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Zeiss Flektogon 20mm f2-8 lens review

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Lens test: Zeiss Flektogon 20/2.8

Using an old manual focus lens on your DSLR

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We’ve just ‘found’ a Carl Zeiss Flektogon 20mm f/2.8 lens.

It’s a good lens, but how does it fare on a modern full frame SLR like the Canon 1Ds Mk3?

flektogon 20mm f2.8 on 1ds3

This is part of our series of brief lens tests, using various lenses we found laying around the office…

The Carl Zeiss Flektogon 20mm f/2.8 lens, manual focus, manual aperture, M42 screw mount.

Using old lenses

It’s quite easy to get adapters to fit an M42 screw fit lens to the Canon EF lens mount. The one I’ve got, came from eBay some time ago. A quick search for ‘EF adapter’ will find several.

If you’ve old Canon FD lenses, note that they won’t work without an adapter that contains an additional lens, so image quality is likely to be somewhat reduced.

The adapter I’m using doesn’t have an AF confirm chip on it, so the camera AF system won’t be much use. If you get one of the more expensive adapters, with a chip, then the camera’s AF indicators can be used to show when focus is achieved.

You still have to manually turn the lens focusing ring, but it’s a little easier when the AF confirm light comes on in the viewfinder. That said, half the fun of using some of these old lenses is having to learn, or for some of us, return to using the lens distance and depth of field scales.

I used liveview on my 1Ds Mk3 to check for best focus for the tests below.

The adapter was originally obtained to use with my Russian MTO1100A 1080mm mirror lens (purchased in 1978) where it works very well.

You should note that some old M42 lenses protrude into the camera too much when focused at infinity – there is a list I found, included in the info at the end of this article.

I’ve also got an adapter to use my Olympus Zuiko 50/1.2 lens on the EF mount. I do use the lens every so often where I want the minuscule depth of field that f/1.2 gives. If I used it enough, I’d probably get the Canon 50/1.2, but the Olympus lens cost over £300 in 1985, so it will do for the time being.

The Canon EF mount is a very flexible design – you can see how much bigger it is than the M42 screw mount below.

M42 to EF lens mount adapter

Note that there is no mechanical activation of the aperture stop-down for the lens. You will have to manually adjust the aperture ring of the lens (and set to ‘M’).

We’ll add more short lens tests over time as we sort through the ‘spares box’.

Zeiss Flektogon 20/2.8

One of those lenses that gets mentioned a lot in the history of 35mm camera lenses.

A lens of East German origin.

lens element layout flektogon 20/2.8Lens data

  • Construction – 9 elements, 8 groups
  • Angular field – 93°
  • Minimum focusing distance – 0.19m
  • Diaphragm action – Fully automatic
  • Minimum aperture – f/22
  • Filter size – 67mm screw-in type
  • Push-on diameter – 70mm
  • Weight – 350g
  • Barrel length – 54.5mm

Carl Zeiss Flektogon 20mm f2.8 M42 lensThe question is, like many classic cars, is it actually any good?

People may go on about oddly named lenses of yesteryear, but often conveniently forget how far lens design and manufacturing has come since the days of film and manual focus lenses.

The nit-pickers in forums may go over images at 100% magnification – levels of magnification unknown to many who acquired up their skills in a darkroom.

But how well do the lenses perform on today’s cameras?

I’m seriously not into detailed lens testing, but a few sample images shot outside my house should give a general idea of lens quality.

I’m comparing the Flektogon with my old Canon EF 16-35mm f/2.8L.

2009: This is the Mk1 version of the 16-35 which started to show its limits with my 21MP 1Ds Mk3. That said, I printed several perfectly good 17″x 25″ photos taken with it.

2015: The 16-35 was sold not long after, as I did more architectural work, which showed up some of its deficiencies. In 2015 my wide zoom is the EF11-24 (review) on a 50MP 5Ds

Sample images

It’s a sunny day in Leicester, outside of my front door. The six example shots are taken at f/2.8 and f/8 at 100 ISO

It’s nice and bright, so the slowest shutter speed was 1/200 and the fastest 1/1600. I’ve used a cable release and my most solid tripod.

The camera is levelled, so the various vertical lines in the picture give a good feel for any distortions in normal photography.

I know some of the ‘sharpness fans’ would insist on using mirror lock-up as well, but life is sometimes just too short… I use a tripod for my architectural/interior work, but rarely ever have one with me when I’m doing landscape print work. I’d have to check, but I believe there are only two shots in the 350+ in the landscape gallery on this site where I used a tripod.

This article tries to give a bit of a feel for using the old lens rather than any detailed optical analysis – and when it comes down to it (IMHO) photography is about actually taking photos. I’d suggest doing some quick tests like this for any new lens you try out, just to get a feel for what differences it might offer.

I’ve used liveview to focus on the brickwork next to the red door over the road. If you move your mouse over the images, you can see the improvement at f/8 compared to f/2.8

First the whole frame – Flektogon.

Original ImageHover Image

Note the vignetting and lower contrast at f/2.8

Next, whole frame Canon 16-35.

Original ImageHover Image

Some vignetting, but the lens is noticeably more contasty.

Note that the field of view is slightly different – the camera EXIF data says 20mm was the focal length for the Canon…

I’ve used the camera white balance in Adobe Camera Raw, to convert the RAW files. There was a slight difference in colour, but hardly enough to show meaningfully in small compressed, non colour managed web images like these here.

Next, the centre of the frame – Flektogon.

Original ImageHover Image

and Canon 16-35

Original ImageHover Image

The corners show the biggest difference (and also why I tend to use the 16-35 at ~f/8 for landscape work.)


Original ImageHover Image


Original ImageHover Image

So, I get a feel for how the low contrast/vignetting of the Flektogon gives a different look to images.

Depending on what I was taking the pictures for, this may be important. Given my general dislike for tripods, you’ll probably guess that ultimate sharpness is not always the key factor in deciding whether I like the results of my photography. Other photographers may take a different approach ;-)

Image processing

I find it helpful too, to know what sorts of options I’ve got in processing my camera RAW files. I’ll normally use ACR in Photoshop.

For some work though, I choose to use a RAW converter such as DxO Optics Pro. It works best for lens/camera combinations that are fully supported, but offers conversions whatever lens you are using.

The image below (f/8) shows it’s slightly improved sharpness and contrast when you fine tune the settings.

using dxo on flektogon image -centre

More noticeable in the corners where I’ve tuned out most of the chromatic aberration.

You can do this in ACR as well

using dxo on flektogon image -corner

The real benefits come with a supported lens, such as the 16-35 (at f/8 again) – not bad for the corner of the frame.

using dxo on EF16-35 image -corner


bright orange flowerJust a few quick tests, but I think I was most surprised by how soft the image was at f/2.8, and how much it improved at f/8.

A few other quick tests showed that even at f/5.6 it was considerably better than at f/2.8.

Since I get bored easily, you’ll have to search out some of the more detailed tests of the Flektogon if you -really- have to see lens test charts and the like.

The picture to the right (@f/8) was taken of a brilliantly coloured flower in my conservatory.

The detail below looks pretty good to me, particularly the smooth out of focus areas.

The lens focuses down to 20cm or so.

I’ve never used a crop sensor camera, but the x1.6 crop from a 50D/500D takes the equivalent focal length to 32mm, so although you just use the sharper parts of the lens image circle, 32mm is not ‘wide’ in my books.

However, if I’d just got a 5D or original 1Ds and didn’t have the cash to get all new Canon ‘L’ glass, it would make a good wide angle lens for landscape use. You’d need to be careful with the post processing to get the best out of it.

Even at f/2.8 the images are very usable, although a focusing screen designed for manual focus or an adapter with AF confirmation would be a great help.

One thing I did notice when focusing the Flektogon with liveview, was that the distance reading on the lens scale was slightly too low.

This suggests that the lens is fractionally too close to the camera image plane.

I was able to calibrate the distance scale by setting the lens at infinity and then focus the image (of something a long way away) by slowly unscrewing the lens from the adapter. The error is only a fraction of a millimetre but can affect image quality.

Once I know the amount to unscrew, I can create a shim washer to keep the lens in the correct position.

I suppose the proper way would be to make something out of thin brass, but I just used very thin card, since it took less than a quarter turn to get the scale reading correctly.

flower detail

Once I’ve got a feeling for what a lens works like, it’s worth remembering that I’ve put it there to take photos with ;-)

The shot below was converted to B/W using Nik silver efex pro after raw conversion with DxO Optics pro V5.3

It’s lost a bit of crispness in reducing it to fit on the web page, but gives a nice feel for what the lens can do.

leicester canal

Leicester Canal

Would I use this lens very much? Seems perfectly OK for some pictures…

Probably not though, given I’ve got the Canon 16-35 2.8L :-) I’ve had the 16-35 for several years now and have found that on my 1Ds and then 1Ds3 it’s a very fine lens – more than adequate for much of my work, when images are processed carefully with software such as DxO.

Flektogon 20 f/2.8 on Canon 1Ds3

1Ds Mk3 with Zeiss Flektogon 20mm f/2.8 lens

Having used manual focus regularly until well into this century I didn’t have any issues with using the lens, although if you’ve only used AF before, then it might take some getting used to.

Also, you will forget to stop the lens down sometimes.

Canon view camera adapterPre-setting the focus distance and aperture and learning about hyperfocal distances is a useful lesson for any photographer. I’d happily recommend a period getting the best out of a lens like this on a DSLR as an excellent way to improve almost anyone’s skills. However, do read my warning about reliance on hyperfocal focusing before relying on it too much.

It’s no harm either having to move to change framing rather than just tweak the zoom a bit…

I may use expensive AF zooms and primes for my paying work, where real image quality can count, but I still enjoy the change in how you think about photography, when you turn off ‘easy mode’ for a bit.

For something even more odd, attached to a DSLR, see my view camera adapter.


An old lens design that’s a bit soft at full aperture but gives surprisingly good results at smaller apertures, with sufficient care in image processing.

Excellent for experimenting with wide angle and full frame on a budget.

There are lots of cheap old M42 lenses about – get an adapter and give some of them a new lease of life.

Just remember that (IMHO) it’s about actually taking photos not just the techy stuff ;-)

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