stacking teleconverters?

How does stacking teleconverters work? ie, if you had a 2x + 1.4x on a 200mm, is it:

1. 200*2*1.4 = 560mm
2. 200*(2+1.4) = 680mm
3.

i am guessing it'd be #1, but looking for clarification.

the other part is, how about the f-stop drop? is it 2+1 = 3 stops smaller? or is it somehow multiplicative.

I've got a 1.4TC mated up to a 70-200 F2.8, and really hoping for some more reach, but unlikely to afford a 100-400mm right now.

wondering how a 2x or another 1.4 TC may play in the game.

putting a 2x converter on a tube full of optical lenses with a focal length of 200mm turns it into a tube of optical lenses with a 400mm focal length

Putting a 1.4x converter on a tube full of optical lenses with a focal length of 400mm turns it into a tube full of optical lenses with a focal length of 560mm

So alternative 1 is correct: 200x2x1.4 = 560mm

The loss of stops is additive since 1 stop loss is a 50% drop of light coming through the lens, so the total light loss is 2+1=3 stops for the 2x1.4 conbo.

And for your last question, a 1.4x1.4 is equivalent to a single 2x converter in terms of focal length and f-stops, however, I *think* that a single 2x converter will give you a better IQ than stacking 1.4:s.

200 x 2 x 1.4 = 560mm
You also lose 3 stops of light.

That means your 70-200 f2.8 becomes a 196mm - 560mm f8 lens and on a non-1 series body you lose AF.

Your IQ will suffer some as well. How much depends on the lens you are using.

I haven't tested this combo out on my 70-200, however I recently shot the moon with the 300L f4 IS and the TC's stacked.

300 x 2 x 1.4 = 840mm Handheld and MF

oredith wrote in post #6358758
How does stacking teleconverters work? ie, if you had a 2x + 1.4x on a 200mm, is it:

1. 200*2*1.4 = 560mm
2. 200*(2+1.4) = 680mm
3.

i am guessing it'd be #1, but looking for clarification.

the other part is, how about the f-stop drop? is it 2+1 = 3 stops smaller? or is it somehow multiplicative.

I've got a 1.4TC mated up to a 70-200 F2.8, and really hoping for some more reach, but unlikely to afford a 100-400mm right now.

wondering how a 2x or another 1.4 TC may play in the game.

You keep adding glass in the optical train and eventually IQ will suffer one way or the other besides, AF issues etc.
That's why folks buy big, heavy, really expensive fast, prime glass.
No free lunch.
And Canon makes money.

Check out a couple of threads I did on the topic back in July. Stacked my 1.4x and 2x on the 500mm, and I included an explanation and photos of the setup.

Osprey @ 1400mm
Osprey @ 1400mm, take two

yeah, i realize that IQ will suffer, but if the choice is between lower IQ, but distinguishable subject, vs. a sharp blob in the middle of the frame, i'll take the lower quality image and try to make up for it in PP.

if i had a bunch of money, i'd love to get a big bazooka lens, but the TC may be my best/only bet for now.

70-200 f2.8 + 2x TC is a serviceable combo...

oredith wrote in post #6359152
yeah, i realize that IQ will suffer, but if the choice is between lower IQ, but distinguishable subject, vs. a sharp blob in the middle of the frame, i'll take the lower quality image and try to make up for it in PP.

if i had a bunch of money, i'd love to get a big bazooka lens, but the TC may be my best/only bet for now.