I posted this on another forum and thought it might be of benefit to anyone who does/is contemplating doing some close-up work. I have a set of extention tubes and thought it would be useful to know what results I'd get with different focal length/different size tube combinations.
This was done in true amature fashion (so allow a couple of millimeters leeway) but it'll give you an idea of which tube you'll need in any situation. I used three Jessops tubes that allow AF, the sizes being 12mm, 21mm and 31mm, but AF was turned off, the camera set on close focus then moved back and forth to achieve focus. The subject was an extended tape measure.
There are two columns, the first readings were taken at 100mm focal length, the second at 400mm.
The first mesurement in any column is the visible area in the viewfinder(all manufacturers claim 100%), and the second is the distance between ths subect and the lens hood. I decided to use this distance as opposed to the focal plane as it is the lens hood that the butterfly/bee/fly is worried about, not how close the sensor is. Insidently, the hood mesures 82mm from front to back so this can be added if you want subject to glass distance.
All mesurements are in millimeters.
...............@100mm...............@400mm
No Ext.
tube........340x225 - 1455............104x70 - 1410
13mm........110x72 - 400..............82x55 - 1117
21mm........76x51 - 255...............73x48 - 1020
31mm........60x40 - 200...............64x42 - 935
I hope this can be of use to a few of you.
Martin.
