- Kenko Video Tele Converter KVC-20 II 2.0x
- XIT Elite series 3.7x AF telephoto lens
- Digital Optics Japan 0.45x Pro Definition with Macro lens
Are there adapters for these which would fit my Canon 1100D? Or should I bother?
I will assume no.
The first one seems to be a filter mounted converter and you need to have a lens with the specific diameter to fit it.
By the looks of it, I don't think any DSLR camera lens are that small.
It looks like something you mount on a GoPro or similar.
The second lens seems to be as cheap as they get, https://www.amazon.com/Xit-XT5837XTL-58mm-3-7X-Telephoto/dp/B00B49LP1O
No, not worth it. The adapter is probably far more expensive than the lens.
The third is meant to put in front of the lens?
They create so much distorsion and vingetting that you loose about 30% of the image usually.
And since it's ~$15, I assume the optics is not the best.
Buy real lenses with the focal lenghts you want/need, even "cheap lenses" ($100) will most likely be better than this.
If I linked to the wrong product obviously I'm sorry, the answer may be different, but most likely not.
Kenko Video Tele Converter KVC-2011 2.0x
Nope. Video cameras tend to have smaller sensors and smaller mounts, so this won't work. Even if you could mechanically couple it, you'd get vignetting from the smaller size. A better bet, designed for dSLRs, would be a proper Kenko HD DGX 2.0x or (optically much better/less expensive) 1.4x TC for Canon EF/EF-S mount (if you can't afford the Canon ones).
However. You do have to keep in mind that if you use them with an f/5.6 max. aperture lens, you're going to lose autofocus capability, and that you'll be adding not just to the focal length, but also the max. aperture of the lens (2.0x adds 2 stops, 1.4x adds 1 stop), and that image quality will not be as good as a telephoto or supertelephoto lens. I tried adding a Kenko 1.4x teleconverter to a 75-300 III, and eventually sucked it up, saved my pennies and got an EF 400mm f/5.6L USM for birding instead.
See also: Teleconverter for Canon EOS 600D?
XIT Elite series 3.7x AF telephoto lens
This will probably work with any 52mm or 58mm filter-sized EOS lenses you've got since it comes with a 52→58mm step-up ring (e.g., the 18-55 kit lens takes a 58mm filter, and the the 50/1.8 lenses use a 52mm lenses). But again, image quality (IQ) will be compromised, and won't be at all the same as if you use a longer lens, like an EF-S 55-250 IS STM.
Digital Optics Japan 0.45x Pro Definition with Macro lens
Again, this is essentially a 58mm filter, which you can screw onto the front of an EF-S 18-55 or, with a 52→58mm step-up ring, onto the front of an EF 50/1.8. And you will get a wider field of view. But again, IQ won't be as nice as, say, saving up and getting an EF-S 10-18 instead.
If you just want a low-cost toy, these screw-on filters aren't bad, but it's probably best to save up your money for "real" lenses, if you plan on making these workhorses in your stable. dSLR gear is expensive, and there's not really a way around that, which is why I tend to tell folks that going interchangeable lens basically means putting together a $1500-$2000 budget or roughly 2x-3x whatever they plan to spend on the camera body+kit, because addition lenses and other bits and bobs of the system that make a good basic setup are going to cost about that much.