Smooth bokeh?

Sometimes when I take a close-up of a flower etc at a wide aperture with my 50-200 at long zoom I get circles in the background rather than a smooth bokeh. Should I use a shorter focal length? Are there any rules I should follow? Thanks

The background circles or shapes are related to the shape of the iris diaphragm in the lens and the aperture used, so with a particular lens you are stuck with it. This is why lenses with more blades to the diaphragm are sought after.

To be sure though it would be best if you post an image so we can see exactly what you are referring to.

It also depends on whether there are highlights in the background. If the background has bright sunlight (or other bright light sources) and you shoot wide open then you'll get the circles.
(One of the advantages of digital - you can shoot and review to get the best angle)
Matt

OK, here's an example.

In terms of composition, the lightest parts of a photograph tend to grab the viewer's attention. In this case, that would be the background, taking emphasis away from your subject.

So really I think changing the viewpoint to get rid of the white areas would be a good idea and would also remove any unpleasant lens effects as well.

Hope that helps!

Thnks John- it does help! A very useful tip. And to Matt as well.