Fisheye isn’t Circular


Today’s Question: I rented a fisheye zoom lens (Canon 8-15mm) to try out, because I’ve never used one. I am not getting the circular images that I was expecting. At the widest zoom setting there is a little vignetting, but the image isn’t a circle. How do you achieve the circular image that to me represents a fisheye photo?

Tim’s Quick Answer: It sounds like you are using a camera with a “cropped” sensor, meaning a sensor smaller than full-frame. To achieve a circular fisheye image, you need to use the lens on a full-frame camera.

More Detail: The Canon 8-15mm fisheye lens ( is indeed a genuine fisheye lens, capable of capturing the classic circular images with an extremely wide perspective. I should clarify that the image itself will still be rectangular, but the circular fisheye image will appear within that rectangle, with the rest of the image area being black.

A fisheye lens like this projects a smaller image circle than other lenses, enabling you to capture the circular image effect that is commonly associated with photos captured with a fisheye lens. However, this lens is designed for a full-frame sensor. A smaller image sensor will crop the image circle, so that you aren’t able to see the full circular effect. Instead, at the shortest focal length you will simply see some vignetting in the corners of the image.

This lens includes a “Limit” switch, enabling you to lock the lens so that you can’t zoom out beyond a 10mm focal length. At focal lengths from 10mm onward, you won’t get the vignetting at the corners of the image, because the image circle is effectively being enlarged to more than fill the area of the smaller sensor.

In this case if you want to achieve circular fisheye images you have two options. You can either work with a full-frame camera using one of the various fisheye lens options available, such as the 8-15mm noted above. Or you can use a fisheye lens designed for cropped sensors, such as the Sigma 4.5mm (