Sidwalkastronomy Loc: New Jersey Shore

Yes typo

tdozier3 Loc: Northern Illinois

OldSchool-WI Loc: Brandon, Wisconsin 53919

Also Sigma makes a !.4x converter which only loses 1 stop as opposed to the 2x with loses 2stops.

Sidwalkastronomy Loc: New Jersey Shore

With my Tamron 150-600 G2 with the 1.4 X the auto focus at times struggles. I'll have to experiment more with this to see if I can adjust my thinking to get it better

CHG_CANON Loc: the Windy City

Being a variable aperture zoom, running from f/5 to f/6.3, you'll probably find the AF fails at / above a certain focal length as the effective aperture gets smaller and the zoom gets longer. It depends on your DSLR too, and the smallest effective aperture that specific camera needs to retain auto focus.

robertjerl Loc: Corona, California

That is because the 1.4x makes it an f/9.0 and most bodies only AF to f/8 and some less expensive and older ones can't do f/8.0. Which body are you talking about that it struggles?

I tried my Tamron 1.4x on AF and found that with bright sun and lots of contrast/sharp shadows it would try to auto focus and occasionally achieve an "almost" focus. That was with a 5DIV and 7DII(using center point only because that is the only f/8.0 point the camera has)

Oh yeah, the new mirrorless bodies often have f/11 AF.

Sidwalkastronomy Loc: New Jersey Shore

I have Canon 77D and T7i for this lens

Sidwalkastronomy Loc: New Jersey Shore

How did you get to F9. Thought I lost 1 stop

amfoto1 Loc: San Jose, Calif. USA

Which Canon 100-400mm do you have? The original push/pull zoom? Or the "II"?

As an alternative you might consider the Canon EF 1.4X II or III teleconverter. Either of those work well with the original EF 100-400mm and extremely well with the 100-400mm "II".

In fact, I have a hard time seeing any loss of image quality at all using a 1.4X II on the 100-400mm II. You would probably see a little with it on the older push/pull version. A stronger 2X TC would be another matter... causing a lot more loss of image quality, I'm sure, but haven't tried it (also would mean no AF on any Canon DSLR).

The 1.4X on the 100-400mm will get you to 560mm at the long end. The only concern might be if your camera is "f/8 capable"... able to autofocus this combo.

That's pretty close to what you'd get with either of the Sigma 150-600mm lenses, or the Tamron.

https://www.bhphotovideo.com/c/compare/Canon_Extender_EF_1.4X_III_vs_Sigma_150-600mm_f_5-6.3_DG_OS_HSM_Contemporary_Lens_for_Canon_EF_vs_Tamron_SP_150-600mm_f_5-6.3_Di_VC_USD_G2_for_Canon_EF_vs_Sigma_150-600mm_f_5-6.3_DG_OS_HSM_Sports_Lens_for_Canon_EF/BHitems/732113-USA_1082154-REG_1277358-REG_1082152-REG

I don't have any of the 150-600mm lenses. I'm happy with the Canon 100-400mm II. Both with and usually without the 1.4X II. (P.S. To save some more $, might consider buying the 1.4X used... there are almost no moving parts in them, so little to wear out and any damage to the optics as might effect image quality would be obvious.)

I have heard and read that the Sigma "Sport" is the sharpest of the 150-600s, the Tamron "G2" is second and the Sigma "Contemporary" the weakest of the three. However, you can compare image quality and other factors yourself at:
https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=972&Camera=453&Sample=0&FLI=4&API=1&LensComp=978&CameraComp=453&SampleComp=0&FLIComp=5&APIComp=0

You might find Bryan's complete reviews of each of those lenses helpful, too.

robertjerl Loc: Corona, California

At 600mm the Tamron 150-600 G2 is an f6.3 lens. The 1.4x kicks it one full stop so at 600mm it is now an f/9.0.
Since the high end and mid range Canon dslr's AF to f/8.0 that means that they either won't AF at all or they hunt around without ever achieving Focus.

robertjerl Loc: Corona, California

Here is the same people's comparison of the four 150-600's on the market a few years ago. As far as I know there have been no changes in the lenses since then so it should still hold true. I have owned both of the Tamron lenses (and both versions of the Canon 100-400L and used them with the 1.4x III extender. They all produce great results when used properly.