Please evaluate original image of zoo goers in front of the zoo entrance arch and evaluate the under exposed faces of the subjects when compared to the colorful arch. The image was shot with my Sony RX10M4 set on manual at 1/125 second; F5.6; ISO 2000 to expose the arch correctly. The focal length was 12.96mm; fill flash forced; red eye reduction on and the resolution set at 300 pixels/inch. To reach my goal of exposing both the arch and the subjects equally, I had to do post editing. The attached edited version involved: (1) cropping (2) lowering the contrast (3) raising the brightness to expose the faces correctly and (5) increasing the resolution. In a few days I am scheduled to take images of the zoo director in the same location and at the same time of night. If I simply move my camera flash closer to him so that my fill flash exposes his face correctly therefore eliminating the need to decrease the contrast and increase the exposure, will there be a need to lower the ISO to decrease the noise in the image, or is the noise in the edited version acceptable?

The M50 and M6 Mark II are mirrorless cameras. The 90D is a DSLR. If you don't know the difference, Google it.

All three cameras use a sensor format called "APS-C" that's quite common and very capable of meeting most peoples' needs.

The M6II and 90D both use a similar 32.5MP sensor... the highest resolution of any camera with an APS-C sensor. In fact, higher resolution than many so called full frame cameras that use a larger sensor.

The M50 uses a 24MP sensor that's pretty much the standard among today's cameras with this sensor format.

Actually, there is a slightly updated M50 Mark II. I don't know how it differs from the older model.

The M6II and M50 (also M50 Mark II) uses EF-M mount lenses. There is a fairly limited selection of those from Canon... 8 total, ranging in focal length from 11mm to 200mm. There are also about a half dozen more with autofocus from other manufacturers.

The 90D uses EF-S and EF lenses, which have been in production since around 1990 and there are literally millions on the used market that will fit and work on the cameras. There are currently around 60 Canon lenses for the camera (after they recently discontinued 24 lenses). There are also a great many lenses for the 90D from other manufacturers such as Sigma, Tamron, Tokina and others. Focal lengths from 10mm to 800mm are available. There are also even wider fisheye and, occasionally on the used market, even longer super telephoto lenses.

EF-S and EF lenses can be adapted to use on the M6II and M50 cameras. EF-M lenses cannot be adapted for use on any other system.

The 90D ($1200 body only) is a relatively full size DSLR with an excellent optical viewfinder. It uses a fairly large LP-E6N battery that gives it about 1300 shots per charge and can take up to 11 shots per second at its max burst rate. There also is option to fit it with a vertical battery grip, so a second LP-E6N battery can be fitted. The 90D has a fairly advanced AF system for a DSLR... with 45 points that cover approx. 50% of the image area in a centered array. The 90D uses a "joystick" to select individual AF points. It can focus as low as -3EV light levels (moonlight) and is "f/8 capable". This means it will be able to autofocus with more lens/teleconverter combinations than some other cameras that are "f/5.6 limited". Switched to Live View, the 90D works similar to the M6II. The 90D has a top shutter speed of 1/8000 and it is durability rated for 120,000 shutter actuations.

The 90D is usually sold in kit with the very good EF-S 18-135mm IS USM lens. When bought in kit with the camera, you essentially get that lens for $300. When it's bought separately, that lens typically costs

The M6 Mark II ($850 body only, $1349 w/EVF & EF-M 18-150mm IS STM lens) doesn't have a built in viewfinder, but an optional EVF-DC2 electronic viewfinder can be fitted to the shoe on top of the camera. The camera is often sold in kit with that viewfinder. The M6II's AF system has 143 points that cover most of the image area. There is no joystick, but the rear LCD screen can be used to select individual AF points. The M6II also has face detection and is said to track subjects better than the 90D in Live View.

The M6II uses a smaller LP-E17 battery and is rated to give about 300 shots per charge. There is no battery grip available for the M6II. The M6II can shoot at up to 14 frames/sec, however I think that is only with focus locked, which isn't very practical. Usually bursts are done when shooting moving subjects and focus needs to track with them. The top shutter speed of the M6iI is 1/4000. I don't know its durability rating, but would suspect it's around 100,000 shutter actuations.

The M50 and M50 Mark II ($600 body only, $700 w/EF-M 15-45mm IS STM lens, $930 w/EF=M 15-45mm & EF-M 55-200mm IS STM lenses) have a built-in electronic viewfinder. The AF system is very similar to the M6II's, but the newer M50II also has subject eye detection and tracking. I am fairly certain the M50II uses the same battery and gets about as many shots per charge as the M6II. The M50II can shoot still photos at up to 10 frames/sec. I don't know if this is only with focus locked or not.

Both the M50 models and the M6II are considerably smaller and lighter than the 90D. Some of the EF-M lenses are also quite compact.

I don't shoot video, so don't know much about it. AFAIK, all three of these cameras can shoot 4K. They all also have articulated LCD screens, though I think the M6II's is limited to just tilting.

All three use SD memory cards (UHS II).

The 90D and M6II have "anti-flicker", a feature which solves exposure problems that can occur under fluorescent and similar types of lighting. I don't think the M50II has this feature.