I took up photography late in my senior year of high school, and since then have invested myself in taking pictures not just in novel places but in novel ways. I recently discovered that covering part of a camera lens leads to interesting background blur effects, and there are several online creators and sellers who make these products. This is my own attempt to create and experiment with such lens filters, and an excuse to learn resin printing at Stanford's Product Realization Lab.

Design decisions

For this project, I wanted to experiment creating lens filters of my own without incorporating optical glass (I leave this for future work). Instead, I wanted to fabricate a unified filter body that could be easily attached to the front of my camera and achieve a desired photographic effect.

Modern camera lenses have an internal thread at the front, where filters, adapters, and other attachments can screw on. Creating an external thread that could fit in this well was a key focus of this project.

The fine details of a filter and its threading could only be achieved with very high resolution, and for optical performance should be printed or painted black. For these reasons, I settled on using resin printing with a black resin for prototyping.

Thread tolerances

Camera lenses have various thread diameters and pitches, which describe how wide and tall the spiral forming the thread is. A standard, moderately sized lens has a pitch of 0.75mm, and my lens (a Sigma 18-50mm f/2.8) has a diameter of 55mm. With these measurements in hand, I wrote an XML file to create a custom thread profile in Fusion, which does not offer in-app selection of these parameters beyond limited presets.

I further used this thread calculator to compute different thread tolerances for the profile; I returned to this tool several times during prototyping to increase tolerances for threads.

Other features

To allow photographers to easily screw in and remove the filter, I added little ridges to the top and sides of the model (see CAD design above). I also added an external thread at the top of the filter, to help with storage of the filters and in case anyone wishes to combine these with additional attachments.

In addition to the swirl filter, I created a slit filter, wave filter, and heart filter, intended to make the background blur (bokeh) of a photo appear as that specific shape.

Samples and conclusions

Here's a demonstration of the swirl filter! The swirling effect of the photo is clearly observable, and is not the product of lens distortion itself but the light that is blocked by the filter in different regions of the field of view.

In comparison, here's a sample from the slit filter:

With this prototype, the slit was made too narrow so it unintentionally blocks the camera sensor's field of view. However, it still provides for a nice effect in the bokeh!

To conclude: I learned lots about resin printing and thread tolerances through these lens filters. Because of the involved post-processing for resin prints, I haven't been able to create all of the filter designs yet, and would like to pursue that next quarter. I'm encouraged by the prototype results with the slit and swirl filter, and see an opportunity here to apply physics of light concepts to more work with camera lenses in the future!