Help! GH4 Vignetting

[bundas]

Hey everybody, I've got what I suspect is some real noobie misunderstanding, so please bear with me.

After months of inner debate and saving up, I picked up a GH4 today, along with a MB Speedbooster XL (0.64x crop) to adapt EF lenses. My last camera was a 60D, and I was really drawn to the possibility of utilizing lenses I'd already invested in. Charged up the battery and threw on my Canon 1.4 50mm, which looks great. Second up was my 2.8 Tamron 17-50, and to my horror, it's got nasty vignetting in the corners. When switched to 4K video, the effect is reduced, but still not eliminated.

What's causing this? I'd read widely online that the MBSP + M4/3 set-up works particularly well with APS-C lenses. I'm really bummed that my go-to lens is incompatible, and would deeply appreciate any explanation or advice from someone more familiar with the format.

[E.J. Peiker]

It says right on the metabones Spec sheet for that speed booster:
"EF-S and third party DX lenses may not cover the full Micro Four Thirds sensor in still photo and FHD video modes (but will cover 4k video mode)"

DX is Nikon lingo for APS-C which is what that lens is so it is not compatible without vignetting with that lens.

http://www.metabones.com/products/details/MB_SPEF-m43-BT3

[bundas]

Double-checking on the Tamron, it's never actually listed as an EF-S, but this review does compare it to the series.
Are all APS-C intended lenses considered EF-S, even without the "S" labelling?

EF-S and third party DX lenses may not cover the full Micro Four Thirds sensor...

This is interesting to me, as it suggests that the incompatibility is not a definite fact for all such lenses. The issue seems to be in the size of a lens' image circle, but I'm still unclear about what range is compatible with my new set-up and how image circle is determined.

Edit: Interesting that B&H recommends using APSC/DX lenses with a speedbooster-equipped GH4:
http://www.bhphotovideo.com/explora/video/tips-and-solutions/how-emulate-super-35mm-4k-video-panasonic-gh4

[E.J. Peiker]

EF-S is a special mount that only Canon uses on their APS-C lenses.  Third party manufacturers, while making APS-C lenses for Canon, use the original EF mount but those lenses don't have an image circle big enough for your speed booster to do its thing.  BTW, Nikon does a similar thing calling APS-C DX and full frame FX but on Nikon they aren't actually different mounts where on Canon they are.  Some third party manufacturers include DX or DC to indicate crop lenses but your best bet is to read the description.  In the case of Tamron, APS-C lenses are called Di II and full frame lenses are just Di.  The 17-50 that you ahve is a Di II lens. Your Speed booster for an EF lens to GH4 takes advantage of the larger image circle to give you a 0.64x on the GH4 but it requires the lens to project a full frame image circle.  The Tamron lens you have does not, it projects an APS-C image circle.  Hope that clears things up further.