Zeiss Biogon T* 2,8/25 ZM

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Last updated October 16, 2011

The Zeiss description for this lens

The Creative Wide-angle Artist

This moderate wide-angle lens offers exciting visual perspectives, but is also one of the easiest to control. The Biogon T* 2,8/25 ZM delivers high contrast across the entire image field and is virtually free of distortion at full apertures. With the aperture stopped down, detail is finely rendered with a pleasing three-dimensional quality. The lens is rangefinder-coupled for easy focusing and the optional 25/28 mm viewfinder is available for accurate image composition. Combined with a digital rangefinder camera with a 1.3 crop factor, the lens has an effective focal length of 33 mm. The Biogon T* 2,8/25 ZM is a creative tool for scenic portraits, inspiring landscapes and expansive architectural photography.

Important specifications

Focal length 25 mm
M8 equivalent 33 mm
Aperture range 2.8 - 22 (1/3 steps)
Aperture blades 10
Focusing range 0.5 m – infinity
No. of elements/groups 9/7
Angular field, diag./horiz./vert. 82/72/52 °
Filter M 46 x 0.75
Dimensions (with caps) ø 53 mm, length 71 mm
Weight 260 g

Performance Data

The following graphs were gleaned from the Zeiss-provided datasheet (PDF) for this lens:

Introduction

A full review of the Zeiss Biogon T* 2,8/25 ZM lens, including specifications, performance charts, overview, sharpness and vignetting tests as well as sample images and links for further research.

The Zeiss Biogon T* 2,8/25 ZM lens is sure to dazzle even the most stringent of lens critics and one that even Zeiss is proud of. It's capable of some remarkable resolution with very well-controlled distortion (which is almost non-existent). The lens really comes into its own as it is stopped down to the optimal aperture of f/5.6 - and with either film or digital, it will truly test the resolving power limit of your medium. It really doesn't get any better than this.

Zeiss regularly puts out a newsletter called, "Camera Lens News." In issue number 24 (February 2006) it was remarked that this lens set a new resolution record approaching 400lp/mm. In the "real world" you'll see about half of that - but no matter how you slice it, that is really impressive. We tried to post a link to that issue or provide it for download - but it is nowhere to be found. The archives of CLN don't go back that far and the original link(s) are dead. Not even the "Way Back Machine" was able to help other than to provide this evidence that it once existed...

When Hasselblad staff photographer Jens Karlsson took demo photos for the first Zeiss Ikon brochure in 2004, his photo of the carousel, taken with the ZM-Biogon 25 stood out for its enormous detail and clarity. So we used a ZM-Biogon 25 in a recent test to determine maximum resolving power. The high resolution film of choice was the SPUR Orthopan UR supplied and processed by SPUR. The result was a whopping 400 lp/mm on film, recorded with the Biogon 25 at f/4 in the center of the image. This value, 400 lp/mm, corresponds to the maximum resolution theoretically possible at f/4; in other words it represents the calculated “diffraction limited” performance at this aperture. It is noteworthy that this test was conducted with a production lens on a production camera, indicating that the film was precisely positioned and flat.

The 25mm (and 24mm) focal length is a bit of an oddball as far as rangefinders go. They were made more popular with the release of the M8 where it makes a fantastic 35mm equivalent lens. This could very much be an "everyday lens" if the speed works for you. The only faster option at this focal length is the Leica Summilux-M 24mm f/1.4 ASPH - which runs several thousands of dollars. The next closest would be the Voigtländer 28mm f/1.9 or f/2 Ultrons - but they each have their own issues (low contrast/flare and focus shift, respectively). Any corner/edge softness or vignetting is non-existent with the M8's crop sensor. The Leica Elmar-M 24mm f/3.8 ASPH is no better a lens. Even with film or the M9, the Leica version won't gain you anything... This particular ZM lens is that good.

Consider reading about all the things they have in common in our Zeiss ZM Lenses overview.

The Lens

Like the other ZM lenses, the Biogon is well-built and solid-feeling. The materials and craftsmanship are both of a high-order. The aperture ring has positive, somewhat firm detents from f/2.8 to f/22 in third-stops. This differs from the Leica standard of half-stops, so it's something to keep in mind if you have a mixed bag. It's useful especially if you shoot slide film but also with the M9 if you're used to dialing in exposure compensation - which is also in third-stops. The focus ring is smooth and well-damped, but not as much as Leica lenses.

Wide open, the lens is not yet optimal; mild vignetting and slight softness in the corners and edges. Though most of the frame is quite sharp. Even wide open, textures and details are finely rendered. While not a fast lens at f/2.8, it's still quite usable in relatively low light and you shouldn't be worried about using it so, performance-wise. The bokeh is also excellent - typically Zeiss but perhaps a touch smoother with less detail than usual. Stopping down to f/4 brings further improvement of vignetting and sharpness into the outer regions.

Stopped down to f/5.6 - this is the magic number. Vignetting is almost gone but the lens is at its optimum, with a rather flat field and stunning resolution. This is where you'll really push the limits of the resolving power of your medium, be it film or with the M8/M9. You could leave the lens at this aperture for what could be considered the ultimate point and shoot camera (as the depth of field is fairly deep at this point) merely by using the hyperfocal distance. On the M8, focused at 16' - the depth of field ranges from about 8' to infinity. With film or the M9 it's a little more; focused at 13' you'd have everything from 6' to infinity in focus!

Depending on what body you're using the lens on, diffraction effects start to set in around f/8-11 In any event, because of the lens' very high resolving power and tremendous depth of field at this point - the images almost defy belief. There is sharp detail everywhere, from corner to corner. Again, if using the hyperfocal distance - basically everything from 4-6' to infinity will be sharp and in focus. Though micro-contrast is slightly less than at f/5.6 - you could essentially leave this lens set at f/8 and just shoot all day long merely by framing and clicking. This makes a great street shooting setup, especially if shooting from the hip. Vignetting is now essentially gone.

On paper there's some distortion - slightly higher than some other ZMs - though it is very well controlled, especially for a 25mm lens. You'd be hard-pressed to see it in day-to-day shooting. Zeiss goes so far as to suggest this lens for "expansive architectural photography" which is critical of distortion. Totally a non-issue.

Flare resistance is outstanding, as per usual with the ZM lenses. The Biogon T* 2,8/25 ZM might flare perhaps a little easier than some of the other lenses, if only because of the additional elements (it features nine elements in seven groups) but it is still quite difficult to induce. With ten aperture blades and stopped down, sunstars are brilliant. Therefore, contrast with this lens is high from wide open and never lets up - colors are deep and saturated, especially blues and greens. Very much a Zeiss lens.

The minimum focus distance on this lens is .5m, which is a bit closer than most (and especially Leica) lenses. When focusing on a Leica body, the rangefinder will disengage (stop moving) once you move past .7m. On the Zeiss Ikon, the rangefinder works all the way to .5m. Nothing to worry about, but something to keep in mind - so don't think there's something wrong with your lens or camera... One neat trick is to measure your forearm-fingertip distance and see if it's the right length (about 20") which you can then use to roughly focus on something closer than you normally could. Stopping down a little will cover any error.

Lens Hood(s)

It's worth making note of the two possible lens hoods that will fit this lens. The first option is the 25/28mm hood, which is round. The second is the 21/25mm hood, which is rectangular. Both are vented to allow for a better view through the viewfinder. The round hood is more effective than the rectangular one - especially when used on the M8 - and is our recommendation. However, the rectangular hood (which is unique in the ZM line) is reminiscent of certain Leica lenses and has a little bit of "coolness factor" to it. Either would make a good choice. Perhaps you should base it on other ZM lenses in your line-up (e.g. 21mm or 28mm) and if you plan to share hoods.

Coding for Digital Ms

This lens is typically given the 6-bit code of the Leica Elmarit-M 24mm f/2.8 ASPH (11878/11898) - which works well on both the M8 and M9 bodies, provided yours brings up the 24/35 framelines. The code for this is 011001. Some versions of this lens bring up the 28/90 framelines instead and is best coded as a Leica Elmarit-M 21mm f/2.8 ASPH (11135/11897). The code for this is 011000 and can be either marked with a template and a Sharpie marker or machined into the flange and properly painted for a more permanent solution via a third-party. The 25mm focal length really requires coding for a decent experience, especially when used with a UV/IR filter as it can introduce fairly cyan corners on the M8 and some red edge on the M9. There is also some vignetting - and the firmware can correct all of this nicely. In fact, on the M9 - the latest firmware (v1.162+) is highly recommended for the best corrections as older versions were lackluster.

For some reason, probably the inconveniently located screw on the flange - our lens didn't like the code for the Leica Elmarit-M 21mm f/2.8 ASPH (as ours brings up the 28/90 framelines) so instead we had coded it as a Leica Summicron-M 28mm f/2 ASPH, which is the "recommended" code in the list of Leica lens codes. This is why you'll see vignetting tests for this combination down below. While it corrects most red edge on the M9, it doesn't help much with vignetting. So then we tried coding it as a Leica Elmarit-M 21mm f/2.8 (non-ASPH) which is a simple code (one bit) - it worked! All red edge and most vignetting is now corrected. While not quite as good as the ideal Leica Elmarit-M 24mm f/2.8 ASPH coding - this is as good as it's going to get without more permanent coding and a mount flange swap to bring up the 24/35 framelines. And really, it's mostly at f/2.8 where there's still some vignetting. We can live with that!

Other Thoughts

If this review sounds a bit "glowy" it's because this lens really is a cut above. With the Zeiss Biogon T* 2,8/21 ZM on the wider side and the Biogon T* 2,8/28 ZM on the longer, the choices around this focal length are all excellent... While you can't go wrong with any of the three, you might want to seriously consider this one first - especially if you shoot an M8!

On film and M9 bodies the 28mm focal length might make more sense if only because of the built-in framelines. However on both the M8 and M9, you can essentially use the entire viewfinder regardless of which framelines your version brings up. The widest framelines are for a 24mm lens on the M8 and 28mm on the M9 - and they're both very close to the edges of the viewfinder. You can even do this with the Zeiss Ikon as the widest framelines are for 28mm lenses; also somewhat close to the edges. This makes the 25mm focal length the widest you can typically go without requiring an external viewfinder - provided that you don't wear glasses when shooting. While the framing accuracy is thus somewhat inaccurate, it's a very workable solution in day-to-day shooting and saves you the cash and bulkiness of an external viewfinder. Something to think about.

There's really nothing that Zeiss could improve upon with this lens. Aside from some minor quibbles, this is one of those "perfect" lenses. Easily as good as the Leica equivalent for a lot less money.

Vignetting

Vignetting was tested using the M9 at ISO 160, firmware version 1.162:

Lens detection set to OFF

f/2.8

f/4.0

f/5.6

f/8.0

f/11.0
 
 
Lens coded as a Leica Summicron-M 28mm f/2 ASPH (11604) and lens detection set to AUTO

f/2.8

f/4.0

f/5.6

f/8.0

f/11.0
 
 
Lens coded as a Leica Elmarit-M 21mm f/2.8 (11134) and lens detection set to AUTO

f/2.8

f/4.0

f/5.6

f/8.0

f/11.0
 
 
Lens coded as a Leica Elmarit-M 24mm f/2.8 ASPH (11878/11898) and lens detection set to MANUAL

f/2.8

f/4.0

f/5.6

f/8.0

f/11.0
 

Red Edge and Coding

A quick and non-scientific test for red edge and vignetting using the M9 at ISO 160, firmware version 1.162 and coded as indicated (see Coding for Digital Ms above for more info). Only the f/2.8 aperture images are shown as worst-case examples. The color temperature difference with the 21mm shot can probably be ignored. We'll repeat this test under better conditions in the future and update. The takeaway from this is mostly just the red edge in the uncoded shot as well as some in the 28mm coded shot. Neither the 21mm or 24mm have any:

 
Uncoded, lens detection OFF
 
 

Summicron-M 28mm f/2 ASPH

Elmarit-M 21mm f/2.8

Elmarit-M 24mm f/2.8 ASPH

Sharpness

More detailed sharpness testing will follow, but test charts don't really do this lens justice. Below are 100% crops of the central regions from some of the sample images below. No sharpening was applied and appear as imported via Adobe Camera Raw - with the exception of the last image which was imported via Capture One, due to better handling of the high-frequency detail (moiré) without actually compensating. With even mild sharpening applied (e.g. Photoshop "unsharp mask" at settings of 120/0.3/0) these images become scary sharp.

Consider however the following image as a teaser. This test is preliminary, and only tests the center performance - but it should give you an idea of what to expect. It was conducted by shooting a test target at .7m which represents a worst case scenario as non-macro lenses are generally optimized for infinity. Image was shot with an M9, mounted on a tripod. No alterations were done to the image except for auto level and it is a 100% crop:

Adobe Camera Raw 6.5 Capture One PRO 5.2

Sample Images

Flickr Pool Images

Further Research

Sample images thread in forum
Biogon T* 2,8/25 ZM  on Zeiss website
ZM Biogon 25mm group on Flickr