I have owned a few TCs (Teleconvertes) over the years, some good, some great, and some so awful that putting a layer of Vaseline on the front of the lens would have been a vast improvement.

A teleconverter or Extender (as Canon called it) is a gadget that fits between the lens and the camera film plane to spread out the centre of the image made by the lens. It sounds like the ideal solution for getting closer to a subject with your lens.  In practice, though, TCs have disadvantages, including their effect on your lens’s maximum aperture and often on the overall quality of your photos. In the days of film what you saw in the viewfinder ended up in the photograph you received back from the company that processed your film. Now jump forward 35 years or more, and you have cameras that have a built-in TC, my Olympus cameras have the option to turn on a digital "Tele-Converter" that does the same as their glass and metal ancestors of the past. 

There were usually 3 kinds of TCs, with 1.4x, 2x, and 3x magnifications, I have one which I got recently that can be either a 2x or 3x one just by changing the rear attachment. The maximum aperture of the lens is affected by the magnification factor. For example, if I use my Canon135mm f3.5 lens, then it would be like having these different lenses on my camera:

1.4x : 189mm f4.9
2x    :  270mm f7.0
3x    :  405mm f10.5

As you can see, the higher the magnification, the longer the lens focal length is, but the maximum aperture gets quite small. It used to be a problem in film days when you had a slow film speed, requiring the shutter speed to be lowered to capture the exposure. On today's digital cameras, I just set the ISO to automatic and use aperture priority with all my older lenses. There could be a potential problem when using focus peaking with a TC attached because of the light loss.

One distinctive characteristic of TCs though, is that they do not change the closest focusing distance of the master lens, and this increases the shooting flexibility. They can convert a super telephoto into an ultra-telephoto, which may sound fantastic but comes with a price, and that is usually in the quality of the resulting image. You can use the most expensive TC, but if the lens you use it on is poor to begin with, then the results from the combination will be very disappointing. The opposite is also true: a poor quality TC on a super quality lens will have the same poor results.

Test Equipment

After looking at the way I was going to test the Tele Converters I decided to re-think and decided to go about it as if I was getting myself a TC all those years ago. The reason for getting one in the first place was for the longer reach, and the cost of getting a new telephoto lens was way higher than just getting a TC.

After the rear lens group fell out of the Canon 2x-B I decided to add a zoom lens and a lens classified as "Standard" in film days of the past to the test arena and I chose the Canon 50mm f1.8 FD as the "Standard" lens and the Tamron 35-135mm f3.5-4.5 (40A) as a Zoom of the day lens.

I finally managed to get the 2x-B lens with the retaining clip back together again, but I don't kind of trust it anymore. I keep wondering if the rear element will fall into my camera and damage the sensor. I tested the results to make sure everything was as it should be and then "Super Glued" the retaining ring to prevent any future fallouts. So far, the lens remains usable, and I haven't experienced any problems with it, even though I still have that slight mistrust in it when out and about. 

In my early photography days, I had a standard 50mm f1.8 and a modest 28mm f2.8 wide-angle. I always wanted the 24mm version, and the everyman's telephoto the 135mm f3.5, but I didn't have the funds for the f2.8 version at the time. There were many things to take into account when using a TC in the early days, a high shutter speed was one of the easiest ways of preventing "Camera Shake" where your photographs turned out blurry because of camera movement while the shutter was open, exposing the film.

The problem was you needed a shutter speed and that was calculated by using the formula 1/FL, where FL was the Focal Length of the lens you were using. So if you had a 200mm lens, your minimum shutter speed should be at least 1/200th of a second. If your camera system didn't have the 1/200th shutter speed then you would choose the next highest which would be 1/250th of a second. This is where things became much harder for the ordinary photographer of the day, ISO was fixed at whatever film speed the camera was loaded with, and you could always make changes to the development process to guarantee that the pictures you had just taken were usable, but what about those taken earlier?

The answer was, of course, you either lost them or they were highly over-exposed. Now we have "Auto ISO" available, and the way sensor technology has improved we can achieve some excellent results at ISO speeds of 6400 and above.

After doing some other tests using the E-M1 II and the Tokina SZ-X 60-300mm f4-5.6 zoom lens, I've decided to use it in my tests to see how it handles and what the image quality is like.

So, with the different combinations of TCs along with the Focal Reducer, we have the following focal lengths and apertures:

 Lens 2x TC 3x TC 0.72x FR

28mm f2.5 56mm  f5 84mm f7.5 20mm f1.8
50mm f1.8 100mm f3.6 150mm f5.4 36mm f1.2
135mm f3.5 270mm f7 405mm f10.5 97mm f2.5
35-135mm f3.5-4.5 70-270mm f7-9 105-405mm f10.5-13.5 25-97mm f2.5-3.2
60-300mm f4-5.6 120-600mm f8-11 180-900mm f10.5-16.8 43-216mm f2.8-4

There are, of course, other combinations, such as putting the focal reducer on the 2x TC to achieve a 1.4x TC or adding the 3x TC to the 2x TC for a crazy 6x TC which if added to the 135mm f3.5 would give a telephoto lens with a focal length of 810mm with an aperture of f21.0 which is pretty poor really but add a 6x TC to the Tokina 60-300mm Zoom for a crazy 360-1800mm f24-34.8, I can't imagine how bad the image quality would be.

OK, curiosity got the better of me, a few shots of the above combination on my E-M1 II:

As a result, with IBIS set to 1000mm, the lens aperture is at f/34 (equivalent to f/5.6 on the lens), the shutter speed was 1/100, and the ISO was set at 500.

Hand-held and with insufficient light for focus peaking to be usable, I should have used a tripod; however, this is the best out of three.

The other two shots.

And below is an edited version which was done in DX0 Optics Pro 10 and saved with Kodachrome 25 Filmpack rendering.

The image is still pretty poor but looks a lot better the further away you are from it.