John, the first thing to keep in mind when getting a macro lens, or any lens for that matter but more important for macro, is that the minimum focusing distance (MFD) listed in the specs is from the sensor and not the end of the lens. This means if you have an MFD of 9 inches you have to take into account lens length and distance from flange to sensor, so you may end up being just 4 inches or less from the end of the lens to a skittish insect to get a true 1:1 macro shot. It also means you will be blocking light unless you are using a ring light, off-camera flash, or other moveable light source like a LED panel.
I have both the EF 50mm f/2.5 Compact Macro and the EF-S 35mm f/2.8 IS USM Macro.
The EF 50mm has a 1:2 or half life size (0.5x) magnification. To get true 1:1 Canon sold an adapter, the "Canon LIFE-SIZE Converter", to get you to 1:1, but it creates limitations when attached by: increasing the lens focal length to 70mm, reducing the maximum aperture to f/3.5, and limiting the focal range. Without the adapter, It does well for larger flowers and subjects that are 1-2 inches in size. This lens was produced in 1987, and although it has really good IQ, that (IQ) doesn't kick in until f/4 and really peaks at f/5.6ish, so it's not that great at it's native f/2.5. My wife used this lens on her Canon 35mm film cameras in the 90's and early 2000's and I used it a bit on my Rebels until I bought the EF 100mm f/2.8 IS USM Macro. I will add that this lens is slow to focus and really doesn't perform well on a modern camera.
The EF-S 35mm f/2.8 IS USM Macro is a true macro, but you really have to get close to get 1:1, which is 0.43 feet from the sensor, add lens and flange to sensor distance and you are really close to the end of the lens. The built-in ring light is only effective to about 6 inches from the end of the barrel, which is adequate for 1:1 macro and fairly small stationary insects but will take you out of 1:1. My wife bought this lens for her T7i and I have used it (and still do on occasion) on my 7D mark II with fair results, but I only use it on the 7D II for the built-in ring light when I don't have available light for my 100mm which is usually a unique situation, think spider or moth in the house at night 🙂 On its own as an all around lens (excluding macro), it is a nice lens with good IQ and seems to be sharp wide open, renders colors nicely, and has low distortion. But as with most entry lenses, it does get better as you stop down.
Just a reminder, true 1:1 or smaller macro lenses are designed differently to account for various distortions caused by shooting really close and is the reason they are usually expensive. Sorry for the long winded post, but I am very passionate about macro and come from an era where the lens made the macro and not post editing software. As I've said in other posts, you can make macro photos using just about any camera/lens combo in post, sort of, and I say that in reference to EB's comments, particularly "reproduction ratio". I know I've left a ton of crap out, but it's hard to remember it all when it's basically muscle or brain memory, if that makes sense 🙂
Newton
