Thank you Dr. Sassi !
I cannot thank you enough .
I really I appreciate your time .

Hello Dr. Sassi !
thank you for the reply !
here is the file : https://we.tl/t-5kLTWT7UQ9

I need some help please !

So I added hair to a mesh and controlled its length curls twist ... in the standart c4d hair material and for the color and spec i used Redshift and then arnold standard hair . However when i render in redshift or arnold i dont ge the result i want . The main problem comes from the lengh parametre in the native hair material . Somehow arnold and redshift does not work well with it . Because when i disable it the hair kinda render properly but i dont get the length falloff i'm aiming for .

I just want the same result i get in the standard render to be in the redshift and arnold render !

I hope it makes sense !

Higher quality image ; (https://ibb.co/9nfqG8W)