The crispness of the lines of images made with sprinkled powder depends on the neatness of the edge of the powder. If you are using Bullseye black, you need to use stiff black 000101-0008 rather than the normal which spreads much more than the stiff black does.
There are various ways to create crisp edges, but in some cases it is better to remove the powder than to push it about.
I have adapted a key board cleaning attachment for my vacuum sweeper to clean up the edges of the powder. The narrow head just needs to have a nozzle put in. I used the casing of a ball point pen and filled the remainder of the head with blue tac. Turn the suction of the vacuum all the way down. If you do not have an adjustable power vacuum, make a hole in the hose that you can control the size of to vary the suction.