EF-S 18-55mm STM kit lens is sharper than the 15-85mm lens - Photozone.de data

The 15-85mm lens has been out for about four years now and was highly acclaimed at the time. Since then, Canon has come out with a line of very sharp and well performing STM lenses, including the ubiquitous and low-cost 18-55mm STM kit lens.

Photozone.de has tested these lenses (and many more), and published resolution figures for them. I have plotted the data up on graphs to make it easier to compare the lenses. To do this for these two lenses at common focal lengths, it was necessary to interpolate the data. The graphs are included at the end of this post.

For those who are not accustomed to scrutinizing graphs, I summarize the findings in words below.

The first graph shows the results for the center of the image. It shows sharpness curves for both lenses for a range of apertures and for a selection of focal lengths. For each focal length and aperture, the 15-85mm lens is significantly less sharp than the newer 18-55mm STM lens.

At the border, the difference in sharpness between the lenses is quite large at wide open apertures, with the difference shrinking gradually up to about f/8. At still smaller apertures, the sharpness differences become much less or disappear.

I owned the 15-85mm lens for a while and my experience with it reflects the PZ data. In ordinary use this lens is merely OK in the center and not very sharp in the borders and corners. This was quite disappointing to me because I wanted the focal length range range, and especially in light of the many positive reviews for this lens.

The 15-85mm lens has a wonderful zoom range, and that is attractive to many people. That might make the 15-85mm the right choice for you. As for me, I sold my 15-85mm and am sticking with the 18-55mm STM. To extend my zoom range, I use other lenses.

Reminder: There are many properties of lenses that are important besides sharpness. They include build quality, light transmission, color, bokeh, chromatic aberration, vignetting, and distortion. Fortunately, the latter three qualities are easy to correct in post-processing, and therefore are less important factors when selecting lenses.

I also did a comparison of the 18-55mm STM lens with the EF 17-55mm/2.8 here.

Interesting comparison. Canon has done well with the new STM lenses - at least, so far as sharpness is concerned. I found the 15-85 more than acceptably sharp when I had a crop sensor camera, so the 18-55 STM must be very good.

Just out of curiosity, how many copies does Photozone test?

dodgyexposure wrote in post #17680414
Just out of curiosity, how many copies does Photozone test?

Probably just one. Sometimes they will do a second sample of a lens if they think there is something wrong with a particular lens, and then they will usually mention what they did.