The Ultimate Guide To Extenders Or Teleconverters

A good friend of mine recently came to me with some questions about lenses. She’s a professional action sports photographer and was seeking advice on the best way to reach about 400mm in a lens package that was still relatively lightweight and portable. I’ve shot many of the same subjects she was talking about, so I immediately recommended using a 300mm f/2.8 with a 1.4x extender.

Her response surprised me:

“I’ve never had much luck with sharpness while using extenders”

I know this is a feeling that a few people have, and yet I also know many people who rely on them for their work and wouldn’t leave the house without them (myself included). Why is there such a great divide?

This seems like a perfect opportunity to dig a bit deeper, bust a few ‘extender myths’ and show you guys how and when best to use them. There’s definitely a few do’s and don’ts when it comes to extenders and unfortunately the internet forums are awash with people who swear they know better, even though they’ve never actually used the things. I think a lot of the bad press that extenders get is based off old lens pairings and old technology, with people re-hashing the same “well Dave said….” stories from many years ago. Let’s set this straight, starting from the beginning…….

F1 in the UK. 70-200 + 1.4x extender

 What Are Extenders?

Extenders, also often called teleconverters, are optical accessories that attach to the rear end of a lens to increase the focal length. The two most common varieties are 1.4x and 2x extenders, though Nikon also makes a 1.7x version as well. As you’ve probably guessed, the number represents the factor by which the focal length gets multiplied. A 70-200mm lens with a 2x extender becomes a 140-400mm lens for example.

There’s no such thing as a free lunch though! Using an extender will reduce the maximum aperture of your lens. A 1.4x extender will cause your maximum aperture to be reduced by one stop and a 2x extender will cause a two-stop decrease. Nikon’s unique 1.7x extender slots in the middle with a one and a half stop decrease.

nikon 2x extender


  • A 300mm f/2.8 lens with a 1.4x extender would become a 420mm f/4 lens
  • A 300mm f/2.8 lens with a 2x extender would become a 600mm f/5.6 lens

You might want to refer to our f-stop reference chart which will help you visualize the various f-stop changes on your lenses, or check out the table below for some common lens examples.

NB: Not all lenses are compatible with extenders. You should always refer to the lens specifications on the manufacturers website before purchasing one. In general, all telephoto prime lenses will be compatible, as will tilt-shift lenses and sometimes macro lenses. Wide-angle lenses are not compatible with extenders, not because you shouldn’t use them, but because you physically can’t use them due to the rear element design of wide-angle lenses. You’ll notice from the photos of the actual extenders, that there is a protruding element that sticks into the back of the lens barrel. Some lenses, wide-angles in particular, have a rear lens element that’s too close to the lens mount to allow the extender’s protruding element to fit into the lens.

Shot using a 1.4x extender on a Canon 400mm f/4 DO IS II.

Advantages Of Using An Extender

The obvious answer to this is that it gives you a longer focal length, but the REAL answer to this is that it gives you a longer focal length at a lesser cost and weight! Long lenses are inherently big and expensive so using an extender can be a great way to get extra reach from your lens without breaking the bank or your back. To return quickly to the conversation with my friend that started all of this, I recommended she used a 300mm with a 1.4x extender because that combination weights about half what a 400mm f/2.8 prime lens does. In her specific situation, weight was a big factor as she had to carry the lens all day whilst skiing.

The second reason you might want to consider an extender is for the added versatility when used with larger prime lenses. Big primes, like a 300mm or a 500mm are wonderful for their purpose, but you can be limited in the type of shots you can get if you are not able to reposition yourself. Take shooting from a safari vehicle for an example. You spend all day tracking an animal and then when you find it, the vehicle parks up so you can observe. With a prime lens you are really left with only a couple of possible composition options and a vertical and horizontal shot. Using an extender will double the number of potential different shots you can get if you are stuck shooting from one spot! That’s important if you are shooting for an editorial or stock client because more layout options are always welcomed. If you are shooting field sports like football then you can also get added reach when the play moves to the opposite end. This is distinct from using a longer lens in the first place because once play moves back to your end again, you want the option to ‘zoom out’, by removing the extender. Obviously not something you can do with all sports, since you don’t want to be trying to change things in play, but for sporadic action like football it can work.

The third reason you might want to use an extender is to get to a focal length that’s not available natively in any other lens. If you used a 600mm lens with a 2x extender, you would have a 1200mm reach, something that’s not possible to achieve any other way. Even a 600mm with a 1.4x extender gets you to 840mm which is a little longer than an 800mm prime (the longest lens being made at the time of writing this article, apart from highly specialist limited manufacture lenses).

So to summarize the advantages, an extender gives you:

  • A longer focal length (obviously)
  • A better focal length/weight ratio
  • A better focal length/price ratio (there are some exceptions)
  • Double the compositional options
  • A way to get to focal lengths that aren’t achievable with a prime lens on its own
Skier in Alaska, 300mm f/2.8 + 1.4x extender

Disadvantages Of Using An Extender

As I mentioned earlier, use of an extender does reduce the maximum aperture of a lens (explanation why further down). Based on the rules of the exposure triangle this means that you might need to shoot with either a slower shutter speed, or a higher ISO if your aperture was within the lost range before you attached the extender. In my experience, there’s a few common scenarios where this often comes into play and the first one is shooting sport indoors or under lights in a stadium. In those scenarios, light is at a real premium and you also need a fast shutter speed to stop the sporting action. A 70-200 f/2.8 is a common lens for basketball shooting, but adding a 1.4x in a dark sports hall can really cause a struggle for light. The same goes with the venerable 400mm f2.8 on the football pitch at night. NFL games have pretty well lit stadiums but it can be another situation altogether at a college game. These are a couple of times when it might be good to avoid using the extender due to the one stop aperture reduction. On the other hand, if you are shooting a static subject either with a tripod, or at light levels suitable for easy hand-holding, then the one stop reduction (with a 1.4x) won’t make the slightest bit of difference to you.

For most people, the biggest disadvantage is the loss in image quality and this is where most of the anti-extender online commentary is centered. It’s not totally misplaced, because there is a reduction in quality, but how much is it?

The protrusion of a teleconverter’s front element means they cannot be used on all lenses. Consult the specifications for your lens before purchasing.

Simplistically speaking, an extender is just like a magnifying glass that enlarges the central portion of your lens’ field of view and projects that onto the camera’s sensor. Since it’s only projecting a smaller central part of the original lens, vignetting is actually reduced when using an extender. Unfortunately, all of the flaws in the original lens become magnified so this means that chromatic aberrations become more apparent, the image becomes softer and there is a reduction in contrast. A 2x extender will therefore always deliver a softer image because it is magnifying the flaws by 2x instead of 1.4x. The actual optical quality of the extender itself doesn’t have as big a part to play in this whole thing as most people would imagine. It’s the original lens’ optical quality that pays a huge part! If the lens didn’t have any flaws then there would be none to magnify, right?

This explains, for the most part, the split in opinions over the use of extenders. In fact it’s the very reason my friend was put off using them. When I questioned her further, she told me she had used one on a 70-200 zoom, but she’d not tried one on a prime supertelephoto lens, a lens that is natively MUCH sharper than a zoom lens. Most people’s assumption is that the image degradation is entirely due to sub-par optics in the extenders, and they forget to think about the quality of the original lens. As the saying goes….. “garbage in, garbage out, magnified by 2”………. Well ok, so I added that last bit myself, but you get the picture!

The final disadvantage of an extender is that it will cause a reduction in focus speed. With most lenses it’s not perceivable in single shot mode without dedicated testing, but it can be seen in AI Servo tracking accuracy. If you’re shooting static objects then it probably won’t be an issue, but if you are shooting sports or wildlife then it can cause a reduction in your keeper rate. How much, depends a lot on the model of the original lens, the camera model and the extender model. Due to all the possible variations, it’s hard for me to state exactly what would or would not be possible to shoot, but you can take a look at some of my examples to realize that there’s still a ton of possibilities……. tack sharp cars coming at me at 200mph for example…..

AF systems depend on light for their accuracy so by reducing the maximum aperture of the lens, we reduce the available light for the AF sensor. In-turn, this means that a 2x extender will have a greater effect on the AF speed. From my experience, for many people the 2x crosses a usability boundary with AF speed reduction and very fast paced sports like motor racing. I’m quite happy with the speed of a good lens and a 1.4x extender, but a 2x puts me into an area when I see my keeper rate drop below a threshold that I’m comfortable with. I appreciate this this is a bit of a generalization since we all have our own thresholds but it’s usually AF speed reduction that stops me using a 2x extender rather than an image quality reduction, and that fact alone might surprise a few people.

To summarize the disadvantages, an extender:

  • Reduces AF tracking speed and accuracy
  • Increases chromatic aberrations
  • Decreases lens sharpness
  • Decreases image contrast
2012 24 Hours of Le Mans
Le Mans 24 Hours, France, 300mm f/2.8 + 1.4x extender

Get Your Technique Down!

It’s often underestimated how much your long lens technique needs to improve when you start using extenders, particularly with longer telephoto lenses. There’s a radical difference between getting a sharp image with a 300mm and a 600mm, if you’ve just added a 2x extender for example. I believe this is another reason why extenders can have a bit of a bad reputation, so it’s worth paying attention to this.

The generally accepted starting point for shutter speed selection for a sharp image, is 1/focal length. That means if you add a 2x extender, you’ll want to double your shutter speed. Long lens technique is a whole article for another day, but keep in mind that you’ll want an elevated shutter speed or potentially a monopod or tripod to combat shake from handholding.

World Cup Downhill, Lake Louise, Canada – 300mm f/2.8 + 1.4x extender

Common Lens And Extender Pairings 

This table gives you the common available options but before buying an extender you should always consult the manufacturers specifications to verify your intended combination will work. With regards to most tilt-shift lenses, the manufacturers tend not to specify them as ‘officially’ compatible because correct aperture values are not passed to the camera, but they should work optically with no trouble. There’s also a few lenses out there for which the third-party Kenko extenders (1.4x, 2x) are able to work, where official ones do not. Canon’s 100mm f/2.8 L IS Macro for example.

A couple of spaces in the table have the value N/A for the Nikon only 1.7x extender where Nikon does not make a lens of that focal length.

photography lens extenders

Extender Usage Tips For Maximising Image Quality

There’s a few things that can be done in order to maximise the image quality you get from a lens/extender combination. Essentially we just need to follow the steps that we normally would when thinking about maximising image quality from a lens. The sharper we can get that original image, the less flaws will be magnified. The main thing is that we want to stop the lens down to increase sharpness and reduce chromatic aberration. Whenever I use an extender, I always try and stop down the aperture at least one stop from where I probably would have had it without the extender. The change in depth of field that this causes, is mostly cancelled out by the focal length extension anyway so there’s usually little to no difference in the overall look of the image, apart from the fact that you are zoomed in further of course. Since I shoot a lot of sports and wildlife where I need to maintain a fast shutter speed, I usually have to increase my ISO to compensate for the smaller aperture that I need to stop down to.

Since contrast is reduced, you also want to avoid using extenders in flat, low-contrast light. If you are able to reposition yourself and you’re struggling with the contrast, move until the sun is further off to one side where it will create more contrast.

In terms of AF speed and accuracy it all comes down to light levels. Try to avoid using extenders in very low light situations, especially the 2X ones. With wildlife photography it’s good to take this into account because much of the action can be at the very beginning or end of the day when light levels are very low indeed. If your plan is to always rely on using an extender then you might want to re-think it because in those low-light moments, the AF speed will be more greatly affected. This is one of the big reasons that I always tell people to buy a lens that suits their shooting without an extender, and use the addition of an extender for ‘bonus’ shots. I’d never recommend buying a lens with the sole intention of always having an extender mounted to it.

Balancing bird. Razor sharp using a 2x extender on a Canon 400mm lens.

Why 1.4x and 2x?

Whilst researching this article I realized all of a sudden that I knew why extenders are typically presented in 1.4x and 2x formats. It hadn’t really occurred to me before but suddenly it was obvious! This does probably fall beyond the bounds of interest to some of you but I’m including it because it interested me to know the answer so there must be a few folks out there who’d also like to know.

F-stop is defined as focal length/diameter and it’s for this reason that the maximum aperture is affected when we use an extender, it’s got absolutely nothing to do with less light being passed through the extenders. If you double the focal length in that equation, with the diameter remaining the same, you can see that the f-stop will be affected. In my article, Understanding Aperture, we talked about the progression of f-stops being in multiples of 1.4 (actually the square root of two, but close enough). Each increase in f-stop is 1.4x the previous one (2.8, 4, 5.6, 8, 11 etc.). The reason that 1.4x is chosen for the extender then is that it’s this multiplication of focal length in that equation that gives an exact 1-stop difference in maximum aperture! I’d always assumed that 1.4x was an arbitrary number that someone has chose at some point, but now I can see that it was actually chosen because in that equation, multiply the focal length by 1.4 changes the f-stop by one stop. Multiplying the focal length by 2x changes the f-stop by two stops because 1.4*1.4 is 2! It’s that same progression again. The powers that be could have chosen any values for the the extenders, but by using 1.4x and 2x, they deliver a one-stop and two-stop reduction in aperture which is just a nice easy way to deal with it! That’s really all it is!

Stacking Extenders

Using more than one extender at the same time is generally not accepted to provide acceptable image quality, but once again it depends somewhat on your intended use for the images. With excellent long lens technique, I believe it’s certainly possible to achieve what I would call ‘decent’ quality images of static subjects from a pair of stacked 1.4x extenders. Note the use of the word ‘static’ though, since AF speed takes a big hit when you try this.

Canon 200-400 bird photography
 Canon 200-400 using both the built-in 1.4x extender AND a second 1.4x extender.

Teleconverters vs Cropping

Can you simply crop in on your image instead of using an extender? Well…. a simple crop would have the same effect, up to a point. Without extending the lens, you aren’t getting the added compression and stronger out-of-focus background that comes from telephoto images though. Less noticeable if you are thinking of using a 70-200 rather than a big tele prime though. Another much bigger problem though is that you can’t accurately frame an image in your viewfinder if you always plan to crop it later. You’re essentially removing a huge part of the artistic process and I can’t wrap my head around why anyone would want to do that. It’s also a pain in the ass to have to crop hundreds of images and the reality is that you probably wouldn’t bother doing them all.

Now, from an image quality standpoint, what people want to know is whether the degradation caused by an extender, is less that that caused by cropping and then re-enlarging that crop to the original pixel dimension. I’ll hold my hand up says I’ve never performed a direct side-by-side…… but only because I think it’s not worth the bother. There’s no way that the extender is going to be a worse option than a crop and enlargement. Photoshop, and programs like OnOne Perfect Resize or Topaz Gigapixel AI do a great job, but it’s always noticeable. Oftentimes when I look at my extender images I can’t even tell if I used one or not when it’s a good lens.

Reader Question:

Is there a quality difference between using an extender or an aps-c sensor with a given lens to extend your telephoto capability (assuming the same ratio)?

This question came in via my personal Facebook page. The answer is yes, there is definitely an optical quality difference because the use of a cropped sensor doesn’t result in any of the image degradations we discussed earlier. None of the lenses flaws are magnified in any way, all that’s happening with a crop sensor is that a smaller area of the lens is being used to capture the image, the central part. This is if we just consider optics though. It get’s a little trickier when you consider that full frame sensors are inherently higher quality than APS-C ones, and whilst that has nothing to do with lenses and extenders, it should be taken into account.


To totally ignore the possibilities that an extender can give you would be a mistake. I hope that some of the sample images on this page can reinforce this notion, although web resolutions can’t be an ultimate judging point, you’ll just have to trust me that the pixel peeping results are very good and that I’ve satisfied clients all over the world with images created with an extender. You can’t just slap one on and expect to keep shooting the way you were without it though. A few simple adjustments in aperture and shutter speed will go a long way to maintaining the quality of your images.

Where To Buy

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Professional photographer based in Yukon, Canada, and founder of Shutter Muse. His editorial work has been featured in publications all over the world, and his commercial clients include brands such as Nike, Apple, Adobe and Red Bull.

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50 thoughts on “The Ultimate Guide To Extenders Or Teleconverters”

  1. “change in depth of field that this causes, is mostly cancelled out by the focal length extension anyway” i thought the depth of field would be as the original image also like the perspective remain unchanged

  2. I am wondering if the 2x seems to lose the ability to autofocus no matter what, I am curious to know if you’ve attempted to use a teleconverter from Sigma, Tamron, etc….?? Other companies compatible with Canon seem to succeed where Canon products for the exact same use are failing a bit. I read an article for the BEST lenses to use for my 5DS R and 4 on the list were Canon, the rest were Sigma or Tamron and Canon hasn’t made something to surpass them yet. It doesn’t surprise me but, when someone drops the coin on a 3600 set up, body only, lol the idea of LOSING AF and some other sacrifices to use Canon to its fullest potential is quite annoying. If other companies compatible with Canon have a 2x that keeps AF and produces the sharp clarity I’m used to…I’d be just as pleased to own that gear as I would be to have the 5DS R in the first place.

    Have you tried 2x converters from Sigma or Tamron for this purpose??? Thanks in advance for your comments!

    • I thought I’d find an example of what I mean… I don’t pay much attention to brand necessarily but I DO read comments sections and reviews….almost TOO obsessively. I hate shopping because I spend so much time reading pros and cons in the ratings sections that it takes me WEEKS to make what I would call an “informed” decision.

      When I asked about second hand, brand compatible 2x teleconverters and whether or not they had BETTER performance that you were aware of, I forgot that ^^^^^ brand in the list. Viltrox. I’d never heard of it before but the person giving the rating has 3 different cameras….including my 5DS R and the customer was more than surprised that the Viltrox allowed his camera to use AF and the shots still came out wonderfully. I mean…I’ve never even HEARD of that brand lol and I have been a photographer for 22 years now. They keep coming out with new stuff and…if you aren’t paying attention, you miss out. I remember the first DSLR I had lol like 18mp. The 5DS R is over 50mp and….you KNOW as soon as you bring it home, it is already obsolete. It is hard to come to terms with spending thousands when you KNOW they are in the process of developing something BETTER already. If they made cameras to last it would be just fine with me. But it seems like DSLRs have gone the way of the laptop. If it is on a shelf…something better is being produced by that company and everyone complaining about lighter laptops being absent from the market has spurred POS everything made out of plastic quality laptops that are LITERALLY MADE to be disposable. It is maddening. I really love the low light capability of my Canons which is why I went with them in the first place. But Nikon has really come along with their color saturation in the last 5 years. It is impressive. Nothing is compatible from one brand to the next between those 2 companies though, so…brand loyalty crises pop up everywhere.

      • Crucially this guy who left the review hasn’t tried the Canon one. I’m pretty certain you would find it performs better than the brand neither of us have ever heard of. It also depends on what lenses you use these things on. Some lenses respond better to them than others. There are some lenses I would use a 2x on without hesitation (400mm f/4 DO IS II) and some I would never recommend it (300mm f/4 L IS).

        • Just saw your comment here on the 300 f4 IS. I just got the Canon 300 f4 IS after a bunch of research. Very happy as my first semi-big prime. You say no 2.x on this lens, which I would agree (I don’t even own a canon 2.x yet) but I have a canon 1.4x ii. Would you use 1.4 on the 300 F4 IS prime? I felt this was the best option when needed getting to 5.6 and then stop down to f8 like you suggest in the article. I have very modern canon body’s which still allow focus even at f8. Goal here is 300 alone on FF and APSC for starting with still slow wildlife and not-fast sitting or soaring birds. (Lots of raptors / hawks here in Colorado). Plan on using the 1.4x on both FF and APSC with the 300 if needed. Right now I typically shoot 80-90% fast ballet dance live indoors and theater indoors using L fast primes. Wanted to try outdoors local wildlife with canon L. Being very iso and aperature sensitive from low light and having dealt with 3rd party lenses hunting in low light, I wanted a canon prime. Canon 300 F4 IS was the choice. yes older, with IS a bit loud but it’s been a wow on the images so far outside. Have not tried 1.4x yet. Just couious you thoughts for 1.4x ii on 300 f4 IS mentioned above. Have seen good shots and good results online. Thx

          • “Would you use 1.4 on the 300 F4 IS prime?” Maybe in an emergency if I wasn’t tracking a fast moving subject. But your needs and my needs are probably vastly different. Try it for yourself and evaluate the images. If you’re happy with them then that is great! Make sure you also test the AF speed though. That lens isn’t super fast, and I was not happy with it when using converter at all. 1.4x or 2x. Given that my 100-400 II’s image quality rivals that of my 400mm f/4 prime and my 200-400 f/4, I really prefer using that over a 300m f/4. Yes it lets in a little less light than an f/4 lens, but IMO it’s made up for by the zoom versatility, smaller physical size, faster AF and better IS.

    • I think there’s a number of things to address here. The main one is an understanding of autofocus. Autofocus systems in a camera require a lot of light to work accurately. When you add a 2x extender to a lens, it takes away a lot of that light, which is why AF with a 2x is considerably slower than without it. It’s akin to trying to focus your camera in the dark. Canon places limitations on an f/8 max aperture for AF usage because with any less light that this, the autofocus systems would really fall below an acceptable standard. There might be some 3rd party solutions that can hack this to work with the 2x extender, but the autofocus will not be very good at all.

      You can read a bit more in this article too:

      As for the “best lenses” list you mention, I would be EXTREMELY wary of these kinds of lists. Mostly they are written by people who haven’t used the lenses, and they are simply trying to cater for a range of people’s budgets within a single article. I’m not aware of a single Tamron lens that is better than the Canon equivalent. Sigma on the other hand have been pushing lens development very hard, and there are Sigma lenses that are on a par with Canon ones, but cost less.

      Also you are suggesting that there are equivalent lenses from these other manufacturers that maintain AF with a 2x when the Canon version doesn’t. That’s simply not true because whether or not the lens maintains AF with a 2x on it is dependant on the max aperture of the lens. If both the Canon lens and the equivalent third party lens have the same max aperture, their ability to autofocus with a 2x will be the same. If the third party lens had a wider max aperture compared with the Canon lens, then you aren’t comparing apples to apples, in which case it’s a bit pointless.

      I’d encourage you to read that other article I linked to. Your 5Ds R can AF with an f/8 aperture lens combination, so any f/4 lens with a 2x extender on it. If you lens doesn’t natively have an f/4 max aperture then you will lose AF, but I’m unaware of any third party lens that can overcome that issue. If your lens was f/5.6 and you put a 2x on it you’d be at f/11. Not only is that barely enough light to focus on a static subject, but it’s also barely enough light to see accurately through the viewfinder because as your max aperture drops, so does viewfinder brightness. There’s just less light coming in! And that’s another reason why Canon has the f/8 max cap.

  3. I have a very curious – solved – headache, guess I’m looking for a professional confirmation. I am not a pro here, and using Nikon D5500. Nikkor 55-300 5.6 lens and a super cheap Kemko 2x converter. Not sure when I got it, but it has helped, once I figured out what was going on. When ever I used the 2x converter, everything would overexpose by 2 stops. I would have expected the opposite, but for some reason the camera meter didn’t jive with reality. Once I figured this out, I was able to adjust the Exposure Compensation down 2 stops and all works fine, including all the other converter use headaches. I guess I’m just trying to wrap my head around the WHY of this. Certainly the sensor should be getting less light, and maybe in doing so, the meter is asking the lens what it is set to, and it gets back 300mm at f8, and gets some indication that there is a 2x converter, boosting the meter level up, causing the over exposure. So to override the camera computer, I have to compensate down two stops? Any thoughts? Thanks.

    • I’m afraid this one has me baffled. That shouldn’t be necessary at all because the camera metres the light coming through the lens after it has been through the teleconverter. This makes zero sense, although if you Google it there are plenty of people having such issues over the years, with third party extenders. Many citing issued with light angle and focusing screens. Essentially, all bets are off once you switch to a third party option like Kenko, especially an old cheap one. I’m glad you have it sorted, but I can’t give you a reason why it’s doing it. Totally weird!

        • Cheers Patrick! If you ever get to the bottom of it all, let me know! I’d be happy to add an addendum to the article just in case anyone else ever goes searching for info on a similar issue.

      • Hi,
        I just wanted to say I am seeing this exact problem of overexposed images with a second hand Kenko 2x teleconvertor. it seems consistent with different lenses. I am glad it’s not just me that it has baffled.

  4. Great article!

    1. In the section “Why 1.4X and 2X?”, you state “Each increase in f-stop is 1.4x the previous one (1.8, 4, 5.6, 8, 11 etc.).” The first number in that series is a typo and should be 2.8.

    2. I am planning to use two 2X teleconverters behind my lens. If I set the aperture of my lens to 2.8, will I actually be shooting at f/11, a loss of 4 stops?

    • Thanks for spotting the typo! Yes, if you stack two 2x extenders you will be at f/11. Although you won’t actually be able to set your camera to f/2.8, it won’t let you. The lowest it will let you set is f/11. You won’t have autofocus at that point, and your viewfinder will be VERY dark, and your images will be significantly softened… why are you stacking 2x extenders?? That’s very unusual for a good reason..

  5. Hi Dan…I enjoyed your article. I am an amateur photographer and frequently shoot my kids soccer games. I have a 5dii and use a 70-200 2.8 sigma lens w/is. I generally get pretty good shots but would like a little more reach. I do have a 2x sigma converter but I haven’t used it much. Assuming a fairly sunny day around noon and using the 2x converter what shutter speed and iso would you recommend? I assume i would want the camera to maintain the lowest fstop (5.6). I also shoot with shutter priority….not sure if this is correct. Thank you in advance for your help and all the best.

    • That’s quite a complex question. f/5.6 will give you the fastest shutter speed, but at the expense of some image quality since teleconverters benefit from being stopped down a little bit. I would recommend you have a shutter speed of at least 1/800 if you are tracking running soccer players, but again this could vary if they are sprinting 16 year olds, or 6 years olds with a little less pace. As for ISO, you should use ISO to achieve the shutter speed and aperture that you need. I really can’t tell you what to use exactly without being there, but you simply need to know that you will have more grain the higher you go. So don’t use an unnecessarily high ISO, use the one that gives you the shutter speed you require.

  6. For underwater photography, there can be good reasons for using a teleconverter with very wide angle lenses, even including a fisheye lens. (For example one may want to narrow the field of coverage while keeping the better corner performance behind a dome.) How would I calculate the change in diagonal field of view of the Nikon 8-15 mm fisheye at 15mm on full format (180 degrees at 15mm) with a 1.4x teleconverter?

    • Wow that’s a tough one. Will a TC even fit on that lens? I’m a Canon guy, but there are many lenses that simply can’t take a TC due to the position of the rearmost lens element. If it is possible, I’m afraid I have no idea at all how you would calculate such a thing for a non-rectilinear lens without experimentation.

  7. On a recent trip to the Galapagos islands I rented a Canon 100-400 and 1.4x extender for my Canon 5DS camera. I found the extender to result in too many missed shots for a few reasons you mentioned 1)slow autofocus, 2) light reduction, 3) camera shake in motorized raft. Upon reviewing my shots, I found that with the 50mp sensor sharp focus was very important to getting a quality image. My best shots were shot without the extender and [properly] using photoshop to enlarge the images after crop. With this camera, I found the light loss to be crippling with an extender. The 5DS does not perform well over 800 ISO. The added shutter speed (> 1/800), slow autofocus, and ISO limits made shots challenging in anything less than full sunlight with the extender.

  8. I have a 300mm f2.8 Canon prime. How does the 2 times converter work on this? Is it a good travel combo – how would it compare to 100-400 mk2 quality?

    • It depends on which version of the Canon 300mm you have? Do you have the IS Mark I or Mark II? Or perhaps something older? The IS Mark II version does quite nicely with the Mark III extenders.

  9. A hugely important issue I haven’t read here is a recommendation for aperture and shutter speed. You mention both but you stop short. In my experience I only get non-blurry results when I step down from f/8 to f/12 or better on my 600mm f/4 with a 2x tele. Also stability is hugely important, when you are shooting a scene at 1200mm your subject will shake, I leverage VR and. I shoot at iso 800, f/13 or better and set shutter speed above 1/2000 of a second to get acceptable results.

    • The problem here is that there’s an almost infinite number of lens and teleconverter combinations and all produce different images. On my older lenses and with older TCs I would need to stop down, but with my newest 400mm prime and Canon’s Mark III TCs I get tack sharp images at the widest aperture and I don’t pay much attention to that need. Even with a 2X.

      I don’t want to make a blanket statement like “you must always stop down” because the internet takes things to heart a bit too much sometimes and people might stop down when in fact it’s not necessary with their particular gear. It’s better to test your own combination and figure out whether stopping down is necessary or not.

  10. Thanks for your post. I have a 600mm Nikon lens and think I might need to upgrade my 1.4II teleconverter to 1.4 III teleconverter. My images don’t seem to be sharp-sharp. Either by my own shake movement or not using the mirror up mode. Or are they some tips on how to use the teleconverter that I’m not understanding???

    • No need to user mirror lock up mode. Many people shoot moving subjects with a tele lens and an TC. It might just be that your particular lens doesn’t work that well with a TC. If you think something is really a long way off you could send the pair off to be calibrated by Nikon. I would have thought that any prime 600mm from Nikon is capable though. Perhaps your expectations are too high? There will be some drop in sharpness.

  11. I haven’t been able to find this anywhere and I have really looked. I have the latest 105mm Micro-Nikkor on a D850. If I have a 1:1 ratio, that means that a rectangle of 36x24mm will fill the frame. Now, if I add a 1.4x to it, how much smaller will the life size be to fill the sensor?

    • To my knowledge, the magnification ratio changes by the same amount as extender. So it would become 1:1.4 and a rectangle of roughly 25.7mmx17.1mm would fill the sensor. I think… Why don’t you give it a try?

  12. Thanks for the useful review Dan.

    In fact, I’m an ardent fan of extenders. Say for arguments sake; I own all the super telephoto premium DSLR lenses. I’m sure you know even the longest glass i.e., 600mm f/4 reaches upto 600mm only on a full frame body. Of course the scenario will dramatically change if it’s mounted on an APS-C body like 7D II. These days I prefer using my full frame body for better IQ. In our situations, birds are sighted far away in most of the cases. And in reality I own only mid-range telephoto lenses for bird/wildlife photography as an enthusiast. My bag includes one 400mm f/5.6 and one 300mm f/2.8 IS II lenses. Bought the latter recently mainly to use with extenders. With a 2x on full frame and 1.4x on a crop body. Tried it with the 2x on crop body and the IQ took a hit though, captured all the shots I wanted whichever was within the range of my sight.

    When I imagine carrying a combo of a full frame body, a 600mm super telephoto lens and one 1.4x extender, always feel like having a porter with me for assistance!

    Bottomline is; do whatever is convenient and suitable for you. Keep capturing the beauties of nature and present to common people in order to motivate them for saving it.

    • Well said Sanjeed! There is no point having gear that inhibits your photography by making things too heavy or difficult to manage. It’ll only gather dust in a closet and your photo collection will not grow. It is for this very reason that I have owned a 400mm for so long, instead of a 600mm.

  13. Yep. A couple of teleconverters gives something of a zoom quality to a prime!

    I take a zoom wildlife shooting when I don’t know what to expect. It gives me framing versatility. If I know what to expect and have a prime to cover it, I can get the best possible image quality.

    Even a good zoom like the Sony FE 100-400 pairs well with a 1.4x TC, and works OK, to my eye, with a 2x TC *provided* there’s good light and enough pixels on the subject. So that lot offers a focal range of 100mm to 800mm and in a compact package. With an A9 the low-light AF is surprisingly good even with the 2x TC but yes, you pay for it with losses in speed and subject isolation.

  14. I’ve noticed that on some teleconverters the lens diameter is quite small (eg soligor cd7) surely this cannot handle the light coming from a fast lens like a f1.4 lens since the lens element diameter is too small. What are your thoughts on this, is there a maximum f-stop for certain teleconverters, it is never given?

    • To start with there are no f/1.4 lenses that are compatible with teleconverters anyway. You need to check which lenses work with TCs by looking at the manufacturer specification, or specifications provided by the maker of the TC if that is different.

      But either way, I still think you are thinking about this in the wrong way. Light is gathered at the front element of a lens and focused towards the rear. It doesn’t really matter how small the element at the rear is. It’s just glass, and glass has great light transmission properties. The reason you lose a stop of light, or two stops (with 1.4x and 2x TCs respectively) is because the TC effectively only captures the image circle of the middle part of the front element. Magnifying that part of the image to fill the full frame. So what you lose out on is the light gathered by the front element around the edges. It has nothing to do with small the optics are at the rear of the TC. Make sense?

  15. Howe does the canon 100-400 mkii work with the 1.4x? (I assume the 2x would not work well with the zoom.)

    Also, you indicated the quality of the teleconverter is less significant for final IQ, but you do reference the canon mk iii converters. Is there much of an improvement in the mk iii vs. the mk ii teleconverters?

    • There is no optical difference between the II and the III. The difference is in the electronics. The IIIs provide improved AF performance when mounted to Mark II and Mark III Canon super telephoto lenses.

      As for performance of the 1.4+100-400, it’s good with static subjects, but pretty useless for AI servo focus tracking on anything that is moving a great distance at speed.

  16. Based on my experience with the older, series II EF 1.4x and 2x, there was no compatibility issue with the EOS 50D, the older, M42 mounted 1000mm mirror lens and the series II converters. So that body+TC+M42 adapter combo was fine.

    Now, the combination of the EOS 7DMk2, the series III TCs (both of the Canon EF 1.4x and 2x TC) and the M42 lenses… only the annoying Error 01 code is the result. I have both of the chipped and the chipless adapters, I tried the TC without any lens and it seems, the newer, much better teleconverters are much more sensitive, regarding to the written compatibility. Only the officially allowed lenses are compatible. You cannot make any photo any other combinations.
    I could make photo with the combination of the chipless M42 adapter and the EOS 7DMk2, but without the teleconverters. The LiveView is working, the video is working, the photo mode is not. The big help would be a kind of Error 01 code hacking.

  17. I’m a Canon DSLR user and using both 1.4x and 2x extenders without any issues of sharpness or clarity. These tiny glass tools are really great and saves me from carrying enormous tele lenses for my wildlife photography. The heaviest I carry is EF 300mm f/2.8L IS II which easily produces a lovely 600mm f/5.6 with fast AF and helps comfortable capture with 2x.

    Thanks to the extenders.

  18. Another way to evaluate the effect of extenders on image capture is increasing pixel sampling of the primary object in a captured frame. I encountered this perspective in learning more about managing diffraction after acquiring a new high-pixel, full-frame camera and and more compact, lighter telephoto lens with a smaller aperture. Previous use of a 21Mpxl camera with wide-aperture lenses kept this factor from affecting my image capture workflow. The bottom line of sampling theory is more pixels on the primary subject in an image provides more headroom to post-process images, compensating for diffraction, movement and noise. Higher-pixel count sensors do this, but extenders increase pixel density regardless of sensor size. While there are many considerations in producing a final image, this is an approach to reduce concern regarding extender impact on image quality and focus on the other artistic characteristics desired in the published output. This is merely a summary, not a complete exposition or comprehensive discussion, but i found the reminder of sampling theory useful in determining how far to push into the diffraction zone with smaller aperture telephoto lenses with and without extenders.

  19. Hi Dan, I have a Canon 6 D (from 2014) and an EF 100-400 1:4.5-5.6L IS II USM Lens. I was thinking of getting an extender for greater flattening in landscapes. Would you recommend the 1.4 or the 2?

  20. “Wide-angle lenses are not compatible with extenders, not because you shouldn’t use them, but because you physically can’t use them due to the rear element design of wide-angle lenses.” Except I have a Nikon-mount Tamron SD 11 – 16mm F/2.8 (IF) DX II that I am using with my FF D810 with a 1.4x and 2x converter with very nice results. It also eliminates the vignetting issue which would result from using a DX lens on a FF camera. And AF still works.

    • Good to know. What I said stands true for the vast majority, but obviously, I don’t have knowledge of every lens design on the planet.

  21. Hi Dan,
    Greetings from the Sunshine Coast downunder.
    Thanks very much for your article. It’s helped me understand using teleconverters. I’ve just bought a Canon 100-400 RF lens and a Canon teleconverter x2. I did check that they are compatible. If I hadn’t read your article, I would have continued to use teleconverters as I had in the past – relying on guesswork and so, continuing to be disappointed. Thanks to your explanation I have a list of checkpoints to follow before I press the shutter (on a tripod, and with a cable or timer, this time.) It’s great to read an article where an issue is explained so thoroughly, clearly, and with such a deep understanding of the subject. Thanks again.

  22. Asking a question in 2023 so may not receive an answer. Canon 6d mk2, have Sigma 1.4 converter (& Sigma 150-600 & 100-400mm lenses). Will this Sigma converter work with Canon lenses? (E.g canon 70-200mm or if I trade in Sigma 100-400 to a Canon lens). Thank you

    • Yes, it will work. However, you’ll get better performance (autofocus and image quality) with Canon extenders on Canon lenses. Given the reasonable price of second-hand Canon EF teleconverters these days, you might also want to keep an eye out for them if you change to Canon lenses.


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