I am a relatively recent convert to the joys (and unpredictability) of pinhole photography, even building one myself not so long ago. As with the majority of my film photography I tend to use black and white film in the pinholes, indeed cannot remember ever having used colour film in one. I have pinholes that accept 35mm, 120 and 5×4 film of which my most-used is a Zero Image 612b, multi-format pinhole that uses 120 film. It is multi-format in that it has a pair of baffles inside that can be moved to facilitate using the camera at 6×4.5, 6×6, 6×7, 6×9 and 6×12.
As a black and white photographer I routinely use filters to control contrast, indeed with most of my film cameras a yellow or yellow/green filter is ever-present on the lens. However, my Zero Image is the basic version and therefore has no bells and whistles such as external filter rings. I lack the tools and skills to adapt the front of the camera working around the sliding “shutter” so have reluctantly accepted the lack of filter options.
I have recently modified the Zero Image to accept filters internally. I did this by taking a 25-37mm step up ring and asking my grandson to take the 25mm thread off (without removing his own fingers). This was then super-glued inside the camera, with the pinhole centrally situated within the ring. Because of the camera’s internal dimensions a 37mm filter ring was the largest filter diameter I could accommodate and still screw filters on/off with my old fingers. By incorporating a screw thread inside the camera and purchasing a few small filters I am now able to use not only contrast control filters but also a 720nm filter to enable me to use infrared film with the pinhole. The only downside is I have to choose upfront what filter I will need and install it before loading the film. In addition, I cannot change the filter part way through the roll. Other than that it works fabulously though and the 37mm yellow filter is rarely out of the camera.
At the 6×12 setting the outer edge of the ring is visible onthe edge of the negative as a very definite vignette BUT once cropped the usable negative area still measures 6×12.1. There are no issues at 6×6, 6×7 or 6×9. I haven’t yet tried 6×4.5 but on this evidence I do not envisage problems, although I very rarely use the smallest negative size with this camera.