Re: EOS Ra + Vignetting with the EF 24mmL lens
Thomas A Anderson wrote:
The black area outside of an image circle isn't attributed to vignetting. The EF 24 f/1.4L II was designed for digital bodies that have distortion correction, which means that like most wide angle lenses, very similar to those on fixed lens cameras, it is designed to actually not fully cover the sensor in the corner but instead relying on correction to crop and then correct the extreme distortion around the edges.
Don't worry about a solution with this combo, even Canon is mystified. The F 24mm wasn't designed with Peripheral Illumination correction in mind since there were no capable cameras with this feature available at the time of release. But they were developing upcoming cameras that were designed to reduce corner vignetting with Light Falloff. The two models that did possess this feature came out a short while later but everyone who owned earlier models of DSLR and wanted the successor Mk 2 version of this lens snapped them up in such larger numbers that there were delays on obtaining mode. No notable complaints were observed beyond 'soft vignetting' in the corners when shooting wide open... and that was entirely expected due to the nature of the lens.
So like the G1X and G7 X, if you go find a viewer that will show the uncorrected RAW file you'll see black corners on the wide angle end. MOST modern digital wide angle lenses are designed with image circles that don't fully cover the sensor.
Most of the Compact cameras with 1" and 1.5" sensors have vignetting when certain focal lengths are used with RAW settings... which is why Canon avoided releasing models with super-wide FOV. Vignette refers to both Hard and Soft Vignetting. Hard vignetting is where the light is physically blocked (mechanically) from reaching the edges of the sensor. Light Falloff (soft vignetting) is a characteristic of lens character and lens design... where the thickness of the lens varies, especially with wide-aperture, wide FOV lenses. The black corners from the EOS Ra are indeed defined as 'vignette', as noted by DXO Mark when they assessed this lens... which Canon described as their "best performing and best built 24mm autofocus lens". It was considered to be "optically excellent" upon release. In most ways, this is a true statement. It's a lens that has always been in very high demand by professional photographers and the higher price bracket had most regular consumers looking at other alternatives. This lens was developed and released into a market a month before introducing any cameras that were capable of applying Peripheral Illumination Correction. The problems didn't surface until the release of the EOS 5D Mk IV... which came out in September 2016.
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TIMELINE.
2008 - Canon EF 24mm f/1.4L II USM released. (September)
2008 - Peripheral Illumination Correction announced. (November)
2012 - Chromatic Aberration Correction introduced.
2016 - Diffraction Correction introduced.
2016 - Canon EOS 5D Mk IV released (September).
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But as you can see from this screen-capture I took last year (which was posted in 2010), this is indeed a problem with this lens but ONLY on certain camera bodies... The only two that come to mind are the EOS 5D IV and the EOS Ra. In both instances this vignette is Hard (physical) but no reason has yet been offered by Canon. Upon contacting Canon, they suggested the use of a lens adapter might be the only possible reason that came to mind. My communications with Canon Europe and Canon International (Canon Global) were bounced around within the company, only to be met with bewilderment. This isn't an issue about the sensor being seated a millimeter too deep... this is something quite unexpected and nobody seems to have an answer. What is equally baffling is that this is not an issue on the EOS R6 and it's not an issue with the popular (for Astro) EOS 6D.
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Now I spoke with Canon's lens developers who modeled the "new" EF 24mm f/1.4L II USM lens back around 2012 when I was still distantly connected to Canon's local branch (before they moved the service center). It was the best in it's class as of July 2008. There was never any discussion about in-camera corrections simply because this was a new feature that was still being addressed at the time this lens was in development. Whilst APS-C users won't need to concern themselves with lens correction, Full Frame cameras VARY quite considerably with this lens....
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Screencap from June 2, 2020 Showing vignette variance with different bodies. The worst performing is the EOS 5D Mk IV - which scored -2.9 EV
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As you can see from the screencaps above (from a year ago), the very same lens performed better on numerous other cameras. Even the EOS 6D (which I still have) did not vignette as badly as the EOS 5D Mk4.
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Whilst Canon have since introduced lens correction for many of their lenses and on many of their DSLR and mirrorless cameras, back when this lens was released, the options were limited. The original 5D wasn't as gifted - but the 2008 release of the EOS 5D Mk II and EOS 50D is what introduced Peripheral Illumination Correction to correct for vignetting (which includes 'light falloff' and 'corner shading' within the definition). Things didn't really improve until 2012 when the EOS 1D X and EOS 5D Mk III were released.
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The answer for the EOS Ra with this lens is to either crop the images in-Camera or to crop them in the computer at home. The in-camera crop may reduce the 30MP to 11MP, which would be excessive and undesirable. Tests made without the lens hood and without any filters were attempted and offered no change. The problem remains unsolved by members of this forum (we had a monster thread on this last year) and even by Canon themselves. I'm told the EOS Ra was discontinued recently, which is in line with Canon's past Astro models only being available for a short time. This is also a way for Canon to wash their hands and wait another 10 years before releasing an alternative.
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Unless used on the EOS 5D Mk IV (or the now discontinued EOS Ra), there's no problem with this lens at all and it continues to perform superbly.
