Focal length question

Djb3000 · September 18, 2014, 05:58:56 AM

Hi.
Does changing the focal length of the camera affect the focus in the image? I have changed it from 31 to 23, but can't decide if it has made the image blurry. Is this likely or are my eyes playing tricks?

Thanks

russe166 · September 18, 2014, 07:41:45 AM

Hi!

You may have to change the 'Aperture' to a higher value. Do not forget to click the icon with the circle symbol to see the focus distance in the preview window, and in the render section check the 'Depth of field' option.

Upon Infinity · September 18, 2014, 02:24:07 PM

It doesn't change what the camera is focused on, no. It just changes the focal length (zoom).

Oshyan · September 18, 2014, 02:29:52 PM

No, it does not change the focus point or the depth of field. You change that separately on the Blur tab of the camera settings.

- Oshyan

Djb3000 · September 18, 2014, 03:55:29 PM

Thanks for the reply. Think I need to brush up on photography theory.

Oshyan · September 18, 2014, 04:14:18 PM

Well, to be clear Terragen's camera settings do not always directly emulate a real camera. In a real camera there is generally a link between focal length, focus, depth of field, aperture, etc. Terragen lets you decouple them for more extreme or creative effects. But yes, if you want to get real-world camera effects, i.e. real-world apertures, etc. then you would need to understand photographic theory and typical lens characteristics.

- Oshyan

TheBadger · September 18, 2014, 04:29:00 PM

^^ that is a great idea for a plugin when you release the SDK, Oshyan! I would happily buy a plug-in that auto matched the TG cam to any real world cam one could own... Someone should make that, I'll but it. Then at least theoretically, you could as a director pick your lenses entirely based on what aesthetics you like from looking in photo forums.

Ha! Smarten what I wrote up and tell me where to send the check!

Oshyan · September 18, 2014, 04:33:54 PM

It's an interesting idea. I suppose what you'd want is some small, easily exchanged file format that defined a "lens" profile. Because there are 1000s of lenses, so no way to get them all listed, at least by one person. If everyone can contribute lens profiles to a shared repository, you could have common formats available quickly.

- Oshyan

TheBadger · September 18, 2014, 04:46:05 PM

Hope one of your alpha's for the SDK looks here. I'll volunteer to help collect some, at least the cameras I have, however that would be done. Im sure someone could just contact the camera/lens manufacturer too, and get all the numbers they would need. Probably cannon and nikkon allready have that in some format for just this purpose.

goldfarb · September 18, 2014, 05:07:42 PM

support for the alembic file format would get you part of the way - you could then import cameras from other applications...

Oshyan · September 18, 2014, 05:11:20 PM

Well, you can import cameras in CHAN or FBX already. We're not talking about camera data from another app but rather real-world matching data. Which granted is probably created by many a production in their own 3D apps of choice and could be exported, but as a more general, less project/workflow-specific thing, it would be nice to have camera data available for some uses. Personally I think it may be overkill to try to put it all together and have a plugin for it, but it's interesting to consider.

- Oshyan

TheBadger · September 18, 2014, 11:41:05 PM

It would also be fun if the plug-in injected meta data attached to the render, that says it was made by the camera and lens the plugin copied. Some one could have a bit of fun with that if they wanted

bigben · September 19, 2014, 06:19:46 AM

The key to zooming and DoF is the ratio of the aperture diameter and focal length of the lens.

f-stop = focal length / aperture diameter

In TG the aperture is entered as mm so if you change the focal length and not the aperture diameter, you will be changing the effective f-stop of the lens and thus the DoF. If you take a default camera with an aperture of 5mm, and you change from 31 to 24mm focal length, the f-stop changes from f6.2 to f4.6, reducing your DoF. If you're using DoF for rendering and you zoom the camera, you want to keep the f-stop number constant for it to look "normal"

I think it would be nicer to have the aperture controlled a little like the camera FoV where you can specify either focal length of FoV. i.e. be able to enter diameter in mm or f-stop number. Changing FoV should then keep the f-stop number fixed, so the diameter in mm would need to vary inline with the FoV. At the moment it's the other way around (and we can't specify an f-stop). Photographers think of DoF in terms of f-stop not physical diameter.