The photographer, setting, lighting, fashion and model are more important than the lens used, but the lens is not unimportant. The Tamron 24-70mm is much cheaper than the Nikon and Canon 24-70’s and it holds it own against them.
This is a manual focus lens that gets rebranded under several different names (Bower, Rokinon, Vivitar, etc.). It’s a sharp lens with strong optical quality and it can be had for a fraction of the price of brand-name 35mm F1.4 lenses.
When we think of portraiture and fashion photography the longer focal lengths of 85mm, 135mm, 200mm, and even 300mm come to mind. Many portrait photographers would pick the 85mm lens if they could only have one lens. These larger focal lengths compress the image in a way that is flattering to the model and that lacks the unflattering distortion of wider lenses.
Wider angle lenses are harder to get right. Considerations about the foreground and background become much more relevant and it’s just harder to pull of that great shot in general. But when one does, it has a feel that a longer focal length lens cannot produce.
My lens of choice was always the 35 mm. It was more environmental. You can’t come in closer with the 35 mm. – Annie Leibovitz
We feel that 28mm is about as wide as is ideal to still maintain a natural look to a fashion photograph. There are of course exceptions to this and reasons you would want a look that is less than natural. Having a 35mm, 50mm, and 85mm lens creates a wonderfully complementary kit. Just don’t forget to use the 35mm.