BebuLamar

I thought the ones that hold on to OLD and outdated thinking are people like me who use Nikon.

ronichas Loc: Long Island

I have the Sony 70-200 F4 and also the 28-105 F4. Also have the the Sony 100-400 is F4.5-5.6. All great lenses I use with the Sony A9 and the Sony A7111. I went to Africa and got great results. The Sigma 15-600 is f5-6.3. Better lens, less weight and super sharp.

Nalu Loc: Southern Arizona

Whether or not a 300mm f/2.8 is considered the "best" lens is of coarse a matter of opinion and obviously it depends on the photographer's application. And whether or not Sony vs Canon versions of the the 400mm f/2.8 or 600mm f/4 are better than the other optically is somewhat of a non-starter. I am sure they are very comparable. But neither of these lenses are worth a poop if the sensor does not record a sharp image. I think it is pretty clear the AF system of the Sony alpha cameras is the best out there and more specifically the A9 and a9II. I don't know how the latest version of the 1DX compares. For me, the Sony a9 beat the crap out of the Canon bodies I was using (1DX and 5DIV). After doing so, I would venture to say the all of the Gmaster lenses I have are on par or better than the Canon equivalents.

But, let me add one more thing. For birds, especially small song birds, I am having tremendous success with the Sony 600/f4 and 400mm f/2.8 with a 2x converter attached. So I am at 1200 and 800 respectively with IMO excellent image quality. I did not have as much luck using a 2XIII on my Canon lenses. Some acceptable results, but not like the Sony lenses on either the a9 or A7RIV bodies.

So, if Sony comes out with the "best" 300mm f/2.8 will I buy one. Nope, not long enough.

wmurnahan Loc: Bloomington IN

my understanding is they even make their own glass to make the lenses. Minolta was a very quality lens maker and then you add Zeiss, one of two premier German lens manufactures/designers.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

And because you say Canon is newer (which is wrong), that it means it is better? Is that what your saying? Again, it matters NOT when their introduced, Sony technology, center weighted lens system, XD Linear Motors (these are so many light years ahead of Canon it's laughable), THREE, count them, three Flourite Lenses located in the middle of the lens body giving it an extreme balance for HAND HOLDING ( again, light years ahead of Canon which is FRONT LENS HEAVY by the way in case you did not know), one extreme aspherical lens and 2 ED lenses located at the back of the lens. On Sony only the front element is out front, that is why it is so well balanced. The Canon is NOT as easy to hand hold as the Sony.
I hate to point this out, but you brought it up, the Canon EF 600mm f/4L IS III USM Lens was introduced in a press release on SEPT. 5, 2018 and the Sony 600 f4 was introduced JUNE 11, 2019.
So it appears Architect1776 your are WRONG AGAIN.
Want to try for a trifecta.

joer Loc: Colorado/Illinois

Having the 600 f4 and 400 2.8 is a good reason for not wanting a 300mm. I won't justify the expense and weight of these lenses so I make due with the 100-400GM and 70-200G lenses and supplement them with the A7R4 which puts me near the same range as you by cropping and at better cost. In APS-C there is 26mp room to spare when cropping further.

What I lack is a large wide open aperture which is vital in many lighting situations. The 300 f2.8 would put me at my max weight limit. I will buy it if priced right. A Fresnel equivalent sacrificing one stop is also a viable option. I suspect both versions would play well with a TC1.4X.

I had been shooting song birds for a very long time using Nikon combinations, including the D500, D850, and early on two Canon kits. In my experience Sony gives me far more keepers, and is easier on my old bones.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Don't disagree with the Sony's ability to focus, especially the new Tracking Expand Flexible Spot focusing system.
BUT, hold on, I shoot with the D500 and D850, they both have the dual focusing software found in the Nikon D5 and in Canon models.
And for my money the Nikon GROUP AUTO FOCUS system is not a lock on tracing system like on my Sony a9, but as long as one of the four showing dots on the GROUP AUTO FOCUS system is on the bird, it's in focus.
I have previously shown an example of the focusing system on the a9, so below is an example of the GROUP AUTO FOCUS system on the Nikon. I find my keep rate almost identical in both the Sony and Nikon camera's. Which approach 99%.
Great Blue Egret flying right at me (hardest for automatic focusing systems) Nikon D500, Nikon 200-500 5.6 lens at 390 mm, 1/3200 sec. at f10, ISO 1600.

rehess Loc: South Bend, Indiana, USA

Thinking in terms of f/2, f/2.8, f/4 lenses is so 20th Century thinking.

This is a very good image, taken using 21st Century thinking - a zoom lens, at a narrower aperture which requires higher ISO. Your Nikon system certainly nailed this one.

Is that nesting material in his beak?

DennisC. Loc: Antelope, CA

The Sony 600 f4 is newer and has tested out to be the lightest, fastest focusing and as good or better image quality than the Canon or Nikons. It’s also the most expensive.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Yes, that is nesting material in his beak. Nesting birds tend to bring greens towards the end of nest building.
Theories include but are not limited to the following.
1. Greens are used as a natural order eating material for chick deposits.
2. Greens are used to soften the bottom of the nest for the delicate chicks to come.
3. Greens act as a air conditioning system to cool the nest during the day and retaining heat for the evening.
4. Greens are used by chicks as an addition to fresh meat they get from parents and used in digestion.
5. Personally I do not know what the true purpose is, but, it makes interesting images.

Toment Loc: FL, IL

Newer older lighter heavier
I forgot the question🤔

Pixtaker

Nalu Loc: Southern Arizona

Please note; I am using an a7Riv with these two lenses. So, with the 600mm plus 2x I am well in excess of 1200mm and still with a lot of pixels to work with. I would not attempt the crop mode with the a9 because of the smaller sensor.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

I would really like to see an image from the a7rIV with the 600 and the attached 2X.
I have seen many complaints about the buffer on the camera, do you find it works well for shooting 10 fps.

CHG_CANON Loc: the Windy City

Older and wiser voices can help you find the right camera brand, especially when you are willing to listen to those who shoot Canon.