Optical versus digital crop - I'll be damned ...

Hi all,
Last week I gave you the story of the "second life" 400mm F/2.8 MKI.
Today the weather was fine so I went to our Nature Reservation Area "Bourgoyen" near Ghent-Belgium. Subject being the Bird Watching Cabin.
This time I was challenged to test the difference between a 1200mm APS-C (600d) setup (+ 400m + x2III) and a digital crop from a full frame (5dII) with 400mm only.
The APS-C was set at F/8 and the 5dII at F/4, both on ISO400 and with a Manfrotto monopod.

Maybe it's just me but to my surprise the digital crop (100%) from the full frame came out better than the optical sollution with the APS-C

Greetings,

Here's the full frame version

Did you focus manually, or AF?

AF on both occasions

With my setup this would never happen. My 7D or 70D + Sigma 120-300 2.8 OS + 2x TC is way better than just a crop from my 6D + 120-300

can you post 100% crops?

I don't understand Gabebalazs, the second picture is exactly a 100% crop from the full frame image, giving it precisly the uncropped image of the APS-C.

My first thoughts also on my combo, but see for yourself.
As I have read from this forum the 600d and 7d share the same sensor

Are you OK with a 2MP final image? If so, then cropping seems pretty close in terms of quality.

I meant a 100% crop from the crop + 2x TC image

They share the same (technically very similar) sensor but that doesn't mean that the AF is the same or your AF hit precisely

Please post a 100% crop from the crop photo, that may help.

Also, when photographing a very distant object, atmospheric conditions may affect the image if it's highly magnified, i.e. taken at 800mm on a crop camera (1280mm equivalent FoV). Maybe this is a case of that.

Your wish is ...

Besides, you could be wright!

thank you. Seems soft. Maybe I should do a test too

If you have time, could you try the same test with a closer object, and using manual focus in live view?

sooo,

wouldn't a more "fair" test be a FF with an extender against a crop with the bare lens?

I'm not exactly sure what is being compared here.

And x2 on the 2MP final image size comment above.

Copidosoma wrote in post #16496240
I'm not exactly sure what is being compared here.

Agreeded. Putting a TC on a lens is going to degrade that lenses image quality. FF sensors do have an IQ advantage over APS-C sensors, I doubt anyone will argue that. Add a 2x TC to the APS-C body lower the f-stop which in turn means a slower shutter speed and I'm no longer sure what you're trying to compair!

There's quite a bit of softening and fringing going on there, that I'd suspect the TC in. Try doing just the APS-C + 400 and FF + 400 + crop and let's see how those compare instead.