ReviewPosted August 2019

Zeiss ZM 25/2.8 Biogon



Some lenses are a bit enigmatic. They might perform impressively under some circumstances, but fall short by others. The rendering can be distinct and perhaps not well suited for certain types of shooting. Sometimes aberrations can pop up and be hard to figure out. Even in terms of handling there can be niggles in use that aren’t apparent from looking at specs or images alone.

The ZM 25 Biogon by Zeiss is not such a lens. It’s very straight forward with few surprises. Overall it’s a truly excellent performer and most of its minor caveats are apparent from the get go.


The Zeiss ZM 25/2.8 Biogon is a mid-speed wide angle lens designed by Zeiss and manufactured by Cosina in Japan.

Unlike for instance Zeiss’s Tessar, Planar and Sonnar designations the Biogon label doesn’t entail a specific design. Instead Biogon lenses can have varying number of elements and differing characteristics. The common denominator is that they’re almost always semi-symmetrical wide or super wide angle lenses.

The ZM 25 Biogon holds true to this tradition with a somewhat symmetrical 9 element design and 82° diagonal angle of view. All elements are spherical and treated with the renowned T* coating process.

The lens is mostly unchanged since its introduction, though earlier copies bring up 28mm framelines and later copies the 35mm ones. Something I’ll back to in a bit.

Another feature of note is that the ZM 25 can focus down to 0.5m – closer than the common 0.7m default.

Lens-mount Leica M Mount
Length 60mm
Weight 260g
Diaphragm 10 blades, f/2.8-f/22, third stops
Elements / groups 9/7
MFD 0.5m
Filter thread 46mm

Front and rear mounts of the ZM 25. Samples from the Leica M3

Appearance & construction

The ZM 25 is reasonably sized and very well made.

It’s not the most compact lens in its range, but considering the angle of view, speed and performance it’s still fairly small. For a rangefinder lens it’s on the upper end of midsized and there is a noticeable bit of viewfinder blockage when shooting using the internal viewfinder. Compared to similar lenses for other 35mm systems it’s tiny.


Aesthetically the lenses in the ZM line are practically identical, with only slight differences in size and proportions.

Like its ZM siblings the 25/2.8 is an elegant lens. Compared to the utilitarian appearance of Leica lenses the Zeiss has more slender lines, a matter of taste which look is preferable.

Available in black and silver as the rest of the ZM line the ZM 25 is nicely finished. In my experience both finishes are very durable and show few signs of wear even after heavy use.

Build & feel

The ZM 25 is all metal and glass. The main housing and all control points are made from anodized aluminum. The focusing helicoid is brass. Front and rear mounts are made from chrome plated brass. The bright metal front mount can cause reflections e.g. when shooting through glass.

The aperture is nicely designed and has ten straight blades.

Tolerances are nice and tight and controls move very smoothly. The aperture settings have well balanced, solid clicks.

Earlier Zeiss ZM lenses had some issues with with uneven focusing feel as well as the optical cell coming loose, wobbling in relation to the focus helicoid. On later batches this seems to have been resolved. Besides that it also seems easy enough to adjust at service, should the issue crop up.

Markings & scales

Markings are engraved and painted using a tweaked version of the font DIN.

Aperture, metric distance and depth of field scales are painted white on a black lens, black on silver ones. Imperial scale and focal length identifier are painted red on black lenses, blue on silver ones.

Viewed from the front with the, unfortunately poor, front lens cap fitted.

Caps & Accessories

Another thing that’s unfortunately shared with the rest of the ZM line is the lens cap – it’s much fiddlier to put on and more prone to falling off than any other cap I have. The ZM caps are simply among the worst I’ve come across and getting a third party replacement is generally a good idea.

There’s a metal hood available as a separate purchase. It’s very nicely made and designed but as it’s very expensive I wouldn’t really advocate for it. The lens is big enough without it and very resilient to flare too, so the hood doesn’t really feel needed.

Leica M4-P


Something else shared across the entire ZM line is the ergonomics. So as I’ve shot quite a few ZM lenses by now there were very few surprises in this department.

Focusing nub

The ZM has the same finely ribbed focus ring with a small protruding nub as all the other ZM lenses.

I still prefer a proper focus tab, but the nub is a decent enough compromise. The little protrusion allows you to use your muscle memory to set your distance more quickly, making the solution preferable to a plain ring.

Having a 0.5m close focus distance can throw a spanner in the works when it comes to taking advantage of that muscle memory though.

The Voigtländer Skopar 25 is another rangefinder lens I’ve shot offering a 0.5m MFD. On that lens the travel becomes off because the 0.5m point is where the 0.7m distance setting is usually at. This makes it harder to rely on muscle memory to preset a distance where you want your focus. At least if you’re switching between lenses regularly.

With the ZM 25 Zeiss did something more clever though. They simply extended the throw to accommodate for the closer focus. This means that the 0.7m position is still where you expect it to be. As a result the full range also acts in a more familiar manner.

The focus nub is a good middle ground between a plain ring and a focus tab.

In my review of the Skopar 25 I quantified all this by stating that with its tab in the 6 o’clock position the focus distance was well under 1m. Most other lenses with a tab end up focused between 1.2–1.5m at that position. With the extended travel offered by the ZM 25 that holds true as well – at the 6 o’clock position focus falls just a hair closer than 1.2m.

This is a pretty minor point, but it does certainly make things a bit easier if you’re alternating between lenses, especially ones with tabs*.

* As I’ve mostly been pairing the ZM 25 with the ZM 50 Sonnar it still hasn’t been totally seamless though. The Sonnar has the same issue as the Skopar, only in the opposite direction – its MFD of 0.9m is at the point where you expect 0.7m to be. This throws the full range of travel off a little. In this regard the ZM 50 Planar would make for a more compelling pairing as the lenses would then handle almost exactly the same.

Here a number of the Biogons features can be spotted – the expensive but nice hood is mounted, the marked third stop increments on the aperture dial and the 0.5m close focus distance. You can also just about make out how subdued that red shade used for the imperial distance scale and focal length identifier actually is.

Third stop aperture settings

Compared to a lot of the other ZM lenses the Biogon is a little less tapered towards the front. This allows for an aperture ring that’s a hair wider than on its siblings. And while changing aperture setting on the other lenses works perfectly fine, it’s an ever so slightly more comfortable affair on the ZM 25.

The aperture is set in third stops with distinct clicks at each increment.

In my opinion having third stop increments is a bit overkill. It makes changing aperture feel slower and more fiddly than with half stop increments. There’s also little practical to gain from this level of fine grained control. Neither depth of field, image quality or exposure really changes significantly enough by each increment to warrant the minute changes. Maybe I’d feel differently if I was shooting slide film, but as it stands I feel half stop control is plenty.



Image quality

The Biogon is an exceptional performer across the board. It’s well corrected and behaves admirably in almost every way imaginable.

Researching the lens brings up various quotes on it being among the highest resolving lenses made by Zeiss and in my use I’ve not seen anything that makes me question this. There’s more to image quality than just resolution though, so let’s break it down.

Resolution & contrast

The Biogon delivers great definition across the frame already wide open. Contrast levels are very high, though towards the corners definition drops a little at wider aperture settings. Resolution is impressive, as expected, though also drops a little towards the corners.

Stopping down to just f/4 improves the entire frame further and overall contrast is excellent at this point. By f/5.6 contrast and resolution are both outstanding. Clarity is excellent at all frequencies and even the smallest detail is faithfully reproduced.

There’s good field flatness and definition remains high at both close and far distances.

In regards to contrast then the Biogon performs impressively overall, giving images a strong sense of realism and presence.

The Biogon offers excellent definition already wide open. Here is an f/2.8 shot from the Leica M 262 (240 sensor) and as you can see the center crop is already just about perfect in terms of contrast. The second crop is from the far upper right but details are still just a fraction less well defined. And already by f/4 you start getting edge performance that’s just about optimal.


Zeiss lenses are generally benchmarks with regards to color – the Biogon is no exception. The palette is warm and saturated while remaining lifelike and subtle. Close hues are separated elegantly and the color reproduction overall is very appealing.

Bokeh & transitions

With its moderate speed and wide angle of view you’re never going to see huge amounts of bokeh from the Biogon.

However as transitions are very distinct and the flatness of field is high there’s still a clear sense of separation between planes. This gives images an appealing depth. It makes the lens a little less forgiving with zone focusing though.

At wider apertures and modest distances some bokeh will be visible. There are some clear outlines and there will always be quite a bit of texture in the out of focus areas. Still it’s pretty decent for a wide angle lens.

Despite being very wide and only moderately fast the Biogon gives very good separation between planes. In this instance the trees outside of the window are blurred despite the kids being a few meters away already.
Leica M3 – f/2.8


The Biogon is impressively well corrected with regards to aberrations. Very few issues are visible even under close scrutiny.

There’s very little distortion and the amount of vignetting is reasonable.

Flare is pretty much a non-issue with very little ghosting or loss of contrast even in challenging situations. Even shooting against the light doesn’t tend to bring much if any flare. Modest amounts of chromatic aberration can be observed in high contrast areas at wider apertures.

When shot on digital there can be significant ray angle induced issues, especially on cameras with thick filter stacks (i.e. most cameras other than the digital Leica M’s). On such cameras the lens tends to underperform compared to native options.

The Biogon is exceptionally well corrected overall. There’s very rarely any signs of flare, even when shot against the light, as demonstrated in the first example above (shot on the Leica M3).
The second image examplifies that the lens can suffer somewhat when shot on digital. Shot on the Leica M 262 without a profile the image shows noticable color shift on the top half. This is easy to correct for and by setting a correction profile in the camera the problem all but goes away. Still it’s worth noting that on cameras with thicker filter stacks issues can be more severe.

Differences between mediums

The overall evaluation of the performance holds true regardless of medium, but at times characteristics can come across differently depending on the capture method.


To my eye the Biogon’s output can sometimes come across as a little harsh when shot on digital. Other than that it offers impressive and appealing output. The high contrast and rich color reproduction certainly makes for appealing looking files.

Color negative film

This is where the Biogon works best to my tastes – the high optical performance combined with the slight roundness coming from film results in wonderfully looking images. The negatives end up rich and detailed and images have a strong presence.

Black & white

I’ve not shot the Biogon much in B&W, but from what I’ve seen it does well. The punchy contrast and well defined quarter tones translate well to monochrome output.

Leica M3 – f/8

Overall rendering

You can’t really argue against the performance of the Biogon, it’s simply exceptional in almost every way. Class leading levels of contrast combined with a rich color palette and good correction of the common aberrations means it’s hard not to be impressed by the Biogon. In objective terms it’s a benchmark.

Subjectively I sometimes get a sense that it’s just too good though. There can be a harshness creeping into the output that I sometimes don’t find too appealing.

Still very few lenses manage to offer a better balanced output with this high level of performance. Shooting the Biogon to me instead becomes more about leveraging its strengths and finding ways to work around its occasionally clinical tendencies. When I’ve managed that I’ve been very happy with the phenomenal performance it offers.

Leica M3 – f/5.6

Specifics in use

I’ve had the ZM 25 for around a year by now. I’ve put it through its paces during my time with it and feel I’ve gotten a good handle on it.

I can’t say I’ve really bonded with the lens though. But to explain why I think I need to back up to how I ended up with it in the first place.

Back during winter last year I started to feel it was time to switch things up on the wide end of my set up. I’d been shooting the Leica Summicron 28/2 for years and while I’d been incredibly happy with the lens overall I felt it was a little bit bigger than what I’d ideally want (an idea coming mostly from enjoying the Voigtländer Skopar 25/4 so much). As the Summicron was getting overdue for a service I got to thinking that maybe I should let it go instead and try something else for a while. I figured that if the switch didn’t pan out I could probably buy back a cleaner copy of the Summicron for less than the price I’d be able to sell it for plus a good service.

So off the Summicron went and the search for a replacement ensued. I had my sights set on either the Leica Elmarit 28/2.8 ASPH or the rare-as-hens-teeth LTM version of the Ricoh 28/2.8 GR lens. Two lenses that felt like they could strike a better balance for my preferences than either the Summicron (too big) or Skopar (too slow).

I waited patiently but neither lens popped up for sale anywhere local (usually the Elmar isn’t too hard to get a hold off, but suddenly… nothing). Weeks came and went and as winter turned to spring I felt like I wanted to add something to fill that wide angle slot before summer at latest.

The ZM 25 wasn’t exactly what I was looking for, but it had still been on my radar some time. An acquaintance of mine shoots almost nothing but this lens and gets fantastic results from it. I also had a chance to try the lens briefly a while back and came away impressed with it. So when a local ad popped up for one at a reasonable price I figured it was more than worth having a go with.

I was happy about the addition. The Biogon slotted well into my setup and made for a good pairing with in particular the Zeiss ZM 50 Sonnar that I enjoy shooting so much. I shot it a lot and the Biogon proved an excellent performer and solid in use. It was certainly a capable and competent addition.

Still there was a lingering sense of having lost more than I’d gained in the switch from the Summicron. Size and weight remained similar but a full stop of light gathering was lost. Both ergonomics and overall rendering were steps down to my tastes. In isolation the field of view of a 25 might suit me better, but as it doesn’t play quite as well with the cameras I’m using (I’ll get back to this in a sec) this also felt like a slight downgrade.

Even compared to the little Skopar it didn’t feel like I was quite gaining enough to warrant carrying the bigger size and putting up with the less enjoyable ergonomics.

Add to this that I’ve been gravitating towards longer lenses lately and you’ll soon realize that the deck was stacked against the Biogon.

I’ve become pretty good at detaching myself from circumstances like these when evaluating lenses though, and I’ll move on with some other observations in a second. For now I’ll simply state that while I’m not in a huge rush I’ll probably move on from the Biogon before too long. Not due to any issues with it per se, as it really has a lot going for it, but rather due to how it plays to my current and very specific preferences.

Right, now let’s get back on track.

Leica M3 – f/8

25mm in practice

I’ve come to really enjoy the 25mm focal length. It’s more dynamic than a 28 but still easier to use well compared to something even wider.

There’s one hurdle for use on M mount cameras however – the lack of appropriate framelines. Of all M mount cameras available only the Leica M8* and Voigtländer Bessa R4A/R4M offers framelines for the focal length.

* Technically the M8 offers 24mm framelines, but it’s close enough.

There are a few ways to get around this when shooting on other cameras.

The most accurate option is to get an external viewfinder. This gives you correct framing at the cost of added bulk and some inconvenience in that you need to switch from one finder to focus* and another to compose. I’ve taken this approach when shooting the Biogon on the Leica M3, using the Zeiss 25/28 finder, and enjoyed it a lot.

* And as noted previously – the lens is pretty unforgiving with regards to zone focusing, so generally you’ll want to use both finders.

A more seamless option however, is to use the 28mm framelines as a reasonable approximation for framing and then compose a little tighter than you’d normally would. This results in a slight loss in framing accuracy, something that some people find unacceptable, but personally I find it close enough. As you’re using the same finder for both focusing and framing to me it’s a more seamless experience. This doesn’t work on older cameras like the M3 obviously, as they lack 28mm framelines, but on more recent cameras this, to me, is the most enjoyable way to shoot 25mm lenses.

With recent copies of the Biogon however, there’s one issue making this a little bit trickier – the fact that the lens brings up 35mm framelines rather than the 28mm ones.

I was a bit puzzled by this choice back when I reviewed the Skopar 25, but has since figured out the reason.

In the 1.33x crop Leica M8 the 25mm framelines are brought up together with the 35mm ones, making for a pairing unique to that camera. So then it makes sense for the lens to bring up the 35mm frameline pair, but unless you’re shooting the M8 it’s not ideal.

Of course on most of the Leica M mount cameras you have the option of pushing the frameline preview lever to the 28mm position instead, getting around the problem momentarily. You can also lock the preview lever in place using a bit of sticky tape or a piece of folded paper stuck between the lever and camera body. This is what I’ve done on my M4-P and M9 and it’s proven a good and simple solution, offering an enjoyable experience.

The only issue has then been shooting the Biogon on the M Typ 262*, a camera which unfortunately doesn’t have the frameline preview lever. Here shooting the lens has honestly felt a bit more like a kludge. I’ve been a bit more reluctant to use the external finder as the camera offers the 28mm framelines, but with no way to access them that’s been the nicest way to shoot.

* The same thing would be true on the M 240, but there you at least have live view as an option. The Leica M-E would also have this same issue.

There is a way to solve this though, and that is to send the lens to Zeiss and have them replace the mount with one that has the 28/90 frameline selector lug length. They reportedly do this change for a modest fee. If I were to keep the lens and continue shooting it on the M 262 and M4-P that’d be the route that I’d take.

Shooting the lens using live view is also a viable alternative obviously, if you’re shooting a camera that offers it, negating most of the discussion above. To me however, that’s a lot less enjoyable and I prefer simply using the 28mm framelines if possible.

Now this was all pretty long winded, but to sum up – the 25mm focal length can be very enjoyable to shoot, even on cameras without the corresponding framelines, depending on how you feel about the different ways to shoot it.

The Biogon mounted on the M3 and a shot made with it on the M 262 – two cameras that are enjoyable, if slightly suboptimal, to shoot the Biogon on.

0.5m close focus

As mentioned the Biogon offers focusing down to 0.5 meters rather than the commonplace 0.7m.

While there aren’t any M-mount cameras that support rangefinder coupling at that close of a distance it’s easy to use when shooting using live view. It’s also not too difficult to guess the distances involved (though a little trickier than with e.g. the Skopar 25 as the transitions are so quick).

Depending on how you feel about the look that shooting a wide angle at closer distances this feature could be a significant advantage or a moot point. Personally it’s not a look I’m crazy about, so I’ve not taken much advantage of this aspect of the Biogon.

Leica M4-P – f/4

Use across different cameras

I’ve used the Biogon across a host of different cameras in the time I’ve had it. Below are some observations in use.

Leica M3

While a somewhat odd pairing this set up has been very enjoyable to use. The large magnification viewfinder obviously doesn’t offer any appropriate framelines (50mm ones are the widest available) but on the other hand focusing is quicker and more comfortable. So composing and shooting with an external finder then becomes a perfectly viable and pleasant way to shoot. The output has also been quite excellent, the rendering works very well with film, and many of my favorite shots from the lens were made using the M3.

Leica M4-P

My dear M4-P is my favorite camera to mount the Biogon to. The combination handles and balances well. If you get a lens that brings up the 35mm framelines, using the frameline preview lever to bring up the 28mm ones instead gives a seamless and accurate enough way to shoot the focal length. Add to that an output that is fantastic on film and you end up with a very compelling package.

Leica M9

The Biogon does very well on the M9 but you need to do something a little unintuitive to get the best out of it – pick the correction profile for the 21mm Elmar instead of one of the 24mm lenses. Without a profile you end up with significant color shifts towards the edges, but the 21mm one clears it up almost completely, leaving a pleasant and impressive output. Shooting using the 28mm framelines gives a nice experience.

Leica M Typ 262/240

The Biogon offers excellent output on the M 262 (as long as you select the 21mm profile, like on the M9) and balances well on the camera. However as the camera’s missing the frameline preview lever it’s not possible to switch from the 35mm ones brought up by the lens, so if you end up with a copy that does this my advice is to get the rear mount switched by Zeiss. Shooting this combination feels a little bit like a kludge otherwise. This is one of few lenses I’ve shot where I feel it might make a bit more sense on the M 240 over the 262, to fully take advantage of its benefits – you can use live view to get accurate composition as well as focus down to the closer 0.5m distance. Still it’s a nice and competent pairing.

There are some drawbacks in terms of performance when shooting the Biogon on a camera with a thicker filter stack like the Sony A7. Still there are positives too – you can compose with perfect accuracy and with a helicoid adapter you can cut the minimum focus distance down very close.

Sony A7

This combination isn’t really ideal. Due to the thicker filter stack on the Sony sensor noticeable ray angle issues can be observed. There are some minor color shifts, but what’s worse is that the outer 4mm on each side of the frame is distractingly smeared at wider apertures. Stopping down to f/8 yields a fairly consistent impression but even at f/11 the resolution isn’t fully uniform. On the other hand the lens is enjoyable to shoot using live view and it becomes trivial to compose and use the closer focus distance (and with a helicoid adapter the MFD can be cut to a very short distance indeed, the performance even holds up at those closer distances). Still it’s not a combination that feels too compelling and sticking to the native options is probably a better bet.

Leica M9 / Leica M 262

Alternatives to consider

The Biogon is a compelling option that’s exceptionally competent and offers reasonably good value for your money. Still, depending on your preferences there are a few other options also well worth considering.

Leica Elmarit 24/2.8 ASPH

I’ve not shot this similarly specced lens from Leica, but it looks pretty nice. Performance is similar by all accounts but ergonomics a little bit better. The price difference is significant though, and the Biogon is a far easier recommendation.

Leica Elmar 24/3.8 ASPH

I’ve not shot this lens myself but it reportedly offers similar level of performance while being slightly more compact. The ergonomics also look better to my eye. On the other hand it’s almost a stop slower and far more expensive, making it a difficult choice to recommend.

Leica Summicron 28/2 ASPH

As I’ve already mentioned that being so familiar with the Summicron 28 is the main reason I’ve not fully bonded with the Biogon. The Summicron is similar in size and weight to the Biogon, but a full stop faster. It also offers better ergonomics to my tastes. Its performance is mostly as impressive as the Biogon’s but with a more balanced rendering and an incredibly appealing signature. Being a 28 also makes it easier to use as there are corresponding framelines on way more cameras. The Biogon is much more reasonably priced however, and in some ways it performs even better than the Summicron, making it a much easier recommendation for most people.

My full review of the Leica 28/2

Voigtländer Skopar 25/4

Another reason why I’ve not become fully sold on the Biogon is this little gem. While a full stop slower the Skopar’s got it where it counts. It’s exceedingly compact but still manages to have very good ergonomics and image quality. The Skopar’s color rendition isn’t as refined and it’s not quite as high resolving as the Biogon at f/4, but stopping down just a little bit makes it pretty hard to tell the output apart. To me the main argument for the Biogon is that the slightly higher speed makes the lens usable under a much broader set of circumstances. Other than that I tend to prefer the Skopar with its lower price being an added bonus.

My full review of the Voigtländer 25/4

Voigtländer Ultron 28/1.9

The Ultron hasn’t really won me over but it sure makes a compelling case for itself. It’s a lot faster than the Biogon, but still similarly sized and close to the same weight. It can be mounted on more cameras and behaves better on many of the mirrorless options. It’s also cheaper. Ergonomics and build is a wash. The Biogon pulls ahead in performance though – contrast is much higher and the overall output is much more impressive.

My full review of the Voigtländer 28/1.9

Zeiss ZM 28/2.8

This slightly longer lens is another compelling choice. I’ve shot it extensively in the past, but haven’t reviewed it. It’s a little bit more compact than the 25 and being a 28 makes it a little easier to use at times. It offers excellent image quality but it’s still lagging the exceptional 25 slightly – contrast isn’t as consistent across the frame and the field flatness is a little worse. Overall it’s a tricky choice between two excellent lenses. Pick the 28 for its more compact size or the 25 for a slight edge in performance. Or just go for the focal length you like best.

Leica M3 – f/4




Bottom line

It’s hard to argue against the Biogon – it simply is an excellent lens. It offers exceptional performance, very nice build quality and ergonomics at a reasonable price. There are some niggles here and there but they are nitpicks rather than significant issues.

So instead of hinging on any significant objective shortcomings a recommendation of the Biogon comes down to two other factors.

If you’re fine with the first point (skip back to the In Use section if you’re not sure) and feel that the overall specs and rendering offered by the lens speaks to you, the ZM 25 becomes a very easy recommendation.

Personally I’ve had a hard time bonding with the Biogon, though I’ve only myself to blame. I got it in-spite of it simply not being quite what I’m looking for in a wide angle currently.

While I’m totally fine shooting the 25mm focal length on a rangefinder I’ve been keen on something more compact. Add to this a rendering that can be perhaps a little bit overly efficient at times and I’ve simply not been as compelled to use the Biogon as with lenses that’ve felt more aligned with my preferences.

Despite not fully bonding with it though, my lasting impression of the Biogon is of its exceptional competence. It’s a straightforward performer with few surprises that just delivers. If you’re less fazed than me with it’s minor shortcomings it’s hard to go wrong with the ZM 25 Biogon.



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Photos in this review were taken using the Leica M3, Leica M4-P, Leica M9, Leica M Typ 262 or Sony A7. Photos of the lens were made using the Sony A7. All film was developed by Team Framkallning and scanned using the Plustek 8200i. Exif-data is intact. Open any image in a new window for a closer look.