Introduction

The Zeiss ZM 21mm 4.5 C-Biogon is the widest of the three “Classic” designs in Zeiss’ ZM line up. It has long been discontinued and it wasn’t in production for a long time, so it is a bit rare and rather expensive on the used market. I always wondered how it would compare to the similarly compact yet newer Voigtländer VM 21mm 3.5 Color-Skopar and now we will finally find out.
Lens is being tested on 42mp Sony A7rII and 24mp Leica M10

Sample Images

Most of the sample images in this review can be found in full resolution here.

Disclosure

The Zeiss ZM 21mm 4.5 C-Biogon was kindly provided free of charge by our reader Matthew for review purposes, thanks a lot!

Specifications

This Zeiss ZM 21mm 4.5 C-Biogon has the following specifications:

• • Diameter: 53 mm
  • Field of view: 90° (diagonally)
  • Length: 31 mm
  • Weight: 194g (without hood and caps)
  • Filter Diameter: 46 mm
  • Number of Aperture Blades: 10 (straight)
  • Elements/Groups: 8/6
    
  • Close Focusing Distance: 0.50 m
  • Maximum Magnification: ~1:20 (measured)
  • Mount: Leica-M

The Zeiss ZM 21mm 4.5 has long been discontinued, it can sometimes be found on ebay.com | ebay.de for about $850 (affiliate links)

Handling / Build Quality

Generally the Zeiss ZM lenses are nicely made, very similar to the Voigtländer VM lenses which are also made by Cosina in Japan.

The focus ring has a nice and even resistance and travels ~120° from the minimum focus distance (0.5 m) to infinity. The focus ring does not feature a real focus tab, but a small focus “knudge” at the bottom.

The aperture ring has one-of-a-third-stop click-stops. It travels a little less than 90° from f/4.5 to f/22 and the stops are spaced equidistantly as it should be.

Most parts seem to be made from metal and all markings are engraved and filled with paint. Instead of a red dot this lens features a small blue dot as indicator for mounting the lens to the camera.

M-mount cameras do not feature framelines for 21mm lenses, so unless your camera is equipped with liveview you need an accessory finder for framing. For the use of my Voigtländer VM 21mm 3.5 Color-Skopar on the M6 I bought an old Leica 21mm finder. As the onwer of this ZM 21mm 4.5 also send me his Zeiss ZM 21mm finder, I am now able to compare them and the Zeiss finder is better in every possible way: material, image quality, distortion, fit to camera. That being said, I paid around 150€ for the Leica one, whereas this one from Zeiss is at least double that.

The lens features a bayonet for attaching a lens hood. It shares the official square hood with the Zeiss ZM 21mm 2.8 and ZM 25mm 2.8. It is a pricey accessory and mainly a cosmetic one. Because it is so short it won’t actually help with shading the lens.

The Voigtländer VM 21mm 3.5 Color-Skopar is thinner at the front and a few grams lighter than the Zeiss ZM 21mm 4.5 – despite being slightly faster. I also added the Voigtländer VM 21mm 1.4 Nokton, one of the bigger 21mm M-mount lenses.

Vignetting

light falloff

Small lenses like this  usually show a high amount of vignetting and this Zeiss ZM 21mm 4.5 no exception. Wide open the light falloff amounts to 3.2 EV and there is only little improvement on stopping down, as it only improves to 2.8 EV stopped down. You can either correct this in Lightroom or directly in camera. There is a Lightroom profile available for this lens.

I checked the vignetting on a Sony A7rII here. The values will be very similar on the Leica M11 and slightly better on the M10. On film the lens will also show less falloff.

It is recommended to have a look at this article first to get an idea how this brightness graph works.

color cast

The “C” in this lens’ name stands for “Classic” and this means two things: no aspherical elements and a semi-symmetrical Biogon design. When it comes to digital sensors, those are not great news. In scenes with an overcast sky, on the later Sony cameras with BSI sensor (and the Leica M10) you may be able to see a very slight greenish/blue color cast in the corners. On the Leica M10 the situation is worse, here we see a strong asymmetrical color cast with the red side of the frame showing noticeable magenta color cast. The situation will be even worse on older digital M-mount cameras, as show here for the M240.

I have a whole article on how to correct this color cast, here it is not that severe, so a simple digital gradient did the trick and I used that for most of the sample pictures in this review.

This is an area where the Voigtländer VM 21mm 3.5 Color-Skopar does way better, as it has been optimized for digital cameras. As we can see from this comparison the Voigtländer is also slightly wider.

Sharpness

infinity (42mp Sony A7rII and 24mp Leica M10)

The color cast in the corner crops has been corrected.

Over most of the frame the Zeiss ZM 21mm 4.5 shows a good performance from f/4.5 on the Leica M10. The corners look a bit worse, peak across frame performance is reached around f/8.0.

On a Sony camera with its thicker filter stack the performance starts to drop in the midfield and the corners look really bad, even stopped down to f/11 they still don’t look particularly good.

I was wondering how the Zeiss ZM 21mm 4.5 compares to the Voigtländer VM 21mm 3.5 on the Leica M10, so I shot them side-by-side to find out.

The Voigtländer at f/3.5 to f/4.5 shows better resolution in the corners, but in the outer midframe – the area shortly before the corners – the Zeiss ZM looks better. Generally the Zeiss also shows slightly higher contrast.

Now at f/8.0 to f/11 both lenses look very similar, only in that outer midframe area the Zeiss still looks better.

close 0.50 m (42mp Sony A7rII)

A minimum focus distance of 0.5 m is not that exciting for a 21mm lens but the good thing is that in the center the performance is really great already at the maximum aperture. These crops are full of moiré after all.

Flare resistance

As always evaluating flare is a complex matter since you can get any lens to look bad if you push it hard enough and a slight change of scenario will affect results a lot.

The Zeiss ZM lenses have generally been good albeit not excellent performers in this category and this is also true for this ZM 21mm 4.5, as it is pretty hard to create unwanted artefacts with this lens. Nevertheless, there are a few things to watch out for.

With the sun outside the frame it is possible to catch a faint ghost in one of the corners as can be seen above.

With a strong light source in the frame also a small crescent can appear (top right corner). These are the two worst artefacts I managed to create, which already is a testament to good performance in this category. The contrast also stays on a high level, even in scenes with strong backlight as seen above and many of the other sample images.

Coma

At f/4.5 Coma can be noticeable but improves significantly at f/5.6, so I recommend to stop down to at least f/5.6 when taking pictures of a city scene with point light sources.

Distortion

The Zeiss ZM 21mm 4.5 shows low but slightly wavy distortion. There is a Lightroom profile available for this. I think it overcorrects distortion a bit and I used a setting of around 40 for this corrected version.

Sunstars

Like most of the Voigtländer M-mount lenses the Zeiss ZM series lenses also feature aperture diaphragms made of 10 straight aperture blades that lead to very distinct sunstars at most aperture vales. Only at f/4.5 and f/22 the opening is mostly round, so no sunstars at these settings.

If you want to know more about sunstar rendering of different lenses have a look at this article.

Chromatic aberration

lateral

Lateral CA are really well corrected, so there is nothing I could show you here.

When it comes to fast portrait lenses – like the Zeiss ZM 50mm 1.5 C-Sonnar – I think it makes some sense to re-release famous older designs – slightly improved – for their “signature” rendering.

But when it comes to slow wide angle lenses, I am not so sure it makes a lot of sense to do that. With slow wide angle lenses like this one, usually everything is in focus anyway, there is not a lot to talk about in terms of rendering.

Sharp across frame, good flare resistance, preferably low vignetting and maybe nice sunstars. These are the criteria most people care about in slow wide angle lenses, no matter if they are based on a modern or a vintage design.

Now the good news are, this Zeiss ZM 21mm 4.5 shows a very good performance in most categories. It is even a bit sharper across frame stopped down than the VM 21mm 3.5 and by f/8.0 most aberrations (except for vignetting) are not really something to worry about.

The problem is, because of its vintage Biogon design, this lens doesn’t play very well with non-BSI digital sensors and these sensors can be found in all the digital Leica M cameras that came before the M11. As is also the case for e.g. the Zeiss 16mm 8.0 Hologon, the Voigtländer 15mm 4.5 MKI/II or the Zeiss ZM 18mm 4.0, also this Zeiss ZM 21mm 4.5 therefore creates strong color cast on those M8, M9, 220/240/262 and M10 cameras.

Sample Images

Most of the sample images in this review can be found in full resolution here.

Further Reading

• All M-mount Reviews
• Review: Zeiss ZM 18mm 4.0
• Review: Zeiss Loxia 21mm 2.8
• Review: Zeiss ZM 35mm 1.4
• Review: Zeiss Loxia 85mm 2.4

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BastianK

My name is Bastian and I am your expert here when it comes to ultra wide angle lenses, super fast portrait lenses (ranging from a 50mm f/0.95 to a 200mm f/1.8) and I also have reviewed way too many 35mm lenses. Don't ask me anything about macro or wildlife shooting though.

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