Sell the R5 and get an R7 and R? Crazy?

mraifman wrote:

My general preference (like many) is maximum reach and greatest subject differentiation when often shooting in low light for wildlife. The latter two preferences point to faster glass and so I've purchased the 300mm f/2.8 mk ii and enjoy using it in these conditions. It is just about the largest lens I can handhold as well, which i value. The downside, though, is 300mm is rarely enough reach for wildlife.

This requires a comment, and there's a lesson here. The aperture diameter determines how many photons the lens can collect from the bird. Generally, more photons are better. Inadequate numbers make noisy images. A 300 mm f/2.8 lens has an aperture diameter of 300 mm/2.8 = 107 mm. A 400 mm f/5.6 lens has an aperture diameter of 71 mm. Thus, the 300 mm lens collects 50% more light!

The focal length can be changed with teleconverters. Also, the image can be sampled in smaller samples, i.e. with smaller pixels, which accomplishes essentially the same result. But the amount of light collected from the bird is what counts for noise.

It's important to note that teleconverters do not change the amount of light collected from the bird. Except for minor transmission loss, the amount of light per bird is determined entirely by the lens aperture.

Likewise, the depth of field when measured relative to the size of the bird, depends only on the aperture diameter and distance, so a teleconverter has no effect! (It is assumed that depth of field in different configurations will be viewed at the same magnification, so the bird appears the same size!

So I am using the 1.4x TC mk iii on it most of the time and occasionally using the 2x mk iii TC but I find the 2x to be soft wide open.

That is interesting, and it's a critical part of the consideration if it's true. The question is whether the softness came from aberrations in the teleconverter, or just from magnification. Is the 300 mm 1.4x is also soft wide open with the R7, when pictures are viewed at the desired magnification? That's the critical question.

So the R7 + 300mm f/2.8 combo seems appealing to me because (unless i'm mistaken) it maintains the lovely depth of field of the 300mm f/2.8 while cropping to create a field of view of more reach.

Yes, that's the way to consider it!

That 300mm f/2.8 becomes an effective 480 f/2.8.

The 300 /2.8 is equivalent to 480 mm f/4.5 full frame.

Now the R7 is lower resolution than the R5, so some of that gain is lost, but there is a noticable extended reach with the R7 in the comparison shots I've seen. The 300mm f/2.8 is very sharp and probably works well on the R7 despite the crop. I would expect to use the 1.4x TC mk iii occasionally on the R7 + 300mm f/2.8 combo to extend reach towards 700mm equiv.

There's a nice figure of merit to use when calculating "reach". (That's an informal term, but it's a good one.) You want to know the number of pixels per duck on a linear scale. That's what the "reach" tells you. The magnification is proportional to the focal length, and the number of pixels per duck is inversely proportional to the pixel size (or pixel pitch for the ultra-fastidious).

So, focal length/pixel size is a figure of merit you can use to compare the "reach" of different camera/lens combinations. It is directly proportional to the number of pixels per duck on a linear scale. (The ultra-fastidious might want to know the number of pixels per degree or pixels per radian. That too is proportional to f/pixel size.)