Why do I see a moiré-like pattern in my Canon 600D viewfinder with the 50mm f/1.8?
Asked 10/23/2013
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On my Canon 600D, when I use the 50mm f/1.8 I can see a clear interference or moiré-like pattern in the optical viewfinder. It’s especially noticeable in out-of-focus areas and bokeh, but it does not appear in the final photos. I don’t notice it nearly as much with the kit lens. Is this normal, and what part of the camera causes it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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It sounds like you're observing the laser etched glass focussing screen. A focusing screen requires a rough surface so an image can be formed for you to view through the viewfinder.
Ground glass used to be used for this purpose but now glass etched in a circular pattern with a laser is used, to improve the brightness of the viewfinder when used with slower lenses. This pattern is probably what you're interpreting as moire.
Here's what a standard DSLR focussing screen looks like close up:
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
12y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this is normal. What you’re seeing is most likely the camera’s focusing screen, not a problem with the lens or sensor.
In a DSLR optical viewfinder, the image is formed on a focusing screen so you can see it through the finder. Modern focusing screens are often laser-etched with a very fine circular pattern rather than using traditional ground glass. That pattern can become visible as an interference or moiré-like effect, especially with a fast lens like the 50mm f/1.8 and in out-of-focus areas.
A slower kit lens may make the pattern less obvious because the viewfinder image is different in brightness and rendering.
Since the pattern does not appear in your photos, it is not affecting the actual image capture. It’s just a viewfinder artifact caused by the focusing screen design.
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