KolariVision Ultra-Thin cover glass modification, Sony a7r and Leica M optics

[Paul Roark]

Some years ago, after seeing the edge performance of a Leica M wide angle lens on an M9 compared to my Canon 5d2 equipment, I became a fan of Leica glass.  While the Leica M9 was my camera of choice for a few years, the Sony a7r series' modern electronics and through the lens viewing won me over.  The OEM Sony's inability to work well with my Leica M wide angle lenses, however, was a major disappointment.  The OEM Sony sensor IR filter/cover-glass was just too thick, causing unacceptable off-axis image softness.

Now, KolariVision has an "Ultra-Thin" replacement glass that is only 0.2 mm thick.  I converted my Sony a7r (v.1) to this and am happy to report that my Leica M glass is once again performing very well indeed, with a several caveats.  First, there are some color artifacts with at least one of my favorite (28mm) Leica optics, but it can be cured with Cornerfix.  Second, the extremely short, relatively symmetrical designs like the ZM 21mm f/4.5 C-Biogon seem to be beyond the limits of what I consider good performance.  Third, there is still some edge softening over what I had hoped for, based on published MTF curves, but the UT converted Sony matches or exceeds the M9 edge sharpness most of the time.  Frankly, I cannot tell if the cover-glass or the lens is the limiting factor at the edge.  At least some of the Zeiss glass for the Sony thick OEM glass (for example the 35mm f/2.8 and the Loxia 21mm, in particular) is better than the Leica-M wide-angle performance at the edge until f/5.6.  The Leica M glass seems to be better in the center at all apertures and beyond f/5.6 at the edge also.  So, for most of my landscape shooting, the Leica M glass will be my choice.

I have documented the most important findings with the Sony a7r and the KolariVision UT-conversion in this PDF:  http://www.paulroark.com/BW-Info/KolariVision-UT-filter.pdf .  I will update the PDF as I get more experience with the system. 

At this point the KolariVision Ultra-Think conversion looks like the best mating of the outstanding Leica M wides to modern electronics for those who want relatively light weight and compact full frame, manual focus system, particularly if one already owns the Leica glass.

Paul
www.PaulRoark.com

[rvamos]

Paul, can the a7rii be converted as well?  Or should I have both bodies?  I am in the same situation as you were - many beloved M lenses and a new a7rii on the way.  Should I shop around for a used a7r (v.1) and have that one converted?  Thanks for the advice

[Paul Roark]

Paul, can the a7rii be converted as well?  ...

Yes, the Sony a7r2 can have its thick coverglass replaced by the KolariVision Ultra Thin filter.  In fact, the a7r2 has some advantages.  Among others, I believe the microlenses were modified such that it may not have the color artifact issues.

I used my older a7r v.1 mostly because this was an experiment.  I didn't know how it would turn out.  The a7r 1 is also lighter, but that is a minor factor.  In retrospect, I wish I'd converted the newer model.

If you do the conversion, let us know how your various lenses work. 

Paul
www.PaulRoark.com

[rvamos]

What are the disadvantes of the conversion?  Would non-M lenses still be usable (like my Leica R or Canon-mount lenses)?

[ErikKaffehr]

Hi,

SLR lenses would be little affected, but new designs developed for the FE-mount may be affected.

Diglloyd has observed a significant loss of sharpness on the Sony 55/1.8 ZA after KolariVision modifying the camera.

Best regards
Erik

What are the disadvantes of the conversion?  Would non-M lenses still be usable (like my Leica R or Canon-mount lenses)?

[Paul Roark]

As Erik said, wide angle (and even 50 mm) optics designed around a thick cover glass will be negatively affected by the thin cover glass conversion.

It's interesting to consider the bind the industry is getting into.  As technology advances and allows us to get closer to the ability to have compact wide angle lenses, the camera companies may have to have yet more lens and mount categories.  I'm sure OEMs are eyeing if not already designing cameras around this new ultra thin IR filter.  (I assume the glass is from one of the large German glass companies.)  I'd guess it would be used first in a dedicated, non-interchangeable lens, compact 35mm camera. 

As good as the digital sensors are now, after seeing how the Ultra-Thin conversion improved the Leica M 50mm and wider lens performance, I would say we are not yet dealing with a mature digital technology; there is considerable room for improvement in our systems.  I wonder what the assumptions are of the Leica M lens designers as they try to compromise performance on their mixed film and digital M camera customer base.  I may have to rent their Apo 50 f/2 just out of curiosity.

Paul
www.PaulRoark.com

[ErikKaffehr]

Hi,

I would think that the industry converges about 2mm of filter stack. This is presently used on all MFDs, Canons, etc. Making the cover glass thinner means that there may be problems with IR-filtering. Leica probably uses 0.8mm, that was used on the M9.

The cover glass thickness doesn't really matter, as long as the lens is calculated for that thickness of cover glass. So, it makes a lot of sense to standardise on say 2mm and design the optics around it.

4/3 uses around 4 mm.

The only advantage of thin glass is that it causes less astigmatism on old (film era) viewfinder lenses, but those lenses are problematic with digital sensors for many other reasons, like vignetting and cross-talk.

Best regards
Erik

As Erik said, wide angle (and even 50 mm) optics designed around a thick cover glass will be negatively affected by the thin cover glass conversion.

It's interesting to consider the bind the industry is getting into.  As technology advances and allows us to get closer to the ability to have compact wide angle lenses, the camera companies may have to have yet more lens and mount categories.  I'm sure OEMs are eyeing if not already designing cameras around this new ultra thin IR filter.  (I assume the glass is from one of the large German glass companies.)  I'd guess it would be used first in a dedicated, non-interchangeable lens, compact 35mm camera. 

As good as the digital sensors are now, after seeing how the Ultra-Thin conversion improved the Leica M 50mm and wider lens performance, I would say we are not yet dealing with a mature digital technology; there is considerable room for improvement in our systems.  I wonder what the assumptions are of the Leica M lens designers as they try to compromise performance on their mixed film and digital M camera customer base.  I may have to rent their Apo 50 f/2 just out of curiosity.

Paul
www.PaulRoark.com

[Paul Roark]

Probably correct, but I hope there is enough of a market for compact Leica-M type systems to support the thinner glass. 

It appears to me that the approach most of the higher end industry is taking to better imaging ends up with huge lenses, using complex retro-focus designs.  I, personally, prize my compact Leica M optics.  The ability to put them onto a state of the art Sony body results in a very good image quality to size & weight ratio. 

When, modern optics like the Loxia 21 I use are designed specifically for the OEM cover glass thickness, they are great.  On the other hand, my Leica-M 28mm f/2.8 (yes, a bit apples and oranges) with the ultra thin Kolarivision cover glass is better in all respects aside from, arguably (but close), wide open edge resolution.  Overall, it's the Leica-M and ZM glass on the Sony body with the Ultra Thin cover glass that wins the contest for me for most (but not all) photo outings.  (I actually keep one Sony with OEM thickness just for the 21mm Loxia.)

I don't doubt that Otus and its approach on more industry standard thicker cover glass will take the prize for the best image, but size and weight really matter to me, and the small/light more classic Leica-M alternatives allowed by the thin cover glass are good enough for my large Epson 9800 printing.  Good enough works for me.

Paul
www.PaulRoark.com