Would a Canon T7i improve low-light wildlife photos more than better lenses over a T3i?

Question

I’m shooting with an inherited Canon T3i and considering a T7i before a Costa Rica trip. My main goal is wildlife photography, mostly mammals at a distance, often in dim jungle light under canopy. I currently use the Canon 55-250mm IS STM and a 50mm prime, plus I have a flash, diffuser, and tripod.

I’m mainly concerned about low-light performance and whether the T7i’s newer sensor would meaningfully improve image quality at higher ISO compared with the T3i. I’ve also read that spending money on lenses may help more than upgrading the body.

Given this setup and use case, would upgrading from a T3i to a T7i make a noticeable difference for low-light wildlife photography, or would a faster telephoto lens be a better investment?

user15871 · Answer

The improvement you would see in going from a lens with a maximum aperture at 250mm of f/5.6 to one with an aperture of f/2.8 (likely at 200mm) will absolutely dwarf any improvement you see between the low light performance of the T7i vs. the T3i.

The vast majority of the improvement in the sensor used by the Rebel T7i/800D compared to the sensor in the Rebel T3i/600D is in terms of dynamic range at low ISO ranging from about 1.5 stops at ISO 100 to a tad over one-third stop at ISO 400. From ISO 800 and higher, the two sensors perform almost identically in terms of dynamic range and signal-to-noise ratio (SNR or S/N ratio).

DxO Labs has not yet tested the Rebel T7i/800D, but it has the same sensor as the 80D.

Basically, if you are using ISO 800 or higher, you'll see no difference between your current EOS Rebel T3i/600D and the EOS Rebel T7i/800D in terms of high ISO, low light performance.

That's not to say there aren't other areas where the EOS Rebel T7i/800D is a significant improvement over the EOS Rebel T3i/600D¹, but low light image quality isn't one of them.

An f/2.8 lens is two full stops faster than f/5.6. That allows you to either:

Use the same shutter time with two stops lower ISO. For the same scene, you'll be collecting four times as much light with the sensor, reducing the amount of noise in the image.
Use the same ISO with a shutter time one-fourth as long. The shorter shutter time will reduce the influence of subject motion on blur. (IS only helps to reduce the influence of camera movement. It does nothing for subject motion.)
Use any combination of the two above factors. You could, for instance, use one stop lower ISO and half the exposure time by one stop. That is, instead of being forced to shoot at ISO 1600 and 1/100 second at f/5.6, you could shoot at ISO 800 and 1/200 second at f/2.8.

_{¹ The primary differences between the EOS Rebel T3i/600D and the EOS Rebel T7i/800D are the autofocus systems (9 AF points vs. 45), the light meters (63 zone monochrome vs 7560 pixel, 63 segment RGB+IR), frames-per-second in burst mode (3.7 fps for 34 JPEGS or 6 raw files vs 6 fps until the card is full with JPEGS or 27 raw files), longer battery life rating (440 images vs 820), and Wi-Fi/Bluetooth connectivity (T3i/600D does not have either, T7i/800D has both).}

Would a Canon T7i improve low-light wildlife photos more than better lenses over a T3i?

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