Fast Lenses VS Slower Equivalents

When we buy lenses, most of us generally try to get the fastest model in every focal length we go with. Like many others I generally believe that the faster lens will give me better performance! My argument is that if I stop down a faster lens by a stop, I will get nicer images that I would out of the equivalent, which would be wide open at the same stop (e.g. 50mm F1.4 is better at F1.8 than 50mm F1.8 at F1.8).

Canon nFD 135mm F3.5 (left) & Canon S.C. 135mm F2.5 (right)

But is this always the case? Turns out it’s not, as you will see in my test below. Let’s take two Canon FD 135mm primes. One is the F2.5 model and other is the F3.5. It’s not surprise that F2.5 model costs much more, therefore one would expect it to be much better than the F3.5 model. The Canon S.C. (breach-lock) 135mm F2.5 is my favorite 135mm primes and it’s worth its price. I’ve used it on a few shoots and it always felt really sharp, even wide open, but turns out the super underrated F3.5 is sharper, even when F2.5 lens is set to F3.5, which should have improved its good performance even more (it does have less CA at F3.5)!

While both lenses look really sharp uncropped (and will look equally sharp in 1080p and maybe even 4k video), when you really crop in the 16mp files (download full res stills here), it’s clear that nFD F3.5 is sharper. It also focuses a bit closer, is more compact, weighs less, cheaper and handles flare in a more subtle way (unless strong flare is what you want).

With F2.5 version in my procession, I was planning to sell the F3.5, but now I’m not even sure if I want to sell it any more. It’s a perfect example when specs don’t necessarily mean anything.

I’ve asked around and this is not an isolated example. There are plenty other examples like these, with one of the most popular being the Contax 50mm F1.7 vs F1.4. Everyone who is familiar with Contax lenses, knows that Planar 50mm F1.7 is sharper that it’s faster brother. I have one of them too and it’s one of the sharpest 50mm lenses I’ve tried, and yet it can be bought for under $200.

The amazing Planar 50mm F1.7


Let me know in the comments section below if you have come to similar conclusions with any of your lenses? 🙂


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5 Responses to Fast Lenses VS Slower Equivalents

  1. I’ve not done tests but often my impression has been that slightly slower lenses can be sharper at full open vs one stop down on the faster version. Also bokeh will be different. Lenses are calibrated differently- faster slr lenses were developed to let in more light but also the full open aperture was calibrated differently – sometimes to get the soft very shallow dof – sometimes sharper – the slightly slower lenses often tend to be a bit sharper wide open so the same line of say canon fd lenses the 1.4 would be calibrated differently at 1.8 as in the 1.8 lens. The 100/2.8 is v sharp wide open – slightly more than the more expensive f2. If I am not planning to use an extreme shallow dof I often buy lenses slightly faster – lighter – cheaper

  2. I owned both the Nikkor 105 AIS f2.5 and the 105 AIS f1.8 … Both are very good. But if I compare them at f2.5 – f4, the slower version is better. Less coma (astro) and no veiling glare due to spherical abberation. And flare is better controlled even with the sun in the frame… So the 105 f2.5 AIS is great… but is still outperformed by the suberb and versatile Tokina 90mm Atx f2.5 that has better bokeh and can keep up with the Nikon D800 36M sensor… Nikkor AIS 50mm 1.8 is better than ais 50 f1.4 up to f2.8 than it is difficult to separate.

  3. Tu hai provato un Canon FD vecchia serie con un Canon FD nuova serie. Logico che un Canon NewFD è meglio di un FL o FD vecchio. Prova un Canon NewFD 135mm f3.5 e un newFD 135mm f2.8 o f2.0 e ne riparliamo.

  4. Cool¡ I think about this a lot. I am not sure if it happens all the time between lenses (that the slower is sharper).. I read about the sharpness of the Contax Planar 50 F1,7 vs the 1,4. The little problem of the 1,7 is that the minimum focus is 0,60cm.. Thanks for the test

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