The answer is “more than you can shake a stick at” … whatever that old idiom means
Meanwhile, the sky was very clear tonight and the moon was just sitting there, daring me to add that other teleconverter and go hunting for mountains or something … so I added the 1.4x Tamron to the 2x Kenko to see how difficult I could make my life.
The results were interesting … massive magnification with quite a bit of blur. Just about exactly what you expect from two teleconverters totalling almost 3x magnification.
In case anyone has not done the calculation yet, the effective focal length is 500*2*1.4*2.7 … which comes to 3780mm. That’s a lot of magnification. This is what that looks like …
So you can see that it is quite the rig. But it does not weight all that much because the mirror lens has so little glass inside. I tested the rig before going outside to make sure it could be focused. No problem. Imagine one of those test targets with the 1” square in the middle hung about 15 feet from the camera. How much magnification would it take to get pretty much just the little square in the middle to fill the frame?
Well, about that much. Although not absolutely tack sharp, this is pretty good for our purposes. Next, the moon. The first thing I notice is the breathtaking magnification. I can get about half the moon in frame … wow.
An alternate rendering of the same image.
The second thing that I notice is how subtle the colours are. Very nice. And just like yesterday, there are many smaller craters plainly visible. Just excellent.
The mountain range that is so prominent at top left is called the Montes Caucasus. Very impressive resolution. So I crop the image on the left side to square it up. So now when I resize to 1000px on the long side, it all looks really big.
All in all, quite satisfying. The quality is not astounding, but the magnification makes up for it. Wicked detail from nothing more than a telephoto lens and some teleconverters.
It does not surprise me much that the surface of the moon was rendered more crisply with just the Kenko TC. 2.8x is asking an awful lot.