There are advantages to getting all your extension in one tube.
In this case this Canon Extension Tube FD 50-u is one rigid tube with baffle at each end to exactly frame the image. There is very little light free to degrade the contrast of the image.
Of course the drawback is you might have too much extension for the lens you are trying to use.
Here is the 50mm lens at its closest focus a little over 300 mm away.
Add 50 mm of tube and this becomes your working distance.
Even focusing the lens to infinity only moves you a bit farther away. The image size of the object changes very little too.
Change to a 135mm lens focused at infinity with 50 mm of extension tube and suddenly this is your working distance. (19 tablecloth squares).
The same 135mm lens focused as close as it can at 1.5 m (4.5 feet) gives this working distance. (16 tablecloth squares)
At this distance the figure is filling the frame height wise. You can fill the 35 mm frame with a business card. If you were working with reflectors and lights the 135 mm lens gives you more room to set them up.
200 mm and 300 mm lenses can work well with 50 mm of extension too. The drawback can be how to support the lens, tube and camera body on a tripod. If the lens doesn’t have a tripod mount you will probably need some form of support bracket.
You can also use 75-150 mm and 70-200 mm zooms with 50 mm of extension. Working distance is proportional to focal length. The drawback of using zoom lenses in close-up work with extension tubes is every time you change the focal length (zoom) you have to refocus. Generally you would move the camera position back and forth to refocus, as playing with the lens focus may or may not get you the result you are looking for.
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