I am an apprising fashion photographer and am currently using a Nikon D3500 body with a AF- P Nikkor 18-55mm 1:3.5-5.6G kit lens. However I want a shallower depth of field which I feel I cannot get with this lens. Can I use I different brand lens such as cannon and do you have any suggestions on what lens would be good to get.
"Depth of field" is determined by various factors, but a rough rule of thumb states that smaller f/stop values gives you shallower depth of field. On your lens, the minimum f/stop values of f/3.5 (at 18 mm) and f/5.6 (at 55 mm) won't reduce the depth of field much, unless you focus really closely on your subject. See this article for details:
en.wikipedia.org
Also note that depth of field is also partly subjective, and it assumes that the viewer has 20/20 vision is viewing a well-lit image from a distance that's equal to the diagonal width of the image. If you step close to the image, the depth of field gets shallower, and if you view the image from a greater distance, the depth of field gets deeper.
But maybe you really aren't interested in depth of field? Maybe you just want a blurrier background? In that case, the math is easier and there are fewer assumptions. There are two things you need to worry about:
- Have a distant background. For maximum effect, make sure that the distance between the subject and the background is at least ten times the distance between the camera and the subject.
- Have a larger "entrance pupil diameter", which is defined as the focal length divided by the f/stop you are using.
For example with your lens, at 18 mm, you can set your f/stop to f/3.5; while at 55 mm you can set it at f/5.6. So we calculate the entrance pupil diameters of both:
18 mm / 3.5 = 5.1 mm
55 mm / 5.6 = 9.8 mm
So you'll get 90% more background blur (assuming a distant background) at 55 mm, even though it has a larger f/stop.
Here are some lenses for your camera, suitable for taking portraits:
35 mm / 1.8 = 19.4 mm
50 mm / 1.4 = 35.7 mm
85 mm / 1.4 = 60.7 mm
105 mm / 2 = 52.5 mm
135 mm / 2.8 = 48.2 mm
200 mm / 2.8 = 71.4 mm
So even a common 35 mm normal prime for your camera will give you about 2 to 4 times the background blur of your kit lens. Beginner portrait photographers with APS-C cameras, such as yours, frequently start out using 50 mm or 85 mm lenses, although in my opinion, a fast zoom lens is very useful.
You probably would want to keep a distance between yourself and your models—say about 15 feet—for personal comfort, minimizing distortion, and practicality, and so your choice of focal length determines how much of your model you show in a single photo. But understand that camera distance is another creative factor, and some do well by being close or very far.
Understand that not all lenses are the same, and some lenses produce different qualities of background blur—otherwise known as bokeh—with some being smooth and others being harsh and jittery. If you look at many high-end photoshoots, smooth bokeh is nearly universal, as you typically don't want it to call attention to itself.
Also, some inexpensive lenses perform poorly when wide open. Unfortunately, getting both good wide-open performance and good bokeh tend be only found in expensive lenses.
As an aspiring fashion photographer, know that your personality and rapport with your models and clients is more important than this, as is your work ethic. Technically, good lighting design and set-dressing are likely of greater importance than your lens. Hair, makeup, and fashion styling are even more important, and having a model with the right 'look' is of supreme importance.
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