Teleconverter Basics (and a little more)

Olympus Teleconverter

Since Olympus has announced a new teleconverter (read more detail below) I thought this would be a good time to write a blog post about TCs. As usual, I am somewhat motivated by the volumes of disinformation/misinformation that I see on the Internet about the subject. I am hoping to pierce through all that garbage with some actual facts and info that might help you better understand TCs and how they can help you.


A teleconverter (sometimes called tele extender or TC) is a secondary lens which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image. They usually come in two lengths, 1.4 and 2X. These numbers represent the multiplier effect of the teleconverter. For instance, a 1.4 TC on a 100mm lens would make that lens operate like a 140mm lens. A 2X TC on the same lens would make that lens operate like a 200mm lens.

As I’ve grown older, I have come to rely on teleconverters. In the past, I’ve had a love/hate relationship with them. When I was a young man and dead broke, I used them to try to get more focal length and hated the results. Then again, when I was young, the quality of the average teleconverter was horrible and my technique not much better.

Now, decades later, teleconverters from manufacturers like Olympus are very, very good. (There are other good teleconverters from other manufacturers but I mention Olympus because I am most familiar with them.) And thankfully, so is my technique.

CaraCara Photo by Scott Bourne
CaraCara Photo by Scott Bourne – captured using Olympus 300 f/4 Pro Lens and Olympus 1.4 teleconverter.


The aperture’s f/number is the ratio between the size of the aperture (viewed through the front of the lens) and focal length. When using a teleconverter the aperture size doesn’t change, but, the focal length does. So when using a 1.4X teleconverter the aperture changes by one stop. i.e. an f/2.8 aperture becomes f/4. And when using a 2X teleconverter the aperture changes by two stops. i.e. an f/2.8 aperture becomes f/5.6.

Most people already know that. What few people talk about is that you may also lose autofocus or at least autofocus speed. You may also lose some of your autofocus points. (My Olympus camera doesn’t suffer from this problem but most do.) If you’re shooting with an older camera and lenses slower than f/2.8 pay attention to this.

With the advent of higher-quality TCs and practice, I have come to the conclusion that with proper technique, and a super sharp lens to connect with the teleconverter, this gear can deliver sharp, pleasing image quality. The caveats are that you start with quality glass and use a properly matched teleconverter, i.e., one made by the same company that manufactures your lens. While technically, other brands may work, in my opinion, best practices require a properly matched converter.


There is (on average) simply no noticeable image degradation when using a teleconverter on a crop-sensor camera. This is because only the center of the lens is being used to render the image. FF sensor users will notice minor image quality reductions with most TCs, but that doesn’t mean they cannot get acceptable results.

Female Cardinal Photo by Scott Bourne
Female cardinal Photo by Scott Bourne – captured using Olympus 300 f/4 Pro Lens and Olympus 1.4 teleconverter.

LEARN HOW TO USE A TELECONVERTER – and practice, practice, practice!

Remember that a “sharp” image at 600mm is easy compared to getting a “sharp” image at 1200mm.

The first thing to know (taking image stabilization out of the equation for the moment) is that the shutter speed rule (i.e. 1/focal length to get a sharp shot when handheld) is also multiplied. So you need to DOUBLE YOUR SHUTTER SPEED when you double your effective focal length.

The use of tripods and/or monopods can help avoid camera shake. But remember, the extreme magnification factor of a 2X TC means you’ll be magnifying EVERY problem. For instance, atmospheric distortion will be an issue (avoid working low to the ground when this is the case – simply standing up rather than sitting down can help reduce atmospheric distortion.)

Proper technique is super important. For those who only use long lenses occasionally, it’s very hard to develop good technique. When I teach at bird photography workshops the first thing I tend to note with new students is their assumption that their expensive telephoto lens will be all they need to get a good, sharp image. If only that were true.

You really need to practice with long lenses and get your technique down. Use a sturdy tripod, and preferably a gimbal head if you’re shooting with DSLRs. (Mirrorless shooters may be able to hand hold but a tripod and gimbal are always nice perks if you can afford them.) Place your feet shoulder-width apart, press your eye firmly to the back of your camera and drape your arm over the center of gravity on the lens. If you’re making any sort of image other than a static, locked down image, and you’re using a modern lens, go ahead and turn on IS. (Check your camera/lens manual to see if your stabilization works on a tripod.) These are minimum techniques for good image making with long telephoto lenses.

For all TCs, I recommend stopping down at least one stop if you are using a zoom lens. On the Olympus M.Zuiko Digital ED 40-150mm f/2.8 PRO Lens (like all zoom lenses) you’re going to be more likely to face chromatic aberration so when using that lens, I suggest stop down. The CA is much less noticeable once you stop down and very easily controlled in post.

In my experience, this is not a problem on the Olympus M.Zuiko Digital ED 300mm f/4 IS PRO Lens.

Another thing to note is that most TCs reduce contrast. The Olympus gear doesn’t suffer from this problem to the extent that my old Canon TCs did, but still it’s something to note. When you are working on a day with very flat, low-contrast light, you may want to avoid using the TC or positioning yourself so that the sun is angled to increase contrast in the scene. This is minor concern but worth mentioning.

Also – Teleconverters don’t work as well in low-light situations. I prefer to use them when there’s good light. They perform better and autofocus much faster.

Bald Eagle Photo by Scott Bourne
Bald eagle Photo by Scott Bourne – captured using Olympus 300 f/4 Pro Lens and Olympus 1.4 teleconverter.


I have extensive experience with the Olympus M.Zuiko Digital MC-14 1.4x Teleconverter and I can guarantee you that it is sharp. The question is – am I sharp?TECHNIQUE TECHNIQUE TECHNIQUE! It matters.

In every case where someone on one of my photo workshops says that their TC is faulty, I personally test it out and produce sharp images for them using their TC and their camera. Don’t blame the gear – blame the photographer. If you apply the lessons I offer here you can get great results.


The “experts” in the camera forums will tell you that you’re better off just cropping your image as opposed to using a TC. I take that to mean they have horrible technique and cannot get a sharp image when using a TC. Which is a very different thing than TCs not being a good choice.

There’s no way that the extender is going to be a worse option than a crop and enlargement. Most post-processing programs do a great job of up-sizing, but it’s always noticeable. Oftentimes when I look at my extender images I can’t even tell if I used one or not. More times than not, I literally have to look at the EXIF data to be sure if I used the TC.


I want to clear up a misconception. I have seen many photographers flatly state that teleconverters don’t offer autofocus on lenses slower than f/2.8. While this may be true for a majority of cameras its not true with some of the more modern high-end cameras.

Even if your camera can autofocus using a teleconverter, remember that if you use a FF sensor, you will also be penalized by slightly slower autofocus acquisition. It is lens, body and situation dependent but it is something to know. Again – on my Micro Four Thirds gear, I don’t notice any difference.

Back when I shot on DSLRs, a 400mm f/4 lens with a 1.4TC (EFL of 560mm at f/5.6 due to the one stop of light lost to the TC) will not yield autofocus that is as fast as a 600mm f/5.6 lens without the TC. The gaps grow closer every year and it’s much less of a problem with new gear. Older cameras/lenses/converters will be more likely to manifest slower AF acquisition.

Bald eagle photo by Scott Bourne
Bald eagle Photo by Scott Bourne – captured using Olympus 40-150 f/2.8 Pro Lens and Olympus 1.4 teleconverter.


It’s possible to use TCs with any variety of lens and camera combinations (check your owners’ manual to make sure your camera and lens pairing is compatible.) Some photographers are even able to stack two teleconverters (a 1.4 TC plus a 2X TC) to get even more reach. I have never tried this but you may want to. (Put the 2X on the camera, attach a 12mm extension tube to the 2X TC and then attach a 1.4 TC to the 12mm extension tube.)

When I attach a teleconverter I tend to attach the TC to the lens first and THEN to the camera. On some cameras, this seems to make a big difference in how well the TC talks to both the lens and the camera, in terms of autofocus speed and also in terms of metering. Consider this a best practice just to be safe.


Olympus is in the process of shipping a new TC. The Olympus MC-20 M.Zuiko Digital 2x Teleconverter is an exciting piece of kit that should be shipping any day. Unfortunately, I haven’t tested it yet. When I do, you’ll find my review here at PictureMethods.

If the 2X is anywhere near as well-crafted as the 1.4, it will be a great addition to my gear bag.


I have had a little field time with the new Olympus 2X, TC and I can prove to you that it is capable of rendering very sharp images.

Golden Eagle Photo by Scott Bourne

This golden eagle photo was made with the Olympus 2X TC attached to the Olympus 300 f/4 IS Pro Lens on my OM-D E-M1 X body. There has been no post-processing except a minor crop and levels correction. Otherwise it is straight out of the camera. No sharpening. To see the best online version of this image, minus compression, visit my Flickr page. You can enlarge it there and see for yourself. Sharp as can be. Oh yeah, and I did use a monopod but not a tripod, at 1200mm EFL!


With my desire to shoot long lenses I am constantly battling the need for big, heavy glass with the need for something that isn’t too expensive and that I can more easily carry. I have increasingly moved to using teleconverters and with practice, most photographers will find this is a reasonable compromise.

DISCLAIMER: Crop factor and the associated focal length multiplier only affects field of view. I prefer to reference this as effective focal length but others use FOV. Feel free to use whichever term you like.

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