Lens compatability I have purchased the above Canon 2x extender and wanted it to fit a Canon image stabiliser 75-300 lens about three years old and a 18-200 with optical stabiliser which is brand new. I cannot work out how either fit together despite having owned extenders in the past and not having any difficulies. I look forward to hearing from you, Thanks, John

Sigma makes lenses with a variety of mounts to fit a variety of cameras. If the lens has a Canon mount then it will work with your XS. If has some other mount, Nikon for example, then it will not.

You can order the Tamron 2x teleconverter here. Be aware that not all lenses are compatible with teleconverters, and you can actually damage some lenses by trying to use them with a teleconverter.

No. This lens is not compatible with any tele-extender.

Sorry if that wasn't the answer you wanted to see, but there it is.

It is an inexpensive lens. It's actually a 650-1300mm lens with a 2x tele-extender to take it out to 2600mm. It's slow, manual focus, without any form of image stabilization, and with no electronics so setting the exposure is also manual. It won't be as sharp as a Canon 600mm lens, for example, but it is a lot cheaper. Also bear in mind that the 2x tele-extender will cost an additional 2 stops of exposure, so with it attached the the already slow lens becomes a very slow lens, giving a very dark view through the viewfinder.

You haven't stated which body you have but the AF will not work with the extender if the effective lens aperture is too low (remember that a 2x extender doubles the focal length but halves the effective aperture).

Canon's own website states: "Autofocusing does not operate if the effective maximum aperture is greater than f/5.6 (greater than f/8 on the EOS 1V and EOS 3)."

There are 2 Canon fittings, EF for all EOS cameras and EF-S for 'crop' cameras. The Canon extender does not fit crop cameras. Whichever make you look at, make sure it will fit the type of mount you have.
If you have not yet bought your lens of choice, Sigma are good and do their own extender compatible with their own lenses but not Canon's. This may be a good option for you

I think you will find your answer here: Canon USA.

It is a link directly to the section on your converter

A stuck lens cover is a fairly common problem, but it is normally easy to fix. A single grain of sand jamming the cover mechanism is normally the culprit, and you want to try to dislodge it: 1) Try blowing lots of compressed air around the lens cover to clean the mechanism. Or use a hair dryer for a few seconds (don't want to heat up the camera). Use no heat mode if possible. 2) Slide a thin strip of paper between the lens cover shutters and the outer support ring. Work it around 360 degres to clear out any debris that may be in there. 3) With the lens barrel extended and pointed downward, tap the lens barrel with a pencil while you extend and retract the lens by powering the camera on and off. Repeat the above three steps several times. If repeated tries don't work (keeping in mind that it usually does), it then may be necessary to open the lens barrel to access the lens cover mechanism.

You can open the lens barrel up to fiix the covers, but only as a very last resort. The above procedures normally work if you try them enough. But for those particularly nasty stuck mechanisms, here's an example repair on a Canon Powershot A400 (do this at your own risk, and it will void your warranty).

Did you tell the camera that you are using an external/additional lens? You have to specify it somewhere in the menu, the camera gives you some options (the lens model numbers) and you need to match it with your lens' model number.

It's the same 3 as with the 1.4x, but be warned it is likely to be a very unsatisfactory solution in all but the very brightest daylight, and the lens will continually hunt for autofocus - you risk burning out your focussing motor.

If you really want to experiment, hold the converter so the writing on it is the correct way up. Looking at the row of gold pins, rotate the lens so they are at the top, or the 12 o'clock position. It is the 3 leftmost pins you want to cover. Use a piece of sellotape (scotch tape) to cover the three pins, you'll have to cut a thin strip to do it. Be careful as the tape could slip as you attach the converter to the lens adding more risk to the experiment if it gets stuck somewhere it shouldn't!

I tried this with my 2x (version 1) and a 70-200f4/L, it tries to focus but fails with the much reduced light. Might try it outside on a sunny day, but also scared of damaging my lens!