Optimized optical tweezersre indispensable tools for micromanipulation for biological tissues. Using electromagnetic theory the spatial intensity profile at the  afocus of a dry objective lens and its trapping stiffness are calculated. Presence of mediums with different refractive indices after the objective introduces significant amounts of spherical aberrations, which degrades the strength of the trap. Here we have shown, that tuning the correction collar of the objective on a value larger than the thickness of the coverslip can compensate for this aberration, which in turn maximizes the trapping stiffness. This tuning possibility allows for trapping at desired depth of the sample under investigation with optical tweezers