Do you still remember when in the summer of 2013 there were rumours about a series of super-telephoto lenses by Sigma? At that time, the grapevine had it that the team in Aizu was quietly working away at a total of four image-stabilised prime lenses between 300mm and 600mm. The two shorter ones, the 300mm and the 400mm one, were being estimated to be as fast as f/2.8 each, while the longer ones, the 500mm and the 600mm, were supposed to be slower by a stop. Since then, the two 150-600mm models, Sports and Contemporary, have been introduced and the famous prime lenses never mentioned again. However, this rumour appears to be based on facts – the patent specification published on the Japanese blog Egami proves that Sigma filed a patent for the optical formula of a 400mm f/2.8 OS Sports as early as September 2013. Below you can see the optical construction – unfortunately, the image is much too small to actually see the number of lenses and groups.
Another patent which was published on Egami at the end of March describes a 24-105mm f/2.8-4 zoom lens. Unfortunately, it seems to be a variation of the 24-105/4 Art. For some unknown reason, the developers tend to file patents for a number of “related” optical formulas at the same time, of which, however, only one is then continued until it is ready for the market.
Last but not least I would like to point you towards the three newest tests of the 24mm f/1.4 Art at Resource Mag, DxOMark and Lens Rentals. At DxOMark one should definitely read the text as well because the “perceptive megapixel” values do not tell the whole truth – at least not the part that is the most important one for a f/1.4 lens. The test by Resource Mag is especially relevant for all those who prefer video-reviews. Over at Lens Rentals, Roger Cicala – after measuring the sharpness and the field of curvature – comes to the surprising conclusion that none of the tested 24 ones can offer a satisfyingly low curvature. According to Cicala, “a 35mm f/1.4 and taking a couple of steps back” is still the best solution for a 24/1.4. At least if one is going for sharp corners or (as much as possible) uniform sharpness. 😉