adjusting camera field of view

bellissimo · Post by **bellissimo** » Thu Oct 14, 2004 3:15 pm

Is there a way to adjust the cameras field of view?
The zoom control is not the equivilant of this function.
When using depth the zoom does not appear to change the viewing angle of the camera...it just enlarges and shrinks the same view. A true camera viewing angle adjustment would change the relationship between objects at different depths. Is this possible right now?
If so thanks and great!...if not...it really is necessary
cheers

kdiddy13 · Post by **kdiddy13** » Thu Oct 14, 2004 4:44 pm

A true camera viewing angle adjustment would change the relationship between objects at different depths.

Actually, this is incorrect. The camera is working exactly as it should. The relationship between objects only becomes apparent due to paralax, which only shows up when the camera's postion changes.

It also won't show up with rotations on the camera (at least not a virtual camera). This is due to the fact that again the camera's nodal point isn't translating while rotating (a truely nodal camera). This paralax, however, will show up when a real world camera pans if the nodal point (where the light rays cross in the lens or camera body before hitting the image plane) is not centered on the tripod, thus allowing it to translate. A virtual camera is always (at least the ones I know of) a nodal camera, that resides at the camera is the nodal point. Since zooming or changing the FOV does not change the nodal point's location, it will not change the paralax between objects.

You can try it out with a camera with zoom capabilities.* Lock the camera down on a tripod or tape it to a table (don't let it move). Zoom in and out. Take notice where things intercect with each other visually and you'll find that relationship doesn't change. There are some things that will, and may cause you to believe the relationship changed, like depth of field changes while zooming, creating a narrower depth of field when you zoom in (less in focus) and a wider depth of field when you zoom out (more in focus). Or if objects are moving around in frame, but again this only shows the paralax between the objects, which is accentuated due to lens changes. Still objects will not change their relationship when the camera does not move.

I hope this helps.

I can get even more technical if you'd like, but it may just be easier to do a search on Nodal Point in Google.

*Take note that the zoom expirement is far from being as precise as doing it with a virtual camera, as every camera has its quirks and tendancies. And zooming may cause a very small shift in the nodal point (again causing paralax), this does not happen in 3D.

Post by **Lost Marble** » Thu Oct 14, 2004 5:53 pm

kdiddy13 is correct (and I bet he's done some panoramic photoghraphy). Moho's Zoom Camera tool does truly change the field of view.

kdiddy13 · Post by **kdiddy13** » Thu Oct 14, 2004 5:57 pm

and I bet he's done some panoramic photoghraphy

Actually, part of my job is doing Match Moving and understanding how the real world camera relates to the virtual camera is a cornerstone. But you're right, understanding this does make panoramic photography much easier.

7feet · Post by **7feet** » Thu Oct 14, 2004 10:51 pm

Y'now, I was also under the impression that it wasn't working like that. So, I just did a quick re-enactment of the classic Hitchcock "Vertigo" shot, where the camera zooms in while tracking backwards, to keep the character the same size but distort the size and relationship of objects outside the point of focus. Worked pretty nice. Learn something new every day. Thanks for pointing that out..

--Brian

kdiddy13 · Post by **kdiddy13** » Thu Oct 14, 2004 10:58 pm

No problem! I'm just glad to be contributing to the Moho knowledge base finally! I feel like I'm finally giving back to the community that's given so much to me (a single tear rolls down my cheek)

bellissimo · Post by **bellissimo** » Fri Oct 15, 2004 5:59 am

well thank you all for your well considered responses,
but everyone is missing the point which i thought was pretty obvious...so please let me clarify because this is important.....
Is there a way to change the apparent lens of the camera...call it what you will...wide angle,telephoto(zoom,viewing angle)??????
If i take a picture with a wide angle at 10 feet and then frame that same picture with a telephoto at 50 feet....it looks very different!
The visual relationship of objects in the scene changes dramatically.
My question is simple...every 3d program I'v ever used allows me to change the apparent lens(viewing angle) of my virtual camera...and thereby control how the scene looks.....so I just assumed it is possible in moho..........is this possible with moho????because as far as i can tell...the zoom control does not have the same effect as changing the viewing angle...if anything it is a dolly in and out effect!

kdiddy13 · Post by **kdiddy13** » Fri Oct 15, 2004 6:19 am

Read through my reply again. I think you are missing the point. Changing the relationship of objects (ie paralax) is solely the result of moving the camera. Zooming, changing the FOV, the lens, whatever you want to call it, only zooms. Dollying, or changing the camera's location is the only way to change how objects in 3d relate to each other.

Just out of curiosity, what 3d program are you using that changes how things look when you change the field of view.

Also, check to see that you have 3d enabled in the project settings and make sure that you have several layers separated in 3d space. Then try to dolly the camera forward (change the z value in translation). You'll find that it does what you want.

If you want to change the field of view, viewing angle, lens, etc. Select the zoom tool and change the value, I believe it's set up to approximate a 35mm camera.

Again, I seriously encourage you to actually try this with a real camera or look again at that 3d program. I think you'll find that changing the FOV or lens does not change the relationship of objects in screen space. That will only occur when you physically translate the camera.

kdiddy13 · Post by **kdiddy13** » Fri Oct 15, 2004 7:05 am

Ok, so maybe the real problem here is that we either aren't talking about the same thing or I'm not explaining the solution clearly enough. So I've rendered out a really quick and dirty demo using Maya. Sorry, but I didn't have time to do a similar demo in Moho, but you can easily reproduce this demo in Moho, the tools are all there.

I've set the camera lens to 60 (or a angle of view of 33.4). A bit longer than how our eye works but it will be fine for this demo.

Here's the first shot. Pay particular attention to where the edges of the objects meet each other in 2d space.

Here's the second shot. I just zoomed in a little bit by changing the lens from 60 to 100 (or an angle of view of 20.41). Notice that the sphere and the cube meet up in precisely the same space, you just see less of your surroundings. There has been no change in paralax, I might have well just cropped a 2d image.

In the following shot, I set the camera lens back to 60 (again an angle of view of 33.4). But this time I dollied forward by 5 units (moved the camera forward by 5 arbitrary units). I tried to get a reasonable framing approximation to the zoom in the previous example. Notice that the relationship between the sphere and the cube has changed, you can now see between the sphere and the cube. A paralax shift has occured.

And while we're on the topic, I might as well finish up the lecture. I moved the camera back to the original position (lens still at 60) and panned the camera about 10 degrees. Again notice that since the camera has not translated, that the relationship between the sphere and the cubes is identical to both the first and second examples.

In this example, there is no pan on the camera. I translated the camera in X to the left. Again I tried to approximate the composition from the previous example. And like the dolly example, notice that the shapes are now in a different relation to each other. A parlax shift has occured because the camera has been translated.

Notice that in all of the examples, no shift in the relation between objects at different depths occured until the camera was translated. Changing the lens (and subsequently the angle of view) had no effect on the relationship between the objects.

Moho's cameras work identically mathematically to Maya's. The names may differ, but the principals all work in Moho. I hope this answers your question.

7feet · Post by **7feet** » Fri Oct 15, 2004 7:10 am

Okeedokee. Here's the first image.

.
This is at default apparent focal length, which is approx 60.

This is with a zoom setting of 20 (the inverse of what a real lense would do, but whatthehell), with a camera translation in Z to give about the same perceptual starting point.

If that's not the changing "visual relationship of objects " that you are looking for, please describe more.

--Brian

Ack! Did the same thing as you, kdiddy. Just a little more Moho, I guess.

kdiddy13 · Post by **kdiddy13** » Fri Oct 15, 2004 7:17 am

the inverse of what a real lense would do, but whatthehell

Correct me if I'm wrong, but I believe that rather than attach a lens value to the camera (and deal with film backs and gauges), Lost Marble has decided to go with an Angle of View value instead. Which does make it work as a real lens, just not in numbers that someone using a normal camera is used to thinking about. Perhaps a minor feature request would be to put the degree symbol next to the field. Is this correct? If so, that is really cool and will allow for some very nice integration into 3D work. Next up, who wants to write a Maya camera to Moho camera Lua script? Anyone? (chirp chirp, silence) Anyone?

7feet · Post by **7feet** » Fri Oct 15, 2004 8:16 am

Hmmm, hadn't thought of it that way. Makes sense. I think in the way that physical film works because I still have (and occasionally use) all of my old movie cameras and it just feels natural to me at this point.

Sorry, I can only add to the silence as far as a Maya cam translator goes. I've barely played with it. I was planning on writing a scriipt to import camera paths from Terragen (from the campath plugin?) I've used Terragen for backgrounds in a few bits, and if I could import camera paths, and maybe convert depth fields(don't know if I have the terminology right) into masking layers I think I'd be pretty happy.
--Brian

bellissimo · Post by **bellissimo** » Fri Oct 15, 2004 4:10 pm

ok.....thanks for your input
I can tell you exactly what the confusion has been on my part
Yes indeed...if I change the Z value of the camera position
and reframe the shot with zoom.....
it gives me the effect i'm looking for!
I suppose the confusion for me lies in the control icons.
The "zoom" icon actually suggests that it dollys the camera in and out.
This is not an unreasonable expectation since all the other camera icons
also physically move the camera. It is rather peculiar that the only way to dolly the camera is to enter a value in the Z field(especially when there are so many buttons on screen for rarely used functions)
In my humble opinion it would most practical to have both a dolly and a zoom button...since the anyone using the depth layers would want to easily move through them. I assume a dolly button was left out because moho is primarily a 2d program.....but with such wonderful functionality as the 3d layers....it really should be a button on screen.
Thanks for all the follow ups
cheers

kdiddy13 · Post by **kdiddy13** » Fri Oct 15, 2004 4:30 pm

No problem. I'm glad we got it all figured out and no one got hurt in the process.

If you have a mouse wheel, you can use that to interactively adjust the "Z" value of the camera. Click in the Z value while having the translate camera tool selected and roll the mouse wheel.

I don't have Moho with me at work, but there may also be a way to do that with a key/mouse combination. One of the other resident experts may chime in on this one.

Post by **Lost Marble** » Fri Oct 15, 2004 4:56 pm

If you hold down the Alt key while using the Track Camera tool (the leftmost camera tool), you can move the camera forward and back.

Take a look at the text the the bottom of the main editing window. It gives you some hints about modifier keys for the active tool.

adjusting camera field of view

adjusting camera field of view

true field of view

dolly/zoom confusion