Is it tacky to stack telephoto extenders?

Got a 2x today for my 70-200 IS II to do some lunar photography, but 400 is still on the short end. Poor form to stack them?

Not poor form but poor image quality.

Buy the 100-400 and use the extender. The moon is bright enough to not worry about the high f of the lens. Some hate the lens, but I have nothing but praise for it.

At 400mm and with a hefty crop, I can get a moon large enough to put into my landscapes, instead of a blurry point of light, which is good...I don't know if I can justify a whole other lens dedicated to that purpose, but it is tempting. The 100-400 is damn ugly. How is the 400 L f/5.6 (non IS)?

I need to get a job where someone else pays for this stuff.

I've had good luck with items that don't move (and stack all the time...especially with good light).
The quality will hold OK with good glass, but the autofocus suffers greatly.

Here's some unretouched examples...
600mm f4L IS was the base lens

600mm


600mm and 1.4X II


600mm and 2X II


600mm with both 1.4X II and 2X II stacked



and just for yuks...

600mm and 2X II


600mm 2X II and 2X III stacked (that's 2400mm).

So that last one is at what, like f/16 or somewhere around that?

Actually, the camera remained set at f/8...it did not recognize the extra 2X, (but was darker). I bumped the ISO from 640 to 2500 for that shot. It gave me an 1/1000 exposure.


Also.
There are many cases where just cropping/enlarging a file will do.

600mm enlarged


600mm w/ 1.4X and 2X

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