Patent: Canon EF 2.8x Teleconverter

[Canon Rumors]

Share

Patent Time
A patent showing a new teleconverter has made an appearance. It appears to be a 2.7 or 2.8x TC. What effect woud it have on aperture? A 400 f/2.8L IS II would become 1120mm at f/8. All well and good, but the missing f/8 autofocus on the 1D X makes this one a bit strange with the current line of camera bodies.

Patent Publication No. 2012-47869

• 2012.3.8 Release Date
• 2010.8.25 filing date

Example 1

• -83.98mm focal length
• Expansion rate β = 1.996
• Lens Construction 5 group nine

Example 3

• -41.91mm focal length
• Expansion rate β = 2.779
• Lens Construction 5 group nine

Canon’s patent

• Rear converter is to increase the focal length, F number, the residual aberration
• When doubled, twice the lateral aberration, longitudinal aberration is 4 times greater rate of expansion, because the F-number is also double, longitudinal aberration is twice per depth of focus
• Rear converter configuration consisting of three groups of positive and negative positive
• Reduce the aberration of the rear converter itself

Source: [EG]

cr

[xROELOFx]

i wonder how much this would damage the image quality.

[thure1982]

It will probably be add good as the 2x iii

[Caps18]

I wonder how much this will drain my bank account.  I have used liveview auto focus at f/8 before and it works.  It is slow, but it works.

[AmbientLight]

To me this is a really strange thing indeed:
If this teleconverter becomes available I bet it will be usable only with some of the really, really good tele lenses and for anything else it will exaggerate lens errors so much, that pictures become almost unusable.

I truly wonder how this would make sense on the business side? 

[sphax]

Soooo ... AF will work ONLY with the 200mm F/2,0L IS ? Which would turn into a 560mm F/5,6 ... weird ! Oh and with the 135mm F/2,0L which would turn into a bizarre 378mm F/5,6 ... I wonder how is that gonna sell ? Well the liveview shooting as mentioned is an option but ...

[D.Sim]

A patent doesn't necessarily lead to a production item... could be just making sure no one takes up a design they've worked on for a while.

[lonelywhitelights]

really, really odd and not necessary at all - seems to be quite pointless to me. Is there anyone that would actually buy this? if so - why? for extra reach at the sacrifice of AF?

[3kramd5]

<p><strong>Canon’s patent</strong></p>
<li>When doubled, twice the lateral aberration, longitudinal aberration is 4 times greater rate of expansion, because the F-number is also double, longitudinal aberration is twice per depth of focus</li>

I read that as it, like the 2X, adds two stops. So a 2.8 lens -> 5.6, not 8.

[Haydn1971]

I'd imagine this would be very popular for Police/Secret Service In that a 400mm 5.6 with a 2.8x convertor would give a FF equivalent of nearly 1800mm on a crop body - that's a good couple of miles of range, set to live view, hook up to mains power and a laptop - sorted

[Ellen Schmidtee]

Kenko make a 3x teleconverter for several years, and I have heard of people stacking teleconverters, so it appears there is some market for it.

[Ellen Schmidtee]

<p><strong>Canon’s patent</strong></p>
<li>When doubled, twice the lateral aberration, longitudinal aberration is 4 times greater rate of expansion, because the F-number is also double, longitudinal aberration is twice per depth of focus</li>

I read that as it, like the 2X, adds two stops. So a 2.8 lens -> 5.6, not 8.

Unless Canon have found make a teleconverter that opens the aperture wider, I don't see how the teleconverter could multiply the focal length by 2.8 without (relatively) closing the aperture by three stops.

[sphax]

Is it possible to mount the Canon 1200mm F/5,6L on it ? I'm pretty interested in a 3360mm F/16 ... 

[AmbientLight]

Unless Canon have found make a teleconverter that opens the aperture wider, I don't see how the teleconverter could multiply the focal length by 2.8 without (relatively) closing the aperture by three stops.

Given that a teleconverter cannot add any light to what it is receiving from the attached lens we end up in a situation that in case this teleconverter patent is eventually transformed into a product, it won't be useable with a lot of lenses, making it fairly limited. Limited usage then requires a high asking price to recover R&D costs, so the overall package makes even less sense compared to using a lens with longer reach and I assume much better image quality.

Can anyone come up with an explanation as to what this patent should be good for?

[marekjoz]

It's as simply as stacking x2 and x1.4 together but reporting proper apperture (currently when stacking only x2 is reported to the camera).
IQ - sharpness won't be as much affected as CA. This is really intented for use rather not in FF where CA increases in corners. It would be really great to have a production announcement of this together with 7d2.