The RF 100-400 will work on the R7, but its Field of Capture: essentially the area it records will be significantly less because the sensor is smaller. What this means in effect is that you are then shooting with something equivalent to a 160-640mm lens on a full-frame camera, and the effective depth of field will be equivalent to an aperture of f/7.2-11.3. If you want a full explanation of this phenomenon see the following: What is Equivalence and Why Should I care, an article from DPReview.
I do not subscribe to the idea that crop factor should be applied to aperture. I think that is an interesting thought experiment from the days when the transition was being made from film to digital.
The digital cameras were capturing a different field of view because the first digital image sensors were not full frame in size. Someone figured out that you can capture the same field of view as a 35mm film camera if you applied a crop factor to the focal length. You could also recreate the same amount of background blur by adjusting your aperture using the same crop factor, PROVIDED that you wanted to capture the same field of view AND background blur.
I do not know of anyone who shoots like that, applying crop factor to exposure settings in order to reproduce what a full frame digital sensor would capture. Do you?
People just pick up the camera shoot photographs. An APS-C sensor will capture the same amount of background blur as a full frame sensor with any lens. The caveat is that the image from the APS-C sensor will have a narrower angle of view.
I agree that the physical aperture of the lens does not change, just like the physical FL does not, but it's about the outcome to the image when the smaller sensor is taken into account - and to me the result is what counts.
Essentially, if one accepts that using a smaller sensor with an ASP-C camera with a given lens has an effect equivalent to using a lens on a FF body with a 1.6x that focal length, then considering that the f/stop is calculated by defined as:
f (focal length)/ aperture. If once considers the equivalent focal length = f x1.6 then the f/stop is increased by that factor too.
I ran this pass several photographers and a physics professor (who also happens to be an photography enthusiast) and he agrees with me, it is also referred to in one of Prof Marc Levoy's lectures on photography. I already quoted one article, but am happy to add more to support my case.
The article that follows bridges these two points of view:
"This really shouldn’t be controversial
You do not need to consider equivalence for a moment when choosing an exposure. You do not have to multiply the f-number by the crop factor, unless you want to understand its behavior, relative to another system. However, it is completely legitimate to do so. The logic behind it is mathematically sound, it holds up in real-world testing, and it can be informative, if you’re interested. It’s an effective tool, whether you have need for it or not." from DPREVIEW 2nd article on Equivalence
There are a couple of videos that demonstrate this phenomenon, the most obvious one is Tony Northrop's one.
HERE Even if you are not a fan of the man himself, he clearly demonstrates the effects and they are undeniable.
I do disagree with his terminology: the lens doesn't "become" a longer focal length lens, nor does the physical aperture aperture change, but the resultant FoV and DoF do because of the reduced capture area of the sensor.
I agree that the sensor has no impact on the physical aperture of the camera, what I actually say is that the result of the recorded image, because of the cropping effect of the smaller sensor with that same lens has an effect on the Depth of field, which is expressed as an equivalent focal length.
Actually, while the light falls equally on each unit area of the sensor, the sensor is smaller and that has a clear impact on the field of capture. You are considering the lens on its own, or the light per unit area and in that context I agree with you, however that is not the issue - it is about comparing the overall image from one system to another. People don't look at an image per sq.mm, they look at a photo as a unit. Watch the Northrop video to which I posted a reference (without bias) and it is clearly demonstrated).
The question was originally if one can fit a RF 100-400 on a crop R7 body. Yes, we likely all agree that it does - so let's put that part aside. I have clearly demonstrated by references the case I am making. Where are yours?
I am not saying the crop factor changes the physical aperture of the lens, and I am not saying it has an impact on the light per unit area of the projected image. I have gone back to amend my post to make sure this is even more clear, if that caused a misinterpretation. You are arguing something completely different from my point.
Let me try to make my point crystal clear.
The physics of a lens do not change - both the focal length and aperture are physically defined by the lens
The image one gets is not purely based on the lens FL and aperture though, it is based also on what the sensor captures
So one has to consider the impact on the image - which is what is the outcome that one wants
When the lens projects onto the sensor the intensity of light / unit area remains the same, but the overall light is reduced because of the smaller area of the sensor. But that is not the real issue and is a bit of a red herring. What is at stake is the curvature of the lens system that focuses the image onto the sensor. Because the sensor accepts a much small area that curvature is reduced, it accepts that from the centre of the lens which has the same effect of using a longer FL lens.
The rules for DoF are:
the closer the object the smaller the DoF
the wider the aperture the smaller the DoF
the longer the FL the smaller the DoF.
because the outcome of the combination of lens and smaller sensor is (as we seem to agree) equivalent to the FoV of a longer FL lens on a FF body, so the physics dictate that the sampled area will also have a different DoF.
Again, I ask you to review the video I linked to from Northrop and tell me where the video is not demonstrating that.
I’m not a fan of Northrup’s controversial series of videos on this topic. He comes across as if this is something that mandatory to do.
Like I said, it was an interesting thought experiment over 20 years ago. No one shoots like that, anymore. Last I checked, light meters do not have crop factors.
You are showing bias toward Northrop without apparently looking at the results - I would urge you to get past that and LOOK.
Furthermore I have provided material from multiple respected sources to back up my statements but you seem to ignore all of that.
The issue of crop factor has come back with a vengeance with the ability to attach RF-S and EF-S (via an adapter) onto a FF R body. The issue is clearly addressed by Canon in its own documentation within the manuals. It has a real effect on the resolution of the resultant image and it does in terms of Field of Capture and DoF.
I fail to see why you are determined to stick with your own statements when you cannot provide documentary evidence to support them, but I can for mine.