خیلی هم موضوع عجیبی نیست اکثر لنزهای زوم فوکال ابتدا و انتهای دقیقی ندارند و معمولا سازنده ها این فوکال ها رو به نفع خودشون روند میکنند. البته تامرون هم همینطوره اما با شدت کمتر نسبت به لنزهای سیگما.
به نقل از سایت TDP
One exception to 150-600mm lenses being equal in regards to focal length is when the specified focal length numbers have been rounded significantly. Long focal length range lenses gain suspicion just for being that.
Using an unscientific methodology involving relating the distance measurement to a properly-framed ISO 12233 enhanced resolution chart relative to framing distances of the Canon and Nikon 600mm prime lens, I estimated that the Tamron 150-600mm option came within 95% of the 600mm prime figure or roughly 570mm. The two Sigma zooms frame the test chart at a similarly-slightly shorter distance than the Tamron, bringing the rough focal length estimate down to slightly under 560mm. However, the Sigma lenses have less pincushion distortion at 600mm and this distortion difference could easily be the reason for any difference in the test chart framing distances between these lenses. Suffice to say that the Sigma lens' 600mm is a very long focal length and it is sure to bring a smile to your face.
مطلب کامل رو میتونید از ریویو این سایت برای سیگما 600-150 از لینک زیر ببینید.
Sigma 150-600mm f/5-6.3 DG OS HSM C Lens Review