# Patent: Canon EF 2.8x Teleconverter



## Canon Rumors Guy (Mar 27, 2012)

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<strong>Patent Time


</strong>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.</p>
<p><strong>Patent Publication No. 2012-47869</strong></p>
<ul>
<li>2012.3.8 Release Date</li>
<li>2010.8.25 filing date</li>
</ul>
<p><strong>Example 1</strong></p>
<ul>
<li>-83.98mm focal length</li>
<li>Expansion rate β = 1.996</li>
<li>Lens Construction 5 group nine</li>
</ul>
<p><strong>Example 3</strong></p>
<ul>
<li>-41.91mm focal length</li>
<li>Expansion rate β = 2.779</li>
<li>Lens Construction 5 group nine</li>
</ul>
<p><strong>Canon’s patent</strong></p>
<ul>
<li>Rear converter is to increase the focal length, F number, the residual aberration</li>
<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>
<li>Rear converter configuration consisting of three groups of positive and negative positive</li>
<li>Reduce the aberration of the rear converter itself</li>
</ul>
<p><strong>Source: [<a href="http://egami.blog.so-net.ne.jp/2012-03-26" target="_blank">EG</a>]</strong></p>
<p><strong><span style="color: #ff0000;">c</span>r</strong></p>
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## xROELOFx (Mar 27, 2012)

i wonder how much this would damage the image quality.


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## thure1982 (Mar 27, 2012)

It will probably be add good as the 2x iii


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## Caps18 (Mar 27, 2012)

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.


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## AmbientLight (Mar 27, 2012)

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? ???


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## sphax (Mar 27, 2012)

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 ...


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## D.Sim (Mar 27, 2012)

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.


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## lonelywhitelights (Mar 27, 2012)

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?


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## 3kramd5 (Mar 27, 2012)

Canon Rumors said:


> <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.


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## Haydn1971 (Mar 27, 2012)

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


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## Ellen Schmidtee (Mar 27, 2012)

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.


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## Ellen Schmidtee (Mar 27, 2012)

3kramd5 said:


> Canon Rumors said:
> 
> 
> > <p><strong>Canon’s patent</strong></p>
> ...



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.


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## sphax (Mar 27, 2012)

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


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## AmbientLight (Mar 27, 2012)

> 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?


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## marekjoz (Mar 27, 2012)

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.


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## Maui5150 (Mar 27, 2012)

so the 70 - 200 F/2.8L IS II becomes a 196 - 560?

While F/8 is not ideal, still might add in some use. The TCs already slow the AF down as it is, so manual focus is not as much a big deal. 

Not sure the price... Probably somewhere in the $600 - $800 range, but if it works with the 70-200 like the 2x does, I could see there being interest


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## marekjoz (Mar 27, 2012)

Haydn1971 said:


> 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



... and closed in a big anti-wind box.


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## smirkypants (Mar 27, 2012)

If you take the DX crop area of a D800, you have an optically perfect 1.5 teleconverter at 16MP. The only downside is that it's slow to shoot. There is no reason why Canon couldn't just create something as good with a 1.6 crop at 18MP. Sensor technology is racing ahead. I would much rather have a camera with an optically perfect built-in 1.6 crop teleconverter and add a 1.4x with a loss of only 1 stop than try to deal with the downsides of this 2.8x beast of a thing with all of its CR and loss of light.


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## maxxevv (Mar 27, 2012)

Would be the perfect companion for the 200mm f/2.0 IS L though ... ;D


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## 3kramd5 (Mar 27, 2012)

Ellen Schmidtee said:


> 3kramd5 said:
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> > Canon Rumors said:
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Maybe they designed it in such a way that it magnifies the apparent aperture (kinda like how constant f zooms work).

Dunno, just speculating based on that single bullet point. What else would it mean?


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## marekjoz (Mar 27, 2012)

3kramd5 said:


> Ellen Schmidtee said:
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> > 3kramd5 said:
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It may not affect any current lens which it is attached to, as simply increasing f number accordingly by 3 stops. Apperture number comes from dividing focal length by real hole size. If focal length increases I don't see a way to increase the attached lens apperture hole.


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## Autocall (Mar 27, 2012)

3kramd5 said:


> Canon Rumors said:
> 
> 
> > <p><strong>Canon’s patent</strong></p>
> ...



you've read wrong: you loose 2 stops with the *1.4 converter*, and tree stops with the 2.0 .
this means 4 stops with the 2.8


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## marekjoz (Mar 27, 2012)

Autocall said:


> 3kramd5 said:
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> > Canon Rumors said:
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I'm sorry you're not right - you loose 1 stop with 1.4 and two stops with 2.0. Assume you have 400mm f4. It means a hole is 100mm wide (400/100). If you add 1.4 TC, you have 560mm. So it becomes 560/100 = f5.6 and f4 -> f5.6 = 1 stop. Calculate it with TC 2.0 and TC2.8 accordingly and you will find it.


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## Autocall (Mar 27, 2012)

marekjoz said:


> Autocall said:
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> > 3kramd5 said:
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yeap, you're right.
sorry


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## gatano (Mar 27, 2012)

let's hope Canon will add (again and officially) F8 focus capability in the next bodies, maybe the next 7DII (or 70D) is aimed at birders and will have F8 focus capabilities + high pixel density, 
let's hope also next FF model (the overly awaited high resolution one) will have some(more than one) F8 focus points to make the 2.8x extender an usable tool 

btw I already can use AF on F5.6 sensitive points staking a kenko dgx 1.4x + 2X tele converters, so also canon must/should be able to make this possible on current and (at least) future bodies

remember that F8 starts to cause some mild diffraction at current aps-c pixel densities, so I'm really surprised canon is working on it


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## sphax (Mar 27, 2012)

Autocall said:


> marekjoz said:
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> > Autocall said:
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I love how you fight about "stops" dudes ... bit of a clue : take F/2,8 or F/4,0 or whatever indeed and just multiply by the number on the extender ... magic


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## marekjoz (Mar 27, 2012)

sphax said:


> Autocall said:
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> > marekjoz said:
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Wow, how did you do that? That's really a case for Penn & Teller


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## Autocall (Mar 27, 2012)

marekjoz said:


> sphax said:
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> > Autocall said:
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apart from the relatively simple ratios, I was concerned by the loss due to the additional elements. 
( a polarizing filter doesn't change the focal but causes 1 full stop loss for example)


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## marekjoz (Mar 27, 2012)

Autocall said:


> marekjoz said:
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> > sphax said:
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You are right - there is additional lost of light on elements inside TC.
And this can be another win over stacking 2.0 and 1.4 - for sure there will be less elements than sum of 1.4 and 2.0.


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## dolina (Mar 27, 2012)

With 2.8x applied

800mm f/5.6 = 2,240mm f/15.68
600mm f/4.0 = 1,680mm f/11.2
500mm f/4.0 = 1,400mm f/11.2
400mm f/2.8 = 1,120mm f/7.84
300mm f/2.8 = 840mm f/7.84
200mm f/2.0 = 560mm f/ 5.6


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## 3kramd5 (Mar 27, 2012)

marekjoz said:


> 3kramd5 said:
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> > Ellen Schmidtee said:
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A 70-200 f/2.8 at 70mm has a maximum opening 25mm in diameter, agree?

A 70-200 f/2.8 at 200mm has a maximum opening... 25mm in diameter. 

AFAIK, there's no physical mechanism opening the blades wider as the focal length increases. Rather, the zooming in optically magnifies that 25mm aperture such that it appears to be 71mm in diameter (at the 200mm example).

I see no reason they couldn't employ that principle in teleconverters.




That said, sure, I probably I read it wrong, hence me asking what they meant by that bullet point.


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## emag (Mar 27, 2012)

Makes more sense (in some ways) to use a telescope


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## Blaze (Mar 27, 2012)

3kramd5 said:


> A 70-200 f/2.8 at 70mm has a maximum opening 25mm in diameter, agree?
> 
> A 70-200 f/2.8 at 200mm has a maximum opening... 25mm in diameter.
> 
> ...



I don't think you understand the fixed f-number zoom lenses properly. If the 70-200mm had a maximum opening of 25mm at 200mm, then it would only be f/8 zoomed in. There is in fact a physical mechanism opening the blades wider as the focal length increases.


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## 3kramd5 (Mar 27, 2012)

Blaze said:


> 3kramd5 said:
> 
> 
> > A 70-200 f/2.8 at 70mm has a maximum opening 25mm in diameter, agree?
> ...



No, it has 2.8, because the pupil is magnified by the front element moving relative to the pupil.

If they could make the blades open to 71mm in the same form factor, they sell it as a 70-200f/1-2.8.

Zooming a lens doesn't mechanically widen the pupil. It optically magnifies it. 

http://www.dgrin.com/showpost.php?p=523730&postcount=2
_There is a lot of mis-information on the Internet about how "constant aperture" zooms work, but the most lucid explanation comes from Bob Shell:

Comments from Bob Shell (January 8, 2003):
"An f-stop is the ratio between the focal length of the lens and the *apparent* size of the lens opening as viewed through the front. It must take into account the magnification factor of all lens elements in front of the diaphragm, because it is the size of the opening that the light "sees" as it passes through the lens, not the actual physical diameter of the diaphragm opening.
It is this fact that allows companies to make constant aperture zoom lenses which maintain a constant f-stop when the focal length changes, because such lenses are designed so that the magnification factor (diopter value) of all elements in front of the diaphragm changes as focal length is changed to hold the aperture value constant."_


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## maxxevv (Mar 28, 2012)

3kramd5 said:


> Blaze said:
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That's interesting.... hmm, think I need to do some reading. Thanks for sharing.


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## Ellen Schmidtee (Mar 28, 2012)

3kramd5 said:


> No, it has 2.8, because the pupil is magnified by the front element moving relative to the pupil.
> 
> If they could make the blades open to 71mm in the same form factor, they sell it as a 70-200f/1-2.8.
> 
> ...



Learn something new every day.

Yet, Canon's teleconverter are connected behind the diaphragm (between the lens and the camera body), so the bottom line is this TC would make the lens 2.8x longer & three stops slower.


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## marekjoz (Mar 28, 2012)

maxxevv said:


> 3kramd5 said:
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> > Blaze said:
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Same thing...


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## Stuart (Mar 28, 2012)

Why do we think this is for an EF mount?


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## marekjoz (Mar 28, 2012)

Stuart said:


> Why do we think this is for an EF mount?



If you follow the source of the news you will find more details and examples like the one below. Such a lens is EF as far. Other examples refer to it as well so it's EF mount.


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## vlim (Mar 28, 2012)

Beside the new 300 F/2.8 or the 400 F/2.8 i don't see any other lens which can afford a TC 2.8 ! 

I've seen terrific results with a 300 F/2.8 L non IS and a TC 2... And some photographers use the TC 1.4 and 2 combined with the 300 F/2.8 (2 x1.4 = 2.8 ) with good results.


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## Blaze (Mar 28, 2012)

3kramd5 said:


> Blaze said:
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Hmmm. It seems I'm wrong then. Thanks for the correction.

It still doesn't completely make sense to me though. If it's possible to magnify the image while maintaining the same f-number, then couldn't they make TC's that go in front of the lens without sacrificing aperture? And why even make variable f-number zooms?


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## AmbientLight (Mar 29, 2012)

1) Putting a teleconverter in front of a lens won't really work for two reasons. First you will not be able to attach it to different sized lenses, for example a 300mm f2.8 and a 300mm f4 lens have significantly different front elements. This alone should be a rather obvious reason. The second part is the optical setup. Here I can only point to the article about lens heritage, to throw some light at the reasons. Let us just say that technically this won't work with multiple different lenses either.

2) Zoom lenses with variable aperture are being built, because they are cheaper to make.


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