Why does bokeh look weaker in the optical viewfinder than in the final photo?
Asked 3/12/2012
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When I took a photo with obvious out-of-focus highlight circles, I was surprised because I hadn’t noticed that effect through the optical viewfinder. The final image showed strong bokeh “orbs,” but in the finder they were much less noticeable.
Why does this happen? Is it because the focusing screen/viewfinder effectively shows more depth of field than the sensor records, because of how the eye perceives the image, because the final exposure makes bright highlights stand out more, or simply because I didn’t notice them at the time?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
28
It's probably a combination of two factors, firstly as you rightly suggest the focus screen plays a role - the view you see in the viewfinder effectively passes through a second aperture and so appears to be stopped down to about f/2.4 - f/2.8
So you can see bokeh through the viewfinder, it will just be much less pronounced due to the smaller effective aperture.
You can readily verify this, put on a fast lens stop down to f/5.6 and press the depth of field preview button (which closes the lens aperture, as if the camera were about to take a shot) you ought to see a darkening. Now stop down to f/2.5 and press the depth of field preview button, now the image in the viewfinder doesn't change as the lens is already stopped down that amount by the focus screen.
See also the accepted answer to this question:
Why is the depth-of-field preview in the optical viewfinder of my Canon 500D inaccurate?
Secondly you were probably focussing your attention on the bottle of merlot, the human eye only sees detail in a very narrow spot in the centre of your vision. The brain moves this spot around to create the illusion that you see the world in detail. If you were concentrating on the bottle you may simply have not actually 'seen' the bokeh in the background.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
14y ago
0
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The main reason is the optical viewfinder/focusing screen. In many DSLR viewfinders, the screen effectively limits what you can see to roughly the depth-of-field appearance of about f/2.4–f/2.8, even if the lens is actually wider. So strong blur and large bokeh discs captured by a fast lens can look less dramatic in the finder.
Exposure and perception also matter. In a dim scene, bright out-of-focus highlights may not seem very prominent to your eye through the finder, but they can stand out much more in the recorded image once exposure and contrast are rendered by the camera.
So yes: it’s mostly the focusing screen/viewfinder design, with some contribution from how bright highlights appear in the final photo versus what you noticed at the time.
A simple check: mount a fast lens and use the depth-of-field preview button. You should see the finder darken as you stop down from wider apertures, but around f/2.5 the finder often won’t show much further change because the screen is already the limiting factor.
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