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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 24 Jun 2012 (Sunday) 22:11
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Why is the bokeh not round at maximum aperture?

 
greenjacket
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Jun 24, 2012 22:11 |  #1

I took some pictures last weekend using 85L at f1.2. Bokeh of head light of car is not perfect round. Does anyone know why and how to get perfect round head light?

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FlyingPhotog
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Jun 24, 2012 22:20 |  #2

Look closely at the back of your lens...

See where the contacts are? ;)


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PUREBRAD
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Jun 24, 2012 22:42 |  #3

FlyingPhotog wrote in post #14627107 (external link)
Look closely at the back of your lens...

See where the contacts are? ;)

Can you explain what you said?
I don't own an 85L, but kinda curious about that effect.

On the left side of the image, the circles have a slice missing on the right side of the circle.
On the right side of the image, the circles have a slice missing on the left side of the circles.

Is this particular to the 85L?


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Scatterbrained
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Jun 24, 2012 22:54 |  #4

PUREBRAD wrote in post #14627191 (external link)
Can you explain what you said?
I don't own an 85L, but kinda curious about that effect.

On the left side of the image, the circles have a slice missing on the right side of the circle.
On the right side of the image, the circles have a slice missing on the left side of the circles.

Is this particular to the 85L?

The contacts on the 85L are essentially mounted on the glass, blocking part of the image. To see this effect in action, you can take a piece of thick paper, cut a square or other shape into it and place it over the front of the lens. With the lens wide open you can throw it out of focus (hopefully with some specular highlights in the background) and move the lens around. As the out of focus elements move around in the frame they'll encounter the cut out and be partially blocked. The OOF specular highlights are essentially being flagged by the cut out (or in the case of the 85L the contacts) when at an oblique angle to the lens.

I have an example here of a cut out in front of a 50L wide open that demonstrates this:

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Mickey Mouse Lights (external link) by tltichy (external link), on Flickr

If you look you'll notice that not all of the "mickeys" are complete. Some of them are cut off in various areas, despite all being created by the same cut out on the lens.

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arentol
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Jun 24, 2012 23:03 |  #5

FlyingPhotog wrote in post #14627107 (external link)
Look closely at the back of your lens...

See where the contacts are? ;)

Wow. Not helpful at all. You would think with 52k posts you could offer something useful to the discussion.

OP, check out this thread, especially post 11.....

https://photography-on-the.net/forum/showthre​ad.php?t=985868

Also look at post 13 for a visual of what Flying is talking about, which is not the cause of your primary issue in that shot, though it can indeed cause some issues.

The good news is that stopping down will help with the issue, so it comes down to finding a happy medium... Perhaps f/1.8 would get the best of both worlds (not sure as I don't have the lens).


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Scatterbrained
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Jun 24, 2012 23:10 |  #6

arentol wrote in post #14627242 (external link)
Wow. Not helpful at all. You would think with 52k posts you could offer something useful to the discussion.

OP, check out this thread, especially post 11.....

https://photography-on-the.net/forum/showthre​ad.php?t=985868

Also look at post 13 for a visual of what Flying is talking about, which is not the cause of your primary issue in that shot, though it can indeed cause some issues.

The good news is that stopping down will help with the issue, so it comes down to finding a happy medium... Perhaps f/1.8 would get the best of both worlds (not sure as I don't have the lens).

Interesting. Actually the visual was post 14, and quite interesting. I can say with the 85L that by f2 it is barely discernable at the edges of the frame, vs at 1.2 where it can be pretty obvious.


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greenjacket
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Jun 24, 2012 23:26 |  #7

Thanks arentol and scatterbrained for offering the explanation and solutions. Very helpful in the future outings.


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Why is the bokeh not round at maximum aperture?
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