And another thing...
In my last post I went into lots of detail about how to use close up lenses and extension tubes with telescopic lenses. Since then I have been trying it out for real with mixed results. In general the extension tubes are better because they dont affect the image quality anywhere near as much as the close up lenses do. There are 2 main issues with the extension tubes. Firstly, because they are cheap, plastic ones they don't fit all that well, there is a little give in the lock position and this can cause the lens to go hunting sometimes. This has, on occasion, lead to complete failure to take a picture, but on the whole I know what to expect now. Secondly you have to find the correct focus by either zooming or moving distance to subject. When you lose focus your instinct is to try and refocus but this doesn't always work. Again I've got used to it. I do use a 35mm extension tube with my canon 100-400mm lens quite regularly, but it is a pain having to take the lens out, insert tube and replace lens. The marbled white above was taken with this set up as were the pictures below.
The close up lenses that screw in to the front of the lens were a different issue. I tried them and thought they were OK until I got home at looked more closely at the pics. The focus wasn't great and there were some serious fringes which really affected the image. I had pretty much given up on them but I thought in the tests they seemed OK at the shortest focal length. I realised that the temptation to zoom had been too strong to resist and this may have been why they were bad. I tried again with a nice compliant subject that gave me time to try out a few settings. The picture of a common blue is below. I used the +4 lens with the canon lens at minimum 100mm focal length and stopped down to f11. The result is actually quite good considering. There is a little bit of fringing but there is detail and sharpness. This was a small beastie so the result must be pretty close to true macro. I am actually quite pleased that I have got respectable results using the telescopic lens for close up work. But it is fiddly and you have to persist. I'll be honest and say that I have been investigating getting a dedicated macro lens for this stuff - its just less messing about. At the moment financially I cant go there and this add-on approach will be useful to get the pictures I want.