I’m not at all sure whether this should be classified as a review, a blog post, or mindless rambling by a crazy photographer. Personally, I’m leaning towards the latter.

I’m not even sure what strange compulsion gripped me to spend $18 to use ancient manual everything FD lenses on my EOS M. I certainly never felt any compulsion to use manual lenses on my regular EOS bodies.

Manual focus is something I’ve especially come to despise. It’s easily doable on a body designed for doing it, but the optimizations being made to autofocus camera viewfinders render it an exercise in futility—at least for me. At least on the EOS M you’re looking at a big LCD not a tiny viewfinder that’s been optimized to be bright instead of accurate.

The manual aperture is less of an issue. For starters, on the EOS M it’s all WYSIWYG (what you see is what you get) anyways. But Canon’s metering system—from the EOS M to the Rebels to the EOS-1 bodies—don’t give a toss about what it’s metering though. It gets more intelligent when it knows more about the lens and environment, but it works just as well looking though plastic wrap as it does through a $10,000 L lens.

But what’s the compelling reason to use old lenses? They’re cheap, but they’re not the pinnacles of modern optical engineering either. Canon’s FD 50mm f/1.8 barely matches the resolution of Canon’s EF-M 18-55mm f/3.5-5.6 IS STM at the same aperture and focal length. Yet, here I am messing around with the FD 50mm f/1.8 on my EOS M.

I digress though; I’m supposed to be talking about the mount adapter not rambling aimlessly.

Overall, the build is decent. The adapter is very solid and all metal. The inside is ridged to reduce reflections from stray light. Though not as fancy as the reflection reduction in the EF-EOS-M adapter, it seems to do well enough. The finish is decent, though there’s one small place on the outer edge of the EF-M mount where the anodizing chipped off on mine. However, though it’s not at all relevant to the function of the adapter, and it’s hidden between the two mount surfaces when the adapter is mounted to the camera anyway. More importantly, I don’t see any indication that it will flake off or wear further—but I will be keeping an eye on it.

Of course, completely passive mount adapters, like this one, are hard to screw up. There aren’t any optics or electronics involved. In fact, there are only 2 critical areas, the two mounts must be parallel, and they must be separated by the proper distance to maintain the register of the adapter lens.

The registration distance (or flange to focal distance) for the EF-M mount is 18mm, and the FD mount’s register is 42mm. This means the mount adapter must ideally put the two mating surfaces 24mm apart. There is a bit of margin for error in this value. Since the FD lenses have a hard stop at the infinity position, the mount adapter can only be shorter than the expected register while maintaining infinity focus.

Putting my cheap digital calipers across the two surfaces gives me a measured thickness of 23.96mm to 23.98mm. Good enough for cheap calipers and it’s shorter than the ideal 24mm, so infinity focus is retained. How much of that is real error, and how much of that is measuring error I’m not sure.

That said, while the conventional wisdom may be that glassless adapters won’t affect image quality, that’s not entirely true. The two mounting surfaces much be incredibly close to parallel, especially if you’re using wide angle lenses. To put into perspective how precise this stuff needs to be to be optimal, the ~30µm shorter register is sufficient to push the infinity from the hard stop back to the left lobe of the infinity on the scale, and the 20 micron difference between the sides, is enough to potentially cause edge to edge sharpness differences when using the widest angle lenses available.

Canon’s FD lenses, when used on FD mount cameras at least, use a pair of levers to communicate, control, and activate the aperture. The smaller of the two, at least on a proper FD mount camera, serves to convey the aperture value the lens is set to the camera, or when the lens is set to A set the aperture value from the camera. The larger is the toggle that actually stops down the lens.

Without engaging the second, larger, lever, it’s impossible to stop down an FD lens with the aperture ring. Now actuating the lever isn’t especially challenging, a fixed pin that pushes against it when you mount the lens would be sufficient, if not entirely elegant.

Fotasy, however, decided to articulate that pin, by tying it to a ring on the adapter that functions effectively like a manual stop down lever. In the open position (rotated clockwise when looking from the camera towards the front of the lens), the diaphragm remains fully open. Rotate the ring about 30° counter clockwise, and the lens’s diaphragm closes down.

It’s actually a very nice solution for a number of reasons. First, it makes attaching a lens a little easier. You can simply line the lens up on the mount as you normally would and lock the locking ring. If the pin was always in the locked position, you’d have to carefully align the pin and rotate the lens before locking it in place or it wouldn’t work right.

Secondly, it gives you the ability to focus at the widest aperture before shooting. This means the placement of focus can be more precise, as you’re placing the shallowest depth of field instead of trying to place the wide depth of field of the stopped down lens.

More importantly, it gives you more light to work with when focusing. This might sound like an odd benefit for a mirrorless camera that isn’t affected by viewfinder darkening the way a SLR might be. However, since the camera has to continuously read out the sensor at a frame rate that’s acceptable frame rate to keep a fluid lag-free image on the screen, this means it has to use a relatively fast virtual shutter speed to keep the viewfinder fed. As a result, when used with a slow lens, and in low light, the image on the display becomes quite noisy even if the resulting images wouldn’t be.

The lock/open ring makes it a quick operation to switch between the fully open aperture for focusing with lower noise, and the stopped down aperture for metering and exposing. Just remember to set the ring to the open position before mounting a lens.

All that said there is one minor gripe I have with the adapter. In a move, I assume was aimed at saving money Fotasy didn’t bother marking the circumference of the barrel with alignment marks. Each of the lens mounts have small drilled reference marks (both painted red) on their faces, however, I don’t find that sufficient for quick alignment. At a minimum, I would have really liked to see a circumferential mark for the EF-M alignment, since its canted orientation is a little hard guess at than the vertical alignment of the FD mount. Both would be preferable.

All told for the $18 it cost, there’s not a whole lot to complain about, and even the big gripe I do have is easy enough to fix yourself with a paint pen or two.

The bigger question I keep asking myself is, why bother with the old glass on an EOS M. Then again, given the current selection of EF-M lenses, and the relatively diminutive size of FD primes, it’s somewhat fitting in a way. That said, if you don’t already have FD lenses, there’s no compelling reason to buy this adapter and FD lenses to go with your EOS M.