Here you see this Bigma Zoom lens in numbers , e.g. compared to other similar zoom lenses, as well the MTF chart for 60, 200, 400 and 600mm focal length. Notice also that the center sharpness gets excellent results at all focal length from 60 to 600 mm (which other zoom lenses do not).

This is also the reason I originally bought the sigma SPORT 60-600 mm lens instead of the 150-600 mm - because i felt the 60-600 lens showed uniquely good optical performance, and the price was highly favorable if you compared that to super lenses that can go for 5500 € (second hand, older generations) to 15000 € (!) for the latest RF-incarnations on mirrorless EOS cameras (Canon 500L& 600L) - but actually are slightly inferior to its EF siblings.

Nasty Canon move

Canon simply punched a bit of metal to the EF lenses turning them into RF lenses, hiked the prices by many thousand Euros, while photographers reported that the optical quality was a bit inferior to the EF Mark III versions. Today the best buy are the EF 600/4 L IS Mark II and EF 500/4 L IS Mark II versions second hand (around 4500-5000 €) You benefit from the lighter weight, much lower price, and increased optical performance compared to the Mark I version, which also is much heavier. Optically they are already at the level of the latter EF mount Mark III versions.

If i ever buy a super telephoto lens with top notch performance, it would be the Canon EF 600/4 L IS II version. I have absolutely no problems with EF lenses on RF cameras. On the contrary, i prefer them.

Back to the Sigma SPORT 60-600 mm: of course I was aware that the performance isn't exactly the same like the best white Canon lenses such as EF 600/4 L IS II and EF 600/4 L IS III, and similar. Yet, the quality is surprisingly very good. Even better, the price was very good, too.

Add light AI sharpness, results into perfectly sharp, fine details !

As you give the Sigma SPORT 60-600mm a light AI sharpness treatment when using 300-600mm - you get suddenly an astonishing amount of finest details chiseled out. Now its fine details do not stand behind those coming from white Canon lenses.

2000 € was far more attractive to pay without regret (and with the high optical quality the Sigma zoom deliver) compared to a lens for 15.000 €. No ? Yes ?

Notice that the Sigma SPORT 60-600 is a EF mount lens in my case. Now that Sigma doesn't make any Canon EF mount lenses - none of the newest can be used with Canon. Because Canon gives a rats ass, to open up the RF mount. Only a couple of days ago Sigma introduced special lenses like the Sigma ART 135mm ƒ1.4 lens, and the Sigma ART 200mm ƒ2 lens. But also the Sigma SPORT 300-600 mm ƒ4 lens.

That would been a truly interesting lens. But we Canon users are now shut out form all the new lenses that are being introduced since 2017 with other camera mounts, except Canon RF

Working at night with a ƒ6.3 aperture 600 mm lens ?

Is very, VERY tricky, and sometimes impossible. (and manual focus often leads to worse sharpness / missed exact focus)

Why all this ? Because the live-view doesn't manage to make the preview image bright enough to set sharpness alt. to focus on something that appears to be reasonably bright for AF to function (here the Canon R6 is better than the Olympus OM-1). I was a bit surprised, albeit shouldn't. I was barely able to focus... (but i will do more tests). Sometimes, against better judgment, i may have forgotten a setting which alters the screen brightness in darkness.

Nevertheless, the Olympus OM-1 with the 300mm (600mm) lens was a better match due to that this is a brighter ƒ4 lens. (1.3 stops brighter compared to the Sigma at 600mm ƒ6.3)