R5+100-500+1.4x or R7+100-500?

Steve Balcombe wrote:

And-roid wrote:

Steve Balcombe wrote:

Robbey TC wrote:

The 1.4 TC reduces the amount of light hitting the sensor by half, or one full stop. (1.4^2 approximates 2)

The 1.4 TC on a 100-500 f4.5 to f7.1 means that you will be either shooting between f6.3 @ 100mm to f10 @ 500mm, or have to double the ISO or halve the shutter speed for each stop foregone (or a combination to achieve correct exposure).

When the R7's FOV is at 700mm (actually between 580mm to 755mm), with the 100-500, the maximum f-stop is f6.3 . This is 1.3 stops better than the R5 with a 1.4 TC will achieve for 700mm (f10). (The R7 moves to 7.1 above 755mm FOV and the R5 moves to f10 above 660mm FOV ...(1.6 vs 1.4 comes into play))

You've omitted one mission-critical fact, which is that a 1.4x crop also reduces the amount of light collected, by exactly the same amount as a 1.4x TC. (Canon APS-C is a 1.6x crop of course, which is even worse.) This is why it is so important to use equivalent f-numbers as well as equivalent focal lengths.

If you do the comparison correctly, the R7 without a TC and the R5 with a TC are equivalent to within a third of a stop. Then, if you also trim the 700 mm (actual) R5 image to match the FoV of the R7's 800 mm (equivalent) image, they become exactly the same with regard to light collected.

Going on from that, the trimmed R5 image is now 7168 pixels wide, compared with the R7's 6960 - 3% difference, which is so close as to be negligible.

This is why the OP and I are so keen to see an actual comparison, without which it is too close to call.

Honestly, you are fighting a losing battle with tc's already, these high f stops on the 100-500 already playing against it! Its alright saying its f10 equivalent on the r7, which ir is for dof, but physics are physics and the R7 gets a better f stop and can even be used at 6.3 and still out reach the the 100-500 with 1.4* on R5, it works out that you are shooting 1.5 stops slower, 1.75* slower stops equivalent!

Physics is physics but you can't cherry-pick the bits of physics to suit your argument while conveniently ignoring others. It would be worth doing some background reading on equivalence for a proper understanding of this.

Honestly, R7 is the way to go for 600+ and ef100-400 even more so!

Ah - for various reasons I also favour the R7, but as I've explained it's not because cropping has an inherent advantage over using a TC.

I look forward to being able to make the comparison for myself, when my R7 finally arrives!

Sure things,

Look, here are the facts;

100-500 is 7.1 @ 500, on R3, 24mp, R5, 45mp, R6 20mp

100-500 is 6.3 upto 470mm, on R7 that's 750mm with 32mp

If you crop any of the above FF in-camera, the max you can get is 17mp on R5, and it will be the same as shooting the R7 but with far less resolution, reduced features in 1.6x crop etc.

However,

If you fit a tc to the 100-500, the max you can get is 660mm f9 or 1 full stop slower than the R7 @6.3 and 750mm equivalent (f10 dof), to crop that difference results in a total equivalence of F10 and 35mp on the R5 but you are shooting 1 full stop slower.

My argument would be, don't push the 100-500 past 6.3, either on R5 or R7 as the small amount of focal length doesn't really help, better to do the extra cropping in post imo. But having no tc in front of the 100-500, well, I don't believe that will not have a huge impact in itself on a 100-500 tele, no matter how good it is!

I find it hard to comprehend that a 100-500 with tc will ever out resolve the 32mp of the aps-c sensor without tc, even in the 6.3 scenario above where the R5 will have 35mp vs 32mp as the tc will soften most of that resolution further, imo. On a prime lens, tc's can provide great results but on zooms, it can't perform miracles.

Having said all of that, I am looking forward to your real world results