T-stop vs F-Stop

[Kayaker72]

Yep.

Of course, there are going to be a number of trade offs with budget lenses. AF, build quality, IQ, etc. Looking through DXOMark's data, while this will vary from lens to lens, I would generally say some of the "budget" glass has T-stops 0.5 to 2/3 of a stop above their respective f-stop whereas the higher end glass is typically has t-stop's less than 0.5 above their respective f-stop.

A quick example, the Tamron 150-600 G2 has a T-stop rating of T/7.9, which is ~2/3 of a stop higher than it's f/6.3 rating. If my numbers hold, the 1.3 stop difference with the Sigma 150-600S would be the largest difference I've seen.