If you use the extension tubes with an adapter for a "proper" lens with an aperture ring, then auto-exposure should work just fine with the advantage that you can control depth of field.I use ext tubes a fair bit, they are a manual set so exposure is guess work initially but works well and gives decent results, imho the electrical connections are not worth having because macro is generally easier with manual focus anyway.
If you use a digital lens with plain extension tubes it is not possible to adjust the aperture and every shot will be at maximum aperture and shallow depth of field. Of course, if you buy expensive tubes with electrical contacts, you can still adjust the aperture but I was responding to chrism8 who mentioned using manual tubes.Not sure what you mean John?
That's a good choice. There are much cheaper sets available from JJC, Meike, etc. but Kenko is the nearest to a gold standard. The one irritation with them is that they don't come with end caps. Well, my M43 set didn't and I can't remember if the Nikon ones did or not.Thanks, I was looking at the kenzo set of tubes on Amazon for 130 quid.
What brand or make Chris?
Thanks, I will have a look at this.you can get extension tube for £20-30, I wouldn't advice buying expensive ones especially not £100+. They don't work any better than cheaper ones in my experience.
Regardless as a rule of thumb if you want greater than life-size i.e. 1x or 1:1, extension tubes work better for wider focal lengths (<50mm) and macro close up lenses like raynox DCR-250 suggest above work better for longer focal lengths (>100mm).
this website is a really useful source for all things macro and they also have calculators for various scenarios and setups
Macro photograpy calculators, including extension tube, stacked lens and focus stack step calculators
Tools and calculators for macro photography, including extension tube calculator, focus stack step calculator and reverse macro working distance calculatorextreme-macro.co.uk
See my earlier post. Cheap, non-auto ones will be fine ONLY if you can set the lens aperture on your lens, not on your camera.Thanks, I will have a look at this.
With Nikon G lenses, the aperture stays closed down to the minimum when on manual tubes.If you use a digital lens with plain extension tubes it is not possible to adjust the aperture and every shot will be at maximum aperture and shallow depth of field.
To add, illustrated with a crappy phone pic complete with camera shake.See my earlier post. Cheap, non-auto ones will be fine ONLY if you can set the lens aperture on your lens, not on your camera.

I'd suggest the DCR150 rather than the 250, it's less powerful so is easier to useIt depends on how much extra magnification you want. Assuming your 100mm lens focusses down to 1:1 then 50mm of tubes will give you 1.5:1. More than 50mm and you could run into mechanical and electrical problems. After that you'll need to look at add-on close-up lenses but you'll need quite a high dioptre to get useful magnification with a 100mm lens. The Raynox DCR-250 is very popular but not easy to use. It's one of those areas where you need to experiment to see what suits you best.