The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 15-85mm f3.5-5.6 IS USM and the Canon 17-85mm f4-5.6 IS USM for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Canon 17-85mm f4-5.6 IS USM is the longer of the two lenses at 92mm. The Canon 15-85mm f3.5-5.6 IS USM with a length of 88mm, is 4mm shorter. On the other hand, the Canon 15-85mm f3.5-5.6 IS USM has a larger diameter of 82mm compared to the Canon 17-85mm f4-5.6 IS USM's 79mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Canon 17-85mm f4-5.6 IS USM weighs 475g, 17% (100g) lighter than the Canon 15-85mm f3.5-5.6 IS USM's weight of 575g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Canon EF-S Mount for size comparison purposes.
Standard Lenses in Canon EF-S Mount for Size Comparison
Filter Threads
The Canon 15-85mm f3.5-5.6 IS USM has a filter size of 72mm whereas the Canon 17-85mm f4-5.6 IS USM has a 67mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 72mm filters that we recommend you to consider for the Canon 15-85mm f3.5-5.6 IS USM:
And these are the 67mm filters that we recommend for the Canon 17-85mm f4-5.6 IS USM:
Lens Mounts
Both the Canon 15-85mm f3.5-5.6 IS USM and the Canon 17-85mm f4-5.6 IS USM has the same Canon EF-S lens mount. Some of the latest released cameras that are compatible with the Canon EF-S lenses are Canon T8i, Canon 90D and Canon SL3.
Focal Range
Canon 15-85mm f3.5-5.6 IS USM has a focal range of 15-85mm and
5.7X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
24-136mm when used on a APS-C / DX format camera.
On the other hand, the Canon 17-85mm f4-5.6 IS USM has a focal range of 17-85mm and 5.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-136mm when used on a APS-C / DX format camera.