Auto-focusing a Canon EF 135mm f/2L with the Sigma MC-21 on a Panasonic S5 II

When I searched myself before getting the Sigma MC-21 EF adapter I didn’t find much information on using this particular combination, so I thought I’d report my findings. This is not a scientific test, just my impressions after using it for a while, and comparing it subjectively to a 5D mark IV. I’ve also tried it out on the original S5.

In short – it works fairly well in photo mode on the S5 II, but not as quickly as a 5D, and you should use continuous AF mode to avoid contrast-detect AF. It is basically unusable on the original S5 and thus the S1, S1H and all micro four thirds models older than the G9 mark II.

For video I wouldn’t consider it usable outside of a controlled environment – it’s too noisy and slow, and I couldn’t get it to work as well as it does in photo mode with continuous AF (C-AF).

Thoughts on performance

I’m no expert so this is conjecture, but I think the reason it performs so poorly at single-shot AF is that the S5 (even the mark 2 model) uses contrast-detect AF in this mode. The Canon 135mm is a design from 1996 with relatively old and slow electronics, and it’s the small fine adjustments when the lens is already close to the mark that take the most time. All Canon’s EF lenses were designed for phase-detect AF systems, and while the focusing is fairly fast on the 5D mk IV, I’m not convinced it’s very accurate. The S5 in single-shot mode takes a lot more time to get the focus right, but it’s too slow as a result.

When your lenses are faster and more responsive (as the Lumix S primes and most modern mirrorless lenses are), it all happens so quickly that you barely notice the motor stepping to find focus, but older lenses for phase-detect systems weren’t designed to work this way.

In continuous AF mode, the S5 II appears to use only phase-detect AF (PD-AF), making it behave more like the 5D. It’s not as accurate as contrast-detect, but when your subject is moving that doesn’t matter so much, and I don’t imagine you’re giving up much if any accuracy compared to a DSLR AF system.

Canon’s mirrorless models might be able to get a bit more performance out of it – they have more of an interest in supporting their loyal customers after all – but by all accounts Canon’s EF lenses perform basically the same on their mirrorless cameras as they do with their best DSLR AF systems. So I would expect to see a bit less hunting than on the S5, but even on a Canon mirrorless body this is not going to feel like a modern lens.


I definitely wouldn’t buy this lens or the MC-21 adapter for use with the original S5. It works OK with the PDAF sensor of the S5 II, but if you want to be unobtrusive the Lumix S 85mm has you covered well enough, and if you want the image quality at 135mm, the Sigma f/1.8 HSM lens is probably the way to go for now.

But if like me you’re moving from Canon EF to an S5 II and already have a copy, I wouldn’t sell it just yet.

One of the things that I really love about this lens is the power your get for the size. It is not a small lens, nor particularly light at 750g, but it is relatively unobtrusive compared to a 24-70mm f/2.8 zoom (to say nothing of a 70-200 f/2.8), while being a whole stop faster. This is doubly so on a compact mirrorless body. Even with a 5D mk4 I think it’s a really nice lens to take to a wedding as a guest, as without getting in the way I can get some nice shots that the official photographer wouldn’t. Just throw a small 35mm in the bag for shots of your own group of friends, and you have all your bases covered in a reasonably-sized kit. The lens hood is large though, so beware of flare if you leave it behind.

With the S5 II the overall size is reduced, but not substantially. It makes for a fairly long combination on the S5 with the MC-21, but not unreasonably so for the focal length. If I’m honest though it’s a tough call to take the Canon 135mm instead of a Lumix 85mm f/1.8, which is much lighter and focuses much faster, particularly for video. But it’s not the same as a 135.

So for now I’m holding onto it. There is no Lumix S 135mm, and Sigma’s 105mm and 135mm L-mount primes are “HSM” lenses that were originally designed for DSLRs, and are substantially bigger and heavier than the Canon. And when they eventually do release “DN” versions that are designed for mirrorless, they’ll probably be similarly big and heavy Art models, when really I’d be more interested in a more compact Contemporary model.

We shall see though. The Canon 135mm f/2L is a beautiful lens, and well-regarded for very good reason. At the moment there’s nothing quite like it available for L mount, especially for the price.

2 thoughts on “Auto-focusing a Canon EF 135mm f/2L with the Sigma MC-21 on a Panasonic S5 II

  1. Deron

    Thank you for this useful post! While I do not own the 135mm, I do own the 200mm f/2.8 L and love that lens. I would imagine that it will behave similarly to the 135 when attached to the S5 II.

    1. Alex Forbes Post author

      Hi Deron, I’m glad it was useful. I actually have an old 70-200mm f/2.8L IS (mk1), but it’s in storage at the moment, and I won’t be able to try it for a couple of months. My gut tells me it will perform a little better than the 135.


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