1 ACCEPTED SOLUTION
@mithun_pal129 wrote:Thank you all for your valuable comments. I forgot to mention that my intension of extender to make my EF 70-200mm L F4 USM to a telephoto lens for wild life / birds. But now as I am staying in Abu Dhabi, there is not much scope of bird / wild life. Hence I don't want to spend much on super telephoto lens and personally I don't want to go for cheap Sigma lens. So I wanted to make 70-200mm lens + 2x extender as 140-400mm. As I got impression 1.4X extender is pretty good but it will give me upto 280mm. I know it is not very good focal length for bird / wild lift photography. But want to know still is workable or if I use 2x extender to make the lens 400mm the auto focus is required for wild life or manual focus can still work at F8. I don't have much experience in wild life photography that is why I wanted to know the things.
In a nutshell... No.
Putting a 2X teleconverter onto a 70-200/4 makes for an "effective" 140-400/8 lens. Due to the reduction in light reaching the AF sensors, your camera will turn off auto focus. A stronger 2X also will "cost" more loss of image quality due to degradation.
It is possible to tape over some of the electronic contacts on the teleconverter, so that the camera doesn't know it's there and will still try to auto focus. However, auto focus will be much slower and will tend to hunt a lot more.
In some situations you might be able to focus manually. However, effective f8 makes for a pretty dim viewfinder, plus modern auto focus cameras like yours do not have some fo the features to assist manual focus, that vintage cameras designed for manual focusing had in the past. Some people change out to a third party focusing screen to add manual focus assist features (split image finder, micro diaprisms, for example). However this requires some careful work to install the focus screen and the different focus screen can effect the camera's metering accuracy, especially making Spot Metering inaccurate.
Adding a weaker 1.4X teleconverter makes your lens into an effecive 112-280mm f5.6, which will still autofocus and will have considerably less loss of image quality, though not as much "reach". If yours is an IS lens, it might be reasonably handholdable. If it's not an IS lens, you will need to watch your shutter speeds more carefully, probably will want to keep to 1/500 or faster to prevent camera shake blur. Or use a tripod, as ebibgs suggests, or at least a monopod. You also will need to limit your camera's autofocus to the center AF point only, I believe.
@ebiggs1 wrote:
On your camera the 70-200mm f4 acts like a 112-320mm f4. With a 1.4x converter you are looking at 448mm on th elong end and f5.6. 400+mm should be long enough for you to get some bird shots. BTW, use a tripod.
While it is technically correct, citing the "crop camera lens factor" this way may not help very much, might be confusing.
The original poster simply has a 70-200mm lens that they are accustomed to using on a crop sensor camera. Now they would like to double the reach of that lens on their camera. Bringing crop sensor lens factor into the conversation is most useful when the user is going from film/full frame to crop camera or vice versa. To someone who has never used a film camera or hasn't used one in many years and is now completely accustomed to how a lens focal length performs on their crop camera, it is a completly moot point.
But what it comes down to is that while you can add a 2X, it's probably not a good idea for several reasons. Auto focus won't work or, with some tricks, will work only poorly. Manual focus will be difficult. And the image quality might take too big a hit, pairing up a 2X with your lens. .
I have 70-200/4 IS, 70-200/2.8 IS ("Mark I"), 1.4X II and 2X II teleconverters. I also have longer telephoto lenses, so rarely have need to add teleconverter to these zooms. However if needed I would use 1.4X on either of them. But even though AF still works on the 70-200/2.8 + 2X combo, I won't use it due to the amount of image quality loss (the newer 70-200/2.8 IS Mark II and 2X Mark III are said to work better together, than my older versions of each).
I mostly only use the 2X on 300/2.8 and 500/4 prime lenses, where image quality is still good. (Note: yes, on some of my cameras the 2X on 500/4 causes AF to stop working, just as it would on your f4 lens, so I only use the combo in a limited way.)
mithun_pal129... At most I'd suggest you get a 1.4X and use that with your lens. See if the image quality is up to your expectations. Then work to get closer to your subjects. Or get them to come closer to you. Practice stalking techniques and study your subjects' behaviours to discover ways to get closer. Work from a blind and use attractants (food, calls). And start saving up for a longer focal length lens.
The Canon 1.4X II and III teleconverters are excellent. All Canon teleconverters have protruding front elements which limit the lenses they can physically be attached to, but the 70-200s are among those where it's possible. Kenko teleconverters are another that I see recommended quite often. They have two different quality levels: A more expensive "Pro 300" version and a less expensive "MC-4". These currently are offered in "DGX" versions that function very much like Canon teleconverters. Older Kenko "DG" teleconverters did not "report" to the camera, the camera didn't know they were there, so would try to focus. From the reviews and tests I've seen, the current Kenko DGX Pro 300 is quite good across the whole image area. The cheaper MC-4 is actually slightly sharper at the center, but not as sharp in the corners and at the edges of the image. Tamron and Sigma also make teleconverters, but I have little experience or knowledge of current versions of those.
Wildlife/bird photography isn't easy. No matter how long a lens you have, there will be times when the subjects are just out of reach and all you can go is sit back and enjoy the show.
These photos of small subjects were shot with various lenses, but close to or less than the same effective focal length as your 70-200mm + a 1.4X teleconverter would be on your camera...
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
"I got a complete view of the advantages and disadvantages of the extender."
There is no advantage. 
