Extension tubes come in different lengths and can be stacked. Some web searching will probably turn up a chart that will give you the specs such as focus distance, magnification, depth of field and exposure compensation for the different tube and lens combination. I have an 8, 16, 32 and 56. One tube may not give you the magnification you need. They work fine and the sharpness depends on your lens since they have no glass. I also have bayonet adapters that I use with some 67mm filters that I had and for some that were not available in B mounts. What is acceptable to you may not be to someone else. Generally speaking, macro photography would call for a high degree of sharpness so the glass you are placing in front of a lens should be of the highest quality.

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