We are getting ready to purchase a 3 megapixel IP camera. It comes with either a 4mm or 6mm lens. We will only be using the camera for still image snapshots on a specified interval. Basically, it's an IP camera that uploads a JPG image to the server every 5 minutes. The camera snapshot settings will be set to be a resolution of 1920x1080 (2 megapixel), so the camera will use some sort of mechanism to reduce it to this size. The 4mm and 6mm will both generate a 1920x1080 image, but from my understanding the 4mm will have a field-of-view of approximately 75 degrees, versus the 6mm which will be 50 degrees. So my question is... will the 1920x1080 image generated by the 6mm camera have more detail in it, than the 1920x1080 image generated by the 4mm camera, for the equivalent field of view from the 6mm camera? That is, will the 6mm camera image have more detail than the equivalent 50 degree section of the 4mm camera snapshot?

And, if we didn't set the camera to reduce down from 3MP to 2MP, would your answer still be the same?

  • How are you planning to get an equivalent field of view from different focal lengths? Do you mean that you're cropping image from the wider lens and then resizing to the same target pixel resolution, or do you mean that you're actually moving closer so the framing is the same (except for the shift in perspective)? – mattdm Oct 30 '15 at 19:52

If your resolution is the same (I think you typed that wrong?) and the lenses are otherwise equal, cropping away pixels will take away sharpness.

You will have more detail with the 6mm lens, than you would have by cropping the 4mm lens to show only that 50 degree area.

  • I guess someone may have corrected the typo, I don't see it. Would we still have more detail if we never reduced it from 3MP to 2MP in the first place? – wayofthefuture Oct 30 '15 at 16:48
  • What resolution is your 3mp? I think 3s are usually 4:3, not 16:9, so a comparison will be difficult; without calculating (and I wouldn't even know how, in that case.), I'd expect the 16:9 to still be better. – icor103 Oct 30 '15 at 17:29
  • 2048 x 1536 (4:3?) – wayofthefuture Oct 30 '15 at 18:23
  • Right, that's 4:3. It's a math question now, not a photography one. – icor103 Oct 30 '15 at 18:29

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