Just got a 5DIV: keep the 80D for extra reach, or go fully full-frame? (1 Viewer)

Hello! I just got a Canon 5D Mark IV and I think I'm in love. What I'm wondering is whether to keep my trusty 80D, for the sake of the extra reach it gives me with long lenses. I assumed all along this was what I would do when I finally got a full-frame camera, but I'm now having second thoughts, and I'm wondering what others' experiences have been.

I'm currently using a Sigma 100-400mm f5-6.3 lens. I love it, but it is a little slower than the Canon 100-400 (which is f4.5-5.6). This tends to mean I end up shooting at higher ISO (since I don't really want to reduce the shutter speed). So here's the first tradeoff: the 5DIV (as one should expect) produces MUCH cleaner images at higher ISO. So while I'm getting a 600mm equivalent focal length with the 80D, and thus a tighter shot and a bigger bird in the frame, I'm getting a significantly cleaner image from the 5DIV. So far, I find I'm preferring the cleaner 5DIV image, cropped in a bit, to the somewhat noisier image from the 80D.

There's also the much more sophisticated autofocus options on the 5DIV.

I love my 80D -- it's been a great camera for me for quite some time, but now that I've been spoiled by the more advanced capabilities of the 5DIV, I'm noticing its limitations more than I did before.

I should add that I do have the Sigma 1.4x teleconverter. I've tested it in good light and found it works well, with maybe a little bit of lost sharpness. In the field, though, losing an extra stop with what is already a pretty slow lens is a killer.

I've read a lot of advice that says keep the APS-C camera for extra reach, and again, that was always my plan. But now, I just don't know. I'm half inclined to say goodbye to the 80D and trade it in towards some new glass, but then I think about the amazing reach I'll have when I get that Sigma 150-600mm Sport lens next month...

I'd love to hear from others who have tackled these questions!

I've been using a 7Dii with my Sigma 150-600 Sport since I bought the lens in 2015.

In January 2019 I bought a 5D iv and I love it, but when I'm out with the big lens it's still the 7Dii that gets the work. I sometimes use the 5D with the big lens, but only when the situation warrants it. For small birds the extra reach of the crop body wins every time, except at very close range, even with the slightly lower image quality.

The 5div @ 30MP vs the 80d @ 24MP is a tough call. The 5div cropped to the same 1.6x as the 80d is only 11MP. If you would not be cropping down much more than that, I'd say the 5div cleaner images might be pretty good, especially for web or 4x6 or 8x10 enlargements. If you wanted to make big prints or crop tighter than 1.6x, the 5div will run out of gas pretty quickly after that. I find 10MP is a good minimum size, though one could go smaller especially for web / mobile.

A 1.4x TC on an f/6.3 lens is going to be tough to get good results from. At f/9, the AF system is only going to work in the center and be pretty slow. The 5div might get some ok shots with it, but I would only use it in an emergency.

Maybe sell the 80d and get the Sigma 150-600 or Tammy 150-600 g2? Those are both pretty nice mid-level lenses. I used the tammy 150-600 g2 on my nikon d850 for a long time before switching to the nikon 500/5.6.

Marc