Stacking two 25mm canon extension tubes
Hello,
I have a 300mm f/4 IS lens and a canon 25mm tube, this combo with the crop factor of my 40D give me a magnification of 0,59 (0,37x1.6).
My question are: If I stack another 25mm on that combo I will have a maginfication of 0,92, almost life size? I'm I right?
How does that combination works? Does the lens still autofocus? Does the image suffer a little with the 2 tubes?
I know from experience that the quality I can get with one tube on my 300mm is excelent, but wonder if with two I'm starting to have problems.
Does any one have opinions about this?
Paulo anjo