What is the Zuiko 100-400mm f/5.0-6.3?

When this new Zuiko telephoto lens was announced, there was almost immediate speculation that this was another Sigma creation, similar to the 75mm f/1.8 prime.  The focal length range and maximum apertures were identical to the Sigma 100-400mm f/5.0-6.3 DG Contemporary lens.  While the more expensive PRO line of lenses are now made in the OM Digital’s Vietnam facility, the new lens was manufactured in Japan, where wages are higher.  This makes sense if Sigma had been subcontracted to manufacture the lens for OM Digital, since Sigma does all manufacturing in Japan in their Aizu factory in the Bandai mountains.  The Zuiko 75m f/1.8 mm is also solely manufactured in Japan and has long been known to have been a Sigma product.  I wanted to review both lenses and see if any differences are significant or not.  By price point, the Zuiko is very nearly twice as expensive as the SIgma and since the Sigma has been on the market since 2017, there are many even less expensive used examples available.

Flashing gif showing the 21 optical elements arranged in 15 groups of the Zuiko 100-400mm f/5.0-6.3 overlaid with those of the closely related Sigma 100-400mm DG Contemporary lens.  The elements match up precisely and the four dark blue Special Low DIspersion (SLD) Sigma elements correspond to the Zuiko ED elements.   Sigma doesn’t bother designating normal glass elements even if they are Super HIgh Refractive and High Refractive.  Sigma actually has two higher performing classes of low dispersion glass, ELD and FLD.

At this point I must thank Sigma Canada for their always generous consideration in loaning me their lens in EF mount.  I obtained my copy of the Zuiko lens from LensRental ¹ which is a superb online service that also delivers promptly.  I will not thank OM Digital Solutions of America, because after repeated attempts at contacting them including having my emails forwarded up the chain by staff monitoring their website, not one individual of the company felt it necessary to even reply.  Apparently I have nothing interesting to say about m43 and nobody reads this blog anyway.  Or my book.

Interestingly, the last three elements in the Zuiko lens appear to have been minimized by at least 20 percent.  It makes sense to reduce their mass since these elements are the moving groups which effect focusing and a smaller mass will only decrease focus time.

The physical resemblance between the Zuiko 100-400mm and the Sigma 100-400 is unmistakable.
Screen Shot 2021-05-25 at 7.22.31 PM
When it comes to telephoto lens (ie high focal lengths) there is little size reduction that can be realized by the m43 format. Fortunately Zuiko added no extra bulk to the Sigma design and in fact managed some small savings even with the addition of the very useful ARCA foot and collar. What is odd is that by the math, the front element of a 400mm f/6.3 should only be 64 mm in diameter. The Sigma front element has been reported to be only 61 mm in diameter yet Sigma chose to place a 67 mm filter thread while Zuiko chose the even larger 72 mm size when it seems unnecessarily large.

The MTF10 curves are in red and the MTF30 curves are in green.  The E-M1X body was placed on a tripod, ISO200 and shutter triggered by remote and the ISO12233 chart framed at each focal length.  The MC14 was not compatible with two examples of the Metabones EF-m43 adaptor that I had on hand, but the MC20 fit correctly.  However the MC20 failed to transmit the correct focal length and aperture to the body affecting the proper functioning of the IBIS stabilization when the Sigma lens was used.

MTF curves for the Zuiko and the Sigma lens, respectively. The top charts are 100mm f/5, the middle are 400 mm f/6.3 and the bottom are 200mm with MC20 (= 400mm)  f/12. Interestingly, the lens does better at the far end rather than the short end, which is atypical zoom lens behavior. Both lenses exhibit very similar MTF curves which is what you would expect if they had identical optical prescriptions.

Focus Speed

With a high rise apartment building at near infinity distance as the target and the lens manually set to minimum distance focus, I’m happy to report the Zuiko lens focuses with near instantaneous speed.

The Sigma lens being an adapted lens was expected to show slower AF speed.  It took 9 seconds and three serial actuations of the shutter release before focus was confirmed and an image taken.  With the focal length limiter switch selected, this time fell to 6.5 seconds with similar shutter release actuations.  If a section of the building wall without a horizontal architectural feature was centered on a single minimum size  focus square, the Sigma lens would not achieve focus … at all.   This was a most disappointing outcome since quick AF response is a prerequisite for all wildlife compatible telephoto lenses.

Stabilization test of the Zuiko lens cropped at 100% scale with Great Blue Heron at a distance of 77m and 400mm focal length f/6.3, ISO200 and 1/200 s.   The lens does not support Olympus Sync IS but the lens OIS can work in concert with the body IBIS.   40 images were taken with lens stabilization and camera body IBIS on (top) and with lens stabilization turned off (bottom). At this maximum focal length the lens OIS should be providing a significant effect but both trials showed a failure rate of 25% – blurred images.  Perhaps I needed to drop the shutter speed even more.  Neither image has been post processed in any way. I redid the trials with approximately 100 images each time at 1/60 s exposure against a stationary target.  Again with lens OIS off, there was a 23% failure rate.  With only IBIS off there was a 32% failure rate.   With both OIS and IBIS off there was a 90% failure rate. 
While I’m not a connoisseur of bokeh, in this Zuiko example it is inoffensive.
But somehow, the bokeh is unpleasant in this Zuiko image. But why?
Tree swallows are small birds that fly rapidly with sudden changes in direction. The Zuiko lens at 400mm was able to track this one and maintain a good AF lock with the new Birds targeting mode on the E-M1X anywhere it appeared in the EVF.


400mm, f/6.3, ISO1250, 1/3200 s   –   A flock of sandpipers.

I haven’t included any images generated with the SIgma 100-400 lens because my primary application with a lens of this type would be with wildlife and the AF speeds are simply too deficient to make that a reality.    I was prepared to endorse the Sigma as a half priced alternative to the Zuiko, but that is simply not the case.  With such poor AF performance, I can only recommend buying the Zuiko.   I regularly use my Zuiko 300mm f/4 Pro with the MC20 to get 600mm f/8 and image quality would be approximately equivalent to what I’m seeing from this lens.  But there is no substitution for the flexibility of a weather sealed zoom lens in the field.  In fact I am scheduled to attend a Moose Safari in two weeks and am thinking of bringing just the Zuiko 100-400 and the E-M1.2.    I’ll be spending many hours in a canoe and even if I had the Zuiko 150-400mm f/4.5 PRO, you do have to consider the possibility of a canoe capsizing accident and losing a $7k lens instead of a $1.5K one.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Image quality comparison. Lower taken with Zuiko 300mm f/4 Pro and MC14 for 420 mm focal length @ f/5.6, ISO 800 1/1250 s. Clearly the 300mm prime hobbled by the MC14 is still better.

Given the great deal of similarity between the Sigma and Zuiko lens, the Sigma could have been a viable substitute for possibly less than half the price for a gently used example, except the AF speed is so slow that it is not suitable for wildlife applications.  Certainly landscapes and portraits are a consideration but OM Digital intended this lens for birders.


¹ Woohoo, I successfully rented a lens from the US while living in Toronto !!


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