Testing the image circle of a lens is rather simple with a test projector but it can be somewhat subjective. There isn’t always a clearly defined hard end to an image when evaluating for coverage. Sometimes a little bit of light falloff is acceptable. A natural vignette can be pleasing but it can also blend into the limit of a lens’ image and make determining maximum coverage rather difficult. I’ve spent years compiling a list of image circles based on my own subjective opinion which was met with great thanks by most – but there has always been the inevitable email or phone call from a disgruntled cinematographer who was disappointed to find that a lens clipped a fraction of a millimeter into the frame of their image despite my records. There are variables, of course, in any analog assessment such as this. Because of this, Duclos Lenses has developed a tool that records the image circle of any lens, saving a reference image for individuals such as yourself to determine to what degree the light falloff is acceptable. This has been a project I’ve been working on for a long time. With the help of our engineers and some back-end support from Phil Holland, I’ve finally been able to complete this tool. I’ll be recording as many lenses as I can in my spare time (who am I kidding… I’m neck deep in lenses and have a one year old daughter) to provide the most usable, comprehensive database of image circles for the industry.
A bit of housekeeping here: I chose a 24x36mm maximum because it will easily demonstrate all of the relevant cinema formats including Micro 4/3, Super 35, Red Dragon, Vista Vision, and everything in between using the integrated scale. Sure there are larger cinema formats (IMAX, Alexa 65, etc.) but those are very specialized and lenses for larger formats are not common by any means. Because lenses are designed specifically for these larger formats, you know they’ll work on those and anything smaller than the format they were designed for.
I’ll be adding my results continuously once I find a permanent home on the web. Check back for a link to that location soon. Feel free to share this post with anyone and everyone or even download the results from a specific lens test. I’m all about sharing knowledge. Enjoy!