Default focal length

sketchup
focallength
default

#1

Is there any rhyme or reason the default focal length is set to 57mm? Can’t seem to find an answer as to why. Thanks.


#2

It’s a 35° field of view. I don’t know why it was chosen but I guess they had to pick something. You can certainly change it and create your own template if it doesn’t work for you at 57mm.


#3

Note that the focal length/field of view in SketchUp is not commensurate with that in a conventional, say, 35mm camera, as the shape of the model window varies. In film cameras the field of view is measured diagonally to the frame whereas in SketchUp the number refers to the vertical direction of the model window. Thus, unless you resize the application window to a portrait orientation, the view in Sketchup is more wide angle than a corresponding one in a camera.

Anssi


#4

Thanks for the detailed answer Anssi and Dave.

We’re basing some views off of photographs and weren’t getting similar results. Changed the focal length to 35mm and the shots now look correct. I guess we were trying to understand why 57mm more than anything else, why not start at something more relative to a camera?


#5

As Anssi said, the angle of view in SketchUp is veertical while the angle of view for a given camera lens is based on diagonal length of the frame. Since the SketchUp drawing window can be made to have just about any proportions, it wouldn’t make sense to try to match the fixed frame proportions of, say a 35mm frame.


#6

Check out Joshua’s tutorial on photogrammetry using Advanced camera tools extension to set up the camera in your model space to match photos.


#7

35 degrees for the pro version and it is 30 degrees field of view for make versions.


#8

In fact it doesn’t depend on the SketchUp version, but the template you use.

Anssi


#9

https://help.sketchup.com/en/article/36261

You can adjust the FOV between 1 and 120 degrees (the default is 35 degrees in SketchUp and 30 degrees in SketchUp Pro)

I guess I wasn’t correct on that point. its the other way, the article of SketchUp website says.
Although I am not sure if this depends on the template.


#10

FOV is but one thing you can save to a custom template, even a scene.


#11

The text seems at least partly to be very old. It refers To SketchUp and SketchUp Pro (so it is at least before the Free version was renamed Make…). I don’t have the version history in my head or elsewhere, but there was a time when SketchUp didn’t have Styles and Scenes were called Pages. I am not quite sure if templates have been there all the time.

Anssi


#12

Scenes and Templates have been around since SU4, though Scenes were called Pages back then. And Pages had the option to save camera. I think Styles was introduced in SU6. Before that, most of the same options were done through the Display Setting dialog and Model Info.

Before File > Save As Template was added, one had to navigate to C:\Program Files\SketchUp\SketchUp XX\Resources\en-US\Templates to either update a template SKP or add a new file there as a new template. The options through Window > Preferences > Templates have always been limited to a few pre-made files and browsing. So a template file could, and still can, be saved anywhere.


#13

I noticed in v2015 Urban Plannin Metre template focal length is set to 57mm and then 67mm for v2016. Curious as to why this was set? Basically I need to make my own template to adjust this? That’s fine, but it still doesn’t explain why those numbers were chosen. Anyway, thanks for the input.


#14

its a bit confusing because it can be shown with focal length vs Field of view. SU will take both “mm” and “deg”


#15

A default focal length of around 55 mm makes sense because that approximates the focal length of the human eye. A much shorter focal length brings the vanishing points so close together that you start to get fish-eye while much longer focal lengths spreads the vanishing parts far apart and the view becomes more like an orthogonal drawing (where parallel lines never intersect).

Of course no human eye is 55 mm in diameter but we are talking about EQUIVALENT focal lengths here. My iPhone6 has an actual focal length of 4.2 mm but since it has a tiny sensor, the net result is an equivalent focal length of 29 mm. That is why, when you take portrait pictures of horses with an iPhone, you get big noses.


#16

Note that the focal lengths and field of view values in SketchUp are not direct equivalents of the same values in a 35 mm camera. In a camera, with its fixed film frame, the values are measured diagonally across the frame, but in SketchUp, with the infinite variety of possible width/height ratios, the measurement refers to values across the vertical dimension of the model window, so that the actual angle is more wide compared to the camera.


#17

Thanks, I was wondering about that. My iPhone has a focal length
equivalent of 29mm but my Match Photo work always yields a FL of about 41.
I wonder if here is a way to tell Match Photo to use 401 since all my
iPhone photos will always have the same focal length.

Regards, Jim
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