Possible and advisable are two different things. Any zoom lens with a range from 28-300 has some serious limitations regarding its optical performance, adding a t/con will seriously compromise this performance further.
You could well do it, but I'd be very surprised if the resulting images would match the ones you have in your head. You are trying to avoid the large expense of a big lens and get the same results on the cheap. I'm afraid it's not that easy. As a general rule, t/cons will not give good results when used on budget lenses, the 28-300 falls into this category. I have tried using a 1.5x t/con on my Sigma 135-400 (another budget lens, but probably better performance than a 28-300) and found the results all but unusable.
I think if you go ahead with your plan, you'll be disappointed.
As for recommendations, I wouldn't say that there are many options beyond spending a reasonable amount of cash. If it could be done on the cheap, everyone would be doing it.
Just my two penneth.
Duncan
|