# TC switchable like built-in TC



## goulab (Mar 29, 2014)

Hi,
It's probably stupid but can we imagine a tele-converter switchable like the one in the new 200-400mm ? I suppose that it's impossible due to the extra lenght that the TC creates between the lense and the camera but i wanted to be sure ! 

Thank you !


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## Mt Spokane Photography (Mar 29, 2014)

At first glance, its not very simple. 

If, for example, you had a tube that a TC switched in and out of, when the TC switched out, it would suddenly be a long extension tube and you could only focus at short range. So, some other optics will have to switch in to compensate. I suspect that happens in the Canon lens.

Lenses with TC's that are built in are not common, but have appeared in the past, and, they are used for some Commercial TV lenses.

I suspect that any practical implementation of the idea for general usage would be difficult or impossible because of the need to matchup the glass that switched in to a individual lens. That would not preclude someone making a dedicated unit for a popular lens like the 70-200 f/2.8L. It might sell for $700, but some would find it very useful.

Why not start a kickstarter project to design and sell one??


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## goulab (Mar 29, 2014)

Thank you for this answer. Indeed, it would be very useful. I keep in mind your idea of a kickstarter project !


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## Jim Saunders (Mar 29, 2014)

I'd like if they'd do this for future telephotos; have the structure present and make 1.4 or 2x an option at purchase. A 70-200 with an integrated 2x would be some fun...

Jim


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## Lawliet (Mar 29, 2014)

Mt Spokane Photography said:


> I suspect that any practical implementation of the idea for general usage would be difficult or impossible because of the need to matchup the glass that switched in to a individual lens. That would not preclude someone making a dedicated unit for a popular lens like the 70-200 f/2.8L. It might sell for $700, but some would find it very useful.



You could switch between a TC2 and a daisychained TC1.4 + the Metabones Speedboosters optics. The latter would counteract the TC1.4, giving you something to avoid the extension tube effect. Some finetuning regarding overall lengths and compensation of aberrations would be required, but it would work regardless of the lens its attached to.


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