Sigma A 18-35 mm f/1.8 DC HSM
4. Image resolution
The following sentences appeared from some time in the same form in all our tests, conducted on the EOS 50D. However, after the test of the Sigma 50-150 mm f/2.8 APO EX DC OS HSM it got out of date a bit because that particular lens, designed without any compromises, was able to get to a record-breaking value of as much as 54 lpmm.
Now it seems we have to revise our text once more. Sigma shows that their zoom lenses can break records and set new standards as much as (or perhaps even better than) the best “primes”. In order not to be groundless let’s check the performance of the Sigma A 18-35 mm f/1.8 DC HSM in the frame centre
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At 18-24 mm and at the maximum relative aperture the MTFs go to a very high level of about 48 lpmm. On slight stopping down to f/2.0 the resolution increases to 50 lpmm and by f/2.8 and f/4.0 it reaches a record level of 55 lpmm. Such a result hasn’t been achieved by any lenses, tested by us on the Canon 50D so far. Amazing!
A bit worse but still excellent performance you can observe at 35 mm. At the maximum relative aperture the MTFs are about 45 lpmm and they increase successfully on stopping down, reaching a very high maximum value of 53 lpmm by f/4.0.
In a range from f/5.6 to f/16 there are practically no differences between particular focal lengths. Their results, within the margin of error, are in perfect accordance.
Let’s progress now to describing how the tested Sigma fares on the edge of the frame.
For obvious reasons the values are not as impressive here but, after all, nobody would expect it and the lens is still doing its job well. At all focal lengths, at the maximum relative aperture the decency level is exceeded without any problems. After stopping down to f/2.2 – 2.5 the lens exceeds 40 lpmm and the maximum values it reaches near 45 lpmm which should be considered a very good performance.
What can be written in the summary of this chapter? Perhaps only this: never in our wildest dreams had we thought that the resolution results of this lens would be so sensational. We thought that a new construction, difficult to design, would be full of compromises, sometimes necessary to swallow if you want to own an f/1.8 zoom lens We are happy to announce we were wrong. When it comes to the resolution there are no compromises almost at all and the lens provides you images of great quality practically for every combination of focal lengths and apertures.
At the end we present crops taken from photos of our resolution testing chart, saved as JPEG files (with the lowest sharpening level) along with RAW files, used for the analysis above.