Stacking 1.4x Teleconverters

[modchild]

I already have a Kenko Pro300 DGX 1.4x TC and when used with my 70-200 f2.8 IS L it works great. Just had a thought though, I know that the 1.4x costs 1 stop of light and that a 2x costs 2 stops. Would stacking 2 1.4x cost 2 stops or more giving you a 2.8x at 2 stops. I know the AF would suffer and IQ would most likely suffer too but would the benefit outweigh the loss. Anyone tried this, if so would you care to share.

 

[Canon Bob]

I already have a Kenko Pro300 DGX 1.4x TC and when used with my 70-200 f2.8 IS L it works great. Just had a thought though, I know that the 1.4x costs 1 stop of light and that a 2x costs 2 stops. Would stacking 2 1.4x cost 2 stops or more giving you a 2.8x at 2 stops. I know the AF would suffer and IQ would most likely suffer too but would the benefit outweigh the loss. Anyone tried this, if so would you care to share.

Your maths is wrong Stuart, you don't get 2.8x
Stacking 1.4x gives you 2x.......1.4 x 1.4 = 2 and costs you 2 stops

Bob

 

[micloi]

To be more exact it is 1.96x but that's splitting hair

 

[modchild]

Thanks guys for clearing that up, didn't know if it would work like a 1.4 x 1.4 or 1.4 + 1.4. Not particularly bothered about doing it, just that I saw another Kenko 1.4x TC on the classifieds and wondered. I was thinking more along the lines of if it got to 2.8x total it'd cost you 3 stops anyway, not really thinking about the math side of it.

 

[Gary Coyle]

Anything stacked with a Kenko will hunt like crazy.

 

[micloi]

Not in every case. I stacked two Kenko 1.4x DGX's on the Canon 80-200mm f2.8 and AF worked perfectly.