Tortie wrote in post #19521669
First off, thank you so much for your detailed response! This is exactly the information that I was looking for.
The world of mirrorless really has changed the business, hasn't it? The only thing about recommending the R50 that's giving me pause is the battery life. 370 shots vs. 1070 on the SL3. That's a pretty substantial difference. I know my friend can carry additional batteries but still something to consider.
How would you say the new RF lenses stack up to the traditional EF glass? Have you had experience with using the EF to RF adapter? Curious how well/quick the lens is able to adapt, for wildlife photography in particular. I will certainly give the RF 100-400 and 100-500 a look as well.
Looks like my friend and I will be watching a lot of YouTube!
Is the world of mirrorless changing? Or is mirrorless changing the world? 
Depends upon who you ask, I suppose.
Honestly, I have NOT personally plunged into the Canon R-system yet. With five Canon DSLRs (and many others in the past), one older Canon mirrorless, and around 25 lenses for use on them, it will be a major transition for me. I shoot a lot of sports and a little bit of wildlife... and really wanted APS-C R-series much like the 7D Mark II cameras that are my primary workhorses. Canon finally produced their first two APS-C models less than a year ago and one of them is close to meeting my needs. My transition to the R-system is "inevitable" so I've been doing A LOT of research and planning. I've consulted with a number of users and watched/read all the reviews!
Regarding battery life, yes the shots per charge drop significantly going from DSLR to mirrorless (the electronic viewfinders mirrorless use are a heavy power drain). I think it's actually worse than you realize, that the SL3 is rated to get some 1600+ shots per charge (instead of 1070). The R50 appears to be rated for between 320 and 440 shots, depending upon the setup and usage of the camera, temperatures, etc.
However, with either most users will get quite a few more shots than what's rated. And with a few power saving tricks they can get even more. The ratings Canon cites are based upon CIPA test standards. Those say that when doing the battery test on a camera with a built in flash, the flash shall be used for 50% of the shots. That's a very heavy drain on the battery. So it skews the results downward significantly. For example, the 7D Mark II DSLRs I have used A LOT have a built in flash that I never use and are rated to get 670 shots per charge. I easily get 1200 to 1400 shots per charge with them. But I also have them set to go into sleep mode rather quickly (one minute... they wake up fast) and also that the rear monitor doesn't automatically display ever image I take. The rear display also draws quite a bit of power. But even without these I was getting well over 1000 shots per charge... wayyy more than Canon said I should, simply because half the shots in their test had to use the flash, which is something I never do (I use accessory flash, when I use them at all).
The R50 uses a small battery, to allow the camera to be kept small and light. The LP-E17 it uses is the same as what the SL3 uses (and the same as my M5 uses). For a long time, they were only available from Canon and were rather expensive. Now there are some third party options, often with higher capacity than the Canon OEM's 875mAh. For example, at B&H Photo they show Bescor LP-E17 clones with 1040mAh and Power2000 LP-E17 that claim to have 1400mAh capacity. I don't have any of these brands and can't attest to their quality, but B&H is a pretty reliable seller. Oh, and since the 3rd party clones have started to appear, Canon has lowered the price on genuine LP-E17 too. Just a little, though... they're still the most expensive ($60ish). A minor warning, some 3rd party batteries are less than fully compatible with the cameras and Canon chargers... watch out for the ones that come with a charger that's required (such as the Premier Tech LP-E17 kit at B&H). If these are ever mixed up and the wrong charger is used, there may be damage.
For the large part, Canon has been quite innovative with their new RF lenses. Their RF 70-200s are smaller and lighter than anyone elses' and even Canon's own EF 70-200s. The RF 100-500mm is half a pound lighter, the same diameter and stores a half inch longer than my EF 100-400mm II. Plus the EF 100-400mm is incredibly sharp for a zoom... and the RF 100-500mm is even better! Rather than just make 16-35mm lenses like they did for their DSLRs, Canon came up with fresh 15-30mm and 14-35mm designs. They did appear to copy over successful 24-70mm f/2.8 and 24-105mm f/4 lenses... but also came up with an f/2 28-70mm (pricey though it may be!).
As of right now there are 34 Canon RF and RF-S lenses (RF-S are "crop only", RF can be used on both full frame and crop). We can expect a lot more in the near future. Canon had about 90 EF and EF-S lenses at the peak of production. They've discontinued quite a few already... there are now 46 listed at B&H. Canon is "all in" with the R-system and lenses for it. They have been exercising their patents fo prevent 3rd party manufacturers from producing autofocus lenses for the system, but have begun to "license" a little... reportedly there's a Voightlander lens coming soon.
There already are a number of 3rd party manual focus/manual aperture lenses available for RF mount. Some of them are pretty interesting. But these will probably not be on a wildlife photographer's shopping list. They just aren't quick to use and speed is often important when shooting critters! Autofocus and auto exposure can be invaluable tools. And the R50's AF system rivals anything on the market for it's capabilities. Especially if it's paired with fast focusing lenses (among Canon, "USM" are fastest).
You and your friend might find Bryan Carnathan's website helpful https://www.the-digital-picture.com/ He's been reviewing and comparing Canon gear for many years and almost everything they've made the last 20 years can be found there in great detail. There are tools where you can do side-by-side comparisons of image quality, flare resistance, distortion, lens and camera specifications and much more.
All the folks I've discussed it with have assured me that Canon EF and EF-S lenses work as well or better than the did on the DSLRs they were designed for, adapted for use on the R-series cameras. It makes some sense... since DSLRs autofocus systems differ from those of mirrorless. DSLR systems use a semi-transparent mirror to allow some light to pass through and be reflected to sensors in the bottom of the mirror box. While it works quite well, there is room for the focus to be slightly off. As a result many of the Canon DSLRs have a "Micro Adjustment" feature to fine tune specific lenses on the camera. This is unnecessary in the mirrorless cameras because the focus sensors are embedded directly in the image sensor itself. There's no way for the focus system and image system to become "slightly misaligned".
Just so you know, as a relatively entry-level model, the SL3 DOES NOT have the Micro Adjustment feature. If any particular lens/camera combo would benefit from some fine tuning, it would need to be done by a camera repair person with the necessary calibration tools. Even then it's unlikely to ever be as precise as the mirrorless camera's AF system.
Another benefit is that since there's no mirror reflecting part of the light to an optical viewfinder, the mirrorless camera's AF system is able to keep working in significantly lower light conditions. For example, the SL3 is rated to be able to autofocus as low as -0.5 EV... while the R50 can focus to -4 EV (basically bright star light). This more complete light delivery also allows the mirrorless cameras to focus lenses with f/11 apertures, where the SL3 cannot focus anything less than an f/5.6 aperture (some of the more advanced Canon DSLRs can focus one stop slower lens or lens/teleconverter combos: f/8).
The SL3's AF system is a fairly crude AF system... very similar to what was in a Canon 20D from 2005... with 9 focus points clustered in the within an oval that covers approx. 30% of the image area. The R50 has 4500+ AF points covering almost the entire image area. With the SL3 you can select an individual point and put it where you want the camera and lens to focus. With the R50 you can set the camera to detect cars, or animals, or people, or faces or eyes and let it do the work. The photographer has to track moving subjects with the SL3, while the AF system of the R50 can track moving subjects. .
Canon also got innovative with their EF to RF lens adapters. Where everyone else was making simple adapters that allow the lens to fit and work (which Canon did too), for a few dollars more they also made one that has a built-in user programmable ring. It can be set up to change the aperture or adjust exposure compensation or any number of other functions. Or, for quite a few dollars more they offer one with a slot filters can drop into, with choice of a variable neutral density or a circular polarizing filter. All of these also allow any EF or EF-S lens made the last 30 years to work on an R50. Now a lot of 3rd party manufacturers have gotten into the act and are offering the same and sometimes even better options. For example, the Meike adapter with drop-in Variable ND filter that costs $159 is said by several reviewers to be superior to the Canon which costs about $530 (by the time you add the "clear" filter that's necessary any time you don't want ND, which is included with the Meike). Meike also offers a line of other types of filters, as do some other 3rd party manufacturers. Canon only offers the three: CPL, VND and clear.
Thanks to 3rd party, there are more than 25 adapters to choose among to adapt EF or EF-S lenses onto an R50, with prices starting around $45 (not including "speed boosters", which are primarily used for video work). I do use some other adapters... most recently got a Viltrox EF to EF-M to be able to use one of my lenses on my M5 camera. It's well made and work just as it should. (P.S. "EF-M" lenses are used on the older Canon M-series mirrorless cameras. There never were very many... only eight Canon and a half dozen from 3rd party... though some were nice, they cannot be adapted for use on any other system I'm aware of.... certainly can't be adapted for use on the R-series cameras.)
Yeah, I thought about the silicone covers mentioned in some other responses. I hesitated to mention them, though... because then we'd have to start comparing cameras too! By limiting us to white cameras, the options had been narrowed down so nicely! 
Have fun shopping!
This was the biggest result for me in extending my shots.
