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

Thanks for explaining all of this. Some responses in line below.

ThrillaMozilla wrote:

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.

OK this makes sense to me in the context of 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.

This makes sense ... I think. OK, I just looked up an aperture diameter calculator and I understand i think. Diameter is a function of focal length and fstop. At 300 f/2.8, it's 107 as you noted. That's the max diameter for that lens. When you add a 1.4x TC, the focal length becomes 420 and the diameter is fixed at max 107 so the fstop increased to f4. Is that the idea? It's not that the amount of light collection is changing - that's fixed at 107mm - but when the focal length is increased, the f stop has to increase to maintain constant aperture diameter.

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.

I don't have the R7 yet (getting this weekend/monday to test) and will absolutely be doing this test. I would think the R7 + 1.4x TC should perform better than R5 + 2x TC but will test that too.

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.

Only in the context of depth of field, right? The light collecting ability of the lens should still be f/2.8, right? Or do I not have that.

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.)

OK, interesting. I hear you. This makes a lot of sense. I did the calculation. The R5 pixel pitch is 4.39 um and the R7 is 3.20. So using the 300mm lens on each yields, a "reach ratio" of 93.75 on the R7 and 68.34 on the R5. So that's a 40% increase for the R7 in the number of pixels per duck...and btw when I did the comparison of Glenn Bartley's photos with the R7 and R5 I noticed I had to magnify the R5 40% to match the field of view of the R7. That now makes sense! Doesn't that suggest the R7 offers 40% more pixels on duck than the R5, assuming the duck is far enough away that neither camera can fill the frame?