Recently I wrote about the new 35mm APO Summicron M and, before that, about the SL Summicron lenses. It occurred to me that I hadn’t written about any of the other APO M lenses, and as the 75 has been my favourite M lens for many years, I thought it would be a good idea to rectify the situation.
There are currently five such lenses that have all appeared since 1998 (there were several APO R lenses before that, but they were all telephoto designs).
- APO Telyt M 135 f3.4 1998
- APO Summicron M 90mm f2 1998
- APO Summicron M 75mm f2 2005
- APO Summicron M 50mm f2 2012
- APO Summicron M 35mm f2 2021
I bought my 75mm around 2007, shortly after acquiring the Leica M8, and it is still in frequent use today. I also have the 50mm, which I bought on release, and am now the proud possessor of the 35mm. Leica was kind enough to loan me the 90 and 135mm lenses for this article.
So, what exactly is an APO lens? The truth is that it’s rather a vague term and not to be confused with apochromatic, which isn’t vague at all!
Longitudinal chromatic aberrations occur when different colours focus at different distances from a lens and cause colour fringing around high-contrast edges.
An achromatic lens is one that is corrected to ensure that two wavelengths of light focus in the same plane. An apochromatic lens is where three wavelengths of light focus on the same plane. This is well and good, but it doesn’t cover the bokeh, so although it’s relevant where an image is completely in focus, it isn’t when it’s not.
With Leica’s APO lenses, chromatic aberrations are reduced by the use of low dispersion glass elements in the lens design. The intention is to reduce chromatic aberration in all areas, both in focus and out of focus. As more APO lenses have appeared they have refined the design, so that they have become more and more successful, culminating in the SL Summicron lenses and the new 35 APO Summicron M.
So, for practical purposes, we might define an APO lens as one which contains one or more low-dispersion glass elements. Indeed Leica has made this statement:
Apochromatic and more
The prefix ‘APO’ in the name denotes Leica lenses with the best imaging performance. From telephotos to wide-angles, all Summicron-SL lenses in the SL-System portfolio bear these coveted three letters before their names. For a long time, this distinction was reserved exclusively for telephoto lenses, as only they could achieve the exceptional quality required.
It is now over 40 years since the first APO lens built by Leica made its appearance – the APO-TELYT-R 180 mm f/3.4, in 1975. In 2012, the APO-Summicron-M 50 mm f/2 ASPH. became the first standard lens to bear this prestigious prefix.
Thanks to technological progress, more complex construction and new manufacturing methods employed in the SL-System, the design engineers were able to perfectly maximise the optical performance.
To us at Leica, APO means more than just the correction of longitudinal chromatic aberration, for which the purely scientific definition of the term ‘apochromatic’ stands.
This is emphasising that the Leica APO lenses (at least the modern ones) aim to remove chromatic aberrations completely.
But this is not just about Chromatic aberration, as Peter Karbe explained to me, the lack of aberrations results in much more contrast at the point of focus than in an ordinary lens, and that this contrast falls off very quickly in front and behind the point of focus. This means that an f/2 lens can appear to have the same depth of field as an f/1.4 lens (or even less in the case of the 75 f/1.4 compared to the 75 f/2 M lens).
I think that this rapid fall-off of contrast confers a special look on the Leica APO lenses, which are very detailed when in focus, but with a quick roll-off into gentle bokeh: Indeed, I think the whole look is ‘gentle’, the in-focus area, although showing a lot of detail, doesn’t have that ‘crunchy’ look that many older lenses have when stopped down.
Leica’s definition of an APO lens seems to be, quite simply, one which utilises low dispersion glass in construction with the intention of reducing chromatic aberrations, both in focus and out of focus.
Reducing the aberrations increases contrast noticeably when in focus, which has the visual effect of simulating a narrower depth of field because the contrast drops sharply as the focus is lost.
This has allowed them to produce a range of f/2 lenses which have the apparent depth of field of faster lenses, This, in turn, allows the lenses to be smaller and lighter and makes it possible to make them very high quality. They are, however, extremely difficult to manufacture, which explains why they are so expensive.
There is quite a lot of information about difficulties focusing the 90 APO on the internet, but nothing about issues with the other APO lenses, even, the 135 APO Telyt.
I was a little surprised by this, and so I thought I’d do some proper testing, not just close up, but at a range of distances. The results were enlightening. Of course, it’s possible that there was a specific problem with my 90mm APO, but I don’t think so as I’ve checked it out with other owners who have similar issues.
For the testing I used my M10-R together with the Visoflex EVF, focusing with the rangefinder and then checking it in the EVF.
135 mm APO Telyt
This is a long focal length for rangefinder focusing, and the frame lines are correspondingly small, but in actual use I found it is perfectly possible, even at f/3.4. Focusing was straightforward and accurate all the way from the minimum focus distance (1.5 metres) to infinity. Stopping down mostly extends the area in focus beyond the point of accurate focus, but it also extends it towards the camera.
90mm APO Summicron
This feels like it was designed principally for portraits. It focuses accurately, using the rangefinder up to about 4 or 5 metres, even at f/2. Stopping down does keep the original focus point in focus, but the in-focus area extends beyond that point, close to the camera remains out of focus.
By 30 metres I found it was back-focusing by two or three metres. So that when I focused on a car number plate 30 metres away using the rangefinder and then checked in the EVF, the point of accurate focus was two or three metres closer.
However, it’s worth mentioning in this context that the 90 APO was designed more than 20 years ago, well before the days of digital M cameras and many of the lenses ‘out in the wild’ are probably quite old, some may have been calibrated to specific cameras (which may have had poorly calibrated rangefinders). It’s hardly surprising that they should be out a bit. Probably if one was to buy a new one it would be much closer to correct.
As an interesting historical aside, the first of the 90 APO lenses were manufactured in Canada and around 50 produced. However, making the lens elements proved too challenging and in 1998 it was decided to move production to Solms.
75, 50 and 35 APO Summicron
These lenses all have a floating element and, as you would expect, focusing is accurate and manageable at all distances (and all f stops), with the area in focus extending both forwards and backwards when stopping
I’ve seen a tendency on the internet chatrooms to refer to the modern Leica lenses, and especially the APO lenses, as ‘clinical’ or ‘sterile’, whereas vintage and older lenses are described as ‘artistic’. To me, that sounds like it’s better to paint a picture with a 50-year-old paintbrush! Which doesn’t mean for a second that I don’t recognise the charm and character of lots of older lenses, but it’s a funny old world where ‘clinical’ = good and ‘artistic’ = not so good!
The modern APO M lenses are far from lacking in character; they have wonderful bokeh, and fantastic detail when in focus. What’s more, they don’t have the ‘crunchy’ look that many older lenses have when stopped down.
All five of these lenses produce wonderful images, right from the widest aperture, there is no need to stop down to improve quality. What’s more, the drawing of the lens doesn’t change when you do stop down.
In addition, they all work really well on the SL family of cameras, the 90mm, in particular, is better on the SL (or with an EVF on an M) because of the difficulty in focusing at distance with the rangefinder.
But the important thing for me is that all five lenses draw consistently, which means that if you’re shooting a wedding or a holiday or just a walk with the dog, then you can swap between different APO M lenses without radically changing the look.
Let’s face it, in this digital age with very acceptable high ISO, fast lenses are not needed for their light-gathering properties. And while it might be fun to shoot at f/1.4, the tiny depth of field makes it a risky undertaking if you’re shooting something that matters. Designing and manufacturing extremely fast lenses inevitably requires some compromises and they generally need to be stopped down before reaching peak performance.
Even though the Leica APO lenses have a greater depth of field than faster lenses, the rapid contrast fall-off as the lens goes out of focus makes the lens look faster than it is, with better bokeh. By giving up on the bragging rights of very fast lenses, Leica APO lenses perform perfectly from the widest aperture.
All these lenses are of fantastic quality, with the 50 and 35 being particularly special. I think they have real character, and what’s more, it’s a character born of modern technical innovation, not one which is a function of out of date design or technical shortcomings.
While most companies are pursuing the goal of faster and faster prime lenses which are growing larger and largeR as a result, Leica has quietly brought out a range of smaller higher quality lenses.
- Peter Karbe for checking an earlier draft of this article.
- Stefan Daniel for arranging the loan of the 90 and 135 and for all his help.
- Peter Farnz and Andy Piper from the Leica User forum for really helpful discussions about what an APO lens really is (or isn’t)!
- Thanks as well to Erwin Rehn, who pointed out that it would be good to have links to higher quality images, so, for the first time you can click on any of the images to get a larger version.
- Finally and most of all, to Emma who cooks magical meals and never complains about the time and money I spend on Leica!