And here it is...proof positive or humble pie?
- antonroland
- Jul 11, 2021
- 5 min read
A second article in one weekend...not something I will be able to keep up but here it is...
This is the result of having fiddled with this idea for a few weeks and the sudden finish is pure coincidental luck.
So am I eating humble pie? Was it the lens or was it me all along? It would seem I will have to go fetch a spoon...
Looking at the images I am prepping from a shoot it seems I am in trouble.
Meet the Carl Zeiss Distagon 21mm f/2.8 lens. This is the lens I have been having a love/hate relationship with for the last few years.
I bought mine in 2012 with my 5D Mark III. I bought it to replace my first generation Canon EF 16-35 and I thought I did well. I was very right and I was also horribly wrong. I mean I wanted a prime lens for superior image quality. I disliked the 35mm focal length but also on the 16-35 everything wider down from the 20mm setting distorted horribly...so the 21mm was the perfect choice. Right? Well...the answer is not that simple...
What I wish for you to take away from this is that that ANY piece of equipment will have a downside. It does not matter how fancy it appears or how expensive it is. Something somewhere will be a slight disappointment. But we don't buy something for the negative aspects. We buy it for the good bits and we know about and work around the less ideal aspects.
Now please don't simply take my word for it. Here are some trusted reviews from The Digital Picture.Com. This guy has been around for a good while and his comparative tests are really good. You can see another review by a brilliantly thorough crowd at Optical Limits here.
Or you can, at your own peril, see what this guy has to say here.
Now don't get me wrong, I have had some serious joy from this lens. It gives amazing results when used within it's limitations. It is also a beautifully made lens with everything metal except for the glass elements. Looking at it, feeling the smooth actions and tight tolerances is quite a thing to experience.
I have made a good few images I was really happy with using this lens. I have also had a good few outings where I trashed everything from that outing. Was it the lens or was it me?
Thing is, 21mm in "full frame" terms is very wide and ironically I find myself shooting at 35mm more often as I did before I bought this lens.
So, let's see if it was diffraction softness or my poor technique that caused my hit-n-miss results with this lens on my Canon 5D Mark III. Diffraction softness is what happens when the lens is stopped down too far and light starts bending due to the extremely small aperture opening.
So was the 22 Mp of the Canon 5D Mark III too much? Did the sensor outresolve the lens? To answer this question we will have to wait a week or three. I am awaiting a friend or two with late model full frame Canon cameras to join me on an outing.
For now I can show you tests using Canon's EOS 5D Mk1 with a 12.7 Mp sensor and my beloved archaic Canon EOS 1Ds MkII with a 16.7 Mp sensor.
Just a quick one thrown in to show you how a film era or full frame 50mm lens would compare to the 21mm full frame perspective. To copy the 50mm perspective you would need to set your crop body lens to approximately 35mm. To copy the 21mm perspective you would need to set your crop body lens to approximately 14mm.
Another thing worth noting is that the building looks like it falls over backward and to a side when shot with such a wide lens. Somewhere in the future we will look at fixing this without having to buy a specialised lens the price of a car.
Now the 5D Mk1 and 1Ds Mk II have very different menu systems so both cameras were set to the most neutral or standard settings either camera allowed.
The darkening of corners (called vignetting) is a very real characteristic of this lens when shot wide open.
No, this is not extreme vignetting. I imagine rather a gremlin in the metering or a shutter speed glitch. It is no problem and instantly fixable. This old girl is running on her third shutter and I rarely if ever need to shoot with a shutter at 1/4000. Now the 1D was shot perfectly on the neutral and centered light meter given the exercise but the camera was not happy capturing a good exposure at 1/4000.
For that reason the exercise will show examples shot at f/4 and f/22. All ISO settings were 100 and shutter speed was taken from a centered light meter in the viewfinder. A f/2,8 lens stopped down one stop from f/2,8 to f/4 should show a good improvement in sharpness so this should actually be a good thing.
If the whole diffraction softness thing is to be believed then the 21mm Zeiss should deliver it's best performance at f/5,6 to f/8 and sharpness should deteriorate from f/11. From f/16 it should be rather nasty soft and horrible at f/22. I have found this to be accurate on my 5D MkIII. But was it REALLY only the lens? Did my technique possibly play a role?
So, 100% crop views from the image centre and edge were taken. Let's see how they compare.
OK, so image sharpness at the edges should not be great wide open and it is not. But it is also f/4 and practically wide open. Wide angle lenses show great depth of field and sharpness, even if only perceived sharpness,should be good.
Now let's see what f/22 looks like...
Quite surprisingly and not as was expected, the centre is nicely sharp despite the f/22 which should have caused some softness.
The edge image quality actually looks quite good at f/22 and clearly better than at f/4. Maybe the 5D Mk1's 12,7 Mp sensor does not outresolve the lens...or maybe my whole diffraction softness argument is crumbling before my eyes...
So let's see what it looks like on the EOS 1Ds MkII's 16,7 Mp sensor.
The vignetting (darkening of image corners) at f/4 is a good bit more pronounced than on the 5D1. This will be a factor in the edge quality.
This is a 100% crop from the centre of the 1Ds MkII image at f/4 so nearly wide open. Focus throughout was on the middle one of the three characters in the column. Image quality is good and sharp as is to be expected.
Edges and corners are where lenses show their weakness. Considering what we are looking at this is really not that bad. In fact quite good.
Due to the stopping down closing the lens and the greatly altered exposure recipe the vignetting is much better.
The image centre looks good as is to be expected. This is where focus was established and so one would expect it to be pin-sharp.
This is the surprising bit. This should not have been the case. If diffraction softness was the big evil it is said to be in this lens, f/22 should have looked terrible and nothing as it does here. It would seem we are getting closer and closer to a verdict of poor technique on my part. The little black dot in the blue sky is sensor dust. They show up from around f/11 to f/16. At f/4 to f/8 you will not even know they are there.
Now if you know me well you will know it can NEVER be MY fault. Poor technique, ME?? So before pleading guilty I will explore one last get-out-of-jail-free card option and that is a late model full frame Canon camera shooting similar tests. Maybe 20-24 Mp is the value where the sensor outresolves the lens and shows the diffraction softness?
Or maybe my sloppy technique really justed sucked and let me down all along? Who knows? Time will tell. Play often and remember to try something that should not be possible at least once a week.
Until then, happy shooting!
Anton
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