Canon 70-200mm f2.8 IS L + D500 Close Up

[chezem]

I'm trying out the combination of my Canon 70-200mm f2.8 L Is lens with a Canon D500 Close Up Filter. I'd also like to try it on my 100-400 L lens too. Does anyone know how to work out what the DOF would be? I know that there are tables for working it out without the D500 but I'm wondering if there might be some mathematical equation that I can use. I took this photo this morning of a miniature rose with the combination and didn't lose auto focus which was good but it doesn't have great DOF even though I took it at f22. I'm hoping that in shots that are further away I might be able to improve the DOF over what I currently get with my 100mm Macro.

http://i5.pbase.com/o6/15/736615/1/74081968.GNat1bsu.WhiteMiniature5.jpg

[1000arms]

Depth of field is limited. Shoot f32 or higher if you can. Try the 250D, it will halve your MAXimum focusing distance (250mm vs 500mm). I use one on my 70-200mm f/4. I do not have a 100mm-400mm to try it on, yet. Try extension tubes as well as extenders.

[chezem]

Thanks 1000arms for your suggestions. I'll give them a try.