Have you seen custom bokeh effect images before?
Do you know how this kind of bokeh image is created? Photoshop?
No. This kind of custom bokeh effect is created by adding a custom made aperture on to the lens.
The Custom Bokeh Effect Concept
“In photography, bokeh is the aesthetic quality of the blur produced in the out of focus parts of an image produced by a lens. Bokeh has been defined as “the way the lens renders out of focus points of light”.” – Wikipedia
To make a custom shaped bokeh, you are going to change “the way the lens renders out-of-focus points of light”.
In other words, the aperture shape. To help you understand this technique, let’s study how bokeh is formed.
I recommend that you get a better understanding of the physics of bokeh, as it can help you to come up with new ideas.
How is Bokeh Formed?
When you use manual focus mode and start turning the focus ring to out of focus, the subject will become blurrier. When the subject is a point of light, the result is what we call “bokeh”.
Above, the image shows the simple physics refraction model of how being out of focus makes an image become blurry.
Light passes through the lens and then converges on to the camera sensor. If the point of convergence can hit on the sensor, the image is sharp.
On the other hand, when the subject is placed too far away or too close, making the point of convergence fail to hit the sensor, images become blurry.
Relationship Between Aperture and Bokeh
Bokeh size and blurriness depends on a few different parameters. However, bokeh shape only depends on the aperture. Bokeh shape is the same as the aperture shape.
Here, I am going to test the bokeh with two lens, Nikon 50mm f/1.8 (aka the nifty fifty) and the Nikon 300mm f4. Both lenses have a manual aperture ring which let you see how the aperture looks under certain f-numbers.
I am going to test both the wide open and the f/8 to see how changing the aperture size affects the bokeh effect.
50mm at f1.8
50mm at f8
This 50mm lens has a 5 blade iris. When it is at f1.8, you can see that the iris is a round shape and its bokeh is also a perfect circle.
When you step down to f8, you can see it becomes a hexagon. The bokeh, hence, becomes a hexagon, too.
300mm at f4
300mm at f8
The 300mm f4 contains a 9 bladed iris. Even if it is at f8, the bokeh is very close to a perfect circle.
Creating Custom Shaped Bokeh
From the experiment, you can see that the shape of the bokeh is highly dependent on the shape of the aperture.
Therefore, in order to create a custom shaped bokeh, you need to create a custom shaped aperture.
Below, I am going to show you a basic DIY method for creating a custom shaped aperture.
This DIY method is great for making simple shapes like stars, hearts and trees.
Tools you Will Need:
- Black cardboard
- Craft knife
- Drafting compass or circle cutter
- Puncher (for more complex shapes)
- Patience (not for sale)
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How to Make your Custom Bokeh Filter
1. Use a compass to draw a circle on the black cardboard. The circle should be the same size as your lens, which is the size of your filter mount.
2. Cut the black cardboard circle with a crafting cutter or circle cutter. You need to fit the black cardboard on to your lens nicely.
3. Mark the centre of the circle.
4. Draw the shape you want to make with a pencil. Don’t make it too big or too small. If you are using the nifty fifty, draw a 1-2cm shape. If you are using another lens, try to draw it a size similar to the aperture at f/8.
5. Cut out the shape with a crafting cutter or use a puncher to punch a more complex shape.
6. Have fun with your DIY bokeh filter.
Using the DIY Bokeh Filter
It is not difficult to use your bokeh filter. Simply place it in front of your lens, use the widest aperture, manual focus to make the view out of focus and shoot.
Metering may fail after you have put on the black cardboard because you have changed the light intensity going in to the camera.
Aperture priority mode, nevertheless, is still a good tool to use for your first try.
You have to use the widest possible aperture to create the custom bokeh. When you are using the custom bokeh filter, you are actually changing the iris of your lens.
To ensure that your DIY filter is the dominating shape, you need to make the aperture on the lens bigger than the cut out in the cardboard.
Manual focus is another trick. As the light intensity going in to the camera is lowered by your cardboard, auto focus may fail.
As you are doing bokeh photography, you need to be out of focus. Manual focus is always the best choice.
Suggested Lenses for Creating Custom Bokeh
Not all lenses works well with this technique. From experience, I have discovered a few factors that make a lens work with this technique.
I have tried to use a Nikon 70-200 f2.8 to create custom bokeh and I failed. However, I had great success with a Nikon 24mm f2.8, a Nikon 35mm f2 and also a Nikon 50mm f1.8.
After some investigation, I think it is because of the lens length – not the focal length, but the physical length of the lens. Shorter lenses give a better custom bokeh effect.
Both 50mm f/1.8 and 50mm f/1.4 work perfectly with this technique. However, a wider aperture lens is always better. It gives a sharper and smoother image.
For creating bokeh, longer focal lengths have an advantage. However, to create custom bokeh, due to the lens length factor, you cannot use a tele lens.
From my experience, I find the best range is 24mm to 85mm.