Understanding Vignetting

There seems to be a lot of discussions about Vignetting as far back as can remember. Many of these discussions are based on misunderstood facts about what exactly vignette is and what causes it. Here I will attempt to share some of the things I have learned by research and by good old trial and error.

First, Lets discuss what it is:

Wikipedia describes it as: "a reduction of an image's brightness or saturation at the periphery compared to the image centre." In other words its the darker corners on your images, wether you are talking about photography or video, its the difference in brightness on the edges.

Now what Causes:

Wikipedia lists 4 main reasons why vignette occurs;

• Mechanical Vignetting
• Optical Vignetting
• Natural Vignetting
• Pixel Vignetting

It explains that in the Mechanical type if light coming into a system is blocked by external objects such as filters, secondary lenses, and improper lens hoods, there will be vignetting caused by this things.

Optical Vignetting is caused by the physical dimensions of a multiple element lens and is sensitive to the aperture and can be completely cured by increasing the aperture of the lens.

Natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays, but rather to the laws of physics.

Pixel vignetting only affects digital cameras and is caused by angle-dependence of the digital sensors

So because Mechanical vignetting is pretty easy to understand, lets discuss Optical Vignetting. Optical vignetting is completely tied to your SLR lens, and depending on the type, brand and the specs of your lens that will determine the amount of vignette you will get. I took 3 lenses and my canon 5DMKII outside to test how much vignette i could get just straight out of the camera, this allows us to see the lens performance in its designed normal configuration.

I consider Canon EF L lenses and Carl Zeiss lenses to be the best in the world, yet here they don't seem to do much better than the old FD 50mm f1.8 lens. So to some degree all lenses suffer from this phenomenon, some more than others but it is a normal part of SLR optical systems.

Vignetting on 35mm adapters

So how does all of this affect us JAG35 users? Well a lot of discussions that I've come across and many emails we get point to the fact that many think that vignetting is entirely due to the DOF adapter itself and they'll ask "how much vignetting does your adapter make?" As I see it, specifically applied to the 35mm application, vignetting is due to 3 main reasons:

• The amount the lens produces
• The amount the 35mm produces
• The amount wrong settings produce

So because we are using SLR Lenses in a way they were not designed to be used, vignetting will be more than on a SLR body, but this doesn't mean there is nothing that can be done about it. In this next section I will elaborate on what very simple techniques you can use to eliminate this unwanted phonomenon.

To be continued..............