El-Nikkor 75mm f/4N partially disassembled

EL-Nikkor Lens Cleaning and Repair

EL-Nikkor lenses are great values for cost-conscious photographers. They are excellent quality, but also very inexpensive and widely available on eBay. With the advent of digital photography and photoshop, darkrooms are being liquidated. EL-Nikkor are especially useful for macro photography as an alternative to a dedicated macro lens, though you’ll need bellows or a focusing helicoid with extension tubes. For macro, they are particularly suited to flat objects like postage stamps. They are also used in UV photography because they pass UV wavelengths better than regular lenses. They are very high quality glass despite the small size and obsolesce of enlarging. The simple construction and relative low cost of these lenses makes them good candidates for rehabilitation should they become contaminated with dust or fungus. They also make good “starter” lenses exploring lens construction and servicing.I purchased my lens for experimentation in UV and macro. I got a good price because it had some “dust” inside. Unfortunately, the dust was actually fungus. The fungus did not appear to be extensive. Anyway, dust or fungus I was going to end up cleaning it internally all the same. There are instructions and written descriptions of how to disassemble EL-Nikkor on the internet, but none were illustrated with photographs. I wish I had photographs, because the descriptions were not clear enough and I made a few wrong turns trying to sort it out. For the good of the order, let me present what I learned.

I am working mainly with the EL-Nikkor 75mm f/4 N, shown in the steps below. The N refers to the “new” model with plastic housing. The older 75mm f/4 has a metal housing. The easiest way to tell from a picture is that older model EL-Nikkor (pictured to the left) has large notches on the grip surface for the aperture ring, whereas the N is the same all the way around. Disassembly of older, metal EL-Nikkors is similar in that front and rear elements unscrew either by spanner wrench or rubber grip; however, the threaded ring on the rear is fixed in the metal models, so that section of this tutorial does not apply.

The 75mm f/4, old or new, is a simple design of four elements, glued in two pairs, one pair in front, the other in back. All EL-Nikkors are generally simple construction; the 75mm f/4 has four elements, but some EL-Nikkors, such as the F/2.8 models, have six elements. Four elements may be better for UV (less glass means less UV light loss), but for macro photography they say lenses with more elements are better. Wikipedia has a listing of EL-Nikkor lenses.

Old Versus New: An advantage of the older version is that it has no light channel to illuminate the aperture indicator; this channel is a significant source of light leakage, which takes some creative taping to mitigate (see below.) An advantage of the newer “N” version is that it has a standard filter thread size of 40.5mm, for which off-the-shelf step-up rings are available. The older metal version has an unusual filter thread size that requires adapters be custom-made, epoxied, or otherwise improvised.

To disassemble the EL-Nikkor for cleaning

Work in a clean environment. The biggest challenge in this process is reassembling the lens without trapping dust inside.

IMPORTANT: Do not remove the three screws on the barrel. These are part of the aperture selection system, and do not need to be disturbed to clean the interior.

The front bezel includes the lip, inset ring and front lens elements as one piece. The front bezel is best unscrewed with fingers or rubber. I used a floppy rubber mousepad and the palm of my hand. Do not hold the aperture selection ring while unscrewing the front element; rather, hold the fixed housing.
Removing the front element also gives good access to the surface of the bottom element by opening the aperture blades. It may not be necessary to remove the bottom elements, depending on what you need to do. It’s best to avoid removing any more than you have to.

The bottom set of elements can be unscrewed with a lens spanner tool or screwdriver, without further disassembly. (I was able to remove it with my fingernails in the spanner slots.)

Note that there is a loose brass washer between the elements and the housing for the aperture blades in both the top and bottom element chambers; don’t lose them.

Removing the threaded base. Removing the base is not necessary to remove the rear elements, though it does expose them for better access should you have difficulty unscrewing the rear elements. Note that in the older, metal-housing El-Nikkors the threaded ring does not separate from the body, at least in the EL-Nikkor 50mm f/4 and f/2.8 that I have experienced.

Remove the three screws holding the metal retaining ring. In the photograph, the rear elements have already been removed.
The bottom threaded ring beneath the retaining ring will now be loose.
CAUTION: There are three ball bearings between the top of the thread ring and the housing. Do not loose them!
Light Leakage: Note the translucent acetate window on the bottom retaining ring and the associated cavity in the housing. This allows light from the enlarger to light the aperture numbers. This is a significant source of light leakage when using this lens on a camera, particularly my intended use for UV ultraviolet photography. On reassembly, I deliberately offset the ring 120° and covered it with gaffer’s tape to reduce leakage; it reassembles fine with the ring in any position. However, I found that there is still significant light leakage even with the ring offset and covered in gaffer’s tape. It spills in around the seam between the retaining ring and the rear lens assembly. I eventually removed the retaining ring and the threaded ring to expose the ball-bearings and the cavity that channels light from the aperture scale window. I taped the cavity with gaffer’s tape. This has reduced the light leakage. In bright light, I also keep a wide rubber band around the exterior of the lens to cover the aperture scale window completely, yet still give me access to that scale. Gaffer’s tape would also work here, though it is not as convenient if you need to remove it to access the aperture scale. In a pinch, cover the external aperture selection window with a finger, if available.

To separate the element pairs

Fortunately for me, the fungus was limited to a few small spots in the interior lens pairs’ surfaces. It was easily cleaned with hydrogen peroxide and lens cloth, finishing with a lens pen after everything was dry. I cannot see any permanent etching or damage to the lens surface. As a further measure, I left the lens in a sunny window for a few days. However, in some cases, the fungus can grow in the glue between glued elements. Separating glued elements is a radical procedure best avoided. Try sunlight to reduce the fungus first.

I have not attempted to separate glued lens elements myself, but here’s what my research tells me. The glass lens pairs are held in place in their metal housing by retaining rings that can be removed with a lens spanner. The glass lens pairs are held together by a cement, often balsa in older lenses. Balsa can be softened in hot water. More recent lenses will have a different adhesive that will need to be removed with a solvent containing methylene chloride. But then you’ll have to re-glue it–just placing them together unglued will not work because the thin layer of air trapped between the lens elements will cause rainbow moire circles. Here’s some information on lens cement.