imgaborfilt - no option for sigma ?

I am using the imgaborfilt function and I noted that there is no option to specify the standard deviation of the gaussian function. Did MATLAB set a default value or is it automatically computed upon specifying the wavelength ? If it is automatically computed, then can someone tell me how it is being done with a link to a paper or something ?

https://www.mathworks.com/help/images/ref/imgaborfilt.html