Strange fringe on subject in front of Christmas lights (not lens or body specific)

YuengLinger

EOS R5
CR Pro
Dec 20, 2012
3,511
1,960
USA
I was teaching my daughter about aperture and depth-of-field by showing how Christmas lights get less blurred out by stopping down. I used her dolly as the subject. I was using a 50mm 1.2 on the R6, but later found that any faster lens on the EOS R body also does this. I did not try on the 80D...

Camera was on a tripod. IS and IBIS were off. I tried with and without a B+H UV filter. I was in manual mode. Anti-flicker on or off, same result. Mechanical or EFCS, no difference. (In fact, I could see it through the EVF before taking a shot.)

You can see in the photo the type of fringing I mean. I don't know that it can be properly called chromatic aberration?

When viewed without zooming in, this fringing gives a "bad green screen" type of effect.

A glass also shows a more ghostly type of the same effect.

I tried searching, but couldn't find anything on point. (Google asked, "Did you mean Christmas lights fingering?")

Stopping down reduces and eliminates the effect as the whole subject comes into focus. It's only the out-of-focus area of the subject.
 

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Joules

doom
CR Pro
Jul 16, 2017
1,726
2,135
Hamburg, Germany
I believe there is nothing wrong with your setup, if that is what you are asking.

As objects get close enough to the lens and obstruct a bokeh ball, their shape becomes part of the bokeh ball. It is what allows you to use a cardboard cutout to shape your bokeh balls like stars or hearts for example. I think the combination of small lights (good point source approximations) and the single color of LEDs makes this more noticeable. I have a shot with a similar effect done with my 600D and Sigma 35 mm 1.4 Art.

Your doll seems to 'cast a shadow' onto your bokeh balls, giving it this weird effect.
 

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Kit.

EOS 5D Mark IV
Apr 25, 2011
2,162
1,505
The only thing that I see as suspicious is the dark grey contour at the left side of the hat (in the viewer's coordinate system). Is it caused by uneven light?
 

YuengLinger

EOS R5
CR Pro
Dec 20, 2012
3,511
1,960
USA
I believe there is nothing wrong with your setup, if that is what you are asking.

As objects get close enough to the lens and obstruct a bokeh ball, their shape becomes part of the bokeh ball. It is what allows you to use a cardboard cutout to shape your bokeh balls like stars or hearts for example. I think the combination of small lights (good point source approximations) and the single color of LEDs makes this more noticeable. I have a shot with a similar effect done with my 600D and Sigma 35 mm 1.4 Art.

Your doll seems to 'cast a shadow' onto your bokeh balls, giving it this weird effect.
The spider seems to have the same effect. Thanks. I think this shows the effect is not strange after all, but common in this situation.

My lens was close to MFD, but not quite. The tree was about seven or eight feet behind the subject. (We were going to take the tree down yesterday morning, but when I saw the images from the night before I wanted to hold off and try again with different lenses and bodies last night.)

I was definitely relieved to see the same results on different bodies and lenses!

I wonder if other light sources behave differently. Incandescent? Hmmm. It is not pretty!

KIt., I don't see the grey contour you are asking about. I just had the doll propped up on a stool, more or less centered in front of the tree. Maybe an ornament or something...

PS The kid already beats me at chess. I'm sure she'll be a better photographer real quick too!
 
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