The Canon camera equivalent to the Nikon D800 would be the Canon EOS 5D Mark III or 5D Mark IV. The Canon lens equivalent to the Nikkor AF-S 24-120mm f / 4G ED VR would be the EF 24-105mm f / 4L IS USM.
The Nikon camera equivalent to Canon's EOS Rebel XTi / 400D was the D40 or D40X. The Nikon lens equivalent to the Canon EF-S 18-55mm f / 3.5-5.6 II was the AF-S 18-55mm f / 3.5-5.6G ED II.
Your test compares an entry-level camera with an entry-level sensor at $ 800 USD dating back to 2006¹ and using a $ 100 "kit" lens at a newer $ 3,000 "full-screen" "professional" camera using a target at $ 1,100. Which do you think will give better results?
It's possible to get much closer to the Nikon result with the same older, lower-level Canon camera, using a more comparable lens that lets you shoot a little further back.
- It seems that you are closer to the subject at 55 mm (?) With the Canon lens 18-55 mm and a little further away at 120 mm (?) With the Nikon lens 24-120 mm. The different distances between subjects (how far away the camera is from the subject) will affect the perspective of the photo.
- The Nikon lens also allowed you to use an aperture as wide as f / 4, while Canon's "slower" lens at 55mm limited aperture to f / 5.6. Assuming you use the same ISO setting on both cameras, this means that you need to use a slower shutter speed (longer exposure time) to get the same exposure value. . When taking pictures with the handheld, longer exposure times may increase the amount of blur resulting from camera movements during exposure.
- The VR function (vibration reduction) of the Nikon lens may have reduced the influence of camera movement, while the lens provided with the Canon Rebel XTi / 400D does not offer image stabilization (image stabilization – its equivalent in virtual reality).
- You may need to also adjust the contrast and color settings of the camera so that Canon matches more with what you get with the Nikon, but I think one of the biggest differences may be due to a bit of off-axis light hitting the front of the Canon lens and reducing the contrast. I guess the lens with the Nikon 24-120mm lenses had the lens hood provided, while the Canon 18-55mm lens that was not supplied with a sun visor did not have a sun visor. did not have one. One of the main goals of a sun visor is to reduce the influence of light sources just outside the frame.
- The target of $ 1,100 on the Nikon is sharper than the $ 100 on the Canon. The Canon EF 24-105mm f / 4L IS USM is also much sharper than the lens kit that came with the EOS Rebel XTi / 400D.
I think I had about the same distance in both images. I've tried to get the same frame, so the focal length is different because of the different size of the sensor. EXIF says 53mm for the Canon and 105mm for the Nikon, not sure of the accuracy.
A 53mm viewing angle on Canon's Canon 1.6X camera is the same as the 85mm on the FF D800. A more appropriate comparison would have been to use the 24-120mm lens on the Nikon at 85mm instead of 105mm. Then you should also consider that, at the same distance to 53mm with the body of the crop, you must use an aperture of f / 2.5 (which your Canon lens can not offer) to get the same DoF as that that you would get to f / 4 using the FF camera at 85mm. Since your Canon 18-55mm lens is limited to f / 5.6 to 55mm, the use of f / 9 at 85mm with the Nikon FF would give roughly the same DoF as that obtained with the Nikon FF Camera and Canon lens.
In the end, the speed affects the outcome here (especially the sharper and faster lens with stabilization compared to the slower and slower lens without stabilization), but a more experienced photographer and more skillful can take more advantage of the older camera and the lower end. we see above. For more information in this direction, please see: The best way to improve the sharpness of the image on the Canon 700D
¹ The equivalent model of Canon's current lineup (which is a much better camera due to technological improvements made between 2006 and 2019) would be the $ 700 EOS Rebel T7i / 800D.