Sigma S 500 mm f/5.6 DG DN OS
11. Summary
Pros:
- sensational image quality in the frame centre,
- excellent image quality on the edge of the APS-C sensor,
- very good image quality on the edge of full frame,
- negligible longitudinal chromatic aberration,
- imperceptible lateral chromatic aberration,
- lack of any noticeable problems with spherical aberration,
- very low distortion,
- moderate astigmatism,
- pleasing to the eye out of focus areas,
- excellent coma correction,
- silent, quick, and accurate autofocus,
- moderate vignetting,
- efficient image stabilization,
- very compact physical dimensions for offered parameters.
Cons:
- significant focus breathing,
- no teleconverter available for the Sony FE mount version.
In case of every photographic lens the constructors have to face two main limitations in form of the basic parameters. It's the focal length and the size of the entrance pupil, a result of dividing the focal length by the maximum relative aperture. Still, there are some tricks how to circumvent these limitations and they have been known for ages.
In case of classic lenses with bigger focal lengths, their physical length is comparable to the value of focal length used. A classic 500 mm lens with just a focusing front element system should be about half a meter long. Sigma managed to reduce that length over two times only because their lens is not a classic lens but a telephoto device. The lens gets the 'tele' prefix when it extends its main plane in the front of its outermost element system. Because of that you can increase the focal length significantly while keeping the length of the instrument reasonably short. It can be done by introducing an additional negative telephoto set of elements right behind the positive focus group. This is also the operating principle behind different teleconverters in photographic lenses and Barlow lenses in astronomic telescopes.
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When it comes to the Sigma, its front element system consists of as many as four big elements and three of them are made of low dispersion glass. Then you get as many as 16 additional elements and their task is to extend the optical plane far away from the lens and also flattening the image and perfect correction of most of optical aberrations. I have to admit we do live in interesting times. I never thought I would be able to handle an amateur telephoto f/5.6 lens with 20 elements positioned in 14 groups with as many as five low disperson elements inside.
Now we know how they achieved the length of 235 mm with a focal length of 500 mm. Now let's think about other parameters: the width of less than 108 mm and the weight of 1370 grams with this particular entrance pupil.
The entrance pupil, with the declared 5.6/500 parameters, amounts to, exactly, 89.29 mm. Such a lens has to use the front element system with a similar dimension – here you can't bend the rules a bit like in the case of the focal length and physical length of the lens. Still, there are some tricks available.
The first one stems from the precise value of the relative aperture. The integer values f/40 and f/8.0 remain the same – you can't do anything with them. The mid-point values, on the other hand, are the result of a leap but not by the 1.4 factor, as it is usually stated, but by a square root of two so exactly 1.4142. As you see, the real aperture stopped down by 1 EV from f/4.0 and f/8.0 is not f/5.6 but f/5.657. It means that our theoretical entrance pupil amounts, in fact, to 88.39 mm. Applying the precise aperture value you gain 1.1 mm when it comes to the front optical system.
The second trick consists of a clever change of focal length and introducing focus breathing. The right amount of focus breathing in this type of instrument is not a problem because almost nobody uses such a model for video recording. Sigma is well aware of that fact so they applied the solution we are going to describe in more detail in a moment.
Even though the declared focal length value of the Sigma lens is 500 mm in reality, according to our measurements for infinity, it amounts to 483 mm. If you apply the f/5.656 aperture our entrance pupil will amount to 85.38 mm. As you see, from the purely theoretical level of 89.29 for the 5.6/500 parameters we got to 85.38 mm, saving almost 4 mm – quite a lot in spite of appearances. These 4 mm influence the diameter and weight of four bit elements from the front optical system in a significant way.
At the same time you have to emphasize the fact that the decrease of the focal length at infinity is a price worth paying. The focus breathing makes the focal length increase in a meaningful way when you shoot at smaller distances. The difference between 483 and 500 mm is negligile for a sport photographer or an astrophotographer who take photos of subjects positioned far away. A spotter might already notice a difference but not in every situation. A wildlife photographer, on the other hand, while shooting birds from several – more than ten meters, will enjoy the fact that the focal length increased for this particular range by even several dozen milimeters. Mind you, all these groups of users will gladly welcome the reduced weight and physical dimensions of the new lens.
Among these technicalities that, in fact, constitute a kind of pean in honour of the excellent approach and great job of Sigma optics specialists, it's time for a tiny spoon of tar.
In 2021 Sigma launched the S 150-600 mm f/5-6.3 DG DN OS model and in 2023 they complemented their line-up with the S 60-600 mm f/4.5-6.3 DG DN OS. The following chart compares both these zoom lenses with the Sigma S 500 mm f/5.6 DG DN OS, tested here. Both of them, at their longer end, offer you 6.3/600 parameters so the theoretical size of their entrance pupil exceeds 95 m, several millimeters more than in case of the 5.6/500 model. It entails the necessity of using a bigger front element system. Each of these two lenses is also a zoom model, with a greater optics complexity. The first one features 25 elements positioned in 15 groups, the second – as many as 27 elements in 19 groups. At the same time their casings, because of a higher number of mobile elements inside, have to be bigger, heavier, and mechanically more complex. Mind you, these casings don't appear to be of inferior quality or less robust than the casing of the S 5.6/500 model. All of that suggests that a more handy, lighter, less complex prime lens, with a lower number of elements inside which are also smaller and physically lighter, its maximum focal length by 100 mm shorter, should be also cheaper than the two zooms mentioned above.
Is it really the case? The Sigma 150-600 mm costs about $1500, the Sigma 60-600 mm – about $2000, and the new Sigma 5.6/500 as much as $3000. I really fail to understand such a pricing. Of course you can say that a less universal prime lens will have a lower sales volume so it has to be more expensive in order to cap the project and its implementation. Still, it sounds like 'squaring the circle' to me. Maybe the sales volume of this lens is lower exactly because it costs about $3000. If its price was closer to the price of the 150-600 mm model, optically and mechanically more complex, the sales volume would skyrocket and all the expenses would be repaid in record time.
However, this small spoon of tar doesn't change the fact that you deal here with a big barrel of delicious mead. It's enough you compare the list of pros and cons to know that there is just one flaw, connected to the very construction of the lens (as the lack of a teleconverter should't be considered a slip-up of the lens itself). Mind you, that flaw for some users can be actually perceived as an asset. Overall we don't doubt that the Sigma S 500 mm f/5.6 DG DN OS deserves fully our 'Editor's Choice' badge.
