Author Topic: Logitech C920 vs C922 Pro Steam Webcam Shootout  (Read 1322 times)

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Offline EEVblog

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Logitech C920 vs C922 Pro Steam Webcam Shootout
« on: April 10, 2018, 02:32:22 pm »
How does the new Logitech C922 Pro Stream webcam compare to the venerable C920?

 

Offline Razor512

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Re: Logitech C920 vs C922 Pro Steam Webcam Shootout
« Reply #1 on: April 10, 2018, 04:37:31 pm »
The C920 and the 922 have basically the same internal hardware, but different firmware.

Beyond that, for the objects in the background such as the bottle looking like it is out of focus, is likely due to the shape of the lens. It is really strange in that the center of the frame is at a different focal plane than the sides of the frame.

You can demonstrate this by photographing items close to its minimum focusing distance.

For example at around 2 inches 5cm, you can exaggerate the difference in the focal planes by taking a picture of anything with that has parts taller than the depth of field of the lens.



With this setup, you can see that with the center of the PCB in focus, the the sides of the PCB lose focus:  full size: https://i.imgur.com/OlXT4wk.jpg



If I focus on the sticker which is farther away from the PCB, the center of the PCB loses focus, but the sides start to get into focus: full size:  https://i.imgur.com/73mJoqC.jpg



Overall, the lens is weird and not very well designed.
 
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Offline EEVblog

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Re: Logitech C920 vs C922 Pro Steam Webcam Shootout
« Reply #2 on: April 11, 2018, 04:49:01 pm »
Overall, the lens is weird and not very well designed.

It's supposed to be a Carl Zeiss!
 

Offline mikerj

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Re: Logitech C920 vs C922 Pro Steam Webcam Shootout
« Reply #3 on: April 11, 2018, 09:09:50 pm »
I suspect the QC on lens alignment may not be the best on these, there's a blog showing how to manually adjust the lens to sharpening things up.
 
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Offline Razor512

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Re: Logitech C920 vs C922 Pro Steam Webcam Shootout
« Reply #4 on: April 12, 2018, 10:00:03 am »
The method provided in those guides are designed for if you want to be able to set the focus to infinity (more useful if you want to use it with a program like sighthound or blue iris to turn it into a security camera, but it will not change the behavior of the unevenness of the focus. Basically you are just chancing the flange distance between the lens and sensor.

At normal distances, it is not too much of an issue, but anything up close and you will see blurring as you get close to the edge of the frame, but that blur is not due to the the optics causing less sharpness towards the edge (all lenses have that issue, including the $20,000 zeiss ones do it, though just to a smaller extent), but you get a optical behavior that is not present on any other lens, even smartphone camera lenses. You get a weird effect where the center of the frame and the sides of the frame are at 2 different focal distances. By adjusting the focus you can get the edges in sharp focus, or the center

It is almost as if logitech wanted to cut costs on the number of lens elements used, and went with some kind of compound lens to allow for focusing while also allowing coverage of the entire sensor.

« Last Edit: April 12, 2018, 01:00:02 pm by Razor512 »
 


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