75-300mm is a really bad lens according to reviews. I have the 55-250mm lens and I like it. One thing that is very important (to me) for telephoto lens is IS and 55-250mm had IS. I took it to the zoo once and it gave me very sharp pics.
Depend on what you really want. 50mm lens is a very, very sharp lens and the f1.8 make it a very fast lens. It is great for low light photography too. But whether you should or should not buy this lens is all up to you.
Scout for 2nd hand...good copy might get at $250. 55-250 is value for money and it comes with IS. There are plenty of 50 f1.8 in 2nd hand market also. If I were you I might consider 2nd hand so that in case I want to upgrade in near future I can just sell it again with less loss.
Of course you can, there's a whole section for selling and buying if you have not noticed by now. Check for fungus, focusing problems and other stuff. Bring along a friend who knows how to check if you are not confident.
Telephoto zoom lens. Read about focal length, field of view and perspective. Should make it clear. There is no such thing as "zoom lens for xxx style" - there is rather an idea in your mind.. thinking about how to create the image.. selecting the right lens.
And shld I buy a canon 50mm 1.8? I read that it's gd for portrait taking.
You should buy once you understand the advantages of having this lens. The price is stable and 2nd hand items won't run out, that's for sure. No point rushing. 50mm focal length is covered by your kit lens.
I don't think you know why you want to get this lens yet. Don't let the BBB control you (*not before you understand why you need it*)
Any lens is good for portrait taking (as in all lens can take portraits). It depends on how you utilize the lens in the given environment. (you can even take portraits with 55-250 , depends on how you frame it)
One can use the kit lens 18-55 and still shoot marvelous portraits with it.
oh, btw, 18-55 + 55-250 is quite a solid combo itself enough to cover "general" photography from wide to portraits to tele.
*don't be too fast to discard the 18-55 if you own one, despite what many may say(e.g. abt the IQ, non USM), I still think it's a great lens*
+1 to that, as long as the foreground and background is outside the DOF, they will appear blur, but a portraits lens will make it very easy to achieve the result without having to tweak with the surrounding, furthermore f1.8 is a very bright lens, can get at ard $100 in the 2nd hand market and I feel it worth to get one.