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sampei
04-15-2010, 07:08 AM
so I've fallen in a (bad??) habit of using the perspective camera mindlessly practically always.
Lately I've been messing around with the lens' focal length and noticing varying results.
I was wondering if anyone can point me towards some guidelines towards this subject that I have yet to consider but that I think is very important when rendering different things in different situations. For example I am in the midst of rendering a human character, and I have been experimenting with various zoom factors etc. and have been taking notes on my results. For example using a 72mm aperture rather than the standard 24mm makes a head look more like a head imho. Obviously it's just an impression, hence this thread !
Should I be using the real lens camera ? It has so many different settings it's a bit intimidating.
Any links, books, vids, tips, tricks and cheats deeply appreciated :)

starbase1
04-16-2010, 04:38 AM
I'm also interested ion this - I have noticed that with some cameras I need to go doubled sided on surfaces for shadows to work correctly, and similar effects...

Info on which camera is best to use when and what the imits are would be very welcome...

rsfd
04-16-2010, 04:53 AM
You could consider to read a beginners book about photography.
This should help you to understand what happens when you use shorter or longer focal lens lengths. On a 35mm full frame SLR camera (film gate 24x36mm) a 50mm lens is considered a "normal" focal length (√24^2+36^2) as it meets the viewing angle of a human's sight.
Shorter lenses (wide angle lenses) show more, longer lenses (tele-lenses) show less then that from a given point of view. This generally influences the optical perspective of a motive as it leads to a more distorted or compressed view.
The real lens camera tries to match the optical data of real existing camera lenses, which could be used e.g. when matching an existing photograph is needed.

sampei
04-19-2010, 05:57 AM
thanks rsfd for the reply and info, I will sure look into photography and film making when I have the time...its an interesting subject and I can see it is closely related to CG. ;)

Captain Obvious
04-19-2010, 06:30 AM
Perspective is a product of the distance between the subject and the camera. Basically, the further away something is, the 'flatter' it looks. The reason is quite simple: if you're one meter away from a subject that's roughly a one meter cube, the distance to the far end of the subject will be roughly twice as far away from the camera as the near end, making equal-sized parts four times smaller.

If, instead, you're ten meters away from the same subject, the near end might be ten meters away and the far end eleven meters away. So equal-sized parts at the far end will be about 80 % of the relative size compared to the same thing on the near end of the subject, instead the 25 % relative size we get when we're just a meter away.

Of course, moving further back makes the subject smaller, but if you just crop the view or use a longer lens you can solve that.

For portraits on regular 135-film (36x24 mm film back; "film height" of 24 mm in LW), lenses of around 75 mm are generally used. This allows you to stand a bit further away and still achieve a good composition.

sampei
04-19-2010, 07:55 AM
thanks cap, that post actually makes a lot of sense. Also shame on me for never thinking of croping renders :foreheads

Captain Obvious
04-19-2010, 08:28 AM
Oh you really really do not need to crop! I mean, you *can* of course, but that just means you're wasting render power... But zooming in and cropping to the same area produces exactly same image, aside from the resolution.

rsfd
04-19-2010, 08:38 AM
there is a slight difference between "perspective" and "perspective":
the "real" perspective is only dependant from the point of view (more exact: from the position of the nodal point of an eye or a lens in space).
The lens focal length has no influence on that perspective.
This is the perspective that determines the "look" of your image/object.
By using different lenses only the field of view changes, the perspective stays exactly the same.

The "optical" perspective (what most people just call the "perspective") additionally depends on the lens focal length, it's something that the human eye usually adjusts, but optical lenses cleary show: the "different" size of objects in relation to the distance of the viewer (what the captain has explained above), which can be exaggerated by using short lens focal lenghts and compressed when using longer lenses.

The film gate's diagonal determines the "normal" lens focal length, the double normal length is usually called the "portrait" lens focal length (on 35mm Full Frame SLR that would be 100mm, but the range between 85-105mm is usually used - other film gates need other lens focal lengths: a classic 6x6 camera has 80 mm as "standard" and 150-180 mm as "portrait", a 4x5" view camera has 150 mm as "standard" and about 240-300 mm as "portrait")

sampei
04-19-2010, 09:31 AM
Oh you really really do not need to crop! I mean, you *can* of course, but that just means you're wasting render power... But zooming in and cropping to the same area produces exactly same image, aside from the resolution.
understood (I hope) ! what got me thinking was also Tobian's tutorial where in order to correct the "parallel distortion" created by zooming out (if im not mistaken?!) to get more of the interior in shot he used a fish eye lens...

rsfd
04-19-2010, 11:06 AM
for archviz interiors, you might try the shift camera.

A typical problem within architectural photography is that vertical lines don't stay vertical as soon as you tilt the camera up- or downwards (to maintain verticals, the camera [in real world: the film back] has to stay vertical too - no tilt allowed).
But then you usually end up with an image where "the top is missing" and you have too much floor. So you use a "view camera (or large format / sheet film camera)" or a "shift lens" and shift the lens upwards.
That's impossible with a 3D cam unless you use the shift cam (or take another route with a grid null).
To get more of the interior, you will use a shorter lens, but it really depends on how much you need too see and where your camera is placed.

Captain Obvious
04-19-2010, 11:36 AM
That's impossible with a 3D cam unless you use the shift cam (or take another route with a grid null).
Nuh-uh! You can also zoom out and crop or do a limited region.

rsfd
04-19-2010, 03:00 PM
ok, cropping is a waste of render time, limited region is possible.
But I was referring to the perspective controls that only a "real world" view camera has. These possibilities aren't reproducible with 3D cams. (e.g. control of focal plane via Scheimpflug principle and the like)

Captain Obvious
04-19-2010, 03:26 PM
A 3D camera can, hypothetically, reproduce ANY optical effect. It should certainly be possible to make a plugin for Lightwave that does the 'Lensbaby' effect as per the Scheimpflug principle. Sure, Lightwave can't do it by default, but it's theoretically possible.

Basically, ray tracing can calculate any Newton-scale optical phenomenon.

Captain Obvious
04-19-2010, 03:29 PM
ok, cropping is a waste of render time, limited region is possible.
If there isn't much in the frame, it doesn't make a big difference.

I used to use the zoom out/limited region trick all the time up until 9.5 or 9.6 when they finally fixed the shift camera.

rsfd
04-19-2010, 04:05 PM
If there isn't much in the frame, it doesn't make a big difference.
but if you need render resolutions of about minimum 3500px x 4500px for print, you may think twice. :)


A 3D camera can, hypothetically, reproduce ANY optical effect.
agreed, but no-one ever wrote such a plugin. (And I just can't :cry: )
A 3D-representation of a real-world view camera would be one of my favorite feature-requests.
The lensbabies btw only offer tilt, but no combination of tilt/shift and the tilt is off-axis too. Combined with poor lens quality it's a nice gimmick as the lomos were some years ago.

Captain Obvious
04-19-2010, 04:18 PM
but if you need render resolutions of about minimum 3500px x 4500px for print, you may think twice. :)
I usually render at even higher resolution :P honestly though, if Lightwave's rendering emptiness, it's pretty quick regardless.