I wonder what the outcome will be of stacking a lens with add-ons like these:
What's the difference between stacking these on the exterior compared to actually replacing the lens?
You are asking about mounting a supplementary lens. A supplementary lens is an inexpensive way to expand the capabilities of lenses you already own. Most common is a close-up lens. These are sometimes called close-up filters. They work just like reading glasses do for us gray-hairs. They come in different strengths. The unit of measure used is the “diopter”. The diopter is an alternate way to express the focal length of a lens. This unit is favored by the optometry community. We photo people buy them as +1 +2 +3 etc. Many cameras lenses lack the ability to work in closer than 2 or 3 feet, so we mitigate by mounting a close-up lens. If your camera has a close-up mode, entered by a button depicting a flower, mounting a close-up lens is moot. I suggest you try a +3 for your first purchase. It will allow you to work in the range of 333mm to 250mm. Most will tell you that a supplemental close-up is bad news, as it induces lens aberrations that degrade. While true, they can give you close-up abilities at lowered cost. By the way, the title “Marco” stamped on close-up lenses is deceptive advertising.
We can mount a supplementary that forces our lens to deliver a wider-angle of view. These are labeled at 0.8 or 0.75 or 0.67 etc.. This value is a multiplier. Say you mount a 0.75 on a 50mm lens. The revised focal length works out to 50 x 0.75 = 37.5mm. How good is this? They do widen the view but they likely induce some distortion. A good one can serve you well if you don’t have deep pockets. A fish-eye delivers an extreme wide-angle view.
Are supplemental lenses the cat’s meow? You get what you pay for! They are generally better than the old salts say, plus they are affordable. Are there better ways? Best is a “micro” lens, it is optimized to work in close. Best is also a wide-angle, as it is optimized to expand the camera’s field of view.
I can't add any more in the way of technical expertise that the other two answers don't already cover - so just to say that, as a beginner I bought the 'kit that has everything' ..
including add-ons to the kit lens for wide & tele & another simple 1-piece 'zoom' that looks more like a filter or magnifying glass than a lens.
They are all now gathering dust.
The wide vignettes badly, the tele is already covered by the other lens I bought at the same time & takes longer to screw in than it does to change lenses.
The 'magnifying glass' is at best for 'special effects'...
This is a 4-layer focus stack & this is as sharp as I could possibly get it.
Yes, I'm in close, the white bit in the centre is maybe 1mm wide, but no stretch of the imagination could call it 'good'. The overall 'haze' & the insane colour aberration combine to create quite a 'feature'.
Now, there is the quite simple explanation that I bought the cheapest I could possibly find & that more expensive would be a great deal better.
I just found it made more sense to buy real lenses.
My next purchase is extension tubes... just air, no glass.
Each add-on reduces the quality and sharpness, introduces lens aberrations and chromatic errors, and - most obvious - reduces the aperture, which results in less light making it to the sensor/film.
The worst piece of glass in your setup - the weakest link - limits the quality of the picture you get. So, adding a relative cheap lens reduces your whole setup to that quality.
If you have a 80-$-camera, that wouldn't matter, but if you have a 2000-$-camera, and get 80-$-results, it matters. if you buy a high-end add-on lens, it is not any cheaper than buying a separate good lens; and changing an add-on is not much different from changing a lens.