70-300L with extension tubes?

[dilbert]

There are known issues with the Canon TC's and the 70-300L, but are there any such problems with the extension tubes (ET) such as th EF 25mm Extension Tube?

If so, can you stack things up so that you have 1.4x TC, then 25mm ET, then 70-300L?

[neuroanatomist]

There are known issues with the Canon TC's and the 70-300L, but are there any such problems with the extension tubes (ET) such as th EF 25mm Extension Tube?

If so, can you stack things up so that you have 1.4x TC, then 25mm ET, then 70-300L?

Yes, you can do that.  The ET won't add much to the magnification, though.

[dilbert]

There are known issues with the Canon TC's and the 70-300L, but are there any such problems with the extension tubes (ET) such as th EF 25mm Extension Tube?

If so, can you stack things up so that you have 1.4x TC, then 25mm ET, then 70-300L?

Yes, you can do that.  The ET won't add much to the magnification, though.

The idea isn't to add to the magnification but rather to use the ET to separate the TC from the lens as a workaround for the problem where the 70-300L cannot (currently) be used with quite few TCs, including Canon's.

[neuroanatomist]

The idea isn't to add to the magnification but rather to use the ET to separate the TC from the lens as a workaround for the problem where the 70-300L cannot (currently) be used with quite few TCs, including Canon's.

For what purpose?  You'd lose the ability to focus at longer distances, which I'm guessing would defeat the utility for what you have in mind.  A 420mm lens that only focuses out to 15' (I'm guessing on that, but I'd bet not more than 20') might not be too useful as a telephoto lens.

[Mt Spokane Photography]

At 300mm, your lens is at f/5.6, which is the limit of all but the 1 series bodies for autofocus.  With a 1.4X TC, that becomes f/8, and with a extension tube, its less light yet.  Don't expect your camera to autofocus.

You can manual focus, but it will be difficult unless you have bright sunlight.