The Canon RF100 500 and Converters may not do what you think they do!

When is a 100-500mm lens, not a 100-500mm lens? When you add a Canon RF 1.4x extender!

Hello, my name is Rich Dyson from Edinburgh Photography Workshop. This is Coffee Break Photography. I bought the excellent Canon RF one hundred to five hundred lens a couple of months ago. It’s a great piece of glass and helped me get some great images recently when I was shooting red squirrels and red kites up in Argaty, near Stirling. I recommend a trip to this farm and booking a few hours in their hide. While this lens has a great focal distance, sometimes you want a little more, and so rather than buying an even longer lens, the other option is to purchase an extender.

Canon produces two extenders, a 1.4 times and 2 times. They can only be used on a select number of lenses in the Canon RF range. As their names suggest, they extend the focal distance of the lens they are attached to by either 1.4 or 2 times. The downside of using an extender is that for the 1.4 times extender, you will lose one stop of light from the widest aperture and two stops when using the 2 times extender. For this reason, extenders are always going to be a compromise. 

I bought a 1.4x extender at the same time as I purchased the RF one hundred to five hundred lens, but it’s only this week that I’ve actually used them together. At first, I had a problem, and after searching Google, many other photographers have had too! I attached the extender to my camera and then tried to attach the lens to the extender, but it just wouldn’t go on.  Nervously, I checked Canon’s website to see if I had missed the fact that the lens wasn't compatible with the extender.  It is one of the compatible lenses, but then I noticed the extra few words that told me where the issue was (in fairness, it is a user error, not Canon’s).

Before I show you the solution, let me show you my old EF version of the extender. As you can see, it’s a little more slimline than the RF version without this protruding bit at the lens side. The EF extender was compatible with almost all the longer lenses from seventy to two hundred, all the way up to the enormous beasts like the twelve hundred millimetre lens. Attaching the extender made the focal distance from seventy to two hundred millimetres, to ninety-eight millimetres to two hundred and eighty millimetres. 

When buying the RF extender, I expected that the one hundred to five hundred lenses would extend the range from one hundred and forty millimetres at the widest to seven hundred millimetres at the longest, but it doesn’t. This protruding bit on the RF extender restricts the part of the zoom that can be used from three hundred millimetres to five hundred millimetres. To attach the lens to the extender, you first need to zoom it to three hundred millimetres; then it will rotate on. As I said, Canon is open and honest about this – it’s on the web page for the extender, and it is on the manual. It's just that we probably don’t read these things closely enough before purchasing.

So, with this lens and extender combo, you are actually getting a one hundred to five hundred without the extender and then a four hundred and twenty to seven hundred with the extender.  

As I said earlier, extenders are a compromise where you lose a stop of light, but there is another way to extend your reach on RF cameras without losing a stop, which will result in another compromise. In the shooting menu, there is an option for Cropping/Aspect Ratio. Inside this option, you have five choices. By taking the option 1.6, you have increased the zoom by a factor of 1.6 – you’ll also see that the widest aperture on your lens remains the same, and it remains the same throughout the zoom. So for our one hundred to five hundred zoom, we now have a one hundred and sixty to eight hundred zoom, and we haven’t lost anything from the aperture. Excellent, you think; I’ve saved all that money buying an extender and getting a better range.

Well, not quite. This mode crops into the frame to give the effect of a zoom, so the file size at 1.6 will reduce. For example, on the R5, without 1.6 selected, the file size will be approximately forty-four point eight megapixels, but with it selected, it will reduce to seventeen point three megapixels. You could do the same thing in your editing software after the event and get the same effect.

The interesting thing with these two approaches is the effect on the depth of field we’ll see in our pictures. Contrary to most popular thought, Depth of Field isn’t just influenced by the aperture. The distance from the subject, the zoom you are using, and the sensor being used will also affect the depth of field we’ll experience in the shot.

The PhotoPills app is a great way to show how all these variables change the depth of field. So let’s look at the effect of the one hundred to five hundred lens at the long end of the zoom, on a subject ten metres away with a full frame camera like the R5. Because we are at the longest end of the zoom, the biggest aperture we can achieve is f/7.1. You can see the depth of field is measured at sixteen centimetres. Now, let's add on the 1.4 times extender. But as we lose a stop on the aperture, I have changed the value to f/10. The zoom has also increased to seven hundred millimetres. This combination reduces the depth of field to eleven centimetres, so even though we have made the aperture smaller, the zoom has helped to give a shallower depth of field. Let's remove the extender and use the in-camera 1.6 times extender. 

Using the in-camera crop essentially converts the R5 from a full-frame sensor camera to a cropped sensor camera like the R50. So, let's return the focal distance to five hundred millimetres and the aperture to f7.1 but change the camera to the R50. The depth of field has been reduced to ten centimetres.

So, what can I take from this? Both ways of increasing the reach of the Canon one hundred-to-five-hundred-millimetre lens are valid. They’ll both have a similar effect on the depth of field, albeit the in-camera cropping approach would give us more reach, increasing from seven hundred millimetres to eight hundred and forty. The downside of the in-camera approach is that you will lose pixels in your image. The downside of the converter approach is that you’ll keep the pixels, but the zoom range will be reduced to a four-hundred and twenty millimetre to seven hundred millimetre lens instead of the one hundred and sixty millimetre to eight hundred millimetre lens using the cropping effect. If pixels are more important to you, the extender will be the best option. If you know you’ll mainly be shooting at the long end of an extended zoom and won’t do much cropping after the event; then the in-camera cropping would work best. Of course, an even more extended option is to combine the two. Theoretically, you could have a six-hundred and seventy-two millimetre to one thousand one hundred and twenty millimetres lens outputting seventeen megapixel photos at f/10. The depth of field would reduce even more to just seven centimetres!

As I have said several times, we must make compromises in photography. I’d love to hear your comments below on the best compromises for you with this combination of cameras, lenses and extenders. 

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My name is Rich Dyson from Edinburgh Photography Workshop. This has been Coffee Break Photography. See you next time.