Canon EOS RF System Which standard zoom ? 5 December 2021

 

The RF 24-105mm f4-7.1 STM works well for many subjects although getting a soft background  can be difficult

As Canon fills out the RF lens catalogue buyers are presented with some interesting purchase choices.

One of these is selection of a standard zoom.

In typical Canon fashion the offerings available range from big, exotic and  expensive  down to compact, entry level and budget priced.

As of November 2021 there are four RF lenses which could be called standard zooms.

Here is a little table with some relevant data. Prices are all over the place in Australia these days so I just give the retail price with GST paid listed by one vendor on the day of publication of this post.

	Maximum aperture value (smallest f stop)	Mass grams	Length mm	Filter mm	Stabiliser	Price AUD
RF 28-70mm F2 L USM	F2	1430	140	92	No	4485
RF 24-70mm f2.8 L IS USM	F2.8	900	126	82	Yes	3799
RF 24-105mm f4L IS USM	F4	700	107	77	Yes	1669
RF 24-105mm f4-7.1 STM	F5.6 approx average	395	89	67	Yes	729

 

You can see that the principal determinant of size, mass and price is the maxim aperture of the lens which equates to the smallest f stop value.

Top of the range is the RF 28-70mm f2 L USM.  Lenses like this serve two purposes:

They allow a degree of visual separation between subject and background which is usually only delivered by wide aperture primes while  retaining the versatility of a zoom. Professional wedding and portrait photographers could find themselves using this lens often. They will want to mount it on one of the bodies with IBIS (R3, R5, R6) as the lens has no stabiliser.

The other function of a lens like this is to establish the Canon brand as being synonymous with high quality optics and high quality in general.

With the 28-70mm f2 L Canon  is seeking to produce the halo effect as described by E.L. Thorndyke in 1920.

Next we have the professional news/reporter/journalist’s primary work lens, the 24-70mm f2.8 L. This is one of the so-called “holy trinity” of working pro lenses, the other two being the 15-35mm f2.8 and the 70-200mm f2.8.

I do not own either of the standard pro lenses. Both have received excellent reviews. There is little discussion about either on user forums. I have seen no complaint about problematic sample variation with these lenses.

I suspect that Canon Pro photographers probably just buy one or both of the pro lenses and use them without being greatly influenced by reviews or user reports. My guess is they expect these lenses to perform at a high level and their expectations are reliably met.

The situation is not quite so clear cut with the next two lenses.

The RF 24-105 f4 L IS USM is ideal for enthusiasts, advanced amateurs and professionals wanting to trim the size, mass and cost of their kit. It has a greater zoom range than either of the pro models. It is quite feasible to leave the 15-35mm and 70-200mm at home and set forth with just the 24-105 f4 L mounted on the camera and the little 16mm f2.8 tucked in a bag somewhere.

The RF 24-105mm f4-7.1 IS STM is the entry level kit lens designed to ease buyers into the RF system without too much price shock. Canon makes this easier by offering the relatively compact, light, affordable  EOS RP for which the lens is a good match.

The RP with 24-105mm STM kit lens provides entry to a full frame mirrorless system at a lower price than many APSC and Micro Four Thirds alternatives.

All this seems straightforward so what is there to discuss ?

The thing is, some reviewers and users have reported that they are getting pictures with the STM lens which are equal to or better than those with the L lens.

Who cares ?

As it happens the 24-105mm focal length range is extremely useful for many types of  use case including travel, family, street, documentary, nature, landscape and just about anything else not requiring telephoto reach.

Given the choice of a larger, heavier version or a smaller lighter version many users including me would be inclined to go for the smaller one if it delivers a level of imaging capability as good as the larger one.

So I bought both the f4L and f4-7.1 STM versions and have used them for many types of photo over a long period.  In fact over time I bought four copies of the STM version in the quest for one which could deliver imaging capability as good as the L version.

I found that each of the STM versions was good value for money and a good all purpose budget kit lens but none of them has been as good as the L version on most metrics.

The STM version is a little better for close-ups with a higher maximum magnification and of course it is smaller, lighter and less expensive.

My own experience has been that the f4L delivers clear, sharp results at all focal lengths and apertures right across the frame with the exception of a bit of softness in the corners at some focal lengths. This cleans up as the aperture is closed down to f5.6. Overall a very good result.

Some reviewers have reported that the f4L is not so good at the long end. Others have reported it is better at the long end.

The only explanation for this is sample variation, which is disappointing in a quite expensive L lens.

By the way my copy of the f4L cost AUD1200 in May 2020. The same vendor is now charging AUD1700, a 40% increase over 18 months, presumably related to supply and demand factors.

Each copy of the f4-7.1 STM has delivered very good sharpness in the frame center at all focal lengths and apertures. In addition each has delivered good sharpness out to the edges at 105mm.

The problems which I have encountered have been at the shorter focal lengths. There are two:

The first is a variably soft periphery, not improved by closing the lens aperture.  Oddly this appears more on the left side in some photos and more on the right side in others. I have found this to be problematic even at small apertures like f11 or f16.

The second is less obvious but equally intractable. This is about the three dimensional distribution of sharpness and the way this varies with focal length and aperture.

You can read about my test procedure here.

For this post I just show one focal length (50mm) and aperture (f5.6) for comparison.

RF 24-105mm F4L at 50mm f5.6

You can see the zone of sharpness is distributed evenly across the frame 

RF 24-105mm f4-7.1 STM at 50mm f5.6

This is completely different and much more difficult to work with

You can see that for a landscape type subject the f4L presents no problems. Sharpness is distributed evenly across the frame from left to right  and fairly evenly front to back.

But sharpness distribution of the STM lens could be problematic for some landscape type photos.    This is baked into the design so will not vary much from one sample to the next.

You can see that the distribution of sharpness is heavily curved towards the camera in the center and away from the camera in the periphery.

This lens is good if you want to focus on a specific subject such as a person but can require a lens specific version of zone focussing  for some types of landscape where you want everything to be sharp from near the camera to the far distance.

For this type of subject  I experiment with focussing closer than the mid point of the frame. This can help but does not always solve the problem as it leaves the lower corners unsharp.

Overall, in my experience the RF24-105mm f4L is much the better of the two 24-105mm RF lenses.  It is the one I use and recommend even though it is larger and more expensive.