Sigma 10-18mm f2.8 DC DN/C ultrawide zoom for Canon RF mount User review 5 December 2024

 

Canon introduced the RF-S 10-18mm f4.5-6.3 IS STM ultrawide zoom for APSC RF mount cameras in 2023. This is a nice compact stabilised lens but is constrained by the small and variable aperture which limit its appeal indoors and in low light.

The constant maximum aperture Sigma 10-18mm f2.8 DC DN/C STM became available for Sony E mount around the same time and now in 2024 is also available with Canon RF mount.

Some people say an ultrawide lens is good for landscape photos but that is not my experience at all unless my subject is actually an eye catching foreground with the background being relegated to minor status in the frame.

I find ultrawides most useful for architectural interiors, with or without a madding crowd.

For handheld interiors a very useful lens is a compact ultrawide with a wide and preferably constant maximum aperture (small f number)  and either an image stabiliser in the lens or in body image stabiliser (IBIS) in the camera body.

When mounted on a Canon EOS R7 the Sigma 10-18mm f2.8 DC DN/C meets these requirements in fine style. This light, compact, moderately priced body/lens combination is capable of delivering high quality professional results equal to or better than anything we could produce a few years ago with much larger, heavier more expensive gear which required a tripod for best results.

Aspheric elements, special types of glass and post capture corrections have enabled lens makers to produce smaller, lighter and optically better lenses than was previously possible.

Description

The Sigma 10-18mm f2.8 is remarkably light and compact. Diameter is 72mm, length 62mm, mass 260 grams.

It is designated Contemporary which in Sigma world is the entry level  with models designated Art and Sports being more expensive.  Entry it may be but the quality is nevertheless very high.  The full frame equivalent focal length range is 16-29mm. Unlike the Canon RF-S 10-18mm it does not have to be unlocked for use.

Build quality, fit and finish are very nice. The zoom action is very smooth and rotates the same way as other Canon lenses.. As with several modern zooms the lens is physically shortest at the longest focal length. There is a focus/function ring but no switches on the lens barrel. The mount is metal with a rubber O ring seal around the edge. 

A standard 67mm screw in filter can be fitted. I have a Hoya HD.2 UV filter mounted on my copy of the lens permanently and all tests were done with the filter in place.

A petal type lens hood is supplied. This mounts with a straight push-in-click action and is removed with a tiny little twist. There are markings to show how to orient the hood for outwards and reverse mounting. Align the bar for hood out, the arrow for hood reversed. It’s a system I have not seen before and it appears to work well with no problems thus far.

The constant f2.8 aperture of the Sigma lens is 1.3 stops wider than the Canon RF-S lens at the short end of the zoom and 2.3 stops wider at the long end. 

The Sigma lens has no image stabiliser.

Function

Single shot autofocus is very fast and consistently accurate even in low light and with heavy backlighting, even with the sun shining directly into the lens. Human/animal/face/eye detect all work just fine with no problems encountered by me.

The lens supports the maximum frame rate of which the R7 is capable.

Optics

There are 13 elements in 10 groups. Four elements are aspheric including the front element, three FLD, one SLD.

The lens is sharp in a large central circle right from f2.8 at all focal lengths.

At 10mm the long sides of the frame and corners reveal mild softness and contrast loss on the test chart although this is less obvious in real world photos. The softness improves at f4 and is almost gone by f5.6.

The peripheral softness at f2.8 becomes less evident as we zoom out to 18mm focal length.

Overall sharpness is excellent on this lens which can be used at f2.8 with confidence.

With Raw capture and conversion in Adobe Camera Raw, the distortion present in uncorrected files is almost perfectly corrected, making the lens very suitable for architectural subjects.

Corner shading is also largely corrected.

Some mild blue/purple fringing is sometimes seen at high contrast boundaries such as foliage against a hot sky at the wide end of the zoom and wide apertures. This is easily corrected in Adobe Camera Raw.  In most cases however color fringing is insignificant.

I can induce veiling flare by placing the sun at or just inside or outside the frame however focussing and image integrity are retained. It is possible to induce a few shaped and colored flares but I have to deliberately  place the sun in the worst possible position relative to the frame to achieve this.

I also note some bleed-over flare of very bright highlights into adjacent dark shadows in areas where there is very high subject brightness range locally.

With sensible camera work flares are not a serious problem with this lens. This is quite an achievement for Sigma as ultrawide zooms have in the past tended to be quite flare prone.

The out of focus rendition (bokeh) such as it is with this type of lens looks smooth with no nasty artefacts that I have seen.

I did notice a bit of coma towards the corners in photos with a lot of tiny Christmas lights in the frame. This could be relevant to astro work which I have not yet tried with this lens.

I saw no apparent focus breathing when racking focus back and forth.

I test the front-to-back and side-to-side distribution of sharpness of my lenses by photographing cut grass at 45 degrees and applying the find edges filter in Photoshop. Some wide and ultrawide zooms exhibit very substantial shifts in the shape and distribution of the zone of sharpness as the lens focal length and aperture are altered. Fortunately the Sigma 10-18mm is well behaved in this regard and will not present the user with any nasty surprises.

When using Raw capture and Adobe Camera Raw the field of view in the output photo at 10 mm focal length is 4% linear larger than we see in the viewfinder. This suggests that the actual focal length of the lens might be around 8-9mm at the wide end. The JPG output size is the same as that seen in the viewfinder.  I see this behaviour quite often with current model wide angle zooms.

Summary

The Sigma 10-18mm f2.8 DC DC/C is a very welcome addition to the catalogue of lenses compatible with Canon RF mount APSC cameras. It is particularly suitable for the R7 which has IBIS and a high pixel density sensor.

Some enthusiastic reviewers have described the lens as “perfect” which it is not quite, but it comes very close with no substantial faults or failings in any aspect of optics or operation.

Alternatives

* The Canon RF-S 10-18mm f4.5-6.3 IS STM is a compact, well behaved alternative with a stabiliser at around half the price of the Sigma. The Canon lens is smaller when not in use but has to be unlocked for use so it ends up almost as long as the Sigma.

The Sigma is sharper than the Canon at all focal lengths and comparable apertures, but only on the long sides of the frame and the corners. On my tests they are equally sharp in the center and on the short sides of the frame.

* As I write this in November 2024  Tamron has just announced that its  11-20 mm f2.8 Di III-A RXD (do they actually pay someone to come up with these confusing designations ?) for RF mount is now in production.

This lens has been available in Sony E and Fujifilm X mounts for some time and has been favourably reviewed many times.  It is not stabilised.

It offers a slightly longer focal length range and is both longer and heavier than the Sigma. I have no personal experience with this lens.

Suggestions

I suggest the Canon when price is an issue, when usage will be mainly in reasonably well lit locations and when mounted on a camera body without IBIS (R10, R50). The Canon is actually a very good and useful lens, better in practice than its modest specifications might lead us to expect.  It can be used in very low light if there is not much movement in the frame. On the R7 I have gotten sharp pictures hand held at 0.4 seconds with this lens in near darkness.

The Sigma is best used on the R7 which has IBIS. The wide aperture and overall slightly better image quality make this the preferred option when a wide aperture and/or best optical quality is required. This is the preferred option for the user who regularly photographs interior architecture and similar subjects.

At this point I am not sure what the Tamron has to offer which might make it preferable to the Sigma.

Conclusion

Three years ago I thought that Canon might be on a pathway to eliminate APSC models from their catalogue. Their support for the now defunct EF-M mount was tokenistic and their initial offerings for the RF-S catalogue were underwhelming, to put it mildly. To make it worse Canon refused for a long time to allow third party lens makers access to the RF mount.

But the entry of Sigma with two zooms and four primes and now Tamron with one zoom initially has given a new lease of life to the Canon crop sensor system.

There are rumors of an EOS R7.2 coming sometime in 2025 with a stacked sensor.  I think such a model if well executed as to performance and ergonomics could prove very attractive to many photographers.

I hope these rumors are correct because I have sold off all my full frame RF mount cameras and all my compact and bridge cameras and fully committed to the R7 and crop sensor lenses.