Darkroom photo enlarger filter carriage system

ILFORD Multigrade filters let you control the contrast of your darkroom prints, but the small notepad-style holder they come with isn't very practical, especially when working under a dim safelight. The filters are prone to collecting fingerprints and grease, and it's easy to drop them by accident. I’ve came up with a solution that addresses all of these issues.

This carriage system is designed for ILFORD Multigrade filters cut to 7×7 cm. It simplifies filter handling in the darkroom, reduces fingerprints on the filters, and enhances the split-grade printing experience. The system consists of four parts: 12 labeled filter carriages, a storage box with lid, an under-lens filter holder for lenses with 40.5 mm filter threads, and a carriage cradle for split-grade printing. The project is split across multiple build plates. Feel free to print only the carriages and the storage box if your enlarger already has a built-in under-lens filter holder.

Filter carriages

The carriages use small notches to hold the filters in place. No locking system is needed. If later you need to remove a filter from a carriage, it can be done easily without any tools or risk of damage. I recommend using gloves or a microfiber cloth when installing/removing the filters to avoid touching them with your fingers.

The smallest ILFORD filters available are 8.9 × 8.9 cm. These should be trimmed to 7 × 7 cm to fit the carriages. This is because my enlarger has a 7 × 7 cm filter chamber, so my filters have been cut accordingly long before this project.

There are two print profiles: one for AMS, which allows you to print the grade labels in a different color, and another for single-color printing. I recommend the multi-color version because the labels are easier to read. If you're printing in color on the A1-mini, Bambu Studio may show a warning about the prime tower being close to an object. You can safely ignore this warning. The layout avoids any interference with the filters, and it prints on A1-mini without issues.

Storage box

The box dimensions are 12.6 × 5.3 cm, and it is 7.4 cm tall. It is designed to make filter grades easy to read and to allow quick access while working in the darkroom. Each carriage slot is offset by 1 cm from the previous one, which matches the width of a carriage grip. This spacing allows for precise and easy filter selection.

The carriages fit smoothly into the slots without being loose. The lid closes tight, so you can carry the filter box without worrying about your filters falling out.

Under-lens filter holder

This filter holder screws directly into a 40.5 mm lens thread and allows you to swap filters under the lens. I use it with my EL-Nikkor 50mm f/2.8 N lens, but it can be used with any lens that has a 40.5 mm thread. It does not block the image projection, and the filter carriages slide easily into the holder. I keep it permanently attached to the lens.

The print profile uses variable layer height to print the thread with thinner layers, increasing precision. Keep that in mind if you want to remix the model with a different thread. This design is based on my earlier stand-alone under-lens holder model for 7 × 7 cm filters. I had been struggling with split-grade printing on my Durst M301 enlarger. While it has a filter drawer that works fine for printing at a single grade, changing the filter for a second exposure can be problematic. Opening the drawer sometimes shifts the condenser slightly, which moves the negative and results in a blurry double print. The under-lens holder solves this issue.

Cradle for split-grade printing

While doing split-grade printing, I realized it would be better to have a cradle to hold one filter while another grade is in use, instead of putting the filters back in the storage box each time I swap grades. The cradle doesn’t take up much space and allows to quickly place the carriage without scratching the filter.

I wrote a blog post about the development of this project.