Wikipedia:Reference desk/Archives/Computing/2015 November 11

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November 11

Digital camera focus length

Not sure if this goes here, or Science, or Miscellaneous. Please move this section if you think it goes somewhere else.

Consider File:Clelland House at maximum zoom.jpg, File:Trinity Memorial ME site, Clarksburg.jpg, File:Court east of Columbia, West Union.jpg, and File:The Stone House historical marker.jpg, all of which I took a few days ago with my Nikon D3200 camera on "Auto" mode, except with manual flash suppression. "Maximum zoom" used the zoom lens, and the others used the normal lens. You can see the lens focus length in the metadata sections of these images. Now the question: since the zoom is adjusted by physically rotating part of the lens (I don't just hit the "zoom in/out" button like on the previous camera), how does the camera know the focal length? Is it because I'm using the auto focus, rather than focusing it manually? I'm nowhere close to being an expert; I don't really understand most of the terminology. Nyttend (talk) 03:01, 11 November 2015 (UTC)

I don't think it's related to the auto focus. I think the lens would just have a sensor inside it which knows the position of the zoom ring and communicate the focal length to the camera. Vespine (talk) 03:19, 11 November 2015 (UTC)

Yes, there is a lot of processing capability in modern lenses, and a lot of data can pass back and forth through the 10 pins you'll see on the lens and the mounting ring. There is a little bit of information in Nikon F-mount, but I haven't struck on the magic Google string to find more details. --LarryMac | Talk 16:13, 11 November 2015 (UTC)