18-55mm vs portrait lens for fashion photography

Chloe

I'm trying to use my 18-55mm lens that came with my camera and a specific lens for portraits. How, if possible, can I use either lens to take fashion pictures (full length) that blurs the background while maintaining focus on the model?

My thought is to use 18-55mm with auto focus using F stop 4 to 5 to capture the model in focus and blur the background. Lens would be at 35mm or 55 mm?
My second thought is to use the portrait lens with a narrower F-stop, maybe 6 or 7, to capture the entire model in focus and let Lightroom do the blurring.

I don't want too much blurring as not to be able to recognize the background.

Please help me on the setting as I just can not afford to buy another lens.

bruto

Since the camera is digital, you can take as many pictures as you need to experiment and delete them.

You do not say what kind of portrait lens you have, so it's hard to recommend which one will do better. As a general sort of rule, depth of field decreases as focal length increases, about halving when FL is doubled. The kit zoom will tend to show everything in focus at 18mm, but since depth of field also increases with distance, your challenge will be to find a distance at which you can fit all of a model into the frame and still control depth of field. If your portrait lens goes wider (e.t.a. I mean if it goes to a more open aperture, not wider angle) than the zoom, you might find you need that.

If you have an idea of what kind of backgrounds you're after, I'd suggest you go out and find the background, take a person, a floor lamp, or something else you can move around like yourself even if you have a tripod, and try different shots at different distances. Distance from camera, distance between subject and background, F stop, focal length; all can be varied. If you forget to write down the settings as you go, remember that you can retrieve all the information for every shot in playback (get the EXIF display).

Not to sound too snarky, but remember the famous advice from Paco in the Good the Bad, and the Ugly, "When you have to shoot, shoot, don't talk. "