Canon EF 2X Extender II (Worth the money?)

[Olympus E300]

Hey gang. When I had my Olympus E-3, I had the 2X teleconverter. I thought that I would use it a lot in conjunction with my 70-300mm lens for wildlife stuff but I found that it slowed down my lens so much, that I found it troublesome. In the end, I didn't use it as much as I thought I would have and sold it. Now I'm on the Canon band wagon and again I have found myself with a 70-300mm lens and again I find myself interested in a 2x teleconveter. My questions for those of you who use this piece of kit are as follows :

1. How many f-stops might I expect to lose with Canon's EF 2X II Extender?
2. Do you use yours as often as you thought you would?
3. How much quality (sharpness, ect) is lost while using one?
4. What would you pay for one when looking to buy used?
5. What are the main differences between the MKII and the MKIII?

Cheers!
- Daniel

 

[curtyoungblood]

Unfortunately, I'm afraid that the answer to your questions is going to be very straight forward. Canon's teleconverters are only compatible with certain lenses, and I don't think the 70-300 is on the list.

No 2X extender for 70-300mm L Series

 

[Olympus E300]

I actually only have the IS USM non L series 70-300mm Canon lens at the moment. Good info though!! Thank you.

 

[curtyoungblood]

Sorry, I didn't mean to assume that you add the fancy L series lens, and I meant to include a link to a compatibility list. The extenders only work with L series glass though. They have a protruding front that will hit the rear element of anything else, and the wider end of the L-series stuff too. Here's that compatibility list: Canon Extender EF 2x Compatibility Chart. There may be some off brand converters that will fit with your lens, but there are mixed reviews on how successful that will be.

 

[Olympus E300]

WoW! I had no idea. Thanks!! This Canon band wagon is getting tricky already...lol

 

[TCampbell]

Hey gang. When I had my Olympus E-3, I had the 2X teleconverter. I thought that I would use it a lot in conjunction with my 70-300mm lens for wildlife stuff but I found that it slowed down my lens so much, that I found it troublesome. In the end, I didn't use it as much as I thought I would have and sold it. Now I'm on the Canon band wagon and again I have found myself with a 70-300mm lens and again I find myself interested in a 2x teleconveter. My questions for those of you who use this piece of kit are as follows :

1. How many f-stops might I expect to lose with Canon's EF 2X II Extender?
2. Do you use yours as often as you thought you would?
3. How much quality (sharpness, ect) is lost while using one?
4. What would you pay for one when looking to buy used?
5. What are the main differences between the MKII and the MKIII?

Cheers!
- Daniel

You have to think about how a teleconverter works and how focal ratios work at a more fundamental level.

The "short" answer is that you always have to multiple both the focal length AND the focal ratio by the teleconverter factor. So a 2x teleconverter means you double both your focal length and focal ratio on the lens.

If you want to understand why... keep reading because it all makes sense when you think about it.

The "focal ratio" is called a ratio because it's the number of times the diameter of your lens' clear aperture area can be divided into the effective focal length of the lens.

I'll use a concrete example:

Suppose you have a 100mm lens, and it has a clear aperture which is 25mm across. Since 25 divides into 100 exactly 4 times, that would be an f/4 lens.

When you add a teleconverter, you multiple the original focal length of the lens by the teleconverter factor (in your case 2x) to reach the new effective focal length. So a 100mm lens with a 2x adapter becomes a 200mm lens. But this has a side-effect on the focal ratio because while the focal length got longer, the physical diameter of the lens' clear aperture is still the same. So now your 25mm diameter of clear aperture divides into 200mm focal length 8 times. Thus converting it to an f/8 lens... and that's going to be a problem for auto-focus systems. Also notice that 4 (the original focal ratio of the lens) X 2x (the teleconverter factor) = 8 (the new focal ratio of the lens).

But what if you had an 1.4x teleconverter with that f/4 lens... now the focal length becomes 140mm (100 x 1.4 = 140) and 140 ÷ 25 = 5.6. So now it's effectively an f/5.6 lens and that is low enough for the auto-focus systems to use.

The reason teleconverters come in 1.4x and 2x is because those numbers are based on powers of the square root of 2 -- which is a key number in photography. The square root of 2 is (rounded off) 1.4. The square root of 2 squared is just back to 2 again. It turns out all "full" f-stops are based on powers of the square root of 2.

f/1 is the square root of 2 to the 0 power.
f/1.4 is the square root of 2 to the 1 power.
f/2 is the square root of 2 to the 2 power.
f/2.8 is the sqare root of 2 to the 3 power.
and so on with f/4, 5.6, 8, 11, 16, 22, 32, etc.

This is because if you have a circle of some given diameter (say it's 10mm across), and you increase the size of that circle's size by the square root of 2 (so now it's a 10 x 1.41 = 14.1mm but we round off in photography) the new circle is EXACTLY twice the "area" as compared to the old circle. When that circle is actually the aperture opening in your lens, you are letting in exactly twice as much light. The square root of 2 also comes into play when working with lighting setups and the subject distance from the light, but that's another thread.

The bottom line here is that ALL 2x teleconverters create a loss of 2 full f-stops and ALL 1.4x teleconverters create a loss of 1 full f-stop. If they don't, then they're not really 2x or 1.4x teleconverters.