If you are a FSLR or a DSLR user you know all about this and can move on to the TAB results and the comic section. If you are a Fujifilm X-camera user, here is some good news.
The Fujifilm MCEX-11 and MCEX-16 automatic extension tubes are in stock. As the names will suggest, these are 11 mm and 16 mm spacer tubes that go between the Fuji X -series camera bodies that have the removable lens mount and the lens itself.
The tubes are free of any glass, but have the appropriate electrical connections to pass commands through themselves from the body to the lens - giving you focus and exposure control as per usual.
They are usable on some wide-angle angle lenses - but not all...and the results are not all that useful with the wider focal lengths. Their real forté starts at the 35mm mark and continues forward out to the longer telephoto zooms.
The action of spacing out the lens means that the whole thing focuses a lot closer than normal - really close, if you will, to true macro work. Of course the depth of field is restricted, as it always is at close distances, but there is no optical interference from glass elements. With a number of the X-series cameras you can set the focus and exposure to manual and then see the effect of stopping down the aperture when you half-press the shutter release button. Really useful.
The MCEX-16 gets you closer than the MCEX-11, but you can predict what the effect will be by consulting the chart that Fujifilm do on their website.
Here is an example of the use of the MCEX-11 with the 35mm f:1.4 Fujifilm lens:
And here is one with the MCEX-11 on the 55-200mm lens. This is not a close-focussing lens at the best of times but this does make an improvement.
The perspective is changed, of course, but that is to be expected. In some respects this extension tube would be perfect for 50mm and longer focal lengths.
Model is a 1:43 1947 Chrysler. The background building is 1:87 scale but if you play with the tubes and focal lengths you can adjust the size.