I am putting together a small table top studio in my basement to begin close-up photography of still life subjects (of sizes that mostly would fit inside say a microwave oven). In preparation for this I remembered reading a side bar discussion and an accompanying chart (PDF below) in one of the Schneider LF lens brochures about the difference between "nominal" and "effective" aperture when using their macro lenses for close-up work. However, I admit I don't really understand what the Schneider brochure was trying to explain, and wanted to ask for help to understand how I should prepare to adjust aperture and exposure when I begin doing this close-up photography? I understand bellows extension exposure compensations, and so if I use a macro or other lens for a close-up I will expect to adjust exposure for bellows extension, but what do I need to consider in regards to "nominal" versus "effective" aperture? My sense is that the practical reality of what the Schneider brochure is explaining is that one should not stop-down the aperture adjustment of the lens too much because you might obtain an "effective" aperture that is so high that you will run into excessive diffraction effects. Is this correct? And what practical advice can LF Forum members provide for these considerations? Thank you...

Schneider Macro exposure correction rules.pdf