I'm doing research on renting a lens for my camera, it's a Canon Rebel T4i for the solar eclipse. What do I look for to see if a lens can be mounted to my camera. I'm thinking of getting a Canon 100-400mm f/4.5-5.6L IS II but is should I also get an extender and if so, which one mounts to the lens and my camera.

  • \$\begingroup\$ What research have you done around lens/camera compatibility, and around lens/teleconverter compatibility? \$\endgroup\$
    – osullic
    Commented Mar 13 at 22:37
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    \$\begingroup\$ What focal length do you want for the eclipse? Do you want to get the large eclipse disk and "diamond ring"? Or do you want to get the corona as well? There are several eclipse-dedicated sites out there, that go into precisely what focal lengths you need, depending on camera sensor size, what you're trying to capture, etc. \$\endgroup\$
    – scottbb
    Commented Mar 13 at 23:18
  • \$\begingroup\$ @scottbb please list the sites. \$\endgroup\$ Commented Mar 14 at 0:37
  • \$\begingroup\$ @osullic I’ve never done a lens rental before so this is my first. Just need to know what type of lens to look for. The one on my camera are EFS if that matters \$\endgroup\$ Commented Mar 14 at 0:37
  • \$\begingroup\$ @GregorySchultz Google is better for that than me. But starting with Mr. Eclipse, even you don't read any other sites, will teach you a lot. \$\endgroup\$
    – scottbb
    Commented Mar 14 at 20:32

1 Answer 1


Here is the moon taken with a 400mm (Sigma 120-400mm) with a 1.4 extender (so 560mm total) on an APS-C camera (Canon 70D).

enter image description here

This is the complete image, no cropping (just scaling), so you can see how much the moon fills the frame and since the sun and the moon are about the same size during the eclipse, you can figure out if the corona fits.


About extenders:

  • To be able to autofocus, the camera need a lens that opens wide enough. In theory the limit for the non-pro Canon DSLRs is f/5.6, even if f/6.3 also (barely) works.
  • If you use an extender, this reduces this maximum aperture, with a 1.4X you lose one stop, with 2x you lose two stops, so a f/6.3 lens becomes a f/9 (1.4x) or f/13 (2x).
  • So standard autofocus longer works.
  • "LiveView" autofocus could work, but you have better test that with moon shots in advance.
  • Manual focus is tricky because unless you have a very stable (i.e. expensive and heavy) tripod and head, touching the camera will make everything shake wildly in the screen.
  • The small apertures put you in the diffraction-limited territory, so you have a bigger image, but not as sharp.
  • Lens manufacturers design extenders for their lenses, and their lenses for their extenders. The only exception I know is Kenko (because they don't make lenses, just extenders). You can't mix brands and expect good results (especially if the lens is a zoom).
  • The extended focal lens makes the sun and moon move even faster across the frame, so you will fiddle more often with the tripod and head, leading to more shake.

TL;DR: if you have a 600mm, use it as it is, don't put an extender on it.

  • \$\begingroup\$ Thanks for the help. After doing some research, it turns out EF lens can't be mounted on my camera as it takes EF-S lenes. \$\endgroup\$ Commented Mar 14 at 1:08
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    \$\begingroup\$ All the EF lenses fit the EF-S mount. It is the opposite which is not true (EF-S lens on EF camera). I use my 70D (and previously my 450D) with many EF lenses (Canon 100m macro, Sigma 120-400mm, Canon 50mm STM...). And I also have EF-S lenses on the same camera (60mm macro, Sigma 17-70mm) \$\endgroup\$
    – xenoid
    Commented Mar 14 at 1:41
  • \$\begingroup\$ They won't hit the mirror when flipping? That's good to know. \$\endgroup\$ Commented Mar 14 at 1:45
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    \$\begingroup\$ They works very well. The EF-S mount is essentially an EF mount with an index that makes it incompatible with the full-frame bodies. The real difference between EF and EF-S is that EF-S lenses can have a smaller "image circle" because the sensor is smaller, so they can be made smaller/more economical. \$\endgroup\$
    – xenoid
    Commented Mar 14 at 1:51
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    \$\begingroup\$ My extender is the Sigma one, designed to work with Sigma lenses. See augmented answer about extenders. Train in advance with the moon. Other good targets for test shots are Jupiter and its 4 satellites and Saturn and its rings, doable with a 600mm. Also, last thing I forgot, get a remote trigger (or learn how to use your camera with the phone app if it supports it). \$\endgroup\$
    – xenoid
    Commented Mar 14 at 9:05

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