EF lens extender recommendations

[bbbacb]

Hi, novice photographer here. I have a Rebel T7 and a Canon EF 24-70 1:2.8 L USM lens. I'm looking for a compatible extender. Any help would be greatly appreciated.  Thanks

[deebatman316]

None of Canon's Teleconverters are compatible with the EF 24-70mm F/2.8L USM series lenses. I would look into a longer lens instead of using a teleconverter. With the 1.4x teleconverter you loose 1 stop of light. With a 2x teleconverter you lose 2 stops of light. With certain camera body and lens combos AF WILL NOT BE POSSIBLE. Most of Canon's DSLR cameras will NOT AF with an aperture smaller than F/5.6 none of Canon's EF or EF-S lenses have a smaller aperture than that. Some of Canon's DSLR bodies can focus down to F/8. Not all of them can only certain cameras can. The Rebel T7 is NOT one of those cameras. Only the EOS 1D series, EOS 5D Mark III, EOS 5D Mark IV, EOS 5DS, EOS 5DS R, EOS 6D Mark II, EOS 7D Mark II, EOS 77D, EOS 80D, EOS 90D, EOS Rebel T8i, EOS-1V (film camera) & EOS-3 (film camera) can AF at F/8.

[Tintype_18]

Demetrius, thanks for the detailed explanation of the situation.

bbbacb, I have a T7. Look at my list of lenses on my signature. Some are not noted for their quality but serve my purpose. And, welcome!

[ebiggs1]

I have not tried it but any of the after market tel-cons should work on your lens and T7 as long especially if you stick with the 1.4x. You will lose one stop but that is f4. The 2x again you will lose 2 stops but that is still inside specs at f5.6 for a T7.  Neither will be good or even pleasant to work with and I don't recommend it. I am not a tel-con fan at all very much preferring native FL.

You have one of the best zoom lenses made in the Canon EF 24-70 1:2.8 L USM lens. It makes no sense to me to put a gadget on it that takes it down.

[johnrmoyer]

I have an EOS 80D instead of a T7. I am just guessing this might work with your camera and lens. I have experimented.

The 2X extender will double F Number, decrease contrast, increase magnification, and add diffraction blur. I find that in the center of the lens on a crop sensor it is good enough if the resulting image can be downscaled and sharpened.

Your camera appears to me to be able to do phase detect auto focus in live view mode as does mine, but since you have a lens capable of F 2.8, you could autofocus wide open using the viewfinder with a 2X extender. My camera will autofocus at F/11 in live view mode in bright sunlight if there is plenty of contrast. At F/16, luck is needed in addition to bright sunlight.

I have a Kenko Teleplus HD C-AF 2X DGX teleconverter.

Two example photos, first autofocus and second manual focus:

An example: https://www.rsok.com/~jrm/2017Sep28_birds_and_cats/2017sep18_robin_IMG_6515c.html

First example is Canon EF-S 55-250mm f/4-5.6 IS plus Kenko Teleplus HD C-AF 2X DGX teleconverter.

enko Teleplus HD C-AF 2X DGX teleconverter was attached. This photo was made hand held through a window from inside the house. F/11 is wide open for this combination of lens and teleconverter. The F6.3 listed is incorrect and two stops should be added. Auto focus was used. The combination of lens and telephoto converter confused the metering with a resulting very high ISO.

Second example is Canon EF70-300mm f/4-5.6 IS II USM plus Kenko Teleplus HD C-AF 2X DGX. https://www.rsok.com/~jrm/2017Feb07_birds_and_cats/2017feb01_cardinal_IMG_0929.html

exif at https://www.rsok.com/~jrm/2017Feb07_birds_and_cats/2017feb01_cardinal_IMG_0929.html

[ebiggs1]

Thanx for clearing that up. I was pretty sure it would work even if others claim it would not. Why some one would, is another question. I am certain none of the Canon brand extenders will even mount on a ef 24-70mm zoom. Personally I would never do it.

[johnrmoyer]

Re: "Why some one would"

• It is fun to experiment
• A third party extender costs less than a long lens
• A third party extender weighs less than a long lens
• When one cannot get closer, an extender increases magnification at a cost of less contrast and more diffraction blur

A recent example of could not get closer: https://www.rsok.com/~jrm/2023Sep06_SaltPlainsNWR/2023sep06_birds_IMG_6195c.html 

F Number	18.0
ISO	200
Shutter Speed Value	1/256
Focal Length	1120.0 mm
Focus Distance Upper	555.79 m
Focus Distance Lower	81.91 m
Lens Model	EF100-400mm f/4.5-5.6L IS II USM +1.4x III
Lens Model	Kenko TELEPLUS HD C-AF 2X DGX

Photo was made with stacked teleconverters. Public is not allowed to get closer. Focus distance is as reported by camera and includes some assumptions of print size and viewing distance. It is easier for me to identify small birds far away with more pixels per bird. Stopping down overcomes some of the disadvantages of stacked extenders, but adds diffraction blur. Canon DLO DPP can remove some diffraction blur if the focal length is reported correctly and the main lens is a Canon. The Canon 1.4x extender does not degrade the image at all if stopped down by 1/3 stop.

Least Sandpiper, Western Sandpiper, American Avocet, and Killdeer at Salt Plains National Wildlife Refuge in Oklahoma, United States on September 6, 2023

[johnrmoyer]

crop from same image made with stacked extenders zoomed to 100% shows some of the imperfections:

In contrast here is one made with the Canon EF100-400mm f/4.5-5.6L IS II USM +2x III and cropped:

Least Sandpiper and Western Sandpiper at Salt Plains National Wildlife Refuge in Oklahoma, United States on September 6, 2023

[deebatman316]

Why would you want to put a low quality teleconverter on a a pro grade lens. You are not only crippling the lens. But you're crippling the camera's AF system. The AF system will definitely take a hit. Not to mention a decrease in the image sensor's performance. 

[johnrmoyer]

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@deebatman316 wrote:

Why would you want to put a low quality teleconverter on a a pro grade lens. You are not only crippling the lens. But you're crippling the camera's AF system. The AF system will definitely take a hit. Not to mention a decrease in the image sensor's performance. 

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Why:

Tradeoffs.

I bought 3rd party teleconverters before I owned any L lenses and Canon teleconverters could not be used on EF-S lenses.

I cannot always get closer and I use the equipment I own.

The lens is not crippled. I get more pixels per bird at a cost of less contrast and more diffraction blur. The diffraction blur is less than that from the long distance over water and smoky haze.

The AF is slower with stacked teleconverters but still might be faster than manual focus.

The lens is not crippled, because the center of the lens is the best part.

The sensor is not changed, only the light arriving at the sensor is changed.