Custom bokeh shapes need a large aperture. The max aperture my lens can reach is
f3.5. Is it big enough for a custom bokeh? I tried but it doesn't work.
Yes. Though you may have to fiddle with your camera settings a bit to achieve it.
I did this once with that lens on a D3100. You will need to shoot wide open of course. Also zooming into your subject will make the depth of field shallower, which you will need to do for this type of bokeh on this lens.
Also the size of the custom shape cutout is important. If you cut the shape out too large for the aperture settings that you use, it will not give you the full shape in the boheh. However don't make the cutout too small either. Hope this helps!
It is possible but presumably you are talking about the aperture shapes in the out of focus area?
If that's what you want then you need to make sure that this area is well outside the focus area that you subject is in.
A good way to test is to lower your aperture, go outside where you have some street lights and manually focus the lens, you should see the shapes around the lights.