Teleconverter

Dec 3, 2020
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I was talking to some guys I shoot with discussing lens and Teleconverter. Wouldn't be nice if canon would come out with a Teleconverter like the one on the 200-400 but that you could use on any lens so instead of taking it on and off all you had to do is flip a lever to have 1.4 in seconds!!!
 
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AlanF

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If not in use it would be an extention tube and limit the focus range. Imo not possible.
The EF 200-400mm with a built-in TC focuses from 2m to infinity when the TC is not in use, the same as the Nikon 200-400mm that doesn't have a built-in TC, so it is possible.
 

Nemorino

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Aug 29, 2020
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I think the initial idea was an additional device which can be used with any lens. The only way would be to put it between lens and camera.
The 200-400 tc is a part of the original lens (do not know the Nikon). This is a big difference.
 
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H. Jones

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The EF 200-400mm with a built-in TC focuses from 2m to infinity when the TC is not in use, the same as the Nikon 200-400mm that doesn't have a built-in TC, so it is possible.
This is because the lens is designed with a very large backfocus distance before the extender segment, so that when the extender is out of the optical path the lens still focuses on the sensor, while the extender elements correct the focus to reach the sensor when it is in place. Regular lenses are designed to focus directly onto the sensor, so when the extender wasn't in place, the backfocus would land in the extender, not the sensor.

This kind of extender would either have to only be an EF-RF adapter(tight size to fit an extender, probably not even possible), or would need corrective lenses to refocus the lens backfocus onto the sensor when the extender is out of place. That would ultimately change the optical characteristics such as reducing light transmission, would vary with lenses, and would increase size/complexity. A regular extender doesn't have any of these challenges.
 
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AlanF

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This is because the lens is designed with a very large backfocus distance before the extender segment, so that when the extender is out of the optical path the lens still focuses on the sensor, while the extender elements correct the focus to reach the sensor when it is in place. Regular lenses are designed to focus directly onto the sensor, so when the extender wasn't in place, the backfocus would land in the extender, not the sensor.

This kind of extender would either have to only be an EF-RF adapter(tight size to fit an extender, probably not even possible), or would need corrective lenses to refocus the lens backfocus onto the sensor when the extender is out of place. That would ultimately change the optical characteristics such as reducing light transmission, would vary with lenses, and would increase size/complexity. A regular extender doesn't have any of these challenges.
The EF 200-400mm works perfectly well on an R series with the mount adapter without any requirement for additional corrective elements. Accordingly, an RF version could be constructed using the same optical formula. We are dealing with telephoto lenses of very long focal lengths that are much greater than the sensor-flange distances, not wide angle lenses where back focus is required. The rear element of an EF telephoto lens is deeply recessed inside the barrels of the current lenses so the distance of the rear element from the EF sensor is considerable. There would be even more room available for an RF version to have a built-in extender.
 
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H. Jones

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The EF 200-400mm works perfectly well on an R series with the mount adapter without any requirement for additional corrective elements. Accordingly, an RF version could be constructed using the same optical formula. We are dealing with telephoto lenses of very long focal lengths that are much greater than the sensor-flange distances, not wide angle lenses where back focus is required. The rear element of an EF telephoto lens is deeply recessed inside the barrels of the current lenses so the distance of the rear element from the EF sensor is considerable. There would be even more room available for an RF version to have a built-in extender.

I'm not talking about the 200-400 1.4x, the original post was about an external teleconverter that you could attach onto any lens that swings in and out, like the 200-400 but instead of built-in, as an accessory to any EF or RF lens. That concept does not work for the reason I described, when the teleconverter is not in place, the accessory would become an extension tube as regular lenses are not designed for the long backfocus needed to swing the teleconverter out.

As you can see on this patent, the backfocus distance of a lens changes drastically when it has built-in teleconverters: https://www.canonrumors.com/patent-dual-internal-teleconverter-telephoto-lens/

Backfocus on the lens without either internal teleconverter:
  • BF: 167.00mm
Backfocus with teleconverter 1 in place:
  • BF: 46.56mm
Backfocus with teleconverter 2 in optical path:
  • BF: 110.04mm
 

Joules

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I was talking to some guys I shoot with discussing lens and Teleconverter. Wouldn't be nice if canon would come out with a Teleconverter like the one on the 200-400 but that you could use on any lens so instead of taking it on and off all you had to do is flip a lever to have 1.4 in seconds!!!
It's called a 90 MP sensor and is rumored to be announced next year :LOL:

You didn't specify which camera it would have to work with. If you want both, the flexibility in reach of a TC and the design advantages of using a super short flange distance, it looks like a high res body will indeed be the only option Canon will offer you.
 
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AlanF

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I'm not talking about the 200-400 1.4x, the original post was about an external teleconverter that you could attach onto any lens that swings in and out, like the 200-400 but instead of built-in, as an accessory to any EF or RF lens. That concept does not work for the reason I described, when the teleconverter is not in place, the accessory would become an extension tube as regular lenses are not designed for the long backfocus needed to swing the teleconverter out.

As you can see on this patent, the backfocus distance of a lens changes drastically when it has built-in teleconverters: https://www.canonrumors.com/patent-dual-internal-teleconverter-telephoto-lens/

Backfocus on the lens without either internal teleconverter:
  • BF: 167.00mm
Backfocus with teleconverter 1 in place:
  • BF: 46.56mm
Backfocus with teleconverter 2 in optical path:
  • BF: 110.04mm
Teleconverters are used with telephoto lenses and it‘s clear to me that’s what the OP is asking about and the type of lenses users would be interested in. If it’s to be used as an interchangeable one, then it would need to have extra elements that are fixed as well as the ones that swing out.
Anyway, I wouldn't want an interchangeable one but a built in one could be useful.
 
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Mt Spokane Photography

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Teleconverters are used with telephoto lenses and it‘s clear to me that’s what the OP is asking about and the type of lenses users would be interested in. If it’s to be used as an interchangeable one, then it would need to have extra elements that are fixed as well as the ones that swing out.
Anyway, I wouldn't want an interchangeable one but a built in one could be useful.
I'd think that such a variable TC would have to have two lens sets that switch in alternately to give the two different magnifications (0 and 1.4X) that both focused on the sensor. I wonder if a zoom TC is possible. I'm sure someone has thought of the idea but I've never seen one, so it must be impractical or wouldn't work.

Canon has used built-in TC's in cinema lenses for many years. There are some fantastic ones that boggle my mind with their range and image quality.
 
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