# Sigma Lenses and Speedlight AF assist beam



## rado98 (Sep 26, 2014)

Hi guys

I have an issue with my 7D and Sigma 30mm ART and I want to know if it is a common issue with all sigma lenses as I am thinking of adding the 17-50 2.8 OS to my bag.

I simply cannot use my 430EXII's assist beam with the 30mm, the AF ends up being way, way, way off. not even f5.6 is a sure hit. Whenever I disable the assist beam the AF becomes "decently" accurate, although obviously much slower, and depending on the scene unable to even focus.

I had the same issue with my 600D. My 40mm 2.8 focuses perfectly using the assist beam.


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## AcutancePhotography (Sep 26, 2014)

Have not had this problem with either my new Sigmas nor my old. But to be honest I don't often shoot with the focus assist.


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## rado98 (Dec 29, 2014)

Hi

Just to keep a record of things in case someone looking for support runs into this thread.

I purchased the Sigma 17-50mm 2.8 for my 7D, with the expectation that the AF would have the same problem as the 30mm. The price difference with similar offerings and the fact that I learn to live with the issue are the reasons.

The 17-50mm backfocuses heavily when using the Speedlight AF assist beam as "expected" and requires a -22 AFMA (-22 achieved using ML). My workaround: I set C2 to use the "All lenses" AFMA custom function and set that to -22. So I use C2 only when I would need the AF assist bean. Normally I would then use the "This lens only" custom function on all other modes.

With the 30mm the workaround is the following: I used the Simga dock and set lens' internal AFMA to -17,-17,-9 and -10, and then set the in camera AFMA for the lens to -20. For whatever reason that works with AF assist beam ON or OFF, go figure. Those settings also improved the overall AF accuracy of the lens.

Cheers


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## Mt Spokane Photography (Dec 29, 2014)

I've never heard that one. I'd suspect something is wrong. Reset the camera for starters, I had to do that once when my AF assist did not work.


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