Canon EOS R7 Primes or zooms Part 2 7 August 2025

 

Sigma 18-50mm f2.8

In March this year I published an evaluation of a prime versus some zooms for the Canon EOS R7. Here is a second such evaluation with some different lenses.

This time I compare the Canon RF 28mm f2.8 STM with the Sigma C 18-50mm f2.8 DC DN, Canon RF-S 18-45mm f4.5-6.3 IS STM  kit lens and the Canon RF-S 18-150mm f3.5-6.3 IS STM enthusiast kit lens.

I first photographed my standard test chart with each lens at 28mm and the available range of apertures with the camera on tripod, then used each lens at 28mm f8 to photograph a detailed landscape scene hand held as is my usual practice.

The test chart is well lit and consists of clearly delineated subject elements with sharp edges, mostly text.

Test scene Sigma 18-50mm f2.8

The landscape scene is more challenging for a lens. I chose a subject with a huge amount of fine detail in the casuarina trees, in low light with low contrast and backlit.

This produced a greater difference between the best and worst lenses than the test chart, particularly towards the periphery of the frame.

New prices are highly variable in Australia both from day to day and from one vendor to the next. An average range is given in the table below.

RF-S 18-45mm f4.5-6.3 IS STM	$350-475
RF 28mm f2.8 STM	$450-550
Sigma C 18-50mm f2.8 DC DN	$700-800
Canon RF-S 18-150mm f3.5-6.3 IS STM	$765-900

 

Sigma 18-50mm f2.8

Canon RF 28mm f2.8 STM

This is an unstabilised, full frame compact lens of unusual design and construction. When mounted on the R7 it extends only a few millimeters forward of the handle, making for a very compact package. The front element is very small. The rear three elements are large aspheric plastic moulded units backed by a glass flat for protection. This lens delivers excellent results on either full frame or APSC bodies with sharpness extending right to the corners even at f2.8. On the R7 it gives us a field of view equivalent to 45mm on full frame. The main selling point for this lens in the present comparison is its compact size. It is the smallest of the four lenses compared here.

RF 28mm f2.8 on EOS R7

Canon RF-S 18-45mm f4.5-6.3 IS STM

This is the basic kit lens usually bundled with one of the budget Canon RF mount APSC bodies, sometimes available separately in a plain box. It is the least expensive of the four lenses compared here and when collapsed for transport is only slightly larger than the 28mm f2.8. Lens test afficionados usually disparage this little zoom but it is actually pretty good. In a large area of the frame indicated by the diagram at f5.6 and f8, I am unable to tell which of the four lenses made the picture. The differences between them are only visible on close scrutiny at 100% on screen on the short sides of the frame and the corners. Here the 18-45mm is a bit less sharp than the other three with more corner shading and purple fringing.  In general photography however it does a very good job. It is stabilised so it can be used to advantage on the R10 making a versatile little kit.

Sigma C 18-50mm f2.8 DC DN

This unstabilised constant aperture f2.8 zoom is a little gem. It is as sharp as the 28mm prime right from f2.8 across the frame except for the extreme corners. At 28mm f5.6 and f8 it delivers image quality equal to the prime. It is very compact for a constant f2.8 lens. On the R7 it makes a versatile high quality kit.

Sigma 18-50mm f2.8

Canon RF-S 18-150mm f3.5-6.3 IS STM

This stabilised 8.3x zoom is the most versatile of the four lenses compared here. It is not quite as sharp as the Sigma 18-50mm when test images are viewed closely at 100% on screen. But a little extra nudge to the contrast, texture, clarity and sharpness sliders in Camera Raw soon fixes that. This one has the greatest zoom range and is the best of the four close up.

Summary

There is no bad choice to be made here. Each of these lenses can reliably make excellent photos.

The choice of one or another will depend on one’s priorities.

The Canon RF 28mm provides the smallest package on the R7.

The Sigma 18-50mm is larger,  just as good optically as the prime and much more versatile with its 2.7x zoom and decent close-up ability.

The RF-S 18-45mm is an excellent companion to the R10 or R50 providing a very compact package with good capability and image quality.

The RF-S 18-150mm is the best choice when a greater zoom range is required. 

Conclusion

Zooms win. Again. The quality of compact consumer zooms has improved so much in recent years that there are no longer many use cases in which a prime might be preferred.

What about the Sigma A 17-40mm f1.8 DC ?

This recent release has been getting rave reviews lately for its excellent optical quality, internal zoom and f1.8 aperture. However I will not be rushing out to buy one.

It is twice the size (expressed as box volume), twice as heavy and twice the price of the little Sigma 18-50mm f2.8 and is also unstabilised.  The comparison reviews which I have seen rate the smaller 18-50mm lens as optically equal to the 17-40mm from around f4, with better close-up capability.  We need to have a compelling reason to use f1.8 to justify the larger lens and I have no such reason.