Autofocus with Extenders on Mirrorless Cameras (Podcast 674)

Autofocus with Extenders on Mirrorless Cameras (Podcast 674)

This week I answer a question from listener Derek Bezuidenhout, who recently asked what happens with mirrorless cameras when we add an Extender or Teleconverter, so I’m dedicating this week’s episode to answering that Derek’s excellent question, which I’ll read out to you now.

As we know, when using an extender we typically lose 1 stop of light for a 1.4X extender or 2 stops of light through the lens for a 2X extender.  And when using an extender on a DSLR, because of the way the focusing mechanism works, either the camera won’t be able to focus at all, or it will only be able to use the centre focus point.
With mirrorless cameras, the focusing mechanism is completely different – it uses the main sensor instead of dedicated focus points. So does that mean that with an extender on a mirrorless body we would be able to reliably use all (or most of) the available AF points, rather than just the middle one?

Derek Bezuidenhout

I can’t believe I didn’t think to mention this in my EOS R reviews, but I didn’t, so I really appreciate this question. Thanks, Derek! I’m sure you’ll be happy to hear that you surmised exactly what happens as you posed your question.

DSLRs Today

The camera manufacturers have made strides in their recent years, enabling most modern DSLR cameras to focus with extenders down to an aperture of f/8. What this means, is if you are using an f/4 lens, and put on a 2X Extender, which reduces your aperture by two stops, your camera’s widest aperture changes from f/4 to f/8, and you maintain autofocus on at least the center focus point, sometimes more, depending on the camera.

If however, the minimum aperture of your lens is smaller than f/4, for example like my 100-400mm lens, with its widest aperture of f/4.5 at 100mm or f/5.6 when zoomed in to 400mm, on a DSLR that only focusses down to f/8, because I would be forced down to f/11 at 400mm when adding two stops, the autofocus stops working.

The Mirrorless Advantage

Because Mirrorless cameras focus differently, as Derek pointed out, at least as far as my Canon EOS R goes, it will continue to focus down to f/11 and what’s more, according to Canon’s website, you can continue to use autofocus across the full range of 88% x 100% on the image frame if you are using Mark III Extenders, which I am. This is the same as when you are using no extenders. Apparently with Mark I or Mark II Extenders that is reduced slightly to 80% x 80% of the total image frame, which is still very good in my opinion.

When we consider that many DSLR cameras bunch the autofocus points up towards the center of the frame, it becomes quite limiting to where you can place your subject in the frame, especially when photographing something like birds in flight, when you actually might want to place the subject much closer to the edges sometimes.

Demo Video

I tried to think of a way to show you the speed of the autofocusing system and how wide an area the camera will focus across, and figured it was probably best to just show you in a video, so I hooked my EOS R up to a video capture box and recorded my screen as I switched between my 100-400 f/4.5-5.6 Mark II Lens with no Extender fitted, to using it with the 1.4X Extender, and then the 2X Extender. I also show the 200-400mm with its built-in 1.4X Extender engaged, and a 2X Extender fitted, so both are focussing at f/11 with the 200-400mm lens at a focal length of 1120mm.

Extender Demo Setup
Using LED video lighting to demonstrate the EOS R autofocusing with Extenders fitted

Finally, I disengage the built-in 1.4X Extender to show you the effects of just having the external 2X Extender fitted. For all of these demonstrations, I was using the Canon Control Ring Mount Adapter to fit these EF lenses to the RF Mount of the EOS R.

Things to note are that autofocus does slow down very slightly, especially when using the 1.4X and 2X Extenders together. Also note that I did these demonstrations in my studio with bird ornaments, so in reality, when the autofocus has further to physically travel, it can be a little bit slower than you’ll see in the video as well. Anyway, here is the video, so please take a look.

I hope you found that interesting or at least useful to see. I find it amazing that we can now use autofocus at this level, down to f/11 apertures.

Upcoming Autofocus Improvements via Firmware Update

I noticed too that Canon have just announced a firmware update to improve autofocus further. On the US website it just says coming soon, but in Japan it is slated for the end of September. Here is what Canon are saying:

AF function improvement for EOS R and EOS RP Cameras

A new firmware update for Autofocus (AF) with the EOS R and EOS RP cameras will soon be available. This exciting new update will offer enhanced AF functions to help you better view, track and capture subjects. The three main components are:

  • Eye Detection AF will be improved so you can better focus on a moving subject’s eye even if it is far away or when the face appears small in the viewfinder. 
  • AF frame tracking is improved so there is virtually no delay between the actual focusing and when it’s displayed in the AF frame, helping you continuously track the subject and shoot comfortably.
  • The AF function works faster overall so even at a distance, you can capture the subject quickly.

This firmware will be available via a free download in the coming weeks. Stay tuned.

I look forward to seeing how these changes affect autofocusing, and I can’t wait to see where the autofocus on mirrorless cameras leads us next. I honestly did not expect autofocus on these cameras to be anywhere near as good as it’s proven to be. Being able to focus on a sea eagle a split-second before it snatches a fish from the sea, as in this photograph from this years Japan Wildlife Tours, I had no complaints, but improvements are always welcome.

Steller's Sea Eagle Snatches Fish from Sea
Steller’s Sea Eagle Snatches Fish from Sea

Anyway, we’ll wrap it up there for this week. Thanks once again to Derek for the great question! Also, note that I’m running behind on the development of my new Mentorship system. Various things and other commitments have kept me a little too busy lately, but I am working on it and hope to release something very soon.

Show Notes

Music by Martin Bailey


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Podcast 236 : The EF 70-200mm F2.8L IS II USM Lens with Extenders

Podcast 236 : The EF 70-200mm F2.8L IS II USM Lens with Extenders

Last week, I released a review of the new Canon EF 70-200mm F2.8L IS II USM lens, and was asked how the version II of Canon’s workhorse lens fairs with Canon’s Extenders (teleconverters)? I’m pleased the reader/listener asked quickly, as I sold this lens on Saturday, but before I took it to the store to which I sold it, I did a few more tests, but with the converters attached this time, so today I’m going to share those results with you as well.

I would like to remind you before we start that these tests take a lot of time and effort, so if you intend to buy this lens and you shop with B&H, please use the link at the bottom of the post, which although does not affect the amount you pay in any way, will send a little commission my way, to help offset the costs of doing these reviews and Web site fees etc. In fact, if you buy anything from B&H, clicking through from the tile here on my blog will earn me a little commission. It’s a great way to help out without digging into your own pockets. If do you want to help out, but don’t shop at B&H, although I rarely mention this, there are donation buttons to the right here on my blog and on my Podcasts page. This Podcast and Blog will essentially always be free, but people have asked for donation buttons in the past, so I made them available. Note too that I add the name of people that are kind enough to make donations to my Thanks page.

ISO 12233 Resolution Test Chart
ISO 12233 Resolution Test Chart

So, I was really pleased that I was reminded to test the new Version II 70-200mm lens, before I sold it on, as I used to use mine with the 1.4X Extender regularly, with my old 5D. It was partly because I could use the old 70-200 with the 1.4X Extender that I sold my old 100-400mm lens. I’d not taken both out with me since 2006. I stopped using the 70-200mm with the Extender though, once I upgraded to the 1Ds Mark III and the 5D Mark II at 21MP, they basically out-resolved the old 70-200mm F2.8 lens even without the Extender, so it goes without saying that images using the 1.4X Extender were just not usable. It was because of this that I’d failed to think of this combination when I did my original tests, but I was pleasantly surprised by the results I found on Saturday morning.

Again, I used the ISO 12233 Resolution Test Chart that I downloaded from Cornell University’s Web site. I tested both the 1.4X Extender and the 2.0X Extender, but I only tested at 200mm with the 2.0X Extender. This was partly because of time, but also because it’s safe to assume that people probably have both Extenders, or just the 1.4X and would only use the 2.0X Extender when you really need the extra reach. I know that if I didn’t need to get out to 400mm, or just short of it, I would probably reach for the 1.4X Extender.

Again, I created some animated GIF files to show you the difference between the two lenses. The first one here shows the center of images shot at 70mm, or 98mm with the 1.4X magnification, 115mm or 160mm with the Extender and 200mm, which of course becomes 280mm with the Extender fitted. All of the images here were shot wide open, at F4, which is the widest aperture available when using the 1.4X Extender.

Also note that I moved back a little when shooting at each of the focal lengths, to fill the frame with the chart, but could only move back so far because of my kitchen wall, so the resulting images are not an accurate representation of the relative magnification of the Extenders.

70-200mm Version II - All Focal Lengths @ F4
70-200mm Version I and II – All Focal Lengths @ F4

You can see that there is a big difference between the old version and the new version of this lens, when shooting with the 1.4X Extender fitted. At the extremes of the focal length, 98mm to 280mm, the lens is still extremely sharp, even with the 1.4X Extender fitted, and the lens wide open at F4. The interesting thing here, as with my findings last week without the extenders, is that the middle focal length of 115mm is actually the weakest. It’s still sharper than the version I 70-200, and very usable in my opinion, but it’s not quite tack sharp, as are the extreme focal lengths.

Although the new version of the 70-200 is sharp wide open at the extremes, usually, lenses get a little sharper with Extenders when you stop the lenses aperture down a little, so next we have six comparisons of the three focal lengths through the entire aperture range, from F4 to F32, in full stops. First is the old version I lens, at 70mm or 98mm with magnification, and you can see that it does sharpen up just a tad at F5.6, to an almost acceptable amount. F8 and F11 are also quite good. F16 and F22 start to lose contrast as well as soften up again, and F32 is pretty much unusable. It’s very soft with little contrast.

70-200mm V1 with 1.4X Extender @ 70mm
70-200mm Version I with 1.4X Extender – All Apertures @ 70mm

Here are the results from the Version II 70-200mm lens, again at 70mm (98mm) through the entire aperture range. Even at F4 the results are very good. If anything, it gains a little contrast when you stop down to F5.6, and perhaps just a tad sharper. F8 and F11 are still good, but perhaps a little less sharp and lower contrast than F5.6, so the old advice of stopping down to F8 when using the Extender may no longer be valid. F16 through F22 start to lose more contrast and sharpness, though probably still usable, and F32 is perhaps usable at a stretch, but probably best avoided. I’m sure you’ll agree this is a huge improvement over the Version I lens though.

70-200mm Version II - All Focal Lengths @ F4
70-200mm Version II with 1.4X Extender – All Apertures @ 70mm

Next we see the Version I 70-200mm F2.8 lens again cycling through the entire aperture range, in full stops at 115mm or 160mm with the magnification calculated in.

70-200mm Version I - All Apertures @ 115mm
70-200mm Version I with 1.4X Extender – All Apertures @ 115mm

In contrast to the new version, the old version I lens is best in the middle focal length, being relatively sharp at F4, sharper still at F5.6 and F8, then slowly tapering off again from F11 through F22, then dropping considerably at F32. This range with this lens  is actually pretty close to the new version of this lens, with the exception that the Version II lens is considerably sharper at F4. This is good news for me, as I shoot wide open most of the time, but if you stop down a lot, especially when using an Extender, remember that the old version is pretty good in the middle focal length range, but weak at the extremes.

70-200mm Version II with 1.4X Extender - All Apertures @ 115mm
70-200mm Version II with 1.4X Extender – All Apertures @ 115mm

OK, so next let’s look at the pair of animations from the two lenses at 200mm or 280mm. First from the Version I lens, we can see that although it gives a poor show wide open at F4, it improves slightly through F5.6 and F8, but then really sharpens up quite a lot at F11 and even F16, though it does start to lose contrast from F16, up through to F32. If you own the first version of this lens though, and use it with the 1.4X Extender, note that F11 is pretty usable when zoomed out fully to 200mm, for an effective 280mm focal length.

70-200mm Version I with 1.4X Extender - All Apertures @ 200mm
70-200mm Version I with 1.4X Extender – All Apertures @ 200mm

We can see from the next animation though, that at 200mm, or an effective 280mm, the Version II lens gives excellent results again. F4 through to F8 are excellent, F11 drops in contrast slightly, with F16 and F22 a little worse, then F32 pretty low in contrast, with sharpness also gradually dropping off through F16 to F32. Still though, this is very usable, and when you consider that you’ll usually be using an extender to get that extra reach, this result on the long end is very encouraging.

70-200mm Version II with 1.4X Extender - All Apertures @ 200mm
70-200mm Version II with 1.4X Extender – All Apertures @ 200mm

All in all, despite the middle focal length being a little disappointing, I think it’s safe to say that the 70-200mm F2.8L Version II lens can be used with a 1.4X extender with little concern of image quality dropping too much.

So what about the 2X Extender? Below, first we have an animation showing the difference between Versions I and II of this lens, with the 2X Extender fitted, shooting wide open at F5.6, which is the maximum aperture when using this Extender. Here you can see that the original Version I lens gives a pretty poor show with the 2X Extender. Most lenses do actually. The only lens I own that I can comfortably use the 2X Extender with is the 300mm F2.8L lens. It produces slightly hard, contrasty edges, but is certainly sharp enough to be usable, especially when I need 600mm but don’t have the big-guns with me. It’s hand-holdable too, if you can get a fast enough shutter speed.

Anyway, we can see here that the Version II lens is absolutely acceptably sharp with the 2X Extender fitted, zoomed out fully, for an effective focal length of 400mm.

70-200mm Version I and II with 2X Extender – F5.6 @ 200mm (400mm)

The next animation shows you the old Version I lens at 400mm, cycling through all apertures from F5.6 to F32, in full stops. Although it does start to sharpen up a little as you stop the lens down, even as much as F32, the contrast starts to drop off too much, and I personally think this combination is just not usable, even in a push, and certainly not hand-held. By the time you get an image even anything remotely resembling sharp, you are stopped down so far that you’d need a multi-second exposure even in good sunlight.

70-200mm Version I with 2X Extender - All Apertures @ 200mm (400mm)
70-200mm Version I with 2X Extender – All Apertures @ 200mm (400mm)

This last animation shows the Version II lens with the 2X Extender stopping down from F5.6 to F32. As I mentioned earlier, F5.6 is very usable, and F8 is perhaps a little better, and F11 is similar to F5.6, then it starts to drop at F16 and F22 is a pretty soft with low contrast. F32 is a little too soft and lacks too much contrast for comfort. Otherwise though, I’d say this is a pretty usable combination.

70-200mm Version II with 2X Extender - All Apertures @ 200mm (400mm)
70-200mm Version II with 2X Extender – All Apertures @ 200mm (400mm)

I will try using both Extenders in the field in the coming weeks as well, and will certainly report my findings back later based on some real-world examples, especially if I find that field use doesn’t quite match what my tests here have shown. In general though I’d say that these tests confirm that the old 70-200mm F2.8L lens was not really usable with Extenders, although it did perform pretty well in the mid focal length range. It also shows us that the Version II 70-200mm F2.8L lens is very usable with the 1.4X Extender and looking pretty good with the 2X Extender as well, which is great for when you just don’t want to take out the longer glass. It is also a viable alternative to the 100-400mm lens in my opinion, which I was not happy with after the days that I used it with my 20D, at 8 mega pixels, which it could just about cope with. There are sharp spots with the 100-400mm, and the slight amount of sharpness is certainly offset by the versatility of the lens, but I won’t miss mine, until Canon decide to release a version II of the 100-400mm as well. That would get me thinking.

Podcast show-notes:

Buying this lens from B&H? Use this link and support this Web site (does not affect the cost of the lens):

You can get the 1.4X Extender and the 2X Extender from B&H as well. ( and

Cornell University’s Resolution Test Chart:

View all of my 70-200mm F2.8L IS II USM Lens images:

Music from Music Alley:


Download the Enhanced Podcast M4A files directly.

An Exercise in Magnification with Extension Tubes

An Exercise in Magnification with Extension Tubes

Extension tubes are really handy. Because they have no glass elements, they aren’t very heavy, and you can couple two or three together and put them into one pouch, and they are no bigger than a small lens, so they fit in the photographer’s vest without taking up much room.

When you put an extension tube between the lens and the camera, your focus distance decreases, so you can focus on things closer than you would be able to without the tube. The caveat is that they also reduce the maximum focus distance, so once fitted, you can no longer focus on infinity.  The wider the lens, the more drastic the change in focus distance. With wide angle lenses, you almost touch your subject before you get it in focus. It can give you some fun effects, but not that practical. Tubes work best with 50 to 100mm lenses, or even with very long lenses that usually have very long minimum focus distances, to allow you to shoot small birds quite large in the frame. Many people use extension tubes for macro or close-up photography, to get larger than life-size, or 1:1 magnification.

Having just bought a second 25mm extension tube (Canon Extension Tube EF 25 II), to give me 50mm, or 62mm with the 12mm extension tube also fitted, and also after receiving a question on my Canon EF 100mm F2.8 L Hybrid IS Macro lens review blog post, I figured I’d do a few tests to see how the combined extension tubes and a Canon 1.4X Extender effect the magnification of the lens.

Play Time!

Play Time!

The 5D Mark II sensor dimensions are 24x36mm, the same size as a 35mm film frame. This means that when shooting at life-size, something that is 36mm wide would be 36mm on the sensor.

For my tests I cranked the focus back as far as it would go, and focused with focusing rails, to get as close as possible. The first thing I noticed as I framed the first test image is that the 100mm F2.8L IS MACRO lens actually focuses slightly larger than 1:1, or life-size, as the resulting image included just 34.5mm of a steel rule. This means that right off the bat, we are actually shooting at 1.04:1, but to show the effect of the extension tubes and 1.4X Extender, I’m going to use 1:1 as the base.

Here are the images, straight out of the camera, with no cropping or rotation or anything (though re-sized for Web of course).

First, just the straight 100mm F2.8 L IS MACRO lens, with nothing attached, giving us a slightly larger but as good as life-size image:

Straight 100mm 1:1 Lifesize

Straight 100mm 1:1 Lifesize

This is with one Canon 25mm extension tube attached. This results in 1.35:1 magnification (below):

One 25mm Extension Tube

One 25mm Extension Tube

This is with two Canon 25mm extension tubes attached, giving us 50mm of extension. This results in 1.73:1 magnification (below):

Two 25mm Extension Tubes (50mm)

Two 25mm Extension Tubes (50mm)

Next I added the Canon 12mm extension tube to the two 25mm tubes, giving us 62mm of extension. This results in 1.9:1 magnification (below):

12mm + 2 x 25mm Extension Tubes (62mm)

12mm + 2 x 25mm Extension Tubes (62mm)

Finally, I tried the Canon 1.4X Extender II. This gave me a 2.71:1 magnification (below):

1.4X Extender + 12mm + 2 x 25mm Extension Tubes

1.4X Extender + 12mm + 2 x 25mm Extension Tubes

Note that the Extender doesn’t effect the minimum focus distant as tubes do, so for this last shot I didn’t have to crank the focusing rails, like in the other shots, though I did fine tune the focus.

Here’s a table of the results, for quick comparison.

Lens and Modifier Width on Sensor
100mm Macro without any tubes etc. 34.5mm 1:1
With 25mm extension tube 25.5mm 1.35:1
50mm (2x25mm extension tubes) 20mm 1.73:1
62mm (2x25mm + 12mm tubes) 18.2mm 1.9:1
62mm Ext Tubes + 1.4X Extender 12.75mm 2.71:1


Well, on the magnification front, you can get down to 1.9 and 2.7X magnification pretty easily, with stuff that you may well have with you anyway. I own the Canon Canon MP-E 65mm F2.8 1-5x Macro lens as well, but I don’t always take it out, unless I know I’m going to specifically shoot macro. Also, although I haven’t yet tested this, I’m sure the Hybrid IS works to a degree, even when shooting larger than life-size, so that is another advantage over the 65mm.

The whole setup does get pretty long with 62mm of tubes and the 1.4X Extender, which can be good for getting close to your subject, but also makes it a little more difficult to balance than the MP-E 65mm macro lens. One other benefit of the 100mm with tubes, is that you have some focusing leeway. With the MP-E 65, you have no focus mechanism as such, although you can increase or decrease magnification which does move the focus. Basically though, you have to use a focusing rail and move whole setup (camera and lens) back and forth to focus.

I didn’t use a controlled constant light-source, just shooting with ambient light in my kitchen, but one thing to note is that for each 25mm tube, I had to increase the exposure by 2/3 of a stop. The 12mm tube needed 1/3 of a stop, and the 1.4X magnifier required an extra stop of light to create images of the same exposure.

One other thing to note is that I was impressed with the image quality right through the range. The whole series are pretty impressively sharp, to say that I’m sticking a lot of distant and even glass with the 1.4X Extender, between the 100mm Macro lens and the camera.

I’m not sure that I’ll use all of these tubes and the 1.4X Extender in the field, but it’s good to know that it’s there as an option.

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Canon Extension Tube EF 25 II |Canon Exension Tube EF 12 II | Canon 1.4X Extender (Teleconverter) |Canon EF 100mm f/2.8L Macro IS USM Lens | Canon 5D Mark II Digital SLR Camera

Teleconverters and Extension Tubes (Podcast 24)

Teleconverters and Extension Tubes (Podcast 24)

Welcome to episode 24 of the Martin Bailey Photography Podcast. Last week I talked about using telephoto lenses. Telephoto lenses can be a challenge to use well due to the additional camera shake brought about from the magnification of the lens. Today I’m going to talk about Extenders as Canon terms them, or Tele-converters as most other camera manufacturers term them, and also about Extension Tubes, which are similar to tele-converters, but behave differently and have different applications, so we really should get into that here too.

If you didn’t listen to episode 23 yet, we basically learned that the longer the lens, the more prone to camera shake your images will be, and I mentioned a few ways we can minimize the risk of this, including the rule of thumb I use, which is using the focal length you are shooting at as the slowest advisable shutter speed. If you are not so confident with this, it might be a good idea to go back to episode 23 first. If you are OK with this I would not say it is essential to listen to these Podcasts sequentially.

Also, before we move on to today’s main topic, I’d like to give you a tip I received by mail this week from Don McKay of McKay Photography out of Portland, Oregon in the US, which is a great way to practice keeping your camera still while hand holding. Don says “one of the biggest problems is when you push the shutter button. Most people push the shutter button too hard and move the camera making a blurry picture. The technique is to temporarily tape a mirror on the lens cap, and set a strong light such as a flashlight in front you, so that you get a reflection of the flashlight on the wall in front of you. Try pressing the shutter button and watch the reflection on the wall. If it moves then you are moving your camera. Practice pressing the shutter button until the reflection no longer moves.” Thanks Don for this jewel of advice. I’m sure many listeners will have fun trying and will hopefully benefit by being able to release their camera’s shutter without introducing as much camera shake as before.

So to get to the main topic for today, first let’s talk about extenders or tele-converters. There are various reasons why you might consider investing in a tele-converter. They are a relatively cheap way to increase the focal length of your existing lenses. This obviously is going to save you money, as you don’t need to buy the longer focal length lens. Also, it saves you carrying around the additional weight of multiple lenses. Sometimes you simply want to get even closer to your subject, even with an expensive super-telephoto lens.

Tele-converters fit between the lens and the camera body, and actually contain additional lens elements to maintain as much image quality as possible without changing the lenses minimum and maximum focusing distances as Extension tubes do, but we’ll get to that shortly.

Orthetrum albistylum
Orthetrum albistylum

First let’s take a look at shot number 697 on my Web site. Remember you can see the photos in iTunes or this first one on your iPod, but you can also go to my Web site at and enter this number into the field on the top page or the Podcast page and click the orange button to jump to the image in my online gallery. You can also navigate to this episode in the list and just click the thumbnail you’ll find there.

In photo number 697 you can see that I have used my EF 100-400mm F4.5-5.6L IS USM lens with the EF 1.4X Canon Extender. I used this lens with the Extender to shoot this dragonfly perched on a broken reed stalk in a park near my home here in Tokyo. I used the Extender as I wanted to fill the frame with the subject, as the background would not have added much to the shot, being just the murky pond water, and also I wanted to allow the viewer to see as much detail in the insect as possible. When you think of shooting insects, you might think of a macro lens, but at this distance a 100mm or even a 180mm macro lens would not allow you to fill the screen with the subject, so the only remaining option to avoid cropping a tiny portion from a shot made with a shorter focal length, is to get out the long lens and put on an extender to make your image.

When you put on an extender or tele-converter, it multiplies the focal length by the number in the name of the extender. In this case 1.4, but if you used a 2 times extender, the focal length would be doubled. I shot the last image at 400mm with the 1.4 extender, so that gives me a focal length of 560mm. Remember too, that like me in this shot, if you use an extender with a Digital SLR, you might also need to calculate in the crop factor to get the effective focal length. I was using a Canon EOS 20D here, which has a crop fact of 1.6, so the effective focal length was approximately 900mm.

The other thing that will happen when you use an extender is you will loose one stop of light for a 1.4 times extender or two stops of light for a 2 times extender. This means that if you use a 1.4 extender with an F5.6 lens, you will have a maximum aperture of F8. If you use a 2 times extender with an F5.6 lens, you will have a maximum aperture of F11. Which means basically if you are in Aperture Priority mode, your shutter speed will be twice as slow, or doubled with a 1.4 extender and four times as slow, or quadrupled with a 2 times extender. Let’s use the dragonfly shutter speeds as an example. The aperture used here was F8. This lenses maximum aperture at 400mm is F5.6 and I had the lens wide open. The 1.4 extender forced the aperture down to F8, which is what I shot at. The shutter speed was 1/160 of a second. I was actually shooting in manual exposure mode here, but had been using Aperture Priority, without the 1.4 extender, the camera would have set a shutter speed of 1/320 of a second, which is half the shutter speed. This is because I have lost one stop of light due to the 1.4 times extender. It is due to this loss of light, and the fact that it was not all that bright a location, that I selected an ISO of 400. Also note here that I was using a tripod, not hand holding.

Japanese White Eye
Japanese White Eye

Let’s take a look at one more example of an image shot again with the 100-400mm lens, but this time with a 2 times extender. Take a look at shot number 575 of a Japanese White Eye bird. This is actually not a great example of the multiplication of the focal length, as I was actually using a focal length shorter than the last example shot, because I shot this before I bought the 1.4 times extender. It was shot at 520mm, which was actually 260mm with the 2 times extender. This was also shot with the 20D, so the effective focal length with the crop factor is 830mm. A quick reminder, but if you look below the shots in the gallery you can see all the camera settings, and you can see that for this shot the aperture is set to F11. This time too the lenses aperture was set at F5.6, but the 2 times extender forced an aperture of F11, which is two stop smaller than F5.6.

We can also calculate what the shutter speed would have been had I shot this at F5.6. We can do this by first halving the final shutter speed of 1/640 of the second to get 1/1250, which is one stop, the same as we’d lose with a 1.4 times extender, and then halving if it again we get 1/2500 of a second, which is two stops, which is the amount of light you lose with the 2 times extender. Again here I was using ISO 400. In this example note too that I was hand-holding, so I needed a shutter speed fast enough to eliminate camera shake. Even with the Image Stabilizer turned on, at 1/640 of a second, some of the shots of this White Eye were blurred and unusable, emphasizing the advice to shoot in bursts when using telephoto lenses, especially when your shutter speed is less than the effective focal length you are shooting at.

One other very important thing to bear in mind is you loose auto-focus with some combinations of camera and lens with the 1.4 and 2 times extenders. I’ve not looked into this for Nikon cameras, but the Canon extenders, you basically need a widest aperture of F5.6 for auto-focus to work. This means that the 1.4 times extender will give you auto-focus, with the center focus point only in most cases, if you use it with a lens with a maximum aperture of F4 or wider. The 2 times extender will work similarly if you use it with a lens of F2.8 or wider aperture lens. This is because F4 becomes F5.6 with the one stop the 1.4 extender costs you, and F2.8 also become F5.6 with the two stops the 2 times extender costs you.

Note too that there are certain combinations of Extenders and lenses that work, and some incompatible combinations. The same goes for extension tubes. So to find out if your expected combinations are compatible, and to see what auto-focus limitations you’ll have, you really need to check your lens’s instructions manual before deciding on what to buy.

One other thing to bear in mind, so it really goes without saying is depth-of-field becomes much shallower as the focal length of your lens increases, of course, depending on how far away your subject is. I talked about this in episode 23 too. I just wanted to note though that there is nothing difficult to calculating depth-of-field when using teleconverters as it follows the normal rules that apply for that focal length. That is, 300mm lens with a 2 times extender and an aperture of F8 has exactly the same depth-of-field as a 600mm lens with the aperture set to F8.

One last thing on extenders before we move on; with regards to actually buying an extender, there was a discussion started in my forum this week in which Wayne Grant from Connecticut, USA mentioned that he’d purchase the 1.4x without question. Wayne considers it a ‘must have’ for telephoto prime lens work (or with the 70-200/2.8 and other fast zooms). But the 2.0x is more optional – a later addition to your kit. I couldn’t agree with Wayne more, although I actually bought the 2.0x first. This is a flaw in my thinking though. Basically the cost of the 1.4 and the 2.0 times, here in Japan at least, is exactly the same, and I followed my Mum’s advice from when I was a kid, which is, “If you gonna have one, have a big-un”. I went for the larger one first, but soon realized that it was too much for most occasions.

So, moving on to the other topic I wanted to briefly cover, and that is Extension Tubes. Whereas we use extenders or tele-converters to increase the focal length of the lens without affecting the minimum and maximum focusing distances, extensions tubes enable you to shorten the minimum focusing distance so that you can focus on subjects much closer to the lens. It is important to note that the maximum focusing distance is greatly reduced also, often to the point where the lens cannot realistically be used for anything other than very close work while the extension tube is attached. The degree to which the focusing distances are reduced depends on the lens you are using it with. Again you’ll need to look at your lens manual to see the focusing distances with the available extension tubes attached.

Sometimes you’ll find that the lens is not compatible, as with Extenders or Tele-converters. Sometimes a zoom lens can only be used only in the telephoto range, and not compatible in the wide angle range. Most of the time as far as I know, you retain auto-focus with extension tubes too, which is handy, but I find that for most very close work, switching to manual focus is better anyway.

Canon does two extension tubes, the EF 12 II and the EF25 II. The number in the name indicates the length of the tube in millimeters. Nikon I believe also does an 8, 14 and 27.5mm extension tube. There are also a very competitively priced set of 3 extension tubes from Kenko that includes 12, 20 and 36mm tubes.

Rape Flower 2005
Rape Flower 2005

I only own the EF 12 II, and one shot with this fitted between my EOS 20D and the Canon EF-S 17-85mm F4-5.6 IS USM lens is number 601 on my Web site. Actually, with this combination of lens and body, the focusing range is incredibly shallow and very close to the front element of the lens. I recall that I actually ended up getting pollen on my protector filter while shooting this. It was shot at F5.6 for 1/200 of a second and the ISO set to 100. You can also use extension tubes with Macro lenses to enable you to get incredibly close to the subject should you want to. This is something that I want to experiment with more in Spring this year, so I might well have an update for you at that time.


So that’s about it for this week. Once again I hope that this has been of some help. Remember that you can contact me with feedback or requests via the Contact Form on the Podcasts page at or with private messaging via the forum if you are a member. With forum members now up to almost 200, it is becoming quite a lively place to discuss photography related issues at all levels, so if you’re interested, come along and register and join in. Of course registration is free and just takes a moment. I’m always interested to hear your views and we have a great crowd in the forum too, so I look forward to hearing from you.

Have a great week, and happy shooting! Bye-bye.

Show Notes
The Music in the first 28 Podcasts is copyright of William Cushman © 2005, used with kind permission.


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