A while ago Metabones announced a revised edition of it's adapter for Canon EF lenses on E-Mount cameras, the Metabones IV. The older version III had problems with internal reflections when used with shift lenses (see my posting on this topic here:
http://www.luminous-landscape.com/forum/index.php?topic=85249.0).
Metabones promises the following enhancements:
• The new design of inner housing in Mark IV has a bigger inner hole. Improving the Tilt shift lens performance.
• The inner hole is painted with matt coating. This can further reduce the internal reflection.
Others have reported, that the problem with internal reflections is less than with the Metabones III, but not yet completely solved (look here:
http://www.nickfrank.de/blog/2014/12/12/metabones-sony-nex-smart-adapter-mark-iv-vs-mark-iii-coated-comparsionreview). On the comparative photograph below you can see that the new coating is indeed less reflective. But after I flocked it inside, reflections are further reduced.
The inner hole of the Metabones IV has a slightly different form and is 2 or 3mm wider on the lens side of the adapter. But on the camera side of the adapter the hole is only 24x36mm wide - like the Mark III - and this is not a mm more than the necessary minimum. Disappointing in my opinion. They could have tried harder to solve that problem - considering the high price and the fact that the only changes they made were for reducing reflections.
So is the adapter worth the upgrade? If you have already flocked your Metabones III - not really. But if you buy new I think the IV is the better choice.
Like for the older version I now made a flocking pattern that you can download and use if you want to flock your adapter too. It is bit fiddly to do (more than it was with the III), but not too much. You can use self adhesive velours for most parts. The only part where it is better to use an ultra-thin flocking paper (like the one from edmundoptics.com) is for the parts that I marked in orange. Because the opening of the inner whole is only 24x36mm the velours is too thick and causes vignetting when the lens is fully shifted. It does this too with the edmund paper - but not that much. To prevent the remaining vignetting I had to make a compromise: I cut one of the orange marked parts to a t-shaped form. The vignetting is gone, more than 90% of surfaces inside are flocked. I used this solution only for the side that causes vignetting when the lens is shifted up - I never shift down that much. The other orange part covers the whole surface on its side. This is the closest I could get to a perfect result. If you have propositions for improvements - please let me know.
Marc