Camera focal length for final renders?

[jeremybirn]

Asking what focal length or what camera angle to use in your render is sortof like asking what composition or what colors to use - it depends on what you want.

In general, using a wider angle lens (lets say in the 20mm-35mm range) and moving the camera in closer to the action will tend to exagerate motion that comes towards or away from the camera, give a greater sense of perspective with limbs closer to the camera becoming much bigger than limbs that are farther away, and give a greater sense of space, exagerating the distance between the nearby character and further characters or parts of the set. Going too wide can start to look unnatural, especially since people usually render without barrel distortion (curvature) that's common in real images shot wider than about 10 or 20mm (I'm using focal lengths from a 35mm still camera, these numbers run differently for motion picture cameras.)

Moving the camera farther away and using a more telephoto lens (lets say 200mm) will tend to flatten space, if a character is in a crowd it will make everyone look as if they are closer together, if can also make him look as if he's closer to the background. You tend to see a more narrow slice of the background or environment with telephoto lenses, so its good if you want to emphasize a small part of the background but wide angle would be better if you wanted to take-in a lot of the surrounding environment.

-jeremy

[gerardo]

I was wondering if it is expected for people to render their head in orthographic view or a certain camera focal length for their final render. And if so, what is the common focal length used for pictures? 75mm?




If you refer to focal length to render heads with "natural" look, yeah about 80mm gives you a nice result :)



Gerardo

[Andrew W]

Using focal lengths in millimetres is not terribly useful unless you also know the size of your film back. For example an 80mm lens on a regular 35mm SLR is a good portrait telephoto but on a Hasselblad or equivalent medium format camera that same 80mm focal length becomes the standard lens, neither wide angle nor telephoto. This is because the area of the film planes is different - the Hasselblad's negative is bigger than the the 35mm SLR. Perhaps an even better example : on a Canon EOS 1 35mm camera my new 28mm lens is pretty wide angle but on my 20D (smaller image capture area) it's a standard lens. The focal length only has meaning if you also know the size of the image capture area.

You may be better off talking about field of view in degrees as this is a good measure of wide angledness or telephoto-ness without having to have the extra film-back info to make sense of it.

Here's (http://www.dudak.baka.com/fovcalc.html) a field of view calculator that might help you get your head around this issue.

Cheers,

Andrew

[Davidxt]

Thanks for all the info everybody. I'll take it into account. Sounds like I have a lot to learn in this area.

[gerardo]

Using focal lengths in millimetres is not terribly useful unless you also know the size of your film back. For example an 80mm lens on a regular 35mm SLR is a good portrait telephoto but on a Hasselblad or equivalent medium format camera that same 80mm focal length becomes the standard lens, neither wide angle nor telephoto. This is because the area of the film planes is different - the Hasselblad's negative is bigger than the the 35mm SLR. Perhaps an even better example : on a Canon EOS 1 35mm camera my new 28mm lens is pretty wide angle but on my 20D (smaller image capture area) it's a standard lens. The focal length only has meaning if you also know the size of the image capture area.

You may be better off talking about field of view in degrees as this is a good measure of wide angledness or telephoto-ness without having to have the extra film-back info to make sense of it.

Here's (http://www.dudak.baka.com/fovcalc.html) a field of view calculator that might help you get your head around this issue.

Cheers,

Andrew


Oh, sure. I'm referring to 35mm motion picture (is the standard in most of 3D softwares) :)
Btw Andrew, thanks for that link



Gerardo

[Andrew W]

Oh, sure. I'm referring to 35mm motion picture (is the standard in most of 3D softwares) :)
Ah, OK fine. One other pitfall is that 35mm motion picture and 35mm stills are also different film back sizes so lenses you like on your SLR are not the same field of view on a movie camera. There are even different 35mm movie camera back sizes too. Another good page (http://hsvmovies.com/static_subpages/formats/shooting_formats.html) with some useful comparison of movie film formats. Welcome to the wonderful world of format hell. Argh! BTW, Vistavision is pretty close to stills 35mm as it is an 8-perf format with the film running horizontally through the camera rather than the more usual 4-perf, vertically running format (http://en.wikipedia.org/wiki/35mm_film).

Hope that helps and doesn't confuse.

Andrew

[jeremybirn]

Oh, sure. I'm referring to 35mm motion picture (is the standard in most of 3D softwares) :)
Btw Andrew, thanks for that link

In Maya you default to emulating a 35mm still camera, and you'd need to switch the film back if you wanted to simulate a 35mm motion picture camera (they are different, the motion picture frames are much smaller and all the lenses become more telelphoto.)

-jeremy

[gerardo]

Ah, OK fine. One other pitfall is that 35mm motion picture and 35mm stills are also different film back sizes so lenses you like on your SLR are not the same field of view on a movie camera. There are even different 35mm movie camera back sizes too. Another good page (http://hsvmovies.com/static_subpages/formats/shooting_formats.html) with some useful comparison of movie film formats. Welcome to the wonderful world of format hell. Argh! BTW, Vistavision is pretty close to stills 35mm as it is an 8-perf format with the film running horizontally through the camera rather than the more usual 4-perf, vertically running format (http://en.wikipedia.org/wiki/35mm_film).

Hope that helps and doesn't confuse.

Andrew


I knew 35mm motion picture and 35mm stills had different film back sizes, but I didn't have a clear info about different 35mm movie camera back sizes. Thank you for those links too, very informative



Gerardo

[gerardo]

In Maya you default to emulating a 35mm still camera, and you'd need to switch the film back if you wanted to simulate a 35mm motion picture camera (they are different, the motion picture frames are much smaller and all the lenses become more telelphoto.)

-jeremy



Yeah, that is the reason for which I said 35mm motion picture; commonly use Lightwave in where 35mm motion picture is the default.



Gerardo

[Gbanvl]

on a Canon EOS 1 35mm camera my new 28mm lens is pretty wide angle but on my 20D (smaller image capture area) it's a standard lens.

I'm not familiar with the EOS 1, but I've used a Canon 10D and have read reviews on cameras in that class extensively. As I understood it the 10D and 20D are both have 35mm equivalent capture areas and their lens systems are interchangeable with 35mm film cameras. A 28 mm equivalent in 35mm camera terms is pretty wide for any camera, is it not?

Thank you for pointing out the necessity of knowing the size of the film back though. I had been thinking that all cameras were defined in 35mm equivalent terms, and had therefore assumed that a camera created in 3DS Max with a focal length of 28 mm would match perspective perfectly with a background image taken with a 28 mm or equivalent lens. Does anyone know whether Max defines its cameras as equivalent to 35mm cameras or to motion picture cameras?

[jeremybirn]

A 28 mm equivalent in 35mm camera terms is pretty wide for any camera, is it not?

As you said, a 28mm _equivalent_ (a lens that gives the field of view you'd expect from a 28mm lens on a standard 35mm SLR) is wide. But a 28mm lens mounted on a Canon 20D with a 1.6x crop factor would be more like a 45mm equivalent.

Just like the size of the film back, a smaller sensor in a digicam gives you a more narrow FOV even with the same lens.

-jeremy

[Gbanvl]

You're right. I realize what I said and that it was pretty inane. I just cant wrap my head around the idea that the sensor size/film back of a 20D is different from that of a 10D or of any standard size SLR film camera. I haven't noticed that that has been mentioned in any of the reviews I've read or the discussions about cameras that I've had. I think somehow we must be talking about two different cameras.

[Andrew W]

I just cant wrap my head around the idea that the sensor size/film back of a 20D is different from that of a 10D or of any standard size SLR film camera.The 10D and 20D have identically sized CMOS sensors as far is I know. The 1Ds and 1Ds Mk2 (The 's' is important here) and the new 5D have full 35mm film sized chips (36mmx24mm) and hence the lenses behave in the same way as they would on a film based SLR. Nikon do not make a full frame chip and apparently have no plans to. The only other full frame digital SLR is the Kodak DCS 14n.

Hope that helps,

A

[jeremybirn]

You're right. I realize what I said and that it was pretty inane. I just cant wrap my head around the idea that the sensor size/film back of a 20D is different from that of a 10D or of any standard size SLR film camera. I haven't noticed that that has been mentioned in any of the reviews I've read or the discussions about cameras that I've had. I think somehow we must be talking about two different cameras.

Like Andrew said, most dSLR's are not full-frame, only a few high-price ones. Reviews I see on dpreview.com list under "lenses" a 1.6x field of view crop for the 10D and 20D. They also mention the sensor size, such as 22.5 x 15.0 mm for the 20D or 22.7 x 15.1 mm (almost identical) for the 10D. Neither are a 36mm x 24mm full-frame sensor.

-jeremy

[Gbanvl]

Ok, well thanks for being patient with me. I guess I've learned something.

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