About five years or so ago, I thought I would not use my DSLR's kit lens the EF-S 18-55 IS1:3.5-5.6 II again except under limited circumstances. This was around the same time I bought my first superzoom the Canon EF 28-135mm 1:3.5-5.6 IS USM. The superzoom is excellent on film and full-frame bodies, but left something to be desired on the APS-C.
For those that are familiar with APS-C sensors, you already understand the problem I'm going to bring up and that is the crop factor. On a full frame camera, the 28-135 range is a wide angle to telephoto zoom range that is great for normal day-to-day photography. The 28-135 range is a bit of a problem on APS-C however as you have no wide angle. The lack of wide angle capability in a Day-To-Day lens is a bit limiting even when you have enhanced telephoto capability.
To understand the impact of the crop factor we need to discuss a few other lenses as well. These lenses are the Canon EF 50mm f/1.8 II or the newer STM version and the Canon EF 28-80mm 1:3.5-5.6 II lens which is film SLR kit lens. Both of these will help explain the APS-C cropping.
Now with the lenses we are comparing out of the way, we need to understand how the APS-C Sensor crops the image by getting the equal to the 35mm focal length. Let's first understand the 35mm focal lengths of all three applicable lenses, remember EF-S is for APC-C only. Let's start with the 50mm prime lens. The 50mm focal length is very popular as it is a standard focal length. The term standard means that field of view is nearly equal to that of the human eye. Usually around 40 to 50 or 55mm is considered a standard focal length for 35mm film. Now let's look at the other two lenses. Note that the shorter focal length is the same on both. At 28mm on a 35mm frame you have a wide angle field of view. At 80mm which is the limit of the film camera kit lens you are into the telephoto range while the superzoom gets you deeper into the telephoto at 135mm. Remember, the longer the focal length, the tighter the field of view is or an increase in magnification, but this isn't the only way to increase the magnification.
To increase the magnification in camera, you can do two things. You can increase the focal length, or change the physical size of the image capture, if you leave the other factor the same, your magnification increases. This is how the size of point and shoot cameras and cell phone cameras was reduced. Smaller sensors and shorter focal lengths can give you the same range of magnification. So what is the change in magnification.
With some early exceptions, Canon APS-C sensors have a 1.6 times increase in magnification compared to their full frame versions. This means we can do some rather simple math to convert to the 35mm equivalent focal length as we simply multiply by 1.6. This makes 28mm equal to 44.8mm, this means our wide angle lens setting becomes a standard focal length with APS-C. This means that my superzoom becomes a standard to telephoto zoom instead of a wide to telephoto superzoom. This means that my 135mm becomes equal to 216mm so I gain on the telephoto side. This also means that my standard 50mm focal length prime lens becomes equal to 80mm or a telephoto lens with an APS-C sensor. Now let's compare the focal lengths of the kit lenses.
This is why I brought up the film kit lens earlier. The 18mm on the APS-C kit lens is equal to 28.8mm at 35mm, but the 55mm is equal to 88mm at 35mm. This means that the kit lenses have about the same equal focal lengths and more importantly the wide angle of my DSLR kit lens is about equal to the wide angle of my superzoom.
Now, can I get a superzoom of a good focal length range for my DSLR when I am doing better financially? Yes, the lens I would be looking for is the Canon EF-S 18-135mm f/3.5-5.6 IS STM. This is a great lens for the APS-C that gives a 28mm to 216mm 35mm Equivalent on an APS-C sensor. The biggest challenge is that this lens is $549 so I may try to find it used like I did for the 28-135mm lens which is now discontinued. I can also get a 35mm lens which is equal to 56mm which is very close to the standard range to compliment my 50mm. Since that would be an EF-Mount lens it would also do double duty as a wide angle prime on my film bodies.