I have been very happy with the results I am getting from the Sigma 18-50mm f2.8 lens on my Canon EOS R7 camera. This lens is very sharp across the focal length range and also very compact, making it an ideal all-day companion for the EOS R7.
Since I made the decision to leave full frame and concentrate on APSC and compact cameras, I have been wondering just how much resolution the 32Mpx R7 can deliver with a really top class lens.
One of the subjects I like to photograph is the bushland around Sydney.
I often find that backlighting gives me the visual effect which I seek.
This can be quite challenging for any camera-lens combination as the foliage is dense and complex with masses of tiny branchlets and leaves which strongly reflect sunlight.
Both the Canon RF-S 18-150mm and the Sigma 18-50mm f2.8 do a very good job, but after reading many glowing reports about the Sigma 17-40mm f1.8 I had to try it for myself, specifically to discover if it could improve on the sharpness and resolution of the smaller lenses.
Spoiler alert, it can, but not by much and we have to pixel peep or make a large print to see it.
It might not be obvious when reading published specifications but on the camera the 17-40mm f1.8 feels appreciably larger and heavier than the 18-50mmf2.8. The full frame focal length equivalent range is 27.2-64mm and the full frame aperture equivalent for depth of field considerations is f2.88.
It requires a larger carry bag and a different approach to the environment around us when we are making photos.
I am sure the 17-40mm will find a happy home with portrait and wedding and event photographers. The wide aperture, soft out of focus backgrounds and excellent sharpness makes it ideal for these types of subjects. It is also excellent for landscape work when the size and mass of the kit is not of great concern.
However for street, documentary or reportage type work I choose one of the smaller zooms as they are less conspicuous.
The 17-40mm f1.8 is one of Sigma’s premium level Art series lenses, like Canon L series or Sony G Master series. It comes in a bespoke box of understated but high quality. A nicely engineered bayonet mount lens hood is supplied.
The lens itself is clearly made to a high standard. It is weather sealed.
The zoom and focus rings turn smoothly with just the right amount of drag. The Canon version of the lens works just as a native Canon lens would do as to the zoom, focus and control rings and the two function buttons.
The lens zooms internally so although it is quite large for a standard APSC lens it does not extend when zooming.
The Canon version does not have an aperture ring. The clicked ring closest to the mount becomes a control ring the function of which can be set in the [Customize Dials] menu.
There are two customizable function buttons on the lens barrel, one for operation by the thumb in landscape orientation, the other for portrait orientation. The function of these can be allocated in the [Customize buttons] menu.
There is an [AF/MF] switch on the side of the barrel.
The filter thread is 67mm.
The 17-40mm does not have an image stabiliser so is best used with a body with IBIS, which in Canon-land right now is just the R7.
The R7 with battery and card with the lens, filter and lens hood together weigh 1272 grams and have an overall depth of 192mm.
The full frame Canon EOS R6-3 with RF 28-70mm f2.8 is actually slightly lighter at 1194 grams than the R7 with Sigma 17-40mm and also slightly smaller as to overall depth when the RF28-70 mm is collapsed for carrying. However that particular RF full frame lens has to be unlocked for use which extends the inner barrel which extends further when zoomed out.
The full frame kit is substantially more expensive in Australia at around AUD4950 than the APSC crop sensor kit at around AUD3360.
I have not tested the RF 28-70mm f2.8 myself but on the basis of published tests it appears the Sigma lens might be a little better than the Canon especially wide open and with respect to distortion and color fringing.
Anyway my point is that the R7 with Sigma 17-40mm f1.8 kit finds itself competing on size, weight and image quality with mid range full frame gear.
So we need to consider what type of photography we prefer and what other lenses and bodies we have in our camera drawer and whether we intend to commit to full frame or APSC before deciding to buy the Sigma 17-40mm f1.8.
The Sigma 17-40mm f1.8 Art is a halo product, an apex performer, right at the top of the APSC lens hierarchy for Canon, Sony and Fujifilm. It makes top tier APSC camera bodies from Canon, Sony and Fujifilm competitive with the best mid range camera-lens combinations from both Canon and Sony. Fujifilm does not offer any full frame camera gear.
Curious is it not, that Sigma is the top lens maker for all three systems. And this despite Sony and Fujifilm already having an extensive catalogue of APSC lenses. I recently viewed a video by YouTuber Curtis Padley who says he has been using Sony APSC cameras for 6 years and nominates Sigma models as his top five lenses for Sony E mount with the 17-40 f1.8 not surprisingly at the top of the group.
I suspect that for many photographers this single lens model could be the catalyst for stepping away from full frame to APSC for all use cases.
The Sigma 17-40mm f1.8 can substantially alleviate crop sensor FOMO which is fear of missing out, in this case missing out whatever enticing benefits full frame might be promoted as having over APSC.
Autofocus on the R7 is very fast, accurate and reliable, driven by Sigma’s almost silent High Response Linear Actuator (HLA) motor technology. The AF box cannot be moved right out to the extreme periphery of the frame. It is constrained to about 80% of the linear dimension of the frame.
Resistance to flare is very good. I torture tested the lens by pointing it at the sun inside and outside the frame. I am able to induce a few small flare blobs and colors but no veiling flare. Contrast is well maintained adjacent to any flare spots. Sensible use of the lens hood will eliminate flare in most situations.
I can see a just detectable amount of blue/green color fringing due to lateral chromatic aberration in the corners on fine foliage against a hot sky but this is easily removed in post processing where evident. In the majority of photos no color fringing is noticed.
Some reviewers have reported longitudinal chromatic aberration (LOCA). On my tests I can see when I deliberately go looking for it some blue color shift in the far out of focus areas and yellow shift in the near out of focus areas at f1.8. Sharpness is well maintained however.
I have not seen any evidence of LOCA in my general photography including close-ups which are usually at f11 anyway.
I am unable to find evidence of the aberration known as coma even when I go deliberately looking for it with small specular light sources near the frame corners at f1.8. So the lens should be good for astrophotography although I have not tested this yet.
In uncorrected raw files there is substantial barrel distortion, present at all apertures and corner shading at f1.8 at the wide end with some pincushion distortion at the long end.
This is easily corrected manually in Lightroom or Adobe Camera Raw. There is however at the time of writing (25 June 2026) a fault with the Adobe correction profile which over corrects the barrel distortion to moderate pincushion.
Maximum magnification is 0.21x at 40mm. This hardly macro capability but is still handy for many types of close-up photography such as flowers or small products. Close focus resolution at f8-11 is very good.
The 11 bladed diaphragm makes for an almost perfectly circular aperture. Sunstars are readily created if desired.
Sharpness and resolution are excellent to outstanding right from f1.7. There is just a touch of softness in the corners at 17mm f1.8 but this resolves as the aperture is closed down to f4-5.6. Otherwise the lens delivers remarkable sharpness, resolution and contrast across the frame at all focal lengths and apertures up to around f11 when diffraction starts to adversely affect sharpness.
Several reviewers have compared this lens to a series of high quality primes and found the zoom is at least equal to and in some cases better than the primes.
This makes the 17-40mm f1.8 a front runner in the paradigm shift away from primes to high quality zooms the like of which would have been considered impossible just a few years ago. This lens really does deliver the imaging quality and capability of a bag full of primes with no real downside apart from the large-ish physical dimensions of the lens.
If we want a more compact alternative, the Sigma 18-50mm f2.8 delivers most of the imaging capability of the 17-40mm in a much smaller, lighter and less expensive package.
I tested the Sigma 17-40mm against my Sigma 18-50mm f2.8, Canon RF 28mm f2.8 and Canon RF 100mm f2.8 L Macro.
I found that the 17-40mm is just as sharp at f2.8 and f8 as the RF 100mm L Macro, which is remarkable given that the RF 100mm f2.8 L Macro is one of the sharpest full frame lenses we can buy.
When the aperture of the 17-40mm is closed down to around f4-f8 the lens maintains a very high level of sharpness right out to the edges. This a feat which only a select few lenses can emulate. To be fair, the main subject is rarely placed near the edge of the frame so in general lenses which are a bit soft around the periphery are perfectly adequate.
The Sigma 17-40mm is marginally better than the RF 28mm f2.8 especially around the periphery and more convincingly better than the Sigma 18-50mm f2.8 again around the periphery. I should point out that these differences are only apparent at 200% on a high resolution 27 inch Mac studio display monitor. For all normal photographic purposes the Sigma 18-50mm f2.8 delivers excellent sharpness.
One important optical characteristic of a lens is the way the locus of maximum sharpness is distributed in three dimensions and how this varies with focal length and aperture. Unfortunately most lens test sources omit measurement of this and that is unfortunate because it can tell us a great deal about the behaviour of the lens.
Some lenses especially long normal primes and some very good zooms produce a flat plane of sharpness which runs through the focus point and which does not change shape or shift with changing aperture.
But many zooms and wide primes produce a curved and often compound curved plane of focus which changes shape or distance from the camera or both as the focal length and /or aperture are altered.
We can readily obtain a visual representation of this by photographing a textured flat subject such as newly cut grass with the optical axis of the lens at about 30 degrees to the flat plane of the grass.
We line up the camera with a focus stick and apply the “find edges” filter in Photoshop to reveal the distribution of sharpness.
The Sigma 17-40mm f1.8 fares very well on this evaluation. At 17mm the distribution of sharpness is not linear but it almost never is at the short end of a zoom. However it is well corrected with no skew, no change in the shape of the sharpness field and no focus shift when the aperture is changed.
At 24mm and 40mm sharpness is distributed in a flat plane with no focus shift as aperture changes.
By way of comparison, the Sigma 18-50mm has good field curvature characteristics but is not as corrected at the wide end as the 17-40mm.
Summary
The Sigma 17-40mm f1.8 lens is a welcome addition to the Canon APSC lens catalogue. It is a superior product in every way which will be appreciated by discerning users who want the best zoom currently available for crop sensor cameras.
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