A note before we begin. This article describes a camera repair I did at a point when I had almost no idea what I was doing. I have since done a lot more repair work and learned a great deal about how cameras come apart, and developed a better feel for when to attempt a job myself versus when to send it to a professional. If I were doing the same job today I would do it differently. So while the story below is honest, it should not be taken as a repair guide. The takeaway is closer to “here are some things to consider before opening up your vintage SLR” than “here’s the right way to clean a prism”.
With that caveat in place: I had a dead fly stuck on the prism of my Mamiya 528AL, visible smack in the middle of the viewfinder every time I composed a frame, and I had run out of patience with it. So I took the top off the camera and dealt with it.
The problem
I had reviewed the Mamiya 528AL the month before this video (covered in a separate piece where I shot a roll of test film through it). Halfway through that shoot, something landed in the viewfinder. A small dark spot, roughly fly-shaped, dead centre in the frame.
The frames themselves were unaffected. The fly was inside the viewfinder system, somewhere between the mirror and the eyepiece, which means it never touched the film path. But every time I lifted the camera to my eye, there it was. Right where I was trying to focus.
I do not collect cameras. I use them. Cameras that I cannot use because there is a fly in the viewfinder are going to bother me until I deal with the fly. I had a choice. I could send the camera to a professional repair shop and pay £40 to £60 for a job that would take them ten minutes. Or I could open the camera myself and have a go.
Reader, I had a go.
The Mamiya 528AL, briefly
For anyone who has not come across this camera before, a quick context.
The Mamiya 528AL is a fixed-lens 35mm SLR produced by Mamiya in the late 1960s. The “528” refers to the f/2.8 maximum aperture of the fixed Mamiya-Sekor 48mm lens. The “AL” stands for “auto lever”, referring to the auto-exposure system that adjusts shutter speed based on the aperture you set. It is a simple, well-built camera with selenium-cell metering and a leaf shutter in the lens. Mamiya intended it for the consumer market.
The viewfinder is a pentaprism design (a solid glass block ground into the shape of a pentagon, used to invert and correct the image from the focusing screen so it appears the right way up in the eyepiece). This is the same kind of prism you find in almost every SLR from the 1950s onwards. The 528AL’s prism sits under the top plate, held in place by a sprung metal retainer.
Cleaning the prism means removing the top plate of the camera, lifting the prism out of its frame, cleaning the relevant face and putting everything back together without breaking anything. In principle, straightforward. In practice, less so, especially for someone who had not done it before.
What I actually did (the honest version)
I started with no service manual, no reference photos, no idea of the screw layout and a Wowstick electric screwdriver from Amazon. The Wowstick is a small powered screwdriver that I had bought a few months earlier on the assumption that it would make camera repair easier. It does make a satisfying dentist-drill noise. Whether it actually helps with precision work is another question.
The first thing I did was identify the screws on the top plate. There were several visible from above: two on the side near the rewind crank, plus one near the film advance lever (which turned out to be both decorative and structural, holding the lever cap in place AND securing the top plate), and a couple of small ones nestled near the accessory shoe.
I removed each one in sequence. I put each one on a clean mat so I would not lose track of which screw came from where. (This is the one thing I did at the time that I would still do today. A clean work surface and a system for keeping screws separated by their location is essential.)
With the screws removed, the top plate lifted off. The film advance arm came off with it, plus a small washer underneath, plus another small spring-loaded part that I did not identify at the time. I noted the order in which they came out and laid them next to the screws on the mat.
Under the top plate was the prism. A solid glass block, surprisingly heavy for its size, held in place by a curved spring-steel retainer clipped over the top. The retainer flexed back when I pushed it gently. The prism lifted straight out.
The fly was on the underside of the prism. Or rather, the corpse of something that had once been a fly was on the underside of the prism. Cleaning it off with a lens-cleaning cloth took about thirty seconds. The other faces of the prism had some fingerprint marks on them (probably from me handling it without gloves) but I cleaned those too while I was there.
I put the prism back in. I clipped the retainer back over. I lined the top plate up and dropped the film advance arm components back in their correct order, then started threading the screws back into place.
This is where it went slightly wrong.
What went slightly wrong
The film advance lever cap is held in place by a fiddly fastener that needs a particular kind of tool. I did not have that tool. I used a pair of pliers wrapped in a soft cloth. The pliers slipped, and I left a small scratch on the chrome top plate of the camera near the lever. The scratch is purely cosmetic. It does not affect any function. But it was avoidable, and looking at the camera now I am still annoyed about it.
I also slightly stripped one of the small screws by over-torquing it with the Wowstick. The screw still holds. The camera still works. But the head of the screw is no longer pristine and replacing it is going to require either a donor camera or a search through specialist suppliers for a matching replacement.
The camera reassembled and fired correctly. The viewfinder is now clean. The fly is gone. The repair was, by my standards at the time, a success. But there is no way I could honestly claim that the camera came out of the process in better condition than it went in. The fly is fixed. The camera is slightly scuffed.
What I would do differently now
Looking back at this video from the perspective of a few years on, several things stand out.
Find a service manual first. For most vintage cameras there is either an original service manual scanned and uploaded somewhere on the internet, or there is a detailed teardown video on YouTube by someone who has done the job before. Twenty minutes of Googling before you pick up a screwdriver would save you several mistakes during the actual job. I did none of this. I just took the top off and hoped for the best.
Use the right tools, not the tools you have. The Wowstick is fine for furniture assembly. It is not fine for camera repair. The torque control is binary (it either turns or stalls) and the screw bits are not designed for the small, soft, slot-headed screws that vintage cameras tend to use. A proper precision screwdriver set with a range of small bit sizes is around £20 to £30 and is the right starting point for any vintage camera work. I have one now. I did not at the time.
Specialist tools for specialist jobs. The film advance lever cap needed a specific tool (a small two-pronged spanner that fits into the two notches on the cap). Pliers with a cloth wrapping are not a substitute. The right tool would have cost £10 to £15 and would have saved the chrome scratch. For the kind of work this camera needed, that specific tool would have paid for itself on the first job.
Take photos as you go. Before each step, take a photo of how things are currently arranged. This gives you a reference for reassembly and saves you from having to remember the order of small parts that all look slightly similar. I did not do this at the time. I do it now on every repair, even ones I have done before.
Know when to stop. If you encounter something you do not understand (a wire harness that you cannot trace, a spring that does not obviously belong to anything, a part that does not seem to fit back together), stop. Photograph it as it currently is. Put it aside. Consider whether the job is one you should be doing yourself or whether it is time to send it to a professional. I have learned this the hard way on cameras since.
Consider the cost of repair vs the cost of damage. A professional camera repair for a prism cleaning is £40 to £60. The Mamiya 528AL is worth roughly £40 to £80 on the second-hand market depending on condition. The maths is roughly break-even on the repair cost, but the upside of professional repair is that the camera comes back in the condition it went in. The upside of DIY is the experience and the satisfaction. For me, on a £40 camera, DIY was the right call. For something more expensive (a Leica M, a Hasselblad, a Rollei), the maths shifts. The more valuable the camera, the more sensible the professional option becomes.
On the prism itself
One thing I did genuinely learn from this exercise is what a pentaprism actually looks like. I had read about them and seen schematics. I had never actually held one. Doing so for the first time was a small revelation.
A pentaprism is a piece of optical glass ground into the shape of an irregular pentagon. The geometry is precisely calculated to bounce the light path through five internal reflections, inverting and correcting the image so that what you see in the viewfinder matches what is in front of the lens. The block is solid. There are no moving parts. It is one of the simplest, most elegant pieces of optical engineering in any camera.
The prism in my 528AL is substantial. The block weighs maybe 60 grams. It catches the light in interesting ways when you hold it up. The faces are precision-ground to micrometre tolerances because any deviation produces visible distortion in the viewfinder image.
A pentaprism is what gives an SLR its characteristic shape (the “hump” on top of the camera body is the prism inside its housing). Cheaper SLRs use a pentamirror instead (lightweight folded mirrors arranged in the same geometry) which is cheaper to make but darker and lower quality. The 528AL has a proper glass pentaprism, which is one reason its viewfinder is as bright as it is despite the modest f/2.8 maximum aperture of the fixed lens.
Should you do this at home?
A genuine question, and one I have thought about more since this video.
If your camera is worth less than the cost of a repair and you have a basic precision tool kit, and the problem is purely cosmetic (a fly on the prism, dust on the focusing screen, fingerprints on the mirror), then yes, attempt it yourself. You will learn something. You will probably succeed. You may end up with a small cosmetic mark on the camera but you will not damage anything functionally critical.
If your camera is worth more than the cost of a repair, or the problem is functional (the shutter is sticky, the meter is dead or the film advance is jamming), send it to a professional. Functional repairs need specialist tools and specialist knowledge of the specific camera mechanism, plus access to spare parts that are not in your kit box. A bad DIY attempt on a functional problem can turn a £100 repair into a £400 repair, or into an unrepairable camera.
For the Mamiya 528AL specifically, with a dead fly on the prism, DIY was within the boundary of reasonable. With the benefit of hindsight, I would have used better tools and read a service manual first. The end result would have been the same minus the chrome scratch.
Next time
This was a short detour into camera repair. The next video on the channel returns to actual shooting, with another vintage camera review (a Gerlach Nixette, a 1950s German folding camera that has impressed me more than expected). After that, more shooting, less screwdriving. Probably.
If you have done your own prism cleaning or other camera repair work and have tips or experiences to share, the comments are open. There is a whole community of people doing this kind of work and we are all learning from each other.
And if you have a Mamiya 528AL with a fly stuck in the viewfinder and you are considering opening it up: read this article. Then read a service manual. Then think about whether you want to scratch your camera or pay £50 to someone who will not.