Macro lens plus extender?

[MiqsPix]

I have a Canon non IS EF 100mm f2.8 macro lens and a Canon 1.4 lens extender mk3. Can I use them together on my Canon 90D? Would there be any benefit?

 

[Gav.]

Check if the element in the rear of the lens will clear the front of the extender, the extender will hit in some lenses!
Canon haven't listed TC in spec's only Ext' tubes, so my guess is don't use it.

But if it fits it will give more mag.

 

[zx9]

Check if the element in the rear of the lens will clear the front of the extender, the extender will hit in some lenses!
Canon haven't listed TC in spec's only Ext' tubes, so my guess is don't use it.

But if it fits it will give more mag.

As above ^^^

FWIW at one time I had a mk1 2x extender which worked well behind a EF180L macro and I don't suppose that combination was listed by Canon either.

First shot taken with the above combination that I have just found.

Look No Wings by Keith Hudson, on Flickr

 

[Snapsh0t]

A useful technique with lenses not designed to take a tele-convertor is to put a small extension tube between the lens and the tele-convertor to make sure there's no contact between the internal lenses. You get a high magnification but lose all but the closest focus. Using an Olympus 60mm macro lens and MC-20 2x tele-convertor with a 16mm tube between them gives around 3x magnification.

 

[Petrochemist]

I do dislike Canon's insistence on calling 'teleconverters' 'extenders'. This latter is too easily confused with extension tubes.
It's quite possible the teleconverter will fit on a macro lens when focus close but foul with it focused to infinity. If either has protruding elements check carefully with a ruler before connecting them, or add a tube as per @Snapsh0t 's suggestion.
If it fits without tubes the magnification will be 1.4x that achieved by the lens alone. If tubes are added they make more difference (in magnification & focus distance) between the lens & TC than they do between TC & body.