Alan's Blog




Lens Apertures – Do You Really Need to go so Wide?

I was struck the other day by how far some people are prepared to go, and how much they are prepared to spend, in order to obtain a lens with a very marginal addition to its 'speed' – light gathering ability. Talk about the law of diminishing returns gone mad!

To increase the speed of a lens, say from f2.0 to f1.0 is merely the equivalent of two f-stops. If your photograph is over exposed or under exposed by this amount it is not always a huge deal in most respects – particularly now we are using digital cameras and software that can easily sort out a great deal of that problem (much more critical when using film).

The approximate half-stop increments in the range are: f2.0, f1.7, f1.4, f1.2, f1.0.
The approximate third-stop increments in the range are: f2.0, f1.8, f1.6, f1.4, f1.2, f1.1, f1.0.

Note: The same numbers (particularly f1.2 - which seems to be out of place) are sometimes included on both of the above scales; for example, an aperture of f1.2 may be used in either a half-stop or a one-third-stop system – as measurements are not shown more accurately than one decimal point. Some lenses, usually cinema / video camera lenses, use the T-Stop which is an f-number adjusted to account for light transmission efficiency as this provides greater consistency in exposure settings – variations of which would be highly noticeable when taking videos – especially when changing apertures and / or lenses.

Consider the cost of gaining quite a small increase in light gathering ability with the 'standard' 50 mm lens:

The Canon 50 mm STM f1.8 (one-third of a stop wider than f2.0) costs £128.50 – the 'original' 50 mm non-STM lens was far cheaper. In fact, I bought a barely used second-hand Canon 50mm f1.8 II in its original box for £69.99 (including delivery) back in January 2019. It serves my needs very well.

The Canon 50 mm USM f1.4 costs £364.00 (one full-stop between f1.0 and f2.0 or two-thirds of a stop between f1.4 and f1.8).

The Canon 50 mm USM f1.2 costs £1598.50 (one-half – or one third of a stop - dependent on which scale you're using - wider than f1.4).

You can read more about this topic at URL:

See what I mean? To gain an increase in speed of one full-stop from f1.8 to f1.2 is going to cost you an EXTRA £1470.00. Or, put it another way, the most expensive lens is almost 12.5 times the cost of the cheapest lens. Is it worth it? For most people, the answer is likely to be a resounding 'NO'. Better to spend the money by adding another lens or two to your camera bag – or not spending it at all!

Another example is the very popular Canon 70 mm to 200 mm 'L' Series zoom lens. They make both image-stabilised (IS) as well as the regular un-stabilised versions:

The Canon EF 70-200mm f2.8L IS USM III costs £2099.00
The Canon EF 70-200mm f4L IS USM II costs £1399.00
A difference in price of £700.00

The Canon EF 70-200mm f2.8L USM lens costs £1499.00
The Canon EF 70-200mm f4L USM lens costs £638.50
A difference in price of £860.50

Both models of this lens show vast increases in price just for ONE additional f-stop in speed!

It gets even sillier as focal lengths increase. The price difference between the 'L' Series Canon 300 mm lens at f2.8 compared to the f4.0 version is an almost unbelievable £4700.00 – also just for one f-stop increase in speed.

All the above prices obtained from URL: on 23 to 25 March 2022.

Of course, there will be those who argue that the more expensive lenses are better quality, both optically and in their build, however, the difference in optical quality is fairly marginal unless you're a real 'pixel peeper' and this is not the case at all for the 'L' Series lenses as they are all optically superb.

As for build quality – even the cheapest lens is made well enough for most purposes – and it's much lighter in weight. In the case of the 'L' Series lenses, there is unlikely to be any difference in the build quality as this range is built mainly for professional photographers to use so they have to be very durable (although I've had one fail which needed a very expensive repair!). However, in all cases, the lens with the smaller maximum aperture (f4.0) is significantly smaller in size and lighter in weight than the f2.8 version.

The other factor to consider is just how often are you going to use the lens at full aperture? I suggest "rarely" would be the answer for most photographers – so why go to the expense of buying an f1.2 50 mm lens? To show-off your wealth?

In these days of high levels of financial inflation, without inflation-proof salaries, it may well be prudent to spend less and still enjoy your photography – buying second-hand is also a winning strategy (refer to URL: I've bought many cameras and lenses second-hand and had good service from all of these items. In fact, I've had more repairs carried out on items bought 'new' than those bought second-hand.

In this situation, one can certainly state that 'less is more'.