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Canon EF 75-300mm Lens Question



I just want ask a question about the EF 75-300mm Lens and the RF 100-400mm IS USM Lens. 

When I was using my previous camera (EOS 4000D) with the EF 75-300mm lens I noticed that when I pressed the shutter button the lens would actually move itself (so like extend out a bit and then it would come back in again by pressing the shutter button) 

Now when I use my new camera (EOS R10) with the RF 100-400mm IS USM lens the lens does not move at all when the shutter button is pressed? 

What is the reason for this and is it supposed to do this?





It is the various elements adjusting themselves during focusing. A cheap lens, like the 75-300 has elements that move during focusing outside the lens, because the design team did not want to add the expense of putting them all inside. A better lens stuffs all this inside the barrel so nothing moves on the outside during focusing. This makes the lens more reliable, since any thing that moves on the outside is a source for dust and dirt getting inside the lens.

My 70-300 does it, too, and while not a cheap lens like the 75 to 300, is more on the economy side of things.

Ah! Thank you for explaining that and that makes sense. So the Canon RF 100-400mm IS USM Lens obviously doesn’t do that which is good as it was expensive….

The images on the R10 also save to a bigger px which is 6000 x 4000. On the EOS 4000D that is smaller for some reason..

The maximum number of pixels is strictly a function  of the sensor. The R10 is specified as 24 MegaPixels, while the 4000D is rated at 18 MP.


Some lenses are "internal focusing" (IF), while others are not.

Some zoom lenses are "internal zooming" (IZ), while others are not.

The non-IF/non-IZ design might be used to keep costs down. But it also might be used to allow for a more compact design.

Your old EF 75-300mm lens is both non-IF and non-IZ. It's a very inexpensive lens.

The RF 100-400mm is IF, doesn't change length while focusing. But it is not IZ, it does change length when zoomed. While not inexpensive, it's also not a very high priced lens.

The RF 100-500mm L lens costs 4X or 5X as much as the 100-400mm. Even so, it is also IF but not IZ. 

An example that does both is the EF 200-400mm f/4L 1.4X, which is much, much bigger, heavier and far more expensive. It's both IF and IZ.

The Canon EF 70-200mm lenses are all IF and IZ. The RF 70-200mm lenses are IF, but not IZ, which allows them to be much more compact than their EF equivalents. Even so, the RF 70-200s are more expensive than their EF cousins.


Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories


"... non-IF and non-IZ."   😁 Technical terms!

EOS 1DX and 1D Mk IV and less lenses then before!