I am not sure how many are aware that this modification is available for the Sony A7 and A7r cameras and other that a little being mentioned on the Sony section of the forums, I've not seen any more info nor discussion continue.
The A7 series of cameras have a rather thick filter stack (the stack consisting of the bayer color array, AA filter and the IR/UV block filter).
This may be fine on lenses designed to cater for this stack thickness, but for legacy lenses this can be a problem.
The light rays striking the edges and corners of the sensor from old lenses can be very acute, the result of which is astigmatism on those areas (ie. off the center)
For lenses with a longer exit pupil (to the sensor), there is enough distance to make this angle less steep.
But on those with short exit pupils (especially RF and RF wides), this can result in large image quality drop.
For much more detailed info on sensor stack thinkness, look here :
The A7 series, So near yet so far
When this camera was first launched, many legacy (esp. RF lens users) were euphoric.
Here was a camera, a fraction of a Leica M9 price with the potential to use RF lenses in a full frame format.
As the camera came out, some shot a few shallow DOF shots with their fast lenses and were sated.
The more careful (and perhaps those shooting genres that required more stopping down to the lens) started to observe that the off-center and/or edges/corners were far from good.
My own experiences, have been the same.
Not all RF lenses work that well on the A7 series of cameras.
Even 50mm lenses the likes of the Leica Summicron V1 and DR can have issues with off center sharpness.
Even on legacy SLR lenses, I felt that they can be better, having experienced better apparent performance on film over what the edges looked like on the A7.
I began to take interest in the discussion that stated in FM Forums regarding the thin filter mod pioneered and offered by Kolari Vision.
Here is a link to the discussion on FM forums.
Its a must read for those who are considering the mod as it also addresses the potential risks and pitfalls.
The initial problem was that the replacement IR/UV cut filter replacement (as thin as the one used on the M9) suffered the same issues of corrosion in high humidity.
Luckily, Kolari has been able to source a more resistant filter (from Schott)
I decided go for the mod and since little info has been shared here on CS, I will try to do so.
The exact link to Kolari Vision is :
This is a AA filter removal + thin filter modification.
More results will follow as I get to compare against a A7K (modded) vs A7 (unmodded)
Note : I don't have an unmodded A7, so any updates will be dependent on meetups with friends who have the camera.
Here is the first one done for an SLR lens.
All shots in RAW and using the same processing.
If there is anything I adjust between the sample shots, it will be a bit of exposure correction (within 0.5ev) if the exposure don't match up.
Pentax SMC K24/2.8
A7_standard Pentax K24 f2.8 at f10 by jenkwang, on Flickr
A7_standard Pentax K24 f2.8 at f10-center by jenkwang, on Flickr
A7K Pentax K24 f2.8 at f10-center by jenkwang, on Flickr