Full frame vs APSC for wildlife

[Scooter]

I was in Botswana early this year (in the rainy season), and took 2 bodies with me. This particular cloudy morning, I had the A7R3 with the Tamron 70-180 f2.8, and I had my A6400 with the 70-350 (comparable focal length of 105-525 f 4.5-6.3). At first, I couldn't figure out the auto focus on the new R3 - I'm so used to nailing everything with the tracking on the 6400. But I pushed on, and used both cameras for lots of sightings, knowing that I had a security shot with the 6400, and trying to learn the R3 in the field. I think both have a very detailed image, but I think I am inclined toward the f/f just based on the background, as the subject for both seems sharp. Can anyone with a better "eye" for differences in optical quality, point out anything I am missing? (and yes, the composition is terrible on the 6400 shot, as we'd moved the truck, and I was definitely in too tight).

• ILCE-7RM3A
• E 70-180mm F2.8 A056
• 180.0 mm
• ƒ/2.8
• 1/500 sec
• ISO 1000

• ILCE-6400
• E 70-350mm F4.5-6.3 G OSS
• 218.0 mm
• ƒ/6.3
• 1/640 sec
• ISO 3200

 

[iamdlewis]

but I think I am inclined toward the f/f just based on the background

That is the difference between f2.8 and about and f10. In theory the R3 can produce a better image but that really isn't going to be that noticeable until you get closer to a 1:1 image size. If you can't tell the difference between them then don't worry about just use the camera/lens combo that gets you the shot.
If you want to try and figure out which one is sharper use the Tamron 70-180 f2.8 on both bodies and take the same photo with the R3 at f4.5 and 105mm and the A6400 at f2.8 and 70mm.

What is more important though is that you enjoy the outings.