Different Filter Stacks and what they mean for us: Sony E | Nikon Z | Leica M | Kolari UT


This post is by BastianK from phillipreeve.net

Introduction

filter stack comparison sony e nikon z fe leica m kolari UT

When Sony released the first affordable fullframe camera with the A7 in 2013 almost none of the enthusiast photographers were aware of issues related to filter stack differences. Filter stack describes what is in front of the sensor and different manufacturers decided to go for different thicknesses here that can influence how our lenses perform. If you stay within just one system this is usually not something to care about, but when adapting lenses it is very helpful to be aware of this topic.

In this article I try to tell you about these differences and for what lenses they matter, so you can find out if it is something that might affect you.

Filter stack trivia

Why is there even a filter stack? It can serve several different purposes. The first is, that it protects the delicate sensor. It usually also features a built-in UV filter and for many cameras also a low-pass (anti-aliasing) filter.

Cover glass from the Sony A7, A7II, Kolari version 2 mod, and Kolari Ultra-Thin mod ©Kolari

When you are shooting analogue film there obviously is no such filter, so for these lenses to perform properly on a digital sensor that filter stack in front of it should be as thin as possible. For SLR lenses it doesn’t matter that much, as thanks to the mirrorbox the rear element of SLR lenses is far away from the sensor, which means the light cannot hit the sensor at angles acute enough to cause any problems.

With small rangefinder lenses (e.g. M-mount or Contax-G lenses) the situation is different. Rangefinder cameras do not have a mirror box and to realize lenses as small as possible their rear elements are often very close to the sensor. This is especially true for wide angle lenses.

There are even companies like Kolari that – for a substantial amount of money – will exchange the filter glass of your camera for a different/thinner one. This is a modification that many people were interested in to get the most out of their compact M-mount lenses on a Sony E or Nikon Z camera.

Cameras included in this comparison

filter stack comparison sony e nikon z fe leica m kolari UT
Sony A7III | Nikon Z6 | Leica M10 | Sony A7rII UT

For this comparison I used the following four cameras:

  • Sony A7III – 24mp, no AA filter
  • Nikon Z6 – 24mp, AA filter
  • Leica M10 – 24mp, no AA filter
  • Sony A7rII UT – 42mp, no AA filter

The first three cameras all feature 24mp, which makes them easy to compare. Unfortunately the Nikon Z6 does feature a strong AA filter, so it does not reveal as many fine details as the others. All these cameras are unmodified as you would buy them from a store.

The Sony A7rII features a Kolari UT modification where the original filter stack has been replaced with a much thinner one. For the following sharpness comparisons I had to scale down the pictures taken with this camera, which puts it at a slight advantage, but that doesn’t matter to draw a general conclusion here.

There are some lists online to be found disclosing the filter stack thickness of different cameras. We need to keep in mind here that they could still be made of different glass types with different refraction indices, leading to different results, despite having the same thickness on paper.

M-mount lenses

filter stack comparison sony e nikon z fe leica m kolari UT
Voigtländer VM 15mm 4.5 II | VM 21mm 1.4 | VM 35mm 1.2 III | VM 50mm 1.0 | VM 75mm 1.5

M-mount lenses are where this is most interesting as especially the old ones are designed for film where there is no filter stack and because they often have rear elements close to the sensor. It means, these lenses will show the biggest degradation in image quality when used on a camera with a thick filter stack.

I used the following lenses for this comparison:

Why did I choose these lenses? First we will see that wide angle lenses are more affected than tele lenses. These are also all high performance lenses that perform very well on the filter stack they have been designed for from their maximum aperture, which means they should be able to reveal those differences.

Color Cast

Voigtländer VM 15mm 4.5 SWH II | f/8.0

The Voigtländer VM 15mm 4.5 SWH II is an ultra wide angle lens with the rear element close to the sensor originally designed for film. Its design leads to acute light rays hitting the sensor and those are the light rays most affected by a change in filter stack. Cosina is aware of this, hence they released the (much bigger) Voigtländer VM 15mm 4.5 SWH III optimized for digital sensors. With longer lenses this is less of an issue, so we only have a look at this 15mm lens here.

To regular readers these results won’t be much of a surprise: the Leica M10 shows the infamous “italian flag” vignetting with an asymmetrical green color cast on the left and magenta one on the right. This is apparently caused by the way the micro lenses are applied on the sensor. The older digital M cameras (M9, 240, 262) perform even worse in this regard, as does the M10r. The M11 on the other hand performs similar to the other cameras depicted here, as it also makes use of a (probably Sony) BSI sensor.

On the other cameras this lens only creates a slight green color cast in the corners and it looks to me like on the Sony A7rII UT we see the least of it.

If you want to learn how to fix color cast in Lightroom have a look at this article.

Sharpness Infinity

Voigtländer VM 15mm 4.5 SWH II

Voigtländer VM 15mm 4.5 SWH II

The Voigtländer VM 15mm 4.5 SWH II actually looks best on the Sony A7rII UT, because it doesn’t have the color cast issues of the Leica M10. Surprisingly here the Z6 follows not far behind, it looks only slightly worse. The Sony A7III looks worst here, already the midframe is affected at f/4.5 and even by f/8.0 the corners don’t look great.


Voigtländer VM 21mm 1.4 Nokton

Voigtländer VM 21mm 1.4 Nokton

The Voigtländer VM 21mm 1.4 Nokton is a very complex modern design and on the Leica M10 it shows an amazing performance from f/1.4. It looks slightly worse on the Sony A7rII UT with the Nikon Z6 following closely behind. On the Sony A7III with its stock sensor it is a complete loss at f/1.4 by comparison: already the midframe looks just awful. Stopped down to f/8.0 it still doesn’t look as good on the A7III as it does on the other cameras.


Voigtländer VM 35mm 1.2 Nokton III

Voigtländer VM 35mm 1.2 Nokton III

The Voigtländer VM 35mm 1.2 Nokton III looks very similar on Leica M10 and Sony A7rII UT at f/1.2. On the Nikon Z6 it is mainly the midframe that looks a bit worse. On the Sony A7III the corners look noticeably worse and also the midframe takes a slight hit. At f/8.0 this lens looks great on all cameras.


Voigtländer VM 50mm 1.0 Nokton

Voigtländer VM 50mm 1.0 Nokton

The Voigtländer VM 50mm 1.0 Nokton is another complex floating elements design with the rear element close to the sensor. On the M10 it shows a surprisingly good across frame performance from f/1.0. The order is unsurprisingly similar: it still looks good on the Sony A7rII UT, a little worse on the Nikon Z6 and noticeably worse on the Sony A7III.


Voigtländer VM 75mm 1.5 Nokton

Voigtländer VM 75mm 1.5 Nokton

The Voigtländer VM 75mm 1.5 Nokton is the longest M-mount lens I was using here. I expected it to perform very similar on all the four cameras and this is indeed the case.

Observations

As was to be expected we see the biggest differences with the wider lenses and at wider apertures and a lot less with the lenses stopped down, as the widened depth of field can cover the field curvature caused by the thicker filter stack to some degree.

We also see that there is a big difference between the performance on a stock Sony A7III and a stock Nikon Z6 – with the latter being a much better choice for adapting M-mount lenses. While the lenses don’t perform just as good as on a Leica M10 or a camera with Kolari UT modification, it is usually only the exterme corners that show a slight degradation in image quality.

But let’s have a look at the next section, before jumping to any conclusions just yet.

Bokeh

Voigtländer VM 21mm 1.4 Nokton

Voigtländer VM 21mm 1.4 Nokton | f/1.4

If you ever wondered why I am hesitant using fast M-mount wide angle lenses on stock Sony cameras, you can clearly see here why that is the case.

With the focus on the tree in the center, the top right corner is clearly out of focus when looking at the Leica M10’s and Sony A7rII’s crops. On the Sony A7III it is completely in-focus though, because the field curvature bends the focal plane so much, that the corners (and also borders) are also in focus – even though they shouldn’t be.

In the Nikon Z6 crop we see that the corners are not as much blurred as with M10 and A7rII UT, but things look still better compared to the Sony A7III.


Voigtländer VM 35mm 1.2 Nokton III

Voigtländer VM 35mm 1.2 Nokton III | f/1.2

Compared to the 21mm discussed before, the situation is not as bad with this Voigtländer VM 35mm 1.2 Nokton III – even though the trend generally continues. The corners are blurrier on the Leica M10 and Sony A7rII UT, only slightly less blurry on the Nikon Z6 and noticeably busier on the Sony A7III.


Voigtländer VM 50mm 1.0 Nokton

Voigtländer VM 50mm 1.0 Nokton | f/1.0

Same differences as we have seen with the VM 35mm 1.2 Nokton III.


Voigtländer VM 75mm 1.5 Nokton

Voigtländer VM 75mm 1.5 Nokton | f/1.5

With its 75mm focal length this Voigtländer VM 75mm 1.5 Nokton is not affected as much by the different filter stacks as the aforementioned lenses. Bokeh in the corners still looks a tiny bit worse on the Sony A7III, but not enough to really worry about. Without a direct comparison this difference will also be hardly noticeable.

Observations

As we have seen in this section, the differences in filter stack thickness can have a huge and easily visible impact on the out of focus rendering of fast wide angle lenses at longer focus distances.

At shorter distances this is usually not a problem, as the depth of field is so thin that the unfavourable field curvature becomes mostly irrelevant.

I use fast lenses in the 21-35mm range at longer focus distances a lot for creating environmental portraits though, so I avoid using such wide M-mount lenses on stock Sony fullframe cameras.

E-mount lenses

filter stack comparison sony e nikon z fe leica m kolari UT
Laowa 15mm 2.0 Zero-D FE | Zeiss Loxia 21mm 2.8 | Sigma 35mm 1.2 Art DG DN | Sony FE 85mm 1.4 GM

Thanks to the Megadap and Techart adapters Sony E-mount lenses can be used with only little limitations on Nikon Z-mount cameras. The lineup of lenses for Z-mount is still very limited – especially when it comes to 3rd party offerings – and even if a lens is available as both, E and Z-mount, the E-mount version is often more affordable, so I was wondering, if their optical performance suffers when used on a Z-mount camera.

I used the following lenses for this comparison:

Why did I choose these lenses? Again we will see how different focal lengths are affected. Furthermore the Laowa 15mm 2.0 has a rear element close to the sensor and the Sigma 35mm 1.2 Art DG DN is one of the highest performing lenses I have used so far, so again these should be able reveal any kind of differences.

Sharpness infinity

Laowa 15mm 2.0 Zero-D FE

Laowa 15mm 2.0 Zero-D FE

The Laowa 15mm 2.0 Zero-D FE is not only an ultra wide lens but also one with a comparably small rear element close to the sensor, meaning the light rays will hit the sensor at acute angles, so I did expect some differences here and indeed that is the case.

At f/2.0 the corners look way worse compared to using the lens on a stock E-mount camera and already the midframe area looks slightly worse. Stopped down to f/8.0 the corners still look a bit worse on the Z6, but this might also be due to its strong AA filter.


Zeiss Loxia 21mm 2.8

Zeiss Loxia 21mm 2.8

Also the Zeiss Loxia 21mm 2.8 has a small rear element comparably close to the sensor and again we see slightly worse corner performance on the Z6 at f/2.8.


Sigma 35mm 1.2 Art DG DN

Sigma 35mm 1.2 Art DG DN

The Sigma 35mm 1.2 Art DG DN is an extremely high resolving lens and in the center of the frame it shows what a big difference the Z6’s strong AA filter makes.

I still see a slight difference in corner performance at wider apertures, but I can hardly call it field relevant.


Sony FE 85mm 1.4 GM

Sony FE 85mm 1.4 GM

With this longer 85mm lens I don’t see any meaningful differences.

Observations

The filter stack differences definitely affect the corner performance of the wider E-mount lenses. From these four lenses I tried, it looks to me that around 35mm this starts to be negligible.

If you want to adapt some of the high performance ultra wide E-mount lenses (e.g. Sony FE 14mm 1.8 GM, Sony FE 20mm 1.8 G, Sony FE 12-24mm 2.8 GM) they will not show as good across frame performance at wider apertures as on an E-mount camera though.

Bokeh

Sigma 35mm 1.2 Art DG DN

Sigma 35mm 1.2 Art DG DN | f/1.2

In this direct comparison the bokeh might look a tiny bit smoother on the Sony A7III, but I don’t see this as a meaningful difference.


Sony FE 85mm 1.4 GM

Sony FE 85mm 1.4 GM | f/1.4

I do not see any relevant difference here.

Observations

It looks like the filter stack thicknesses of the Sony A7III and the Nikon Z6 are similar enough not to cause any harm to the bokeh. However, the situation might be worse with wider lenses like e.g. the Sony FE 24mm 1.4 GM. For anything 35mm and up I do not think this is something to worry about though, so I wouldn’t mind using my Sigma 35mm 1.2 Art DG DN or my Sony FE 85mm 1.4 GM on a Nikon Z-mount camera.

Conclusion

When the first Sony fullframe E-mount cameras hit the market, one groundbreaking feature was, that you could adapt all kind of legacy lenses to them. It was also the first time, the compact fullframe M-mount lenses could be used on a significantly more affordable camera. At that time most people weren’t aware of filter stack differences.

With today’s high performance lenses with short register distance it actually makes a notable difference for what filter stack they have originally been designed for though – at least when it comes to wide angle lenses. The compact M-mount lenses work best on a Leica M10 or a Kolari UT modded camera. In terms of color cast the Kolari modded cameras actually perform better than all the Leica M cameras that came before the M11.

When it comes to Nikon’s Z-mount cameras there were a lot of rumors regarding their filter stack thickness and how well they work with M-mount wide angle lenses. I don’t like rumors, I like facts, so I decided I need to check for myself. And what we found out here is, that they may not work as well with these M-mount wide angle lenses as a Leica M or Kolari modded camera, but in many cases they come very close. And they play much better with these lenses than stock Sony E-mount cameras.

If you are looking for a camera to adapt legacy lenses to in 2024, you should definitely have a closer look at Nikon’s Z-mount cameras. Furthermore it is also possible to adapt Sony’s E-mount lenses with surprisingly well working AF to those Z-mount cameras, making them the most versatile fullframe cameras you can find today.

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Further Reading

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