f/4=F/4 discussion

Remove the dot at the end.

One of the more practical tips that follow from equivalence is: to have larger sensors use their size advantage, you need to give them more light.

The only reason larger sensors are considered superior in low light is the available lenses while shooting at non-equivalent settings.

Yup. Big formats need a lot of light. It was true with film, and it's true with digital.

Can we, please, pretty please, stop dragging film into it?

The issue is that photography's long history of film influences digital cameras and workflows. In this case, many people have carried over from film to digital that one should target the same exposure for a small format as a large format.

I found in the film era that having thin negs was more important the smaller the format.

There is a difference between a concept and an implementation.

The concept is simple: same angle of view, same shutter speed, and same aperture diameter
You don't need any math to understand that.

Now to put it into practice you need a little math. Fortunately it is much simpler than f/2 and f/4 is a two stop difference, but 1/2 to 1/4 is only a one stop difference.

The key to matching angle of view is knowing the crop factor of your body. Given this it's easy to get the angle of view in units of "50mm equivalent focal length". Just multiply the actual focal length by the camera's crop factor. If two camera/lens combinations have the same "50mm equivalent focal length" then they have the same angle of view.

Shutter speed is the same, so no issue there.

Aperture diameter is as easy as effective focal length. Divide the focal length ("f") by the aperture. So "f/4" would have an aperture diameter of the focal length divided by 4.

Consider a full frame body an a 2X crop body. Perhaps the full frame has a 50mm lens at f/8. That's a 6.25mm aperture diameter (50mm/8).
On a 2X crop body, you would need a 25mm lens for the same angle of view (50mm effective focal length), and f/4 (25mm/4) for that same 6.25mm aperture diameter.

You may notice that the relationship between focal length and between f/stops is simply the crop factor.

All very simple.

Yes, things weren't simple in the days of film.

However, the big difference is that when shooting film you pretty much need an exposure centric workflow. Every shot starts by choosing a target exposure. You then load film that's compatible with that exposure. Everything else revolves around hitting that exposure. If you want more depth of field, you close down the aperture, but most photographers were taught that they needed to use a longer shutter speed (or more subject illumination) in order to maintain that same exposure. That's not required when shooting digital. If you want more depth of field, you can stop down and simply accept a lower exposure. If the camera is set to Auto-ISO, it will adjust and the camera-produced JPEG won't be any darker.

With film, you start by choosing the exposure. With digital, you can choose depth of field and motion blur and work with whatever the resulting exposure happens to be.

Film is very different from digital. A lot of film analogies (grain-noise, chemical processing-digital conversion, exposure, etc) are not working very well. Few people studied textbooks on film latent image and processing. The ideas they present about film oftentimes are based on misunderstandings cultivated through popular sources. Say, they refer to film response as to S-shaped, but that's the property of developed film, and in log-log (D-Log E). Raw can't be even begin to be compared to processed film, "digital negative" is mostly nonsense.
BTW, Kodak in their lecture on choosing film formats in 1976 were explaining to us that latitude differs between formats.

Not the way I was taught to do it. Nor many others I know.