Combining a macro lens with extension tubes

When shooting insects I normally use my Canon RF 100mm macro lens, that has a maximal magnification of 1.4. When I need additional magnification I combine it with my Raynox DCR-250 close-up lens. That brings the maximal magnification up to 2.25. On the APS-C sensor of my camera you must multiply this with the crop factor of 1.6, to get an effective magnification of 3.6. Stated differently, at maximal magnification the image will contain an area of just 10 mm wide. 

There is a second way to increase the magnification, which is to use extension tubes. I have some 31 mm of Meike MK-RF-AF1 extension tubes. If I add these instead of the Raynox DCR-250 I get exactly the same maximal magnification, but at a slightly larger working distance, 7 cm instead of 5 cm. I thought the Raynox was the better choice because you can just click it on the front of the lens when you need it, while the extension tubes require you to remove and replace the lens on the camera body. Also, using extension tubes you lose some light. But was I right? Today I decided to test it out.

There is a major disadvantage with using a close-up lens like the Raynox DCR-250. The minimal magnification also goes up a lot. I can only focus up to a distance of 12 cm from the lens (the working distance), at which point the magnification of the lens is still 0.85. For anything larger than 15 mm in size you cannot use it, as you can no longer create a good composition. So you keep adding and removing the close-up lens, depending on the size of the insect. Because you have such a small range between minimal and maximal magnification and, hence, maximal and minimal working distance, focusing is rather difficult. A small change in focus has a big effect. You notice that the autofocus regularly struggles with that.

So what about the extension tubes? For my combination, the maximal working distance becomes 43 cm, which is way better. At that distance the lens has a magnification of only 0.3, which, on my APS-C camera, means it shows an area of with 75 mm. This allows me to shoot almost any insect, except butterflies and dragonflies. So even though it is more work to put it on, there is not much need to remove it.

In terms of focusing, I found out today that it works much better than the close-up lens. It was considerably easier to get sharp shots with large magnification, even when shooting handheld. The two examples above were both shot handheld, albeit with some support for my hands. They are close to the maximal magnification you can get. I did not apply any cropping. Using aperture F/13, the depth of field is better than I had expected.

You do lose some light when using extension tubes. I had to move my ISO from 200 to 320. (I use a not very strong, diffused flash.) So you should only use it when you plan to shoot small insects.

My conclusion is that I made the wrong choice. I should use the extension tubes instead of the close-up lens for additional magnification. Only when I am at a place where changing lenses is a bad idea (like when there is a lot of dust), or when I only very rarely need the additional magnification, the close-up lens is the better choice.