If you care about great image quality and sharp photos, the Canon EF 75-300mm f/4-5.6 III USM Lens is not for you. And Photoshop cannot enhance details that are not there.
I'll leave you with the word directly from Canon Marketing:
Compact and lightweight 4x telephoto zoom lens ideal for shooting sports, portraits, and wildlife. The newly developed Micro USM makes autofocusing quicker and quieter. The improved zoom mechanism also makes zooming smoother. The front part of the zoom ring now sports a silver ring for a luxury touch.
I love that part about the "silver ring for a luxury touch."