In practical terms, given that you appear to be shooting consumer grade lenses on a crop-sensor camera, I suspect that there will be limits to what you can achieve with respect to both shallow depth of field and bokeh. The distance to the out of focus objects and the nature of the objects also plays a role - distance lights are the part of the image that shows of the bokeh well. Some lenses will feature beautiful bokeh and other lenses will produce less pleasing results (hint - lens cost is often the determining factor here too).
#Aperture 3.5 depth of field plus
When it comes to bokeh, this is even more complicated as it refers to the look of out of focus areas in your image, so once again, the aperture used (usually something close to being wide open) and distance to the subject PLUS design characteristics of the lens itself. Lenses that have this feature tend to have both a very limited focal length range AND tend to be expensive. Most of the lenses I use are constant aperture lenses, which means that the maximum f-stop is constant throughout the focal range. Aperture (f-stop) is just the ratio of the focal length one is using divided by the diameter of the entrance pupil of your lens. In terms of the lenses you are using, the maximum aperture does vary. amount of magnification) and sensor size.
#Aperture 3.5 depth of field manual
They are related to other factors, such as the aperture you use (and that will be in any of the shooting modes aperture priority, shutter priority, program mode and manual mode), distance from the subject (i.e. Sanjib - the depth of field and bokeh are not related at all to using the aperture priority mode of your camera. I think you should read the tutorial first that might answer your last question to Peter. Most macro lenses reach the same magnification, so the subject is the same size regardless of the lens, but the background will be more blurred with the longer lens. This is one reason some people avoid short-focal-length macro lenses. In many cases, the visual appearance depends on both DOF and background blur, so if one wants a very blurred background, one is better off with a longer lens. That is because the longer focal length lens has a narrower angle of view, and its therefore capturing a smaller amount of the background and spreading it more to cover the same framing. Nonetheless, if the background is not very close to the subject, the background will be more blurred with the longer focal length. So, what happens if you switch from a wide angle to a telephoto and step back so the subject occupies the same portion of the frame? Depth of field will stay the same. If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length! Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to magnify the subject when one is unable to get closer.