(Editor’s note: Tim Grey returns with another guest post. This one answers why the blades that form the aperture in a lens makes a difference.)
There are many reasons to choose one lens over another, both when making a new purchase and when choosing which lens to use for a particular photo. But have you ever stopped to consider how many blades there are in the aperture assembly of a given lens? You might be surprised at the impact the structure of the lens aperture can have on your photos.
Aperture Basics
The lens aperture is designed to regulate the flow of light through the lens. When the aperture is stopped down to a smaller opening (a higher f-number like f/16 or f/22), less light passes through the lens to the image sensor (or film) in the camera. By opening up the aperture to a larger opening (a smaller f-number f/2.0 or f/1.4), more light is able to reach the image sensor. In other words, you can use the lens aperture to adjust the overall exposure for a photograph, along with adjusting the shutter speed and ISO setting. There’s more to choosing an aperture than just setting the exposure. The selected aperture also has an impact on depth of field. Stopping down the aperture creates more depth of field in a photo, and opening up the aperture reduces depth of field.
But there’s even more to the aperture than that.
Blade Count
In theory, the lens aperture forms a circular shape. In actual fact, that shape is not a perfect circle, in part because the lens needs to be able to use the same blades to produce apertures of different sizes. The result is that the aperture shape is more like a polygon or a hexagon or an octagon (you get the idea) than a perfect circle. The “imperfections” in the circle, where two neighboring aperture blades overlap, is what creates the rays of a sunburst effect when the lens is stopped down and a sharp light source is in the frame. And, of course, the number of those imperfections depends on the number of blades used to assemble the lens aperture. In other words, the number of blades in the lens aperture assembly determines how many rays will emanate from the light source in the photo. But the relationship isn’t actually that direct. As it turns out, if the lens has an even number of aperture blades, the starburst effect produced by that lens will include the same number of rays in the starburst as blades in the aperture. So, for example, a lens with a lens aperture consisting of eight blades will produce a starburst effect with eight rays.
However, if the lens aperture consists of an odd number of blades, that lens will produce a starburst effect with twice as many rays as there are blades in the lens aperture. So, for example, a lens with nine blades in the lens aperture assembly will produce a starburst effect that includes eighteen rays.
Making the Choice
Of course, not all photographers are fond of the starburst effect in their photos in the first place. For them, the best approach might be to avoid scenes with sharp light sources, or to make sure not to stop the lens aperture down too much when those types of light sources can’t be avoided. With most lenses you won’t see a significant starburst effect unless you stop the lens down beyond about f/8, with a stronger effect at around f/16 to f/22. Other photographers, myself included, actually like the starburst effect, even though it may seem to be a bit of a cliché. Whenever the scene I’m photographing lends itself to a starburst effect, such as a night view of a city skyline or when the sun can be included in the frame on a clear day, I’m likely to stop down the lens aperture to achieve a starburst effect.
By keeping in mind that the number of blades in the lens aperture will have an impact on the nature of the starburst effect that lens is capable of creating, you can make a choice about which lens to use based on the desired starburst effect.
I’m not sure that this issue will be an important enough factor to impact a photographer’s purchasing decision. For myself, I’ve never actually decided which lens to purchase based on how many blades the lens aperture included.
However, on many occasions I have chosen which lens to take with me on a given trip, and which lens to use when photographing a particular scene, based on the lens aperture blade count. Sometimes I like the more “sparkly” look of a starburst effect with many rays of light, and other times I want a cleaner effect.
An Informed Decision
When it comes to choosing which lens to use for a photograph, it is helpful to consider the many ways that choice might impact the final image. In the case of creating a starburst effect in a photo, the number of blades is worth considering.
Been shooting Nikon for years, and just cannot get the long ray sun stars that everybody is talking about or you see in portfolios……..did some looking and all the best seem to be either shooting Canon or using 3rd party lenses………..Nikon just does not step up to the bar on this effect, or I just don’t get the method……..used everything from 18 to 200 mm, used f11 to f32, used ISO from 200 to 1600, tried every shutter speed those settings will work with, shot golden hour, mid-day, mid-afternoon & morning, used trees – buildings – mountains as blockers……..just can’t… Read more »
Hi Bill
I’m also a Nikonian 📸❤️
You should buy another better lens:
24mm f/1.8G
Or Tokina 16-28 f2.8 FX or Tokina 11-16mm f/2.8 for DX camera.
Or Sigma 20mm f/1.4
Or Nikkor 24mm f/1.4G
At around 8pm or 30 minutes before Sunset, find a tree that you still can see the Sun, then Shoot at F16.0, ISO 800, speed 1/60s or 1/100s
Show me your work then ^.^ you’re gonna love it 📸❤️
Obviously i understand that different lenses gave you different results but my goodness i didn’t realize it came down to this – phenomenal post. I do try and incorporate sunburst shots in my photos especially Wedding pictures but i had no idea my lens build could determine what happened to the final result.
The shape of bokeh points is also affected by the number of blades.
Agreed, and I think that’s FAR more important than sun rays. OoF highlights that are pentagons, I find distracting. They’re hard to not see.
I wonder if lens coatings have helped reduce flares as Bill seems to have trouble reproducing them.
Been shooting Nikon for years, and just cannot get the long ray sun stars that everybody is talking about or you see in portfolios……..did some looking and all the best seem to be either shooting Canon or using 3rd party lenses………..Nikon just does not step up to the bar on this effect, or I just don’t get the method……..used everything from 18 to 200 mm, used f11 to f32, used ISO from 200 to 1600, tried every shutter speed those settings will work with, shot golden hour, mid-day, mid-afternoon & morning, used trees – buildings – mountains as blockers……..just can’t… Read more »
Obviously i understand that different lenses gave you different results but my goodness i didn’t realize it came down to this – phenomenal post. I do try and incorporate sunburst shots in my photos especially Wedding pictures but i had no idea my lens build could determine what happened to the final result.
The shape of bokeh points is also affected by the number of blades.
I wonder if lens coatings have helped reduce flares as Bill seems to have trouble reproducing them.
The information in your article was enlightening – thank you.
Let’s say there are two similar performing lenses of same focal length. One has 5 straight blades and the other 10 straight blades. If shooting both at the same exposure settings, would there be a significant difference in the quality of the rays?
Thanks. That’s really interesting. If you wanted to go deeper, you could explain why odd number double and even numbers don’t. I don’t understand how or why that would happen but of course.. I don’t need to. Just theoretically interested in how that is possible. Great article thought. Thanks.