4x5 enlarger conversion, DIY LED head
This article was originally part of a website I maintained. The website is no more, so I wanted to update some information and place the contents of the old page here for anyone who may still find it interesting. This project was one I thought was really interesting and fun. In it I took an old medium format Beseler 23C enlarger and converted it to work with large format 4x5 film. I also made a homemade light source for it using LED lighting.
What I thought was incredibly useful about this project is the size of the enlarger. If one looks at the currently available choices of 4x5 enlargers, you'll notice they're really big, bulky and heavy machines. The baseboards alone are 20x24 inches or bigger. Fully assembled these enlargers are far too heavy for one person to move and wont fit through most doors. At the time when I wanted to make black and white prints at home it was a temporary arrangement in either a bathroom, in a utility room working on the flat top of a washer and drier set, or in a broiling hot garage (I now have a permanent darkroom setup). Every single bit of equipment had to be sized so that I could lift or move it myself fully assembled, and it absolutely had to be portable.
I chose an older Beseler 23C II-XL condenser enlarger for my 4x5 conversion project. The slim but tall size of the enlarger easily fits through narrow doors, the chassis is solid and sturdy and most importantly the enlarger isn't too heavy for one person to pick up for moving around. The modifications aren't difficult with a minimum of tools needed. Nearly everything original to the enlarger is reused--with the exception of the glass condensers and upper lamphouse as they were never meant to cover a large format 4x5 frame. Please note: the changes I make to this enlarger (the bellows in particular) make it unusable for 35mm film. Its sole function is to handle 4x5 film.
The enlarger frame. Disassemble the enlarger down to the flat carriage attached inside the frame rails. Be careful to handle the bellows with care, as both the top and bottom set will be reused. The lower bellows are simply glued to the bottom of the negative stage and can be carefully pried free with the flat end of a large bladed screwdriver. The upper bellows can be removed by grasping the ring shaped top half--where it attaches to the condensers--and pulling down. These are similarly glued to the upper half of the negative stage and should be carefully pried free as well. Clean all the various parts thoroughly as this is the ideal time to do so.
The first modification is to the negative stage. Beseler 4x5 negative carriers are too big to fit on the 23C, but interestingly Omega 4x5 negative carriers are ideal. I used contact paper with a self adhesive backing to draw an outline of the Omega carrier on the negative stage of the 23C then milled out the opening with a Dremel tool. The Dremel bits are small and this task can be a little tedious yet careful attention to following the outline exactly (and lots of test fits with the Omega carrier) will create a neat and exact fit. The exact same process is done with the much thinner upper negative stage; this will become the base for the LED head. The second change is to the bellows. As-is, the original 23C bellows work but are stretched to the limit for 4x5 use. To ensure plenty of bellows extension I glued the upper and lower bellows together with contact cement into a extra-long set, and re-attached it to the bottom of the negative stage.
The next change to the enlarger is to its maximum focus travel. On the 23C a pair of long chromed steel rods serve as the supports for the lamphouse, negative stage and lens stage to attach to. As originally built there is just barely enough travel on these rods for the lens stage to focus a 135mm lens for an 8x10 sized print from a 4x5 negative. With the top lamphouse removed, about half the length of these rods stick up above the negative stage completely unused. The two rods of my 23C (check your particular model as this varies) are held in place by four set screws on the back of the negative stage. By loosening these set screws the rods can be dropped down adding many inches of new focus travel. The now longer lower lens stage needed a surface to rest on, so I cut and added a length of 1/2" thick plywood (as well as sanded, primed and painted for a nice finish) to extend the flat carriage for the lowered chrome rods. The plywood extension is held in place with six screws drilled through the back of the metal flat carriage inside the enlarger rails. Don't be put off by the use of plywood--a short length of it here is actually quite rigid!
The last task is the addition of some counterweight. The 23C has two long metal springs running up both the sides of the frame that assist the carriage in smoothy cranking up and down. With the old lamphouse and heavy glass condensers gone some weight needs to be added to the carriage to re-balance it. I found some old telescope counterweights--small, heavy, and already finished in black to blend in with the enlarger. I bolted these to the rear of the moving carriage to keep them solidly in place.
The lamphouse design. LEDs are a fascinating project to use for a darkroom enlarger. They're easy and fun to work with, but you do need to be careful in choosing the right kind for the best results. This article shows the second LED head I've built for black and white printing. The first version I made I simply grabbed a bunch of lights and put them together in a head to see if it'd even work. For this head I wanted to find the best combination of components.
The very first thing I wanted to do was find out just how variable contrast black and white paper reacts to various LED colors. I'm not skilled nor technically savvy enough to assemble and solder individual LEDs by hand, so I purchased instead some incredibly nifty premade LED strips from superbrightleds.com. The strips I chose--called the NFLS series--work on a safe low voltage twelve volts DC, are available in a variety of colors and neatest of all they're built on a flexible self adhesive base which can be cut to any length with ordinary scissors. To make assembling the LEDs even simpler the website offers solderless interconnects which I would strongly recommend--the soldering pads on these LED strips are very small and are difficult to neatly heat solder wires to.
To test how darkroom paper would react to the various colors of LED lights I ordered samples of useful colors--green, blue, white, ultraviolet, and a all-in-one red-green-blue LED--and mounted these to a plastic board. This board was then clamped to my enlarger with the LEDs pointing downwards to the baseboard in a contact printing setup. Each set of lights was turned on individually for printing. I made contact prints of a Stouffer 21-step wedge on fresh Ilford Multigrade IV RC paper. The various printed densities of the step wedge would indicate the contrast each color of light generated with the paper. The paper was given enough exposure so that steps one and two of the wedge printed as maximum black. Step number three in the prints is a very dark gray, barely distinguishable above black. This was repeated for each color. By following this pattern I ensured that each print had enough exposure to show a full range from paper base white to deepest black.
Based on my simple experiment I decided to use white LEDs only in my new enlarger head. On the web forums I frequently see people proposing the idea of a green and blue LED enlarger head. The idea is that because variable contrast paper is sensitive to these colors--green for soft contrast and blue for hard contrast--a enlarger head could be made using just these two colors for infinitely adjustable contrast. I wanted to include green and blue LEDs in my tests to see if they'd indeed work.
Sadly they're great in theory but don't work out in practice. The green is actually okay, but the chief culprit and major obstacle is the blue. The problem as it turns out is that green LEDs aren't just green and blue LEDs aren't only blue. You wouldn't think it to look at them while they're on, but blue LEDs are actually a combination of green and blue light. That little bit of green is what screws up their use for the hard or high contrast grades. Print with a blue LED and you won't get above the equivalent of a grade 3 paper. Green, interestingly, presents no problems and will print soft grades easily. To see this for yourself you can build a simple spectrometer from instructions on the web. A spectrometer is very useful as it takes light and then separates it into all of its component colors. Below are the step wedge tests I made and samples of various light sources useful to the darkroom with my homemade spectrometer. Please carefully note the green sneaking into the spectrum of the blue LEDs.
There's also one other problem with a blue-only green-only LED enlarger head: the sensitivity of VC paper changes *drastically* with the color of the light. In my testing I noted that green-only exposures take a a fair amount time to expose paper fully. Blue takes but fractions of a second. Variable contrast paper does not have an even response to the two colors of light. Adjusting the amount of blue and green will have the added headache of simultaneously changing the basic print exposure time.
Ilford (and once upon a time, Kodak) solved this for variable contrast paper with their VC printing filters by building in varying amounts of neutral density into each filter. Every filter has slightly different amounts of neutral density so in use when a #2 is replaced with a #3, the underlying basic exposure for the paper is still the same.
Based on all of these experiments I wholeheartedly chose white LEDs for my enlarger. It's far simpler to build with one color and despite what the forums say there's absolutely nothing wrong with under the lens printing filters.
Building the lamphouse. The base the LEDs are attached to is a sheet of 3/16" black acetal plastic seven inches by six inches from U.S. Plastic. Each LED strip is six inches long, not including the interconnects. Installation is easy, just cut to length, peel and stick. There are several horizontal rows and one vertical row in this design. There are a total of 225 white 4500K LEDs in my lamphouse.
The most practical way to even and smooth out the numerous sources of light from so many LEDs is diffusion, so I ordered a sheet of 1/8" white acrylic (manufacturer #2447, 54% light transmission) from U.S. Plastic to use as a light diffuser for the LED head. The next task was to determine the optimum height the diffusing plastic sheet should be from the LEDs. If the sheet is located too close to the LEDs, the light from the LEDs creates dozens and dozens of hot spots. Pulled farther away, the lighting can be made completely even but too far creates light falloff. The trick is to get it close, but just far enough away so the light is completely uniform.
To determine the optimum diffusion distance I made a series of mat board frames at various heights to incrementally space the acrylic plastic from almost touching to a few inches away from the LEDs. The various spacers were placed on the LEDs and the plastic on top of the spacer. The LEDs were turned on and the arrangement was then photographed with a digital camera; the exposure in the camera was locked in manual mode with the white balance also locked. Each spacer was photographed using the same exposure and white balance. In the computer I opened each photograph, cut and pasted each image into a long single row, and hit the collage hard with the levels tool in Photoshop to exaggerate and highlight any unevenness of light on the plastic sheet. The first visually even surface was my optimum distance.
The entire assembly is fitted in a mat board enclosure I carefully made to fit the top of my enlarger exactly where the old condensers used to be. These LEDs generate little to no heat, so no heat sink is needed and just about any material can be used to house them. The interior of the box is lined with several layers of aluminum tape making it completely light-tight. The top slides on and off like a shoe box and has a small hole for the power cord.
An important note abut power supplies. You don't need anything fancy. A ordinary very common twelve volt wall-plug-in transformer is all you need. No "drivers" or "PWM controllers". What you will however likely need is a mechanical relay to go between the power supply and your darkroom timer. Here's why:
Nearly all of the plug in power supplies you'll find are going to be what's called a "switching" adapter (take a look at the charger of your cell phone for an example). What that means is the adapter will take a wide variety of voltages at the wall, very handily detect the amount of current the device it's connected to requires, and will automatically adjust and supply the correct amount of electricity. Very nice. The problem is that it takes these adapters several seconds or more to do this feat once they're plugged in. If you take one of these power adapters and plug that directly into your enlarger timer for the LED lights in the enlarger--every time you trigger the timer that adapter will have a delay--two seconds or more--while it detects and powers up before the LED lights will illuminate.
This can be solved with a mechanical relay. The relay works a bit like a remote on-off light switch. Inside the relay is a very small electromagnet (the "coil") that when powered, makes a mechanical connection between two switched outlets. When the electromagnet turns off, it breaks the connection.
How it works: connect the outlet of your enlarger timer to the electromagnet "coil" side. When your darkroom timer is triggered, this will power the magnet and cause the relay to physically connect its terminals. On the switched part of the relay are the connections for the LED lights. The power from the wall adapter goes into one set of terminals, and the matching connections to the LED lights in your enlarger go to the corresponding terminals of the relay.
The power adapter for your lights is plugged directly into the wall--it will now be fully powered up and ready to go instantly. When the darkroom timer is triggered, it energizes the electromagnet in the relay, which makes the mechanical connection between the wall adapter and the lights in the enlarger.
If wiring these connections make you a little nervous (did for me, thankfully I had help) there is a second option. While the switching type adapters are now very common, you can still find the older "fixed" or "linear" adapters. These don't have the circuitry in them that adjust to different voltages. They do have to be matched to voltages and you have to choose one that provides just enough current for the load of your LED lights. They work because when these adapters receive power (like in the outlet of your darkroom timer), they instantaneously provide current to whatever they're connected to. There's no delay at all with these. The only downside is they're a bit bulkier and heavier than the switching type adapters, and you must carefully add up the electrical load of all the LEDs to match as closely as possible to the output of the adapter. The plus is that it's not difficult--just plug it into the timer--and you don't need a relay for it.
The enlarger in use. It works very well! It fits through small doors with ease, it handles 4x5 film, and the entire project can readily be done by one person in the corner of a their garage or desk. The light source is a bunch of LED strips in a mat board box, yet the illumination absolutely even and completely homemade. Pretty cool! Overall dimensions of the modified enlarger are 17 1/2" wide (including side elevation handle), 26" deep, 45 1/2" tall and the weight of the enlarger is 45 pounds.
With under the lens filters, I have no problem printing any of the contrast grades from -1 all the the way to 5+. Curiously, each numbered filter matches grade for grade and step for step how my fluorescent Aristo v54 lamp prints. So, if you're looking for a cold light and can't find one, or you need a light source for 5x7, 8x10 or bigger--this is a very credible option.
I spent many months and went through a lot of parts, trial and error to complete this enlarger. Benefit from my mistakes! I would be happy to help with or discus any part of this project.