EOS Rebel T8i shows no focusing aids when using 2x Extender

[wgander]

My Sigma 150-600mm lens works fine with my camera but when I use it with the Canon EF 2x Extender there's no focusing aids on the screen/viewfinder. Is this a limitation of the Extender? Is there a way to see the focusing spots? Manual focusing at 2x is difficult without a tripod. I've been doing mostly wildlife photography.

[wq9nsc]

Your camera AF system is limited to working with a lens setup that provides at least a f8 aperture when wide open.  The 2X extender combined with the Sigma 150-600 results in an minimum aperture that is beyond the AF capabilities of your camera body.

Rodger

[wgander]

Would Canon 1.4 extender work?

[stevet1]

wgander,

While some customers report no problems with autofocus, others mention it doesn't work in AF mode.

From Wiki[edia:

Some EOS bodies are unable to autofocus when the maximum aperture of a lens is smaller than f/5.6. Professional-level bodies are capable of autofocusing lenses with a maximum aperture of f/8, but only with the centre autofocus point.[5] With a 2× extender a 400mm f/4 lens would have an equivalent focal length of 800mm and a maximum aperture of f/8, in which case autofocus would only be available with professional bodies. With the same converter a 400mm f/5.6 lens would have a maximum aperture of f/11 and autofocus would be disabled.

You might want to read this archived article from Canon on using extenders:

https://web.archive.org/web/20190601165556/https://cpn.canon-europe.com/content/education/infobank/l...

Apart from reduced maximum aperture, another potential drawback of using Extenders is loss of autofocus. On most cameras, autofocus stops when the maximum effective aperture drops below f/5.6, irrespective of the amount of light available. However, there are some EOS models that allow autofocusing at maximum apertures down to f/8.

-more-

Steve Thomas

[johnrmoyer]

I suggest trying live view mode.