Canon 100-500 and 1.4 extender

I bought the excellent Canon RF 100mm-500mm 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.

Extending your zoom

Canon produces two extenders, a 1.4x and 2x. 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 1.4x extender, you will lose one stop of light from the widest aperture and two stops when using the 2x 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 100-500mm lenses, but it’s only this week that I’ve actually used it. 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).

What used to happen

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 1200mm lens. Attaching the extender made the shortest focal distance on this 70-200mm, 98mm and the longest, 280mm.

When buying the RF extender, I expected that the 100-500mm lens would extend the range from 140mm at the widest to 700mm 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 300mm to 500mm. To attach the lens to the extender, you first need to zoom it to 300mm; 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 in 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 100-500mm lens without the extender and then a 420mm-700mm with the extender.

The other way to extend

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 100-500mm zoom, we now have a 160-800mm 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 44.8MP, but with it selected, it will reduce to 17.3MP. You could do the same thing in your editing software after the event and get the same effect.

Impact on Depth of Field

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 100-500mm 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 16cm. Now, let’s add on the 1.4x extender. But as we lose a stop on the aperture, I have changed the value to f/10. The zoom has also increased to 700mm. This combination reduces the depth of field to 11cm, 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 1.6x 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 500mm and the aperture to f7.1, but change the camera to the R50. The depth of field has been reduced to 10cm.

Which is best?

So, what can I take from this? Both ways of increasing the reach of the Canon 100-500mm 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 700mm to 840mm. 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 420mm – 700mm lens instead of the 160mm – 840mm 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 672mm – 1120mm lens outputting 17MP photos at f/10. The depth of field would reduce even more to just 7CMS!

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.

Please give us your feedback.

If you’ve got any questions or comments, leave them below. You can sign up for the Edinburgh Photography Workshop monthly newsletter, where you’ll get regular updates on exciting things happening in photography and some great tips. Sign up by clicking here.

About the author

As well as running Edinburgh Photography Workshop, Rich Dyson is a professional photographer. His photographs are regularly used in newspapers such as The Times, Guardian and Daily Telegraph. He also had two solo exhibitions and was featured in a members sponsored exhibition in the Scottish Parliament. You can see and buy his photography at richdysonphotography.com.

———————————————————————————————————————-

SUBSCRIBE to this YouTube Channel at    / @edinburghphotographyworkshop  

SIGN UP for my newsletter at https://bit.ly/EPW_SignUp

Argaty Kites Link: https://argatyredkites.co.uk/

———————————————————————————————————————-

I recommend Kase Filters – find out more at https://bit.ly/EPW_Kase