Anybody know of a calculator or simulator for size of bokeh balls?

Gavjenks

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I'm not seeming to find one, but I would like to have better knowledge and prediction of this aspect of my photography, ideally avoiding doing a bunch of real experiments myself if possible.

Note: this is not DOF I'm asking about. It's partially DOF, but also partially focal length (makes the exact same bokeh ball in the same DOF larger if longer FL), and distance of the point source compared to your subject. But I'm having trouble figuring out in exactly what relationship.

In other words, I want to be able to predict from a set of parameters about a point source of light how large a bokeh ball from it will be on my sensor ("how many pixels" roughly)



I don't want to calculate it in the field or anything, but it would be helpful in choosing locations or lenses to bring with me to a shoot.
 

unpopular

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Frankly, I am not sure how much knowing would help. Many lenses behave differently at different focal distances, and that the size is only one quality of bokeh that will influences the "feel" a lens has in it's oof region. Bokeh is really more about the interaction of unconfused circles of confusion, and I think that shape and edge quality will have much greater impact.
 
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Gavjenks

Gavjenks

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the size is only one quality of bokeh that will influences the "feel" a lens has in it's oof region.
Yes, but having to learn 5 different variable by experience and intuition is still harder than having to learn only 1 or 2 variables by experience and intuition. If I can get down the technical variables that apply equally to all lenses, then there's less of a learning curve for each individual one.

Don't take my usage of the word "bokeh" too strictly. I'm just interested in this thread in better understanding the size of OOF points of light, only.

Nerdy, what is the point
I said what the point was in my post: Being able to more accurately predict the possibilities of bokeh at a given location and with a given set of lenses, without actually going there and seeing by trial and error. For example, I can say "if I bring this 70-300mm f/3.5-5.6 lens, and I know that I have 30 feet of space between the furthest back I can stand and the background at the intended location, I know ahead of time that I can achieve up to ____ sized bokeh for sure, without having to go there or test it, in case doing so is expensive or in case I have limited time to scope the place."

Or, alternatively, being able to write up a reference cheat sheet to keep in my bag, so that if I only have a limited amount of time with a person (like an impromptu street portrait), I can quickly look up one aspect of the desired bokeh for that shot and get what I want my first time with only seconds to prepare, if bokeh is important to me in that shot.

Yes, that's only one part of bokeh. But that's one less part I have to stand there and use precious mental resources for, or guess and check time for.
 
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bratkinson

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With no concrete 'evidence' in mind, or from any experience at calculating 'bokeh ball size' (no snide remarks intended), I would have to think that it's more than 2 or 3 'factors' in its determination.

To wit:
1. focal length of lens (or zoom lens current focal length)
2. aperture
3. subject distance
4. distance from subject to background (or foreground items if considered for bokeh)
5. number of aperture blades
6. make and model of lens - ie, Canon 50mm 1.2L at f2.8 vs Canon 50mm f1.8 at f2.8 vs Canon 24-70 f2.8L at f2.8 vs <3rd party> 24-70 f2.8 at f2.8. ==ALL== would give different bokeh results due to the design and manufacture of the lens...elements, coatings, type of glass, etc.
7. Type, element material, shape, etc of small, external lights such as Christmas tree lights...LEDs? Grain of wheat bulbs at 12v? at 16v? all those variables

And that only considers the 'size' of the bokeh balls. Throw in colors, brighter at the edges or at the center, or off center brighter, and, of course, the -qualitative- "is it what I want?/is it good enough/better/best?".

So, in my simple list above, already there's 7 variables to deal with, don't forget 'air quality'...clear/hazy/smokey (what KIND of smoke?), humidity, time of day, amount of light coming in window and angle of the sun, cloudy...and the list goes on and on...
 
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Gavjenks

Gavjenks

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5. number of aperture blades
6. make and model of lens - ie, Canon 50mm 1.2L at f2.8 vs Canon 50mm f1.8 at f2.8 vs Canon 24-70 f2.8L at f2.8 vs <3rd party> 24-70 f2.8 at f2.8. ==ALL== would give different bokeh results due to the design and manufacture of the lens...elements, coatings, type of glass, etc.
7. Type, element material, shape, etc of small, external lights such as Christmas tree lights...LEDs? Grain of wheat bulbs at 12v? at 16v? all those variables
Not concerned about any of these. Don't need precision to the 4th decimal place or whatever. I'm happy to assume that tiny faraway lights are effectively actual single points, even if they truly take up 4 or 5 pixels. And pretending blades are magically totally circular is close enough. This is for artistic decision, not laboratory research. I'm concerned about differences of 20-30% or so in bokeh ball size, not 104 pixels versus 102, etc.

Not sure what you mean by #6 - only interested in radius, not quality here. Which should be a deterministic in the same way as if the lens were actually a single element AFAIK.
 

jaomul

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Do you take photographs at all?
 

Dikkie

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Ghaaaa, he's not asking about circles of confusion, but about bokeh balls.

I think the distance and amount of the light is a good parameter.
 

Helen B

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Ghaaaa, he's not asking about circles of confusion, but about bokeh balls.

I think the distance and amount of the light is a good parameter.

Unless you know enough about the lens to be able to calculate the point spread function, the formulae given in that Wikipedia article are about as good as you'll get and they give the best estimate of the size of the 'bokeh ball', as you call it, is the circle of confusion (when there is no lens-specific information and you ignore diffraction). Don't confuse 'circle of confusion' with 'maximum acceptable circle of confusion' as used in DoF calculations. The thing that is often called 'circle of confusion' on the internet is usually the 'maximum acceptable circle of confusion', not the actual circle of confusion. The web is like that.
 

runnah

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I like the term "Circle of confusion".
 

Helen B

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Have you given this site a shot? Newest Questions - Photography Stack Exchange

This is the sort of question that tends to do well over there (well-defined, with an actual "right" answer possible).

This forum laughs at the notion of a "right" answer. Ha ha ha. Just like that.


(The nearest thing to a correct answer has already been given, I think - by photoguy99. )
 
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deeky

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I like the term "Circle of confusion".

I have to admit, "Bokeh balls" makes me smile a little every time I read it.

"Oh, Bokeh balls!!!"
"Got him right in the Bokeh balls."
"Dude, grow a pair of Bokeh balls already."
 

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