tryinghard wrote:Will extension tubes help to fill the frame more with the insect or will they degrade image quality ? As always any thoughts or feedback appreciated.
A lot depends on the lens you are using. Lens designs are optimised at the design stage for working at particular distances or image sizes — usually somewhere between 10 feet and infinity. Extension tubes with a non-macro lens can get you into a region where the lens simply doesn't perform well any more.
Macro lenses are better suited to close-up and macro work. For them, an extension tube is much the same as having a longer helical focus thread. Unfortunately, many modern macro lens designs in the DSLR world don't focus by extending the distance between lens and image plane but by a complex sort of inverse zoom effect where the closer you focus the shorter the focal length becomes. I have no idea how these lenses would work with extension tubes.
An often overlooked means of focussing closer is with Portra lenses (dioptre lenses) which screw into the front of the lens like a filter. If you pay the extra and get multi-element Portra lenses they usually correct a regular lenses optical characteristics in order to produce better close-up results. They are small light and compact and you don't lose exposure through lens extension.