Tele extenders

[FredSchall]

I would like to purchase a Canon tele extender. Do I want a 1.4x or 2x and do I want series II or series III. Advantages, disadvantages? Thoughts? No big deal on series? Thanks 

[jrhoffman75]

What lenses do you have?

The Mark III versions are optimized for the latest versions of the super-teles.

Discussion about 1.4X III: Canon EF 1.4x III Extender Review (the-digital-picture.com)

Discussion about 2.0X III: Canon EF 2x III Extender Review (the-digital-picture.com)

[Waddizzle]

What camera body are you looking use with the teleconverters?  The teleconverters are not compatible with any lens.  Check your camera’s User Guide for “lens groups”.  The 90D has a “Supplementary Information” User Guide that contains the “lens groups” info.

[FredSchall]

100-400 ef usm II. It will work. Thanks.

[Waddizzle]

I guess this means that you’re using a 90D.

Okay, the 90D Lens Groups schedules suggest that an EF 1.4x III “will work” with the EF 100-400mm f/4,5-5,6L IS II USM.  But, how well it “will work” actually work?  Let’s look at what we know will happen.

You will lose a full stop of light on exposure because the effective maximum aperture is reduced by a full stop.  Your total number of available AF points will be reduced to 27, because the reduced maximum aperture reduces the amount of light reaching the AF sensor.

A reduced amount of light reaching the AF sensor almost always means reduced AF speed as a result.  In the case of the 90D, I would only use the center AF point with the 1.4x teleconverter.  

I feel this is why using a TC reduces image quality.  It isn’t the extra glass as much as it is probably the compromises imposed on the AF system.  Some of this can be overcome by exceptions written into the camera firmware, but I doubt if this is the case for a 90D.

[ebiggs1]

Before you decide on which to get you need to know if it can even be used with your lenses. IMHO, never buy a 2x tel-con but I don't like and use any tel-con. There is always a great debate as to whether it is better to use a converter or simply crop more in post. You may find you are just as well off in post and save yourself some money.

[ebiggs1]

Addendum.

The downside is you lose IQ. You lose a stop or two depending on which converter you select. Your AF speed will slow and you may lose AF altogether or have just one AF point.

There are two lenses that do work well with a 1.4x tel-con. Never the 2x however. The ef 70-200mm f2.8L and the ef 300mm f4l IS. The nice thing about the 300mil is it has the IQ to give up, but it becomes a 4200mm f5.6 lens with IS. Canon's fantastic and unique ef 400mm f5.6L does not have IS. So the converted 300mil is a good give and take.

The ef 70-200mm f2.8L just works all way around with a 1.4x.

[FredSchall]

How about the 1.4 on a 100-400 ef usm II. ??

[jrhoffman75]

It will depend on your end use. 
I have a 1D X Mark III and I print 13x19 as my largest output. 
I ran an informal test with the 100-400 Mk II lens with the 1.4X III compared to cropping to equivalent framing in Lightroom. 
I used a lens test image to be more challenging compared to a random shoot image. 
i could see no difference between the two images. 
Try cropping some of your images and see how they stand up. 

[FredSchall]

Thanks. 100-400 ef usm II.