TCs and compatibility—Theory

[Shakespeare]

I've read the sticky, but the reasoning behind many of the caveats made me wonder just why things are happening.

Why—is it compatible only with select L lenses? What’s Canon’s reasoning behind it?
How—is it made incompatible with other Canon lenses…is it mechanical or electrical?
What—happens if I try to stick the 50mm 1.8 on it?
Why—does it have such a problem with the 100-400?
Why—does the 2X cost the same amount as the 1.4X? Is this a case of admitting that the 2X isn’t as good a product even though it’s more powerful?

[CoolToolGuy]

I've read the sticky, but the reasoning behind many of the caveats made me wonder just why things are happening.

Why—is it compatible only with select L lenses? What’s Canon’s reasoning behind it?
How—is it made incompatible with other Canon lenses…is it mechanical or electrical?
What—happens if I try to stick the 50mm 1.8 on it?
Why—does it have such a problem with the 100-400?
Why—does the 2X cost the same amount as the 1.4X? Is this a case of admitting that the 2X isn’t as good a product even though it’s more powerful?

Why-They are only compatible with the lenses that will fit onto them.
How-the front element of the TC extends into the lens.
What-Good luck, without glue it won't happen.
Why-I don't know
Why-not sure, but they are pretty much the same, just a little more magnification on the 2x

Best I can answer them.

Have Fun,

[RichardtheSane]

I've read the sticky, but the reasoning behind many of the caveats made me wonder just why things are happening.

Why—is it compatible only with select L lenses? What’s Canon’s reasoning behind it?
How—is it made incompatible with other Canon lenses…is it mechanical or electrical?
What—happens if I try to stick the 50mm 1.8 on it?
Why—does it have such a problem with the 100-400?
Why—does the 2X cost the same amount as the 1.4X? Is this a case of admitting that the 2X isn’t as good a product even though it’s more powerful?

Why - what Rick said
How - what Rick said
What - what Rick said, but to add blutac may help too
Why - Only problem I know of with the 100-400 is that it won't AF when a TC is used on any SLR other than a 1 series. This is because of limitations in the camera AF system which are directly related to the light loss associated with TC use.
Why - well the 2x does degrade image quality a lot more than the 1.4x. THey are both a tool at the same level, and can only do one thing, so they are both priced as a tool capable of doing just one thing.

[robertwgross]

I'll throw in two pence worth:

Canon isn't stupid. Most of their product strategies are fairly well planned.

Canon knows that if you take a wide lens and try to put one of their teleconverters on it, the combination probably will not get good results. Similarly, if you take a mushy consumer lens and try to put a teleconverter on it. So, Canon makes this into a strategy of moving you toward the better lenses for teleconverter compatibility.

By the same token, if you have a mushy lens, you can put a mushy non-Canon teleconverter on it, but Canon won't make any claims about a quality image this way.

---Bob Gross---

[CyberDyneSystems]

To expand on Bob's points.

the Canon T-cons and the lenses on which they fit are designed to work together.

It is no accident that they work,. it is built into them. Not just the T-con,. but the lens from ground up is designed to function wiht the T-con.

Only the optics that Canon knows will function well optically with a T-con has the time and energy put into development and design to make it so...

Thus,. the other lenses won't work,. both physically,. (no they simply won't fit) and optically.. (in this case because they simply can't,. optics, physics,. etc.. prevents them from working together to a satisfactory level of quality)

Asking why not is similar to asking why your 1986 Honda Civic crcc can not haul a 45 foot trailer. :lol: Or more similar,. why your .45 1911 can not chamber a .45 Winchester Magnum cartridge.

[RJSorensen]

Freedom Arms down the road has a conversion for that round . . .

[condyk]

:lol: Or more similar,. why your .45 1911 can not chamber a .45 Winchester Magnum cartridge.

A metaphor that could only originate in the US of A
:rolleyes: :rolleyes: but I get the point, which is well made!

Useful mto know this stuff ... about the T-Con's I mean.

[Tom W]

I've read the sticky, but the reasoning behind many of the caveats made me wonder just why things are happening.

Why—is it compatible only with select L lenses? What’s Canon’s reasoning behind it?
A few reasons - since teleconverters do take a little off the image, you will want the best quality image to start with. Second, there's much to be gained by putting a TC on a 200mm + lens, given that the 500 mm lenses are quite expensive. That is where the L-glass is.
How—is it made incompatible with other Canon lenses…is it mechanical or electrical?
Mechanical - but primarily for optical reasons. The front element of the teleconverter protrudes into the rear of the lens. This cavity isn't present on shorter focal lengths because of the way wider lenses are designed. Canon could compromise and make an optical compromise on the teleconverter to allow use on the shorter lenses, but this isn't really necessary when the same effect can be had with a relatively inexpensive lens. For example, you can take your 50 mm to 85 mm by buying the 85 f/1.8 lens and retain the aperture and image quality.
What—happens if I try to stick the 50mm 1.8 on it?
It won't fit.
Why—does it have such a problem with the 100-400?
If your not using a 1-series camera, then you're asking more of the autofocus system than it was designed to deliver. F/5.6 is the smallest maximum aperture that can be used with non-1 series cameras. Sigma cheats with their 500 f/6.3 which reports f/5.6 to the camera to allow AF to work. This is only 1/3 stops slower than f/5.6 so autofocus degradation isn't very significant. However, the 100-400 with 1.4X converter has a max aperture of f/8, which doesn't allow as much light into the camera. While you can tape certain pins and "fool" the camera into thinking that it has an f/5.6 or faster lens, the actual autofocus system is being taxed with this setup and has more difficulty operating.

On a 1-series, the AF system is more sensitive and can be used with f/8 lens and lens/converter combinations. With that combination, I have not had AF problems on my 1D Mk II.
Why—does the 2X cost the same amount as the 1.4X? Is this a case of admitting that the 2X isn’t as good a product even though it’s more powerful?
Supply and demand - The 2X isn't as highly demanded as the 1.4X for a couple of reasons. One, it is not optically as good as the 1.4X - that is the nature of teleconverters. Second, you lose 2 stops with the 2X instead of 1 as you do with the 1.4X, which limits the number of lenses that you can use it with.

[MarkH]

If your not using a 1-series camera, then you're asking more of the autofocus system than it was designed to deliver. F/5.6 is the smallest maximum aperture that can be used with non-1 series cameras. Sigma cheats with their 500 f/6.3 which reports f/5.6 to the camera to allow AF to work. This is only 1/3 stops slower than f/5.6 so autofocus degradation isn't very significant. However, the 100-400 with 1.4X converter has a max aperture of f/8, which doesn't allow as much light into the camera. While you can tape certain pins and "fool" the camera into thinking that it has an f/5.6 or faster lens, the actual autofocus system is being taxed with this setup and has more difficulty operating.

On a 1-series, the AF system is more sensitive and can be used with f/8 lens and lens/converter combinations. With that combination, I have not had AF problems on my 1D Mk II.

Of course the 100-400 with a 2x TC is even more of a problem, giving an aperture of f11, even a 1 series body will have trouble with AF at f11. Mind you, at f11 you could manually focus, you should have a reasonable depth of field to give you some margin for error.

[Tom W]

Of course the 100-400 with a 2x TC is even more of a problem, giving an aperture of f11, even a 1 series body will have trouble with AF at f11. Mind you, at f11 you could manually focus, you should have a reasonable depth of field to give you some margin for error.

It won't just give trouble - it won't work. Unless you tape the appropriate contacts on the lens to "fool" the camera. Then you'll likely just have to put up with hunting and such, with frequent failure to lock onto the appropriate (or any) subject.

I haven't tried that combination, and probably won't unless I use manual focus. I'm not going to tape contacts. Tried it once on my 10D with the 100-400 and 1.4X TC and had some serious focus problems. So erratic that I feared damaging the lens - it oscillated rapidly back and forth around the correct focus spot.

[mbze430]

the 2x isn't so bad. At least on the 180mm Macro. Personally I think it produce useable pictures.

http://mysite.verizon.net/turbo2/album/Nature/Animals%20&%20Insects/slides/Seagull01.html

[Tom W]

I've been known to stack the 1.4X and 2X on a 300 mm f/4 lens myself. You're right, the 2X is good. The 1.4X is better, and no converter is best. But 600 mm lenses aren't cheap.