Hi macro enthusiasts,
Today, I tried out the technique of mounting a lens backwards onto the front of the existing macro lens in order to get more magnification which I need only occasionally. I put a 28mm on the front of a 50mm (true macro) lens using a male-male coupling ring. After a few goes, finally managed this with the 28mm set to infinity and the 50mm set to 1:1.
Was quite disappointed to see that the combined magnification was less than 1:1, [although the shot itself was OK for my purposes]
Pixel pitch for the shot was 18.24um (SD9 Foveon sensor, LO res). 7mm's worth of ruler spanned 330 pixels at 100% on my screen. 330 x 18.24um = 6mm on the sensor. Was expecting more than that! Tried setting the 28mm to close focus but it made little difference and the lens was then actually touching the ruler, making lighting a bit difficult.
Maybe I was defeated by principal planes, focal ratios and stuff?