Canon 70D Optics

Zoom
The Canon EF-S 18-135mm IS STM lens offers more zoom ratio than the typical kit lens, with good performance for its class.

This lens has a generous and versatile optical zoom ratio of 7.5x with a 35mm equivalent range of about 29-216mm, thanks to the 70D's ~1.6x crop factor. And it's optimized for quieter, smoother focusing during live view and movies with a new stepper motor ("STM") design.

Sharpness and contrast are pretty good across most of the frame at 18mm and f/8, though there's some mild blurring in the corners. Chromatic aberration is well-corrected by the 70D's processing, so it's not a factor here. (See below for more on C.A.) At 35mm and f/8, sharpness across the frame is also good, but some softness is still visible in extreme corners. Sharpness at 135mm and f/8 is better than average, though softness in the corners appears to be a little higher. (It's difficult to determine corner performance as well as sharpness at full telephoto in these shots as they are meant primarily to demonstrate zoom capability; see below for lab test results and also read our review of another sample of this lens on SLRgear.com.)

Macro
A larger-than-average macro area with good detail. Flash throttled down well.

The Canon EOS 70D's macro performance will of course depend entirely on the lens in use. With the 18-135mm STM lens set to 135mm, the Canon 70D captured a somewhat larger-than-average minimum area measuring 3.01 x 2.00 inches (76 x 51 millimeters). Details are good but a touch soft in the center of the frame at f/8, and only a little softer in the corners. (Most lenses have some softening in the corners at macro distances, however the 18-135mm STM performed better here than most.) Some minor vignetting can also be seen in the extreme corners. The Canon 70D's flash throttled down well producing a good exposure, while coverage was even with no detectable shadow from the lens barrel.

Geometric Distortion
Higher than average barrel distortion at wide angle and moderate pincushion distortion at telephoto with the 18-135mm STM kit lens.

The Canon EF-S 18-135mm STM lens produced images with about 1.0 percent barrel distortion at wide angle, which is higher than average and noticeable in some shots. At the telephoto end, there was about 0.5% pincushion distortion, which is also higher than average though not quite as noticeable. The Canon 70D does not correct for geometric distortion in its JPEGs, as uncorrected RAW files have identical amounts. Geometric Distortion is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

Chromatic Aberration and Corner Sharpness
Low chromatic aberration in JPEGs with the 18-135mm STM lens because the 70D suppresses it by default. Some mild to moderate softening in the corners.

Chromatic Aberration. Chromatic aberration in the corners with the Canon 18-135mm STM lens is low to very low at both wide angle and telephoto, because the 70D now suppresses lateral chromatic aberration by default. See below for examples with chromatic aberration correction disabled.

Corner Softness. The 18-135mm STM lens produced some slightly soft corners when wide-open at maximum aperture. At full wide angle, corners on the bottom of our test target are slightly softer than the top, and blurring extends pretty far into the frame. The center of the image has decent sharpness, just a touch soft. At full telephoto, the top right corner is the softest, and slightly softer than wide angle, but blurring doesn't extend as far into the frame. The lens is fairly sharp in the center, though not tack sharp.

Vignetting. Vignetting or corner shading is not an issue in the above crops, but that's because the Canon 70D's Peripheral Illumination Correction is enabled by default. See below for comparisons with it off.

Performance at f/8: Chromatic aberration in the corners is still low to very low due to processing, as expected. Sharpness in the corners improved when stopped down to f/8, though not dramatically so (and at f/8, diffraction limiting has probably already started to set in.) As you can see, the Canon 70D's Peripheral Illumination Correction slightly over-compensated at wide angle, producing a somewhat brighter corner crop than the center.

Overall, optical performance is good for a 7.5x consumer lens priced under $500, and the default C.A. suppression the 70D applies is a welcome change.

Chromatic Aberration Correction
The 70D features Chromatic Aberration Correction to reduce lateral C.A. with Canon lenses.

As you can see, the Canon 70D's Chromatic Aberration Correction feature was very effective at removing almost all the lateral chromatic aberration in our 18-135mm STM lens test shots above, leaving very small amounts of blue and red fringing. Unlike prior Canon EOS models with this feature, Chromatic Aberration Correction is now enabled by default for supported lenses.

Peripheral Illumination Correction
Like most other Canon DSLRs, the 70D features Peripheral Illumination Correction to reduce vignetting or lens shading with Canon lenses.

The Canon 70D provides what the company calls "Lens Peripheral Illumination Correction," which corrects for lens shading (commonly called "vignetting"), attempting to produce a more uniform exposure across the frame by compensating for the light fall-off seen with some lenses in the corners of the frame. Mouse over the Off and On links above to see the effect on the 18-135mm kit lens at wide angle and telephoto at maximum aperture. PIC is enabled by default.

Peripheral Illumination Correction (and Chromatic Aberration Correction) are supported for many Canon lens models, in both RAW and JPEG workflows. For JPEG shooting, the correction is made at capture time, while RAW shooters can access the function in Canon's Digital Photo Professional software. From the factory, the 70D body ships with correction data for about 25 lens models. Canon's EOS Utility software allows correction data for lenses (including models as-yet unreleased) to be uploaded to the Canon 70D. When using third-party lenses, Canon recommends disabling lens corrections.

Accuracy
Fair accuracy from the optical viewfinder, though very good accuracy from the LCD in Live View mode.

We measured the Canon 70D's optical viewfinder's coverage at just over 97%. This is a little short of Canon's 98% coverage specification, but within the tolerance of our test. The resulting image was however slightly offset with respect to the sensor, which is unfortunately quite common with optical SLR viewfinders. Live View mode using the LCD in record mode was more accurate, resulting in close to 99% coverage, and of course the image isn't tilted or offset.