for fooling purposes only. I wanted to see how much closer I could get with another extention tube, but I dont have another, so I improvised.
I took a body cap and lens dust cover, and put a gap in between, with a cyanoacryllic glue doused piece of fabric as the gap. it now feels like concrete. I've tried to pull the whole unit apart, no luck, its nasty glue. need a special chemical debonder to remove.
so yea. with all of my tubes on, i get a minimum focus distance of about 6.5ft on my 400mm L glass. 11ft without any tubes. When i add this gizmo, i get about 4.8ft focus distance, and you can really really see details. lol..
heres a sample pic.
I think it will be useful for shots where i need to get suuuper close, but otherwise its a pointless extention.