As I mentioned in Getting Up Close the Cheap Way,
there are various ways to make a lens focus closer. Last week, I was playing with the reversed 50mm lens, taking some shots of Flowering Vinca blossoms. After I was done, I realized that I had forgotten one part of that process, switching to manual exposure and adjusting the shutter speed based on the metering.
So, I decided to dig out my extensions tubes and go back out to see how they compared with the reverse technique. I have a set of Auto Extension tubes that pass on all the digital information between the lens and the camera body. Operation is exactly as if the lens were attached directly to the camera. The difference is the lens will focus closer but will not focus at infinity.
Like reversing a lens, image quality is not altered with extension tubes since all you're adding to the lens is space - there is nothing inside the tube except air. Conversely, adding an auxiliary lens to the front of a lens will affect image quality.
The tubes I have are a set of 12mm, 20mm and 36mm tubes. They can be used separately or in any combination. Here is a photo of the set I have all connected to each other.
I used just the 36mm tube with the 50mm lens and shot the same blossom as I had with the reversed 50mm lens. The 36mm tube resulted in almost the identical magnification as the reversed lens. Below are the two photos. As it turned out, the reversed lens shot was only about 1 1/2 stops over exposed so I was able to darken it sufficiently.
|Taken with reversed 50mm lens|
|Taken with 50mm lens and 36mm extension tube|
So, yes, I suppose I will use the extension tube rather than reversing the lens when I want extreme closeups with the 50mm lens. The tubes can also be used on longer lenses but the amount of magnification is less. Also, extension tubes do not work well on zoom lenses as zooming totally changes the focal point. And with extension tubes, there is light loss so shutter speeds will be slower (all other settings being equal) than with reversing a lens.
Herre is a link to a set of extension tubes for Canon very similar to the ones I have. The link is to a set sold by Adorama and costs $180. A singe Canon 25mm tube costs $140. Link to Tubes