Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Lens Review
In a significant move, Sigma have now released the first of their lenses for Canon RF fit crop sensor mirrorless cameras, with a constant f/2.8 maximum aperture. The lens is already well known in L mount, Sony E mount and Fujifilm X mount, so now let’s see how the RF version fares, specially tweaked to perform at its best with Canon’s APS-C mirrorless cameras. With the 1.6x Canon crop factor, the lens gives a similar field of view to using a 28.8-80mm lens on a full frame 35mm-format camera. In this review, we are using the 32.5MP Canon R7 body.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Handling and Features
The initial impression is of a light, compact and very well made lens, no doubt aided considerably by Sigma’s use of Thermally Stable Composite materials. This new version has been tweaked for Canon RF mount cameras and indeed it does match superbly with the R7 used in this review. There is no claim regarding general weather resistance, just that the brass bayonet mount has a dust and splash resistant structure. The rubber seal would seem to be the extent of it. The lens is billed as weighing in at 290g, and according to my measurements, that is actually 296g for this Canon RF fit version. The lens measures a svelte 65.4mm x 74.5mm.
There is a supplied petal lens hood that bayonets cleanly and positively into place. There is no retaining catch, nor is there any need for one as the hood locks in firmly enough. Within the bayonet fit for the hood is a standard 55mm filter thread.
First up is the wide zoom ring, clearly and accurately marked at 18mm, 24mm, 28mm, 35mm and 50mm. Zooming towards 50mm does physically extend the length of the lens. Behind this is the electronic focusing ring, also programmable as a control ring, depending on the functions available on the camera. For example, it can be set to exposure compensation, the feature being activated by a half pressure on the shutter release. This prevents accidental operation, so is a useful feature.
AF is via a virtually silent stepping motor and is crisp and very fast in operation. There is no AF/MF switch so these functions are the purview of the camera menus. Servo AF is supported. Focusing is down to 12.1cm (0.397 feet) at 18mm, for a maximum magnification of 1:2.8. At 50mm, focusing is down to 30cm (0.984 feet) for a maximum magnification of 1:5. The closest focus sample images make it very clear that at 18mm there is considerable curvature of field, so edges and centre cannot be in focus at the same time for flat subjects. This is much better at 50mm. However, the close focusing ability is still very welcome and useful and there will be many situations where the curvature is not a problem.
Optical construction is 13 elements in 10 groups, including 1 SLD (Super Low Dispersion) and 3 Aspherical. The diaphragm comprises 7 blades, with a rounded aperture.
Finally, we have Sigma’s usual high quality brass mount, and this has a rubber seal against dust and splashes, as mentioned above. The lens bayonets very smoothly onto the Canon R7, a good indication that the tolerances are well matched.
There is no image stabilisation built into the lens, but as the R7 offers 7 stops of IBIS that is well covered. All in all, a very satisfactory ergonomic design. So how does it perform in the technical tests? Time to find out.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Performance
At 18mm, central sharpness is very good from f/2.8 to f/5.6, excellent at f/8, very good at f/11, good at f/16 and fair at f/22. The edges are very good from f/2.8 to f/8, good at f/11 and fair at f/16 and f/22.
At 28mm, central sharpness is very good at f/2.8, excellent from f/4 to f/8, very good at f/11, good at f/16 and fair at f/22. The edges are very good from f/2.8 to f/11, good at f/16 and fair at f/22.
At 50mm, central sharpness is very good at f/2.8 and f/4, excellent at f/5.6 and f/8, very good at f/11, good at f/16 and fair at f/22. The edges are very good from f/2.8 to f/8, good at f/11 and fair at f/16 and f/22.
This is a commendable performance and takes the concept of the kit lens into new territory, a definite and positive step upwards.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit MTF Charts
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How to read our MTF charts
The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.
For this review, the lens was tested on a Sony A7R III using Imatest. Want to know more about how we review lenses?
CA (Chromatic Aberration) is almost banished, especially at the centre of the frame. We are rapidly moving towards CA control being a symbiotic partnership between lens and camera, freeing the lens designer in many ways. The result is lenses with very low CA measurements, which has to be a good thing.
Distortion is also partly lens design and partly electronic co-operation, so figures are impressively low. Barrel distortion measures -0.73% at 18mm. At 28mm, there is just +0.10% pincushion, rising slightly to +0.42% at 50mm.
Bokeh is perhaps not the main strength of the lens, the gradation at f/2.8 being somewhat feathery rather than smooth. However, as we stop down it is acceptable but not exceptional.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Chromatic Aberration Charts
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How to read our CA charts
Chromatic aberration (CA) is the lens’ inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.
Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.
For this review, the lens was tested on a Sony A7R III using Imatest.
Flare is very well controlled, even with very severe lighting conditions. Any artefacts that can be induced are relatively insignificant and do not impinge upon the clarity of the shots.
Vignetting is impressively low, especially for a zoom lens, but if the slight corner darkening, especially at 18mm, should be noticed, then there are always software solutions.
| Aperture | 18mm | 28mm | 50mm |
| f/2.8 | -1.3 | -0.6 | -0.8 |
| f/4 | -1.2 | -0.5 | -0.7 |
| f/5.6 | -1.1 | -0.5 | -0.6 |
| f/8 | -1.1 | -0.5 | -0.6 |
| f/11 | -1.1 | -0.5 | -0.5 |
| f/16 | -1.1 | -0.5 | -0.5 |
| f/22 | -1 | -0.5 | -0.5 |
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Sample Photos
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Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Aperture range
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Value For Money
The [AMUK]Sigma AF 18-50mm f/2.8 DC DN Contemporary RF Fit|Sigma+AF+18-50mm+f/2.8+DC+DN+Contemporary+RF+Fit+lens[/AMUK] lens is priced at £479.00
Alternatives might be:
[AMUK]Canon RF-S 10-18mm f/4.5-6.3 STM|Canon+RF-S+10-18mm+f/4.5-6.3+STM[/AMUK], £379
[AMUK]Canon RF-S 18-45mm f/4.5-6.3 IS STM|Canon+RF-S+18-45mm+f/4.5-6.3+IS+STM[/AMUK], £339
[AMUK]Canon RF-S 18-150mm f/3.5-6.3 IS STM|Canon+RF-S+18-150mm+f/3.5-6.3+IS+STM[/AMUK], £549
The new Sigma lens clearly offers new possibilities with its fast and constant f/2.8 aperture, so taking this into account it looks very fair VFM.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Verdict
This lens has quite a few things going for it, matching so well with the Canon R7 body. It is a definite step upwards from the average kit lens, both in performance and in quality of manufacture. This makes the price look very fair. The fast f/2.8 aperture for once does not mean an overly large or heavy lens; in fact it is commendably compact, light and an absolute doddle to handle. AF is fast, images are crisp, and there is so much to like. Yes, the bokeh is merely acceptable and somewhat raspy at open aperture in particular, but it is a minor negative, and there is no hesitation in awarding the accolade of Highly Recommended.
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Pros
- Very Good to Excellent sharpness
- Fast f/2.8 constant aperture
- Well controlled CA
- Very low distortion
- Very good flare resistance
- Dust and moisture sealed mount
- Moderate vignetting
- Close focusing to 1:2.8
- Excellent AF performance
- Light and compact
- Fair price
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Cons
- Bokeh can be a little raspy
- Close up field curvature at 18mm
[REVIEW_FOOTER]R_features=4|R_handling=5|R_performance=5|R_value=4.5|R_overall=4.5|A_level=4.5|A_text=Highly Recommended – An excellent, versatile, fast standard zoom that matches the Canon RF system beautifully|E_id=8027[/REVIEW_FOOTER]
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Source: Photography News
Sigma 18-50mm f/2.8 DC DN Contemporary RF Fit Lens Review
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