This F-1 has
an FD 300mm f/2.8 lens on it but
between the two is an FD 2x extender resulting in a 600mm f/5.6 lens. Such a small device for such a big result.

Lens Extenders

How to Make Little Things Large

Canon created various extenders for lenses from the FD to the EF series. These are lenses that can be inserted between the camera and a main lens to increase the effective focal length of that lens. Its a neat trick.

The downside is that the extender results in the light intensity on the film plane being lower, i.e. you lose one or two f/stops.

The first examples of these extenders I can find are for the FD series and they pose a bit of a problem. I can find very little about their origin or how they came 

about. I am not even sure how many FD extenders there are. And there are reams written about their performance but there seem to be no definite conclusions. So lets deal with what we do know and have a little look into how good they are.

There are four FD extenders that I know of. They are divided into A and B extenders and they either multiply the original focal length by 1.4 or 2. The various manuals and brochures are somewhat confusing about this but they seem to agree that A extenders are for lens focal lengths of 300mm or more and B extenders are for lenses up to 300mm. What seems uncertain is how short a focal length they will work with. However, I gather that shorter than 100mm the quality may start to deteriorate.

Extender FD 2x-A

The extender FD 2x-A is intended for lenses of 300mm or greater. It effectively doubles their focal length and costs 2 f/stops in lens speed.

It was using this extender on my FD 300mm f/2.8 Florite lens that I became aware of the problems of shooting with long lenses, specifically, camera shake and unstable air. Which suggests to me an explaination for the confusion on the internet about how good these things are. Poor results may not be the fault of the extenders but of poor technique with long lenses.

All of the lens controls are passed back and forth between lens and camera through the extender so that the lens can still be used normally.  Even the full aperture signal pin height is transmitted to the camera body via a floating plunger.

The extender is a small device and weighs very little compared to the camera or the long lens attached to it. It is a way to carry two lenses for the price of one. And using it on very long lenses can give you access to focal lengths for which prime lenses are not made.

My copy of this extender, serial number 26743, was made in November 1979 according to the Date Code.


Instruction Sheet, Publication II 01-053D, packed with each FD 2x-A Extender.

So, with which lenses do we use this extender? If you read the Instruction Sheet above, it says “It can be used with any FD telephoto lens with a focal length between 100mm and 800mm and with any FD Zoom Lens having 100mm within its range.” This is repeated in several brochures that list this extender alone. However, in the brochure Canon Interchangeable Lenses, Publication C-IE-075AL, it says that “Extender FD 2x-A is for all FD lenses that have a focal length greater than 300mm, including FD zoom lenses which have 300mm within their range.”

It appears that prior to the development of the FD 2x-B the wider range was recommended but I suspect that it suffered at the lower focal lengths and the 2x-B was developed specifically to address these issues. So the instruction now is to use this extender with the longer focal lengths..

Extender FD 2x-B mounted on an FD 135mm f/3.5 medium telephoto prime lens.

Extender FD 2x-B

My copy of the Extender FD 2x-B, serial number 43475 was manufactured in September of 1982. Brochures which you can find in the Library that show only the 2x-A extender says it can be used with almost any FD lens. Then when we come to the brochure Canon Interchangeable Lenses, Publication C-IE-075AL, it says that “Extender FD 2x-A is for all FD lenses that have a focal length greater than 300mm, including FD zoom lenses which have 300mm within their range.” My reading of this is that the 2x-A extender came first as an all purpose extender and the 2x-B came later to address weaknesses in the first extender at shorter focal lengths. 

The Extender FD 2x-B is specifically for lenses of less than 300mm and FD Zoom lenses that do not reach 300mm focal length. My reading gives me the impression that the shorter the focal length of the lens the poorer are the results with an extender. In practice I think that the best results will be with lenses between 135mm up to 300mm.

Like all 2x extenders this one will cost you 2 f/stops. If you are metereing through the lens the camera will adjust for this automatically because it will be metering the lower light level. However, using a hand held meter, the aperture given by the meter should be opened up by 2 further f/stops.

Page 28 from Brochure “Canon FD Lenses”, Publication C-CE-132B

Extender FD 1.4-A

The Extenders FD 2x-A and 2x-B are relatively common and on E-bay are running around $50.00 give or take a few. However, the Extender FD 1.4-A is not so common and sells for around $150.00 to $200.00. This is the one extender I don’t have at this point.

As you no doubt expect, the Extender increases the lens focal length by 1.4 and it costs the user one f/stop. This is an “A” type extender and so it is for use on lenses 300mm or larger. The only written information I have been able to find on it is shown on the left. Click on the image to read the full brochure.


One thing you should note about this extender: it does not fit all lenses and could possibly damage a lens if you tried to force a fit. Look at the above images from the side of the Extender. On the front, which is on the right, you can see that the extender sticks out beyong the lens mount. This portion extends into the lens attached to it and can potentially impact a metal light baffle or even stike the rear element of the lens. So, be careful mounting the lens to make sure there are no conflicts.

This is an F-1 with an Extender 2X between it and an FD 300mm f/2.8 Flourite lens.

The Extender FD 2x looks like the others listed above but the Full Aperture Signal Pin is a solid pin and not a floating one as on the others.

Extender FD 2x

When I acquired my FD 300mm f/2.8 Flourite prime lens it came boxed with an Extender FD 2x serial number 10736. This appears to be almost identical to the Extender FD 2x-A. The one feature that seems different is that the Full Aperture Signal Pin does not float but is a solid fixed pin which means that this extender can only be used with an f/2.8 lens if you want accurate metering in the camera. That is why the User Manual on page 10 warns that this extender can only be used with this lens.

I don’t know if there were other lenses that shipped with a similar extender. There well may have been.

I see no reason that this extender could not be used with any lens of 300mm or more so long as it was either an f/2.8 lens or you used a hand held light meter and added two stops to the reading.

Page 10 of the Manul for the FD 300mm f/2.8 Flourite lens describes the use of the EXtender FD 2x.

Shooting with an Extender

So now we get to it: how do these extenders actually perform? But first, a few words of caution. Canon lenses were designed for optimum performance as they were manufactured. An extender is an afterthought, an addition, which is intended to be used with various lenses that were not designed with the extender in mind. The result is that you get a train of lenses that were never meant to be used together. You are adding non optimized lens groups, more glass surfaces and more glass thickness. This does not bode well for the performance of the lens combination. Keep that in mind.

Secondly, by creating longer lenses you create problems of technique. The average photographer cannot simply take a 200mm lens and slap on an extender making it a 400mm lens and take good pictures. Long lenses have issues of their own and require a different method to capture good images. Camera shake is introduced, aperture and shutter speed are affected, and not in a good way, and atmospheric conditions become an issue. I am not sufficiently expert in the use of long lenses to get into a dissertaion on the proper method of using them but do be aware there are issues. And don’t let bad technique give you poor results that you blame on the extender.

On the left above is the image of a building taken with my FD 300mm f/2.8 Flourite lens used with an Extender FD 2x-A making a 600mm combination. It was tripod mounted and the self timer made sure the camera had time to settle down before the image was taken. On the right is a portion of the same image of the top floor of the building. Look at the edges. You know that the concrete edges are straight but in the image they are wavey like the ocean. This is turbulance in the air causing the image to “shimmer”. In judging the extender performance you must be certain to eliminate such effects.

Extender FD 2x-A

Image of a brick wall taken with FD 300mm f/2.8 Flourite lens at f/8.0 without an extender. Note the lack of vignetting and the rectilinear lines. The image has not been corrected in Photoshop in any way.

The top image expanded to 600% certainly speaks well for the 300mm lens! However, the image has begun to pixelate and this is the limit to enlargement.

The same image with use of the Extender FD 2x-A. The image is still rectilinear without vignetting. It cannot be a better image than the subject lens but it certainly looks at least as good.

The top image taken with the Extender FD 2x-A at 300% so that the enlargements are the same size. This image is detailed and not pixelated.

Several things become apparent. The 300mm lens is excellent. The images above, and all of those below, are taken with lens and extenders mounted on a Canon R with a 30 mpx sensor. They also show that the extender does give added resolution. Not only that but it adds no visible distortion or vignetting to the image. Now lets look at two more images.

This scene is the full frame from the 300mm lens used above.

This image is the same scene using the 300mm lens with the Extender FD 2x-A.

Side by side we have the chain link fence in the middle of the image. On the left is the fence taken without the extenter. It is heavily pixilated when enlarged to 600%. On the right is the same fence using the extender and enlarging to 300% No pixelation and much greater detail. The extender makes a real difference.

Well, so far the FD 2x-A is standing up very well. Lets try one final image.

Full frame image taken with my FD 300mm f/2.8 Flourite lens.

Same picture, same lens, with the FD 2x-A Extender.

On the left is a section of the image without the extender. On the right is the same section with the extender. They are at 600 and 300% respectively. Once again the benefits of the extender are obvious.

So there you have it. The Extender FD 2x-A performs as advertised. If used properly it does double the focal length with little or no loss of sharpness. Now, I have only tested the center of the image and there may be some loss of sharpness on the edges.  Also, Canon says lenses 300mm or longer so I have not tried shorter ones. Seems to be no point. 

The extender can only give as good an image as the lens attached to it. And remember that the extender will double any defects in the lens. So, use quality glass for the best results.

Extender FD 2x-B

For lenses under 300mm Canon produced the Extender FD 2x-B. It is longer than the 2x-A but operates exactly the same way.

I tested this one on my Canon R using an FD 135mm f/3.5 lens. These are not rigourous tests but they do serve to give us an idea if the extender functions as advertised.

This is the full frame image using the Extender FD 2x-A with the 135mm lens.

I got these reversed. This is the 135mm lens without the extender.

Once again, the extender produces more detail with little apparent distortion.

The results appear to be the same with the 2x-B. But rather than cover the same territory, lets have a look at how things are at the edge of the frame: same garden, same flowers.

On the right below is the image with the extender. On the left edge near the top there is a stake and it disappears into a yellow and white flower. See it? Let’s have a close up look there.

Full frame image with the 2x-B.

Full frame image without the 2x-B.

On the right is the pixelated image from the 135mm lens alone enlarged to 600%. Considering it is right on the edge this lens is a fine one. On the left is the image with the extender. The clear advantage we say above is not here. The image actually has less detail and there is some color fringing evident. The extender is close, but, in this case, it gets no cigar!


It is obvious to me that if you are shooting with the FD lenses then the Canon Extenders will perform as advertised. Both the A and B extender, on the correct lenses and with good technique, will yield fine images at twice the focal length of the original lens. It would appear that on the edges of the frame the image does degrade somewhat but look at the magnifications we are using to see it: 300%! There seems to be no doubt, at least in my mind, that these things work as advertised.

Let me leave you with one final image. This is taken with my 300mm lens again using the Extender FD 2x that came packaged with it. I think this proves my point!

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