Someone over at Sony rumors is spouting off that the Canon sensors are all FSI (front side illuminated) and basically have poor dynamic range (trash) compared to Sony's BSI (back side illuminated) sensors. Can anyone explain the difference as if they are speaking with a child? My brain starts to hurt after a long day at work and I try to read a photon chart. But its sort of a big decision: Sony or Canon for church event photos and videos. Once we start buying lenses its hard to climb out of that hole.
I'll take a stab. I have used Canon's Rebel, Rebel XT, T2i, 80D, 6D II, 5D IV, R6, R6 II, R5, and R3. All of my personal glass is EF, mostly L, both primes and zooms, 20mm -> 600mm. This is my opinion based on my experience. No doubt others will contribute other excellent points and experiences!
BSI is physically organized to be more efficient at capturing light than FSI -- in theory. But, in the real world, only the effect matters.
Car engines come in varieties of combustion chambers, oxygen injection, etc. Each one is also, to a degree, special to the manufacturer in terms of their experience making that kind of engine, the skill of their design team, the ability of their factories, and their choices in materials. It's possible for a V8 to outperform a V6 and a V6 to outperform a V8 -- the implementation matters as much as the general technology. The driver helps too.
Yes, many Sony sensors are BSI but their architecture is unique to Sony's capability and Canon's sensors are unique to Canon's manufacturing capability. And all of the technology tricks/secrets that each company possesses.
All of Canon's mirrorless sensors are great. If you know how to use your camera well for your situations then the R8, R6, R5, R3, and R1 can all do very well. The nitpicking you see in these forums is specific to each of our individual experiences, needs, and capabilities -- don't fret over any of it. I have full confidence the R6 II and R6 III will each take magnificent photos when used to their fullest, but there are slight strengths in each case. Nothing you cannot overcome with good attention.
That stated, the R6, R6 II, and R6 III each can capture 14-bits of dynamic range -- that's 16,384 shades or tones from pure black to pure white. A JEPG, which is often used in book printing, offers 256 shades/tones. Getting the full use of that range also depends on the lighting, lens, shutter speed, etc.
The R6 II has 102,400 ISO and a sensor released late 2022. The R6 III has ISO 64,000 and a sensor released late 2025 -- three years of time in which Canon can perfect its tricks. ISO is how the sensor translates light (photon strikes) into dark and bright in a unit of time. Pictures can become noisier if the sensitivity is high and the available light is minimal, but Canon puts significant energy into making that noise look good -- such as by approximating film photo graininess. A lot of the extra work carried out by the more advanced computer chips in each generation is put towards making the best interpretation possible. The more recent the camera, the better the effect. Strobes / flashes add extra light, as you probably know, that significantly overcomes most of the worry here. But even in limited natural light with fast action these sensors will provide a solid start and include enough additional data that you can probably get any photo you make an effort at when taking the picture shine by the time it's ready for print or online.
Canon's colours also tend to be generally acceptable as desirable or satisfactory across its camera and lens range.
Don't forget the shape of the camera bodies and placement of buttons and organization of menus. That matters when speed matters. Anything out of place or that tickles an annoyance will slow you down, take you from the moment, etc. I'd say the body is easily worth 50% of the decision if you're moving at speed, given that most modern options are going to at least be good in capability.
Finally, modern cameras include Canon's formulas that understand lens imperfections and sensor attributes such as anti-alias overlays to create adjusted final images in TIFF (PC/Mac) or HEIF and JPEG (in-camera) form from the RAW file. Even amazing glass often benefits. Not all other camera manufacturers seem to include this capability, and not all third party lenses participate.
There is also the lens investment you might already have in place. Even if a Sony camera were a smidge better in the sensor department than what you choose to afford on the Canon side, if you have a solid lens collection and your muscle memory is trained for the placement of zoom rings, buttons, etc. than you will probably do better out of the gate with familiar equipment than new equipment.
But, in the end, you should do what you are comfortable with. I assume if you're shooting weddings you're mostly doing it for money, and since it's your rent you should go with your gut. You might consider downloading sample raw images from each competing camera model from reputable review sites and play with them in your image editing application(s). Pay attention to grain, colours, contrasts, and the ability to make them brighter or darker by a few stops. See how the files behave.
What makes sense for you will very likely be different for each of us. I'll push my R6 original to 25k ISO with fast outdoor action and be thrilled with the images I have to work with. Others here will think I'm nuts or blind. Our use cases are probably very, very different. And once you throw in strobes the game changes dramatically -- to such as extent all of the Canon series cameras are probably on equal footing.
