Canon L lens / teleconverter AF question.

TylerW

First post, btw, but anyhow, thanks for the forum. This looks really good.

Anyhow, I'm really looking into the Canon 70-200 f/4 L lens, and a 1.4x teleconverter to extend the reach. I'm trying to decypher what it means that with the teleconverter, it only is able to autofocus the F/4 L lens if the camera is capable of a maximum aperture of f/5.6, which is the widest aperture I'd e able to achive with this combination of lens and converter.

What does this all mean? Will AF be possible with this combination? Will it still be available to me if I stop down to f/8? Am I better off just shooting with the sigma 50-500 and forgetting all this white plastic canon nonsense?

Oh yea, I'm shooting on a 10d, if that makes any sort of difference.

Thanks in advance for responses!

wxwax

When you add the 1.4 extender to your 70-200 f4, it removes a stop from the lens' maximum aperature.

Without the extender, your maximum aperature is f4. Once you add the extender, your maximum aperature will f5.6

Your autofocus will work fine. But remember, losing a stop means less light is getting into the camera. And all autofocuses work better with more light. By removing some of the incoming light, you will notice that your autofocus is slower in not-so-bright lighting conditions.

Welcome to dgrin, glad you're posting!

Steve Cavigliano

Welcome to DGrin Tyler

Sid's explanation is spot on. You do lose a stop with a 1.4X and 2 stops with a 2X TC. Since you don't see it in a loss of shutter speed, we say that you are losing a stop of aperture. While you do lose a stop of light (1/2 the amount of light as without the TC attached), the opening at the rear of the lens does not change. So your depth of field will be similar to what you'd see without the TC attached. IOW, if you attach a TC that doesn't report aperture, like the cheap Tamron, and have your lens wide open. Your camera will show F4.0 aperture. Actually the amount of light coming into the sensor is akin to F5.6, but your DOF will be the same as if you were shooting F4.

Make sense?

It doesn't to me either...lol But, it's twue, it's twue

Steve

Artur C.

Great explanations
Keep in mind, that with a f4 constant aparature, your max with the 1.4x will be f5.6 which will allow the autofocus to work fine, this becomes a problem when you are using a variable aparature lens such as the Canon 100-400 f4-5.6L. When you reach a focal length (zoom) where the aparature becomes anything above f4 with the TC extended you will loose autofocus capability. Depending on your shooting needs this may or may not be an issue.

-Art
http://www.north-scapes.com

TylerW

Artur C. wrote:

Keep in mind, that with a f4 constant aparature, your max with the 1.4x will be f5.6 which will allow the autofocus to work fine, this becomes a problem when you are using a variable aparature lens such as the Canon 100-400 f4-5.6L. When you reach a focal length (zoom) where the aparature becomes anything above f4 with the TC extended you will loose autofocus capability. Depending on your shooting needs this may or may not be an issue.

-Art
http://www.north-scapes.com

Ok, this has probably answered the most questions - so basically, if I'm using a zoom lens that at full zoom has a max aperture of f/6.3, then I'd lose AF capability with a teleconverter. But, at the other end of the lens, where it can open to say f/4, I can set my aperture on the camera to whatever I like, and AF will work just dandy. Right?

pathfinder

Yup!


Any aperture smaller than f4 on the main lens, ( eg f55.6, f8 , f11 yada yada) coupled with a 1.4 TC will be one full fstop less light gathering ability, thus f4 + 1.4TC = f5.6 which will AF on a 10D.

f5.6 + 1.4 TC = f8 which will not AF on a 10D ( at least without taping electrical contacts on the back of the lens )

f8+1.4 TC = f11 - no can AF, even with a 1DMkll.

As Ian said, 2X TC cost two whole fstops of light, which means for all intents and purposes, your main lens needs to be f2.8 to retain effective AF. ( I do know that a 1DMkll will AF at f8 centrally, but it is not a picnic doing it) For a 10D, less than f5.6 won't fly - and the viewfinder begins to get real dark also.

System

this canon site

http://www.usa.canon.com/consumer/controller?act=ModelDetailAct&fcategoryid=154&modelid=7462

lists the lens that will work with their ef 1.4x II extender- maybe other lens will work but not af?-

and the ef 70-200mm f2.8L IS is my favorite lens, and some day I would love to try an extender on it with the 20d--effectively 450mm range (is that right, somebody?, anybody?)-

george

TylerW

gefillmore wrote:

this canon site

http://www.usa.canon.com/consumer/controller?act=ModelDetailAct&fcategoryid=154&modelid=7462

lists the lens that will work with their ef 1.4x II extender- maybe other lens will work but not af?-

and the ef 70-200mm f2.8L IS is my favorite lens, and some day I would love to try an extender on it with the 20d--effectively 450mm range (is that right, somebody?, anybody?)-

george

That range sounds about right.

I'd like to move up to the f/2.8L eventually, but I'm getting into a lot of this quickly, so I really can't justify doubling the cost to go down two more stops of aperture. Seeing as most of my interest in this lens is for race photography means I'll be shooting under a lot of bright sunlight, so the f/4, with a converter and a polarizer I should still have plenty of light.

Pezpix

One other advantage to the 1.4 extender is that combined with the 70-200 f/4 glass is that youcan get nearly the same reach as the 70-300 DO IS USM glass for about half the price.

Just a sidenote to the 70-200 f4 non-IS as its filter threads is 67mm as opposed to the 70-200 f/2.8 which is 77mm. (Just in case you put some expensive filtration in front)

I just bought the 70-200 f/2.8 recently and need to sell my 70-200 f4 lens btw, send me a PM if you are interested Tyler

TylerW

PM sent!

STLMach1

To a newbie like myself, I can't tell everyone how helpful threads like this are. Reading this has help immensely.

Thanks for all the great input on this!
Michael

Chase

STLMach1 wrote:

To a newbie like myself, I can't tell everyone how helpful threads like this are. Reading this has help immensely.

Thanks for all the great input on this!
Michael

Another option to consider, especially if you plan on using the TC a lot is the sigma 100-300 f4. It will get you at the 300mm without a TC and w/ a TC to 420mm. PLus it has amazing image quality.