Issues with Sigma MC-21 EF to L-Mount Adapter

Hi Folks. Until now I was able to adapt the Canon 40mm f/2.8 as well as the Tamron 35mm f/1.4 and Tamron 85mm f/1.8 without issues with the Sigma MC-21 adapter to my Lumix S1R.

Today I tried to adapt the officially supported Sigma Art 50mm f/1.4 and I had issues with the auto focus. When I turned on my camera the LED on the adapter lit up green, so far so good. However, auto focusing at infinity and in AF-S mode always focused closer than infinity. When using pin-point AF it worked maybe half the time. The auto focus also had front focus issues when trying to focus on fine detail also at closer distances. It worked on larger high contrast areas, like black letters on a white book cover. Eye focus in AF-S on the other hand worked without a miss.

When adapting the Sigma 50mm via the viltrox ef-l adapter, normal AF-S was accurate in all situations and distances. Only eye focus AF-S missed every time.

Why is the MC-21 struggling with this lens? Shouldn't eye focus AF-S be more difficult for the adapter than normal AF-S?

Arthur85 said:

Hi Folks. Until now I was able to adapt the Canon 40mm f/2.8 as well as the Tamron 35mm f/1.4 and Tamron 85mm f/1.8 without issues with the Sigma MC-21 adapter to my Lumix S1R.

Today I tried to adapt the officially supported Sigma Art 50mm f/1.4 and I had issues with the auto focus. When I turned on my camera the LED on the adapter lit up green, so far so good. However, auto focusing at infinity and in AF-S mode always focused closer than infinity. When using pin-point AF it worked maybe half the time. The auto focus also had front focus issues when trying to focus on fine detail also at closer distances. It worked on larger high contrast areas, like black letters on a white book cover. Eye focus in AF-S on the other hand worked without a miss.

When adapting the Sigma 50mm via the viltrox ef-l adapter, normal AF-S was accurate in all situations and distances. Only eye focus AF-S missed every time.

Why is the MC-21 struggling with this lens? Shouldn't eye focus AF-S be more difficult for the adapter than normal AF-S?

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Don't know Arthur, but Sigma simply updated their older lenses to more current issue standard reverse engineered EF firmware so they did not have to try and delve into the maze of early gyrations of Canon EF lens firmware (like Metabones did and continues to do). As a result they were issuing firmware updates via their lens docker device which also allows fine tuning of focus. Why the Viltrox might work better is that Viltrox has tried to make a wider range of Canon EF lenses compatible and in this case covers all "adjusted" Sigma lenses and probably those that were not firmware updated as well.

I found that both Fotodiox and Viltrox adpaters were not only capable of driving all Sigma EF mount lenses with firmware updates but also more other brand EF lenses oem Canon or otherwise.

Sigma only promises to make Sigma EF mount lenses compatible by lens firmware updates to the later issue reverse engineered Canon EF firmware standards. Any other brand lenses that work (including Canon EF) are simply a bonus.

Hi Tom. Thx for your reply. Do you have a MC-21? What are your experiences?

I'm not sure I understand your explanation fully. Sigma must have done something better than viltrox, otherwise eye focus in AF-S mode wouldn't work so well with the Sigma 50mm HSM Art adapted via MC-21, much better than via the viltrox adapter. How come normal focus point AF-S is so unreliable with the MC-21, but not with the viltrox?

And do you know if the focus fine tuning adjustments made through Sigma's USB Dock are also applied when a Sigma lens is adapted via the MC-21?

Arthur85 said:

And do you know if the focus fine tuning adjustments made through Sigma's USB Dock are also applied when a Sigma lens is adapted via the MC-21?

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Should do. I have not had to adjust any focus issues with the USB dock myself. I nearly tried this fro my Sigma DC 50-100/1.8 but the precise point of focus seems to have sorted itself since PDAF.

Arthur85 said:

Hi Tom. Thx for your reply. Do you have a MC-21? What are your experiences?

I'm not sure I understand your explanation fully. Sigma must have done something better than viltrox, otherwise eye focus in AF-S mode wouldn't work so well with the Sigma 50mm HSM Art adapted via MC-21, much better than via the viltrox adapter. How come normal focus point AF-S is so unreliable with the MC-21, but not with the viltrox?

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This comparison is now getting old but does show that for not-Sigma EF mount lenses both Fotodiox and Viltrox are more widely compatible.

https://www.dpreview.com/forums/post/64144183

The MC21 seems to work perfectly with all the Sigma EF lenses I tried and a good number of Canon EF mount lenses. Sigma achieved this by updating the firmware on some of their older EF mount lenses. This can be done by using their docker device. However I am not completely sure if Sigma has provided firmware updates for any of its truly old EF mount lenses.

The definition of Sigma's brief is to make all their EF mount lenses work with their MC21 and other EF lenses are a bonus. Third party adapters also work with Sigma EF lenses plus a wider range of other-brand EF mount lenses. The third party adapter manufacturer's brief is to try and make their adapters as widely compatible as possible with all EF mount lenses.

Note that the Sigma approach is to make their own EF mount lenses compatible with their adapter. Third party adapters try to make their adapters compatible with as many EF mount lenses as possible.

I brought the S1R, MC-21 and the lens to Sigma's service partner in Switzerland today. They tested another 50mm Art lens with the MC-21 yesterday and had inconclusive results. Let's see what they will find out.

I got them back from the service center. The lens' firmware had to be updated to version 2.03. They did some test photos said everything works as expected and the same as other MC-21 adapters with the Sigma Art 50mm HSM.

They didn't charge me anything for their testing or the firmware update, which I appreciate very much. In general, really nice and professional people at Ott & Wyss.

Back home I did some additional tests at infinity and I think that now infinity focus is achieved when using the pin-point focus almost every time. The normal 1-area AF-S still focuses to close. I guess for landscape work I can just focus manually or use pin-point focus.

AF-S 1-area is still unreliable also for closer distances. So I will use ether pin-point or AF-S eye focus, which works fine for subjects with eyes.

Disclaimer: If you don't check focus accuracy at 200% pixel peeping level, AF-S 1-area should be OK in most cases, especially if you shoot stopped down a bit.