One of my favourite tools for astrophotography is the Canon EF 50mm F/1.8 lens which I use for wide field deep sky images. It’s the single cheapest lens on the market, as evidenced by its all-plastic construction and the scratchy grinding noise made by its autofocus motor. But it’s also fast, small and light, and it performs way above its price range. It’s the perfect accessory for an astronomer on a budget, like me. Unfortunately, kids and photography gear don’t mix, as I found one day when I came home one day to find it broken on the floor.
I’d only had the lens for a month or two, and bad weather had stopped me from taking it out to see what it could do. I wanted to be ready for any gaps in the clouds, so I left the camera set up on its tripod, lens mounted, ready to grab and go outside at a moment’s notice. But opportunities for a father of five are few and far between, so the camera stood for almost a week. It was inevitable that the kids were going to go upstairs and play with my toys. My five year old found the camera and was thrilled because now she could play Fashion Photographer, and brought her little brother up to strike poses for her while she pretended to take pictures.
To this day, nobody’s saying exactly what happened, but there was an accident. There was some tipping over of what might have been my camera, and there was some damage. When I came home, I found the camera upright on its tripod, pointing in a different direction, and with the lens’s focus ring sitting at a very strange angle. As near as I can work out, they must have forced the ring against the motors (I’d left it in AF mode), extending the barrel to its maximum length. When it fell over, the barrel was bashed back into the lens body, derailing it and leaving the front lens element pointing at an angle away from where it should point. I should have taken a picture to include here, but I had other things on my mind at the time.
The first thing I did (after making a bit of a noise, and conducting a shamefully biased investigation) was to try and figure out the extent of the damage. It looked bad, but none of the parts were obviously cracked or broken. Some gentle manipulating of the focus ring caused the barrel to snap back inline and, to my astonishment, that left all the movements apparently operating smoothly. I powered up the camera, and fired off a few shots and confirmed that everything did indeed seem to be working. Both manual and autofocus worked, images of objects in the room were still pinpoint sharp, and there was no obvious sign that anything had ever been wrong. Hooray for plastic!
Everything seemed fine, that is, until turned the focus back in to infinity before removing the lens in preparation for packing it away. I happened to tip the camera forward, and the entire inner assembly of the lens simply fell out of the lens body. Fortunately the internal wiring saved it from plummeting to the floor, but it was a distressing sight and I had to go have a lie down. Afterwards, I found that I could simply slip the innards back into the lens casing and everything would still work. Amazing. All I had to do was keep the focus dialled away from infinity and the lens would stay intact. But this was a less than ideal situation. First, I own the lens specifically for astrophotography, so that the lens works exclusively at infinite focus. And second… well it was obviously still broken, and a lens that simply falls apart if you choose the wrong settings is an accident waiting to happen. And on top of everything else, when I tried it on the stars that evening, I found that “infinity” was actually now beyond the range of the lens – it could only focus on relatively nearby objects.
Now a normal person would simply send the lens in for repairs, but I’m on a budget. So I turned to google. And it turns out that there are many, many resources for people who want to learn how to repair camera lenses. I found disassembly guides for my exact model lens, I found videos on YouTube showing that same lens being repaired, and I studied all of it. But I still couldn’t quite find the courage to crack open the cover and start poking my clumsy fingers inside those delicate, precise optical components.
Until a month or two later when my parents travelled across the country to stay with us for a few nights. One evening, the story of the lens came up and my mother cheerfully said “Well why don’t you get your Dad to have a look? He’s very good at fixing things!”. The look of panic on his face spoke volumes but suddenly our manly honour was at stake, so we cleared the dining room table, fetched my smallest screwdrivers, and sat down to watch more disassembly videos.
So how did it go? Well I can’t in good conscience ever recommend to anybody to try their own repairs because it is a very delicate piece of equipment, packed with sensitive optical components and fragile electrical connections. But we found it surprisingly easy to get into. In a world of disposable plastic goods, it was refreshing to find that some things are still engineered to be repairable and the whole thing disassembled cleanly and easily (apart from an access panel held on with a bit of double-sided tape which needed to be heaved off with brute force. Very frightening). But eventually we got to a point where the video could no longer help us. The unit in the example had a broken-off section of gearing inside the focus ring, and the rest of the tutorial focused on gluing it back together again, but I could not find any parts that looked damaged at all. My best idea was a small retaining piece of metal which acted as a stop – a plastic tab inside the focus ring was supposed to bump against the metal part, which would limit the motion of the focus ring. Focus to infinity and the plastic should almost hit the metal. To disassemble, remove the metal so that the focus ring can turn a little further, and then all the other tabs align with the slots in the body and the internals simply slide out. So somehow, with no obvious sign of damage, the ring was allowed to travel too far (so that it reached the disassembly position), while at the same time not turning far enough to reach infinity. We thought that the metal might have bent when the lens struck the floor, so we tried to bend it back before reassembling, only to find that the innards still slipped in and out at will.
To cut a long story short, after much head scratching and “I don’t know, it’s a mystery to me”-style mutterings, I suddenly noticed that the lip of the outer casing was lined with a sprung retaining ring. This ring contained the slots which lined up with the tabs on the internal mechanism for disassembly. And there was a visible gap between parts of the ring and the plastic outer casing. A more careful inspection showed that the ring had shifted out of its seating, and had rotated a few degrees. Eureka! This misaligned ring had not only moved the disassembly position ahead of where it belonged, but was also blocking the focus ring from ever turning far enough to reach infinity! With reckless abandon, I dug my thumbnail into the slot and shoved it back in what I assumed was the correct direction. It shifted slightly, then rotated a little more before suddenly popping back into its groove with a loud snap. One quick reassembly later and it seemed that we’d fixed it. The mechanisms turned smoothly, the lens barrel had lost all its slop, and best of all, a quick star test a few hours later showed that it was once more focusing at all ranges. Success!
All that remained was to try and capture an actual astronomical image, for which I chose the Southern Cross which fits nicely in the lens’s field of view. So how does it perform? Click on the image and judge for yourself!
Okay it’s not perfect. Gamma Crucis is noticeably distended, but that’s actually normal for this lens when opened wide to f/1.8 – it’s not exactly an expensive top-drawer item. I’d usually stop it down to about f/3.2 or so to reduce those optical aberrations. But look at Acrux! Zoom in and you can just about see its companion! So yeah, pretty good, and proof that I didn’t make things worse by trying to fix it myself.