Once, I wanted to buy a lens hood for a 55-year-old Yashica Mat-124G. To my surprise, an original hood cost half as much as I paid for the camera body. Maintaining analog camera gear can be tricky, as parts are no longer produced and often have to be salvaged from donor cameras. This is where 3D printing becomes especially useful. It also allows you to design entirely new tools that were never available in the first place.
Recently, I visited a friend who has a 3D printer at home. I was impressed by the quality of the printed models he showed me. They were far ahead of the results I saw ten years ago. At that moment, I realized that having a 3D printer could help me solve a problem I had with my photo enlarger. Coincidentally, Bambu Lab had a sale starting two days later, and I ordered an A1 Mini Combo with AMS. I was on the fence between the A1 and the A1 Mini, but the printer had to fit into the same IVAR rack where my enlarger stands in the storage room. I decided that, for my application, an 18 × 18 × 18 cm build volume would be enough. After getting familiar with the slicing software by printing other people’s models, I ordered a caliper and started designing my own.
The problem 🔗
Photo editing existed long before photoshop, and enlargers allow you to control contrast by blocking specific parts of the light spectrum using color filters while printing on a variable-grade photo paper. There’s also a technique called split-grade printing, where you expose highlights with one contrast filter and shadows with another. This technique gives very precise tonal control over the photo.
My Durst M301 enlarger has a drawer between the condenser and the lens for inserting color filters. It works great when I just need to make a print using a specific grade. The problem comes when changing filters during split-grade printing. After printing the highlights with one filter, opening the drawer and replacing it with a higher-grade filter can shift the condenser slightly. It moves the negative and results in a blurry double print.
Another solution is to place the filter under the lens. However, my enlarger isn’t equipped with an under-lens filter holder, so I had to DIY my own setup using a spoke with a clothespin, attached to the rack with sticky tape. Unfortunately, I don’t have a photo of it anymore. Of course, using such a makeshift setup was cumbersome. For example, if I moved the enlarger head up or down, I had to unstick the spoke, reposition it, and tape it back in place. On top of that, I only had two spokes at home, both used for DIY dodging tools, so I had to disassemble one of them. These inconveniences led me to avoid split-grade printing unless it was absolutely impossible to make a print in a normal way.
The idea and the first prototype 🔗
The IVAR rack I use for my enlarger has holes for pegs in its columns. At first, I thought about designing a filter holder with a mount that fits into these holes. This would make it quicker and easier to reposition the filters, since there would be no need for sticky tape anymore. While I was measuring the depth and diameter of the holes with a caliper, I suddenly realized a better solution. The enlarger’s lens, like most camera lenses, has a thread. So why not design a holder that screws directly into the lens thread? That would be even better than attaching it to the rack. It would move along with the enlarger head, wouldn’t obstruct access to the enlarger, and I could just keep it permanently attached.
Since I had no experience with 3D modeling, I started with a very basic program: Tinkercad, a tool often used for teaching kids. I modeled a simple square holder and cut out a small section to allow grabbing a filter. I connected it to a cylinder with a 40.5 mm thread that I found online by four angled sticks.
Because a 3D printer extrudes plastic layer by layer, it needs to print supports for any overhanging parts. When I sliced my model, the software added several supports to the threaded cylinder. Three of the four connecting sticks broke immediately when I tried to remove the supports. On top of that, the filter didn’t fit between the angled sticks because the distance between them was smaller than the square base I had calculated to hold the filters. The good news was that the thread matched the lens perfectly. Fortunately, 3D printing allows to iterate quickly based on feedback, so I took these issues into account in my new design.
The second version 🔗
For the next version, I used a conical shape to connect the threaded cylinder to the base. To save filament, I cut away unnecessary parts. I made sure the angle was steep enough so the slicer wouldn’t add any print supports. I also slightly modified the front of the holder by removing the border. Increased vertical spacing and clearance ensured that the filter fit easier. When slicing the model, I used dynamic layer height and reduced the layer size while printing the thread for higher precision.
To my surprise, the second version printed flawlessly. After confirming that the filters could slide in and that the holder didn’t block the enlarger’s projection, I happily published the model along with the printing profile on MakerWorld. That same night, I successfully battle tested it by making a split-grade print.
The user experience 🔗
Even though the split-grade printing issue was resolved, I still wasn’t fully satisfied with the overall experience. The ILFORD filters I have came in a small notepad-style holder, which is not very practical, especially when working under a dim safelight. You have to find the correct page based on the grade, place the used filter there, then find another page, carefully grab a barely visible in the dark thin piece of plastic by the edge without leaving fingerprints. If the notepad is not closed accurately, the spring can catch other filters and may even scratch them. The filters are also prone to collecting grease, and it is easy to drop them by accident.
I came up with a new idea. What if I designed a carriage with a grip, like a small frying pan, to hold the filter inside? Or even better, an entire system that includes carriages with labeled grips, a storage box with a lid, and the adjusted under-lens filter holder that fits the carriages?
Designing filter carriages 🔗
By this time, I had learned the basics of Autodesk Fusion and quickly prototyped a two-piece carriage. The filter is placed on a square base with four notches, and a small square piece of plastic is inserted into the notches to lock it in place. It turned out that the lock was unnecessary, as the notches alone were enough to hold the filter securely. I slightly rearranged the notches and added four more so that each side had two. Twelve minutes later, the second prototype was on my table, and I confirmed that the filter sat tightly in place.
After slightly increasing the handle size, I copied the model twelve times and added grade labels in white to make them easier to distinguish under the safelight. Four carriages fit on a single build plate of the A1 Mini. After three iterations, I had all twelve carriages printed and assembled. I also updated the under-lens filter holder model I had made earlier to accommodate the carriage.
Designing the storage box 🔗
My main goal was to make the grips visible and easy to grab. I did some calculations and designed a slotted box where each carriage slot is offset by 1 cm from the previous one, matching the width of a carriage grip. The resulting box turned out to be so long that it would take up too much working space. Besides, it didn’t even fit on printer’s build plate.
The solution was straightforward: the long row of twelve slots was split into two rows of six. The spacing between the rows still allow to read the grade labels and grab a required filter.
The box dimensions are 12.6 × 5.3 cm, and it is 7.4 cm tall. The carriages fit smoothly into the slots without being loose. The lid closes tightly, so if you are using a public darkroom, you can carry the storage box without worrying about your filters falling out.
The cradle 🔗
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 between grades back and forth. The cradle doesn’t take up much space and allows to quickly place the carriage without scratching the filter.
The final product 🔗
I’ve already had several darkroom sessions with the carriage system, and it’s been a game changer. It works flawlessly and looks great. Split-grade printing is no longer a hassle, and as a result, the quality of my prints has improved.
The models, along with detailed descriptions, are available for non-commercial usage on MakerWorld.
The feedback 🔗
I shared the project on r/Darkroom and received positive feedback from the community.
Where were you and 3D printing 50 years ago when I needed you. Very, very nice.
Such a clever and cool thing and love those little tabs with the grade number printed on them. Sure beats handing those fragile filters!
I’ve been thinking about making something like this for my Focomat IIa as well for some time! I think I’m gonna steal your storage box design 😁
I use a color head, so I do not have a filter drawer. If I want to get into split grade in BW, using the filter wheels and the fact that the exposure time changes for each filtering grade is annoying. So that’s a neat idea
Brilliant!!
Oh, awesome! I have been meaning to model this exact same thing and hadn’t gotten around to it!
Someone also told me to wear gloves.
Wear gloves. Should be wearing them anyway when handling negatives, chemicals, and these filters.
I agree that wearing gloves is important when handling chemicals and negatives. But I can only imagine how much harder it would be to swap filters with gloves under a safelight, since doing it with bare hands is already cumbersome.