Can I join two lenses 18-55mm & 55-250mm to make it 300mm and above?

Hahaha, no!

But there are such animals called converters which you can insert between the camera and the lens to multiply the focal length to 2X, 3X and such.

You are right that getting gorgeous closeups of birds usually requires a lot of focal length. Canon makes a cheapo 75-300mm, but it probably loses more to softness at the 300mm end than it gains in magnification over the EF-S 55-250mm IS. There is a good, expensive 70-300mm IS that will get you a little more magnification with very good sharpness, but not a lot. Longer focal length comes at a steep price, and for really good quality even steeper. If you look at reviews at

http://www.slrgear.com/ many lenses with focal lengths greater than 300mm do have some noticeable decreases in sharpness at the longer focal lengths. Those that deliver great sharpness at these focal lengths are very, very expensive.

No you cannot join them together! From a physics point each lens is designed to focus an image, that means it's construction is different to that of just adding another single element to a lens, so the physics wouldn't work. Then there's all the mechanics in the lens and how you would get that info back and forth. Finally the longer the focal length of a lens the greater camera shake becomes an issue, so even at the top end of your 250mm lens you either high shutter speeds, or to use a tripod to stop camera shake!

First and foremost you can't use a teleconverter on a Canon EF-S lens.

http://www.wexphotographic.com/blog/canon-teleconv...

Second, you can't "stack" 2 lenses together.

You can't. Just does not work that way. On some zoom lenses you can use a teleconverter which will increase the apparent focal length but you cannot screw one lens onto another. @Edwin: Well I stand corrected. And reading the blurb I see the point, sort of.

It doesnt work that way. However, you can look for teleconverters which can increase your zoom by 2X

NO!!!!

Three options:

Telecoonverter - but you lose two stops of light, thus your 250mm at (probably f5.6) becomes a 500mm f11 - needs bright light or high ISO

Buy a longer lens - 400mm or more.

Crop the pics.

As others have said, a tele-converter is the only way to extend it. Tele-converters are inexpensive compared to lenses, but still aren't cheap. They only work fully with Auto-Focus (AF) on some very fast (wide aperture) lenses such as the 80-200mm f2.8 varieties. Your lens will almost certainly lose AF if you put a tele-converter on it.

If you are going to lose AF anyway you may as well buy a cheap 500mm or 600mm catadioptric (CAT) lens instead.

Are you aware that the long end of your long lens, 55-250mm, is the equivalent of a 400mm lens on a 35mm or FX camera? Maybe you should try it before you start changing it. I've had a lot of success with my 18-270mm, 405mm equivalent.

Having said that, one can never have too much zoom. Teleconverters are an inexpensive way to get that. They usually come in 1.4x and 2x. The down side is that you lose a stop or two.

250mm To In