as distortion is a more prominent problem when modelling them! :D

[DeathBrain]

Just adding some tips :
The distance between object(s) and camera is also important :)
Maya's default camera such a wide angle of 35, coz the default set to a 35mm film format output (34.81 Angle of view)

Btw I think this is good information (http://www.dpreview.com/learn/Glossary/Optical/Focal_length_01.htm) from dpreview.com :)

[ceql]

Yea, when you're modelling a head with a zoom lens = camera has to be further away (but since it's zoomed, everything still looks big anyway and there's less distortion cuz you're further away), hooray! :)

[Maya's default Angle of View (FOV) is 54.53, which is focal length 35mm]

[DeathBrain]

Yea..i mean Angle of View 34.81 for 35mm (Academy) :)

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