Help needed re extension tube
 

I received a viltrox extension tube set for christmas and have tried to use it but it won't focus, using either manual or auto focus. Is this only for certain lenses i.e. macro? Hope you don't think this a stupid question from someone who's taken photos as long as me.

Extension tubes should work with any lens that you have but the effect they have can vary massively from lens to lens. I assume that you have attempted to focus on something very close up as tubes not only reduce the minimum focusing distance but also stop a lens being able to focus to infinity.

electrical contacts
 

Do your extension tubes have electrical contacts? I found this article on Wikipedia while trying to answer you question: Extension tubes without electrical contacts will not allow an electronic automatic camera to control the lens, thus disabling autofocus and in some cases forcing a user to shoot wide open unless the lens offers manual aperture control. More expensive extension tubes contain electrical contacts allowing the user to use autofocus and electronically control the aperture of the attached lens.:confused:

Looks like the contacts are there. Tried focusing close up and mid distance. Have read negative stuff about the Viltrox ones so I may need to return them!

You really need auto extension tubes the electrics of which are compatible with your make of camera.ie I have a set of Kenko tubes that are compatible with my Canon but they would not work with any other make.
None auto extension tubes will work but give no control of the lens, focussing or aperture or anything so a lens used with a none auto set-up would have to be capable of being controlled completely manually which is rarely the case these days regarding aperture control.
Be aware that depth of field is very narrow so when moving back and forth searching for the plane of focus it is all too easy to go right through the plane of focus and not even see it. The shorter the focal length of of the lens in use the greater the magnification and the depth of field is tiny.Sometimes it is even quite hard to find the subject let alone focus on it! Welcome to the magic of macro, a fascinating world but challenging.

Very challenging indeed - mine are compatible with my Canon,I guess I just need to spend time on this

I sorted it. Thank goodness.

Extension tubes do some strange things to the focal plane, as well as narrow the depth of field and shorten the focal range (you cant focuss to infinity, or indeed anywhere distant). I have tried mine on telephoto and wide angle zooms as well as macro lenses. If anything a fixed length macro is the easiest lens to use them on! With a zoom lens, the change in focal plane that occurred on zooming even a little was quite dramatic, and it took some careful adjusting of zoom and manual focus to get things right.

After spending some time with it, I have worked out exactly what you were saying Gordon. Works well with my Canon 100mm macro lens and I experimented with the different tube lengths to see how much closer I got. There didn't appear to be any drop in quality. Was pleased.

With short lens and long extension tubes the focal plane can be so close to the front lens element to be of no practical use. With wide angle lens the focal plane can end up inside the lens and therefore never focus.