Distortion is an annoying issue for many photographers who like straight lines such as interior or architectural photographers. Also, photographers who do art cataloging and preservation photography may be paranoid about the idea that tiny distortions could be subtly altering the impression of the image they’re photographing.
Because distortion varies from lens to lens it can be annoying to try and manually remove the effects of distortion, especially when using a zoom lens, as the amount of distortion always varies with the focal length. This is why programs such as Adobe Lightroom made correcting distortion an automatic correction for almost all of the popular lenses from companies like Canon, Nikon, and Sony.
With the advent of such automatic corrections perhaps it was only a matter of time before the cameras started making those corrections also, which they inevitably did start doing.
Apparently the results of doing this were such a success that now lenses are intentionally designed with loads of distortion in them which now HAS to be corrected in camera or in a program like Adobe Lightroom or the image just won’t look right.
Not surprisingly a lot of photoraphers are disturbed by this trend that the photos MUST be corrected now because the distortion is essentially ruining the photos if it isn’t corrected.
Well, here’s why intentional distortion in lens design isn’t as bad as you might think.
A lens with no distortion is better than a lens that has distortion. But, a lens with no distortion may cost more, be larger, heavier, have less zoom range, and perhaps be slightly less well performing in other ways. Consumers too often forget that these lenses must provide sharp details down to 1 micron or even smaller in order for details viewed at 100% in Lightroom to appear “sharp”. The problem grows in difficulty when the sensor is larger relative to the lens size. So, making lenses “smaller and lighter” isn’t as easy as it may seem, especially for 35mm full frame cameras.
The goal then with intentionally designed in distortion is that lenses may be smaller, lighter, and cheaper, while also being sharper across the frame, even after the distortion correction… Simply because they’re basically not covering the full frame but covering what they’re covering with finer resolution than other lenses might.
Photographers often have a bad habit of always viewing their photos at 100% when checking the sharpness, if you do this you’ll never really see the potential benefits of making lenses sharper by keeping them distorted, it will usually look a little bit soft at least. The reality is that for spherical lenses, focusing sharp rays all the way out to the very edge or the corner of the frame isn’t an easy feat, in fact, it’s darn near impossible which is why it basically never happens in consumer lenses.
There are two simple ways to get around this, make the lens elements larger, which compresses details into the sensors resolution range, or, reduce the coverage of the lens and use the sensor’s resolution to compensate for the lost optical coverage.
Working with intentionally distorted lenses isn’t the easy cop out that everyone seems to think it is. It’s actually a tough engineering problem in it’s own right. And it’s a problem they’ve embraced to try and deliver better performing lenses to consumers at better prices.
The key thing to realize about intentionally engineered distortion is that if the designers can keep the sharpness across the frame about the same, from center to the distorted edge, well, the photographer is in luck. Whereas most traditionally designed lenses falloff towards the edges of their image circle, lenses with engineered distortion are typically very sharp at the edges of their image circle.
Basically, with intentional distortion, more resolution is put into a smaller area which allows the lens to focus finer details out to the edge of the image circle. This means that even though you do lose resolution when the distortion correction is applied, you will always lose an amount relative to the sensor resolution (assuming the lens resolution surpasses the pixel pitch of the sensor) which then means that the final corrected resolution in the corners will be higher when the sensor resolution is higher.
Basically think about increasing the resolution of the sensor as increasing the pixels available AFTER the distortion correction is applied. Once you understand this then you’ll understand how an image with distortion correction on an R5 might actually have more information in it than even a near perfect traditional style lens on a lower resolution camera like the R6, R3, or R1.
Essentially what lenses with introduced distortion do is transfer the resolution limitation from the lens to the sensor where recovering fine details is actually easier than doing it optically.
To give a more specific example, assume you’re shooting with a traditionally corrected lens such as a Canon EF 11-24mm f/4 L and compare it to the newer and intentionally distorted Canon RF 10-20mm f/4 L. Well, if you shoot both lenses wide open what you’ll see is that the RF 10-20mm f/4 L is better across the entire frame. Because the RF 10-20mm f/4 L transfers the resolution recovery onto the sensor, the 10-20mm f/4 L will recover more resolution on higher resolution cameras like the R5 than the EF 11-24mm f/4 L could achieve when adapted to the same camera.
If you always view images at 100% pixel view you might not see the difference as easily, but, if you compare the images at maybe 66% view, you’ll see that the 10-20mm f/4 L is looking very consistent across the frame even next to the 11-24mm f/4 L.
A big part of this isn’t necessarily lens design it’s also meeting design parameters in manufacturing. The EF 11-24mm f/4 L is a BIG lens with a very large piece of glass on the front that has to be just as perfectly executed as the smaller elements in the RF 10-24mm f/4 L. When thousands and thousands of these lenses are rolling out of the factory its basically just statistics that ensures the RF 10-20mm f/4 L will be better across the frame.
The bottom line isn’t to say that the EF 11-24mm f/4 L is an inferior lens because it isn’t if we consider all aspects (flares), but the point is to say that there are real advantages to letting the designers work with the idea of introducing distortion to increase other performance characteristics such as sharpness.
If you only take away one thing remember that while traditional lenses like the EF 11-24mm f/4 L are optically limited in the corners, the RF 10-20mm f/4 L will be more limited by the sensor’s resolution, especially when stopped down a couple stops.
The only unavoidable problem with correcting intentional distortion in lenses like the RF 10-20mm f/4 L is that certain optical phenomenon will appear distorted AFTER the correction is applied. This is specifically noticeable with lens flares and most especially sun stars.
If you don’t have to worry about large sun stars and flares in your photography then there is not a lot to worry about with lenses that require optical corrections in order to properly cover the frame.
If you are expecting to shoot a lot of sunstars and flares then you’ll probably need an optically rectilinear lens like the EF 11-24mm f/4 L.
