Jonathan Slack: Leica APO M lenses

[jonoslack]

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I recently 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 5 such lenses which have all appeared since 1998 (there were several APO R lenses before that, but they were all telephoto designs).

• APO Summicron M 90 f2 1998
• APO Telyt M 135 f3.4 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 buying my M8 and it's 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 were kind enough to loan me the 90 and 135mm lenses for this article.

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May the Force be with you (Botallack, Cornwall 2016)
Leica M10 with 50 APO M 1/1000 ISO 100

 

APO Lenses

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 which is corrected to ensure that two wavelengths of light focus in the same plane - an Apochromatic lens is where 3 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.

Joel Meyerowitz at the launch of the M10  (Wetzlar 2017)
Leica M10 with 50 APO M 1/90 ISO 400 f2.8

 

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.

Vroom  (Young riders in Xingping in 2012)
Leica M9 Monochrom with 75 APO M 1/180 ISO 1250 f4.8

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.

Making a Splash (Glykanera, Crete, September 2009)
Leica M9 with 75 APO M 1/160 ISO 350

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.

Peter Karbe, Leica  (Wetzlar 2018)
Leica M10 with 75 APO M 1/350 ISO 200 f2.4

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 f2 lens can appear to have the same depth of field as an f1.4 lens (or even less in the case of the 75 f1.4 compared to the 75 f2 M lens).

Waiter at the Blue House, Loutro  (Crete 2015)
Leica SL with 75 APO M 1/80 ISO 125 f2

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.

To Summarise 

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 focus is lost. 

This has allowed them to produce a range of f2 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.

Fags and Fingers  (China 2012)
Leica M9 Monochrom with 75 APO M 1/125 ISO 320 f2.8

 

Focusing

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’s perfectly possible, even at f3.4. Focusing was straightforward and accurate all the way from the minimum focus distance (1.5 metre) 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 f2. 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 2 or 3 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 2 or 3 metres closer. 

Helen's Purple Poppy (Middle Fen Cottage, June 2021)
Leica SL2 with 90 APO M 1/5000 ISO 100 f2.4

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 down.

Keith doing his Marlon Brando impersonation (Dunwich, June 2021)
Leica M10-R with 35 APO M 1/60 ISO 100 f5.6

 

Image Quality

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!

Clint & his Moll; Dotty (Middle Fen Cottage March 2021)
Leica M10-R with 35 APO M 1/4000 ISO 100 f2

The modern APO M lenses are far from lacking 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 5 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.

Vespa Man (Gunton Arms September 2020)
Leica M10-R with 35 APO M 1/1000 ISO 100 f2.4

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 5 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.

 

Conclusion

Lets face it, in this digital age with very acceptable high ISO fast lenses are not needed for their light gathering properties, and whilst it might be fun to shoot at f1.4, 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. 

Busted! (Cambridge Folk Festival July 2019)
Leica M10-R with 50 APO M 1/250 ISO 100 f2

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.

Stop! (Central Italy May 2016)
Leica M10-R with 50 APO M 1/250 ISO 100 f2

All these lenses are 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.

Whilst most companies are pursuing the goal of faster and faster prime lenses which are growing larger and larger as a result, Leica have quietly brought out a range of smaller higher quality lenses.

Matty (Middle Fen Cottage May 2019)
Leica SL2 with 75 APO M 1/60 ISO 6400 f2
 

Closest Focus with the various APO M lenses
For the 35 APO I've shown both the rangefinder limit (0.7 metre) and the 0.3 metre needing EVF or Live View
Each image represents the whole of the frame

The Lenses (Middle Fen Cottage June 2021)
Leica SL2 with 75 APO Summicron SL 1/160 ISO 1250 f2

Lust (The Birmingham and Worcester Canal 2021)
Leica M10-R with 35 APO M 1/60 ISO 100 f4.8

 

Acknowledgements

• 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)!

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[Shu_downunder]

Can I criticize that this article is too shot and sample images are too less?🤪

 

Can I ask a question - Does APO mean anything to a monochrome body?

Edited October 8, 2021 by Shu_downunder

[jplomley]

Fantastic article Jono! Any predictions regarding a 28 mm APO M lens? Or is APO correction at wider focal lengths more of a challenge for the M lens size? 

[Gobert]

I like the article.

In the meantime I’ve sold my 75 APO, not because it is an APO; I simply could never become friends with 75mm.

I own the 135 as well. In my view it is a brilliant lens if you understand it.

I am still considering to trade in my Lux 50 for a 2nd APO 50.

 

Question

the glass of the first APO’s in the eighties was more than regular lenses vulnerable for moisture. Is that still the case?

[Gobert]

2 hours ago, Shu_downunder said:

Can I criticize that this article is too shot and sample images are too less?🤪

 

Can I ask a question - Does APO mean anything to a monochrome body?

Of course. The APO performs brilliantly on the monochrom if you are looking for resolution.

[ocean2059]

@jonoslack: Excellent writeup as usual. Thank you. 

[Bikie John]

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Very interesting @jonoslack, thank you. It has stirred up some very old memories. For a while I used the 90mm AA for live music in dingy pubs and had a vague but unspecific feeling that it was not so good at greater distances, but never got around to quantifying it. Your article has brought a lot of clarity, I shall have another look at it.

John

[SiggiGun]

Thanks for this @jonoslack.

Currently I am in love with the new Apo35M. Everytime when I  put a Apo-Summicron on my camera,  I try to use it at f2.0..... 

Magic! Especially under difficult light conditions 

 

Edited October 9, 2021 by SiggiGun

[Stein K S]

Great reading Jonathan!
 

I feel the urge sitting here with my rather new 50 Lux asph bc, to ask if you think your descriptions/profiles overall also count for this lens? I ask since I do believe that Mr Karbe once suggested that this Lux is also designed according to ¨apo principles¨… Or is there even more to the lenses that actually carry APO in their names?

Edited October 9, 2021 by Stein K S

[Steve Ash]

I wish there is a revision of the article adding an apo summicron-m 28 in the not to far future.

[MarkP]

Thanks for this article Jono, I had been thinking about just this issue as of late.

I have all these lenses except for the 90 APO-Summicron simply because it’s a rarely used focal length for me. So the 90 Macro-Elmar-M is an adequate compromise (actually an excellent lens) for when I need a 90. For years  I’ve successfully resisted my OCD GAS to buy the 90 simply for the sake of ownership and what would be very rare use.

I recently acquired the 35 APO-Summicron so went back and compared all the lenses for consistency of imaging.  I completely agree with you. Regarding focusing the 135 APO-Telyt (mine has been off to service previously to confirm calibration when I had it 6-bit coded), it does require more disciplined technique to get reliable focus accuracy and avoid blurring due to camera-shake, especially without an EVF. I tend to avoid going faster that f4.0 simply to give me a whiff more room for focus error and find this makes a big difference. 
 
Interestingly, I threw in the 24 Elmar-M & 21 SEM and found they also imaged sympathetically.

Regarding the ‘character’ of the newer vs older lenses, I too have a large number of the older Mandler lenses. They may not have the same optical ‘perfection’ of the current range (APO and non-APO), but the final photographs are neither ‘better’ or ‘worse’, just different and used accordingly to serve the purpose of getting the final image I want. 
 

ps.  I’d love to see a 28 APO-Summicron in production.

Edited October 9, 2021 by MarkP

[LocalHero1953]

When I got out of the M system a couple of years ago, I felt a real wrench selling my Apo-Summicron-M 75 and a bit of one selling the 90 - I knew how much they had served me as I learned portrait photography. And the 75 was also an excellent walk-around lens for travel - I usually paired it with the Elmarit 28mm Asph.

I now have the 75 & 90 counterparts for the SL system (and the 35), and I still sense astonishment at the clarity and contrast when looking through the EVF - it's the same with the 90-280 zoom. Your explanations about why I get that feeling, Jono, make complete sense - thank you!

I miss equivalents for the CL for travel (no 50TL), though perhaps that is as much because of the smaller sensor than because the lenses are lesser quality. My most common practice is either the Summilux-TL 35 Asph on its own or the combination of Apo-Macro-Elmarit-TL 60 and SVE-TL 11-23 Asph - I certainly have nothing to complain about there.

 

Edit. I did find the Summicron-M 90 was imperfectly calibrated and sent it off to be fixed, which it was - I never explored whether it was related to focus distance. It's the only M lens I ever sent for calibration.

Edited October 9, 2021 by LocalHero1953

[spydrxx]

Thanks for the clear explanation of apo and how Leica designs it’s apo lenses to incorporate oof contrast fall off. It clears up many of the comments I’ve seen on this site. Perhaps in the future I’ll try one of these lenses.

[jonoslack]

On 10/8/2021 at 1:55 PM, Shu_downunder said:

Can I criticize that this article is too shot and sample images are too less?🤪

 

Can I ask a question - Does APO mean anything to a monochrome body?

Hah - I'll take that as a compliment, and yes, it does mean something on a monochrome body (just the same thing)

all the best

Jono

[jonoslack]

On 10/8/2021 at 2:06 PM, jplomley said:

Fantastic article Jono! Any predictions regarding a 28 mm APO M lens? Or is APO correction at wider focal lengths more of a challenge for the M lens size? 

Thank you so much - definitely a labour of love!

It was 8 years between the 50 and the 35 APO . . . I guess we might have to wait a similar amount of time for the 28 (but I think the principles are the same - look at the 28 APO SL). 

All the best

Jono

[jonoslack]

On 10/8/2021 at 4:34 PM, Gobert said:

I like the article.

In the meantime I’ve sold my 75 APO, not because it is an APO; I simply could never become friends with 75mm.

I own the 135 as well. In my view it is a brilliant lens if you understand it.

I am still considering to trade in my Lux 50 for a 2nd APO 50.

 

Question

the glass of the first APO’s in the eighties was more than regular lenses vulnerable for moisture. Is that still the case?

I didn't know about moisture problems with APO lenses, so I guess it isn't still the case.

I have both the 50 Lux and the 50 APO, and use them both

best

Jono

[jonoslack]

19 hours ago, Steven said:

Ah ! This is brilliant. My G A S had disappeared these past few weeks and I felt deprived. You fixed it, Jono. Thanks! 

😂 Thank you Steven - Pleased to be of service 🤪

All the best

[jonoslack]

6 hours ago, Stein K S said:

Great reading Jonathan!
 

I feel the urge sitting here with my rather new 50 Lux asph bc, to ask if you think your descriptions/profiles overall also count for this lens? I ask since I do believe that Mr Karbe once suggested that this Lux is also designed according to ¨apo principles¨… Or is there even more to the lenses that actually carry APO in their names?

Hah!

Well, the reason I left it out was that Leica don't call it APO, but of course I'm very well aware of Peter Karbe's comments, and as the 50 'lux is definitely the little sister of the 75 APO, I would think it's part of the team. But I do think there is a thing about making a lens f2 and being able to make it either a)smaller or b) better.

Whatever, the 50 'lux is a lovely lens, I have one and use it often.

best

 

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Hallo,

Look here: Leica M

[jonoslack]

5 hours ago, Steve Ash said:

I wish there is a revision of the article adding an apo summicron-m 28 in the not to far future.

So do I Steve, but it was 8 years between the 50 and the 35 . . . . . 

[Jeff S]

12 minutes ago, jonoslack said:

 But I do think there is a thing about making a lens f2 and being able to make it either a)smaller or b) better.

 

 

Hey Jono, I know that you’re very familiar with Karbe’s thoughts on the Summilux ASPH, and I thought this old interview (apologies for posting before) especially addresses his joint concerns of reducing aberrations while maintaining compactness.  I found his comments about reinventing glass types, at significant expense, particularly interesting.

https://www.shutterbug.com/content/leica-lens-saga-interview-peter-karbe

Jeff