Performance wide open?

[Mr. Lips]

Speaking in generalities here, assuming the same focal length and quality, how does the optical performance of an f/1.4 lens set at f/3.5 compare to an f/3.5 lens set to f/3.5?

I'm thinking that since the 3.5 lens is being shot wide open and the 1.4 lens is stopped down a little, the 1.4 lens might perform better at f/3.5.

Thoughts?

[Pieter]

In general I think you're right, but there are so many exceptions to this rule that I wouldn't overgeneralize this. In the end it really comes down to specific lens design and quality level. For example, the Sony 24mm f/2.8 G is sharper at f/2.8 than the Samyang AF 24mm f/1.8 at f/2.8.

You might argue that these are not comparable due to different quality levels, but even the Sony 50mm f/1.4 GM is sharper at f/1.4 than the Sony 50mm f/1.2 GM stopped down to f/1.4. These are same generation lenses of exceptional quality, yet the slower lens is sharper than the faster one.

[Cameratose]

Every lens has its sweet spot. You can find charts and tests online for quite a few that will show performance at different settings. 

[XKAES]

While I agree with everything that has been said, 9 times out of ten, when you need to take a picture, you'll probably need to use an f-stop that isn't exactly the BEST f-stop -- resolution-wise -- for that lens.  Maybe you want to increase the DOF to get more in focus -- or maybe you want a shallower DOF.  Maybe the shutter speed that you want or the ISO that you need will prevent the use of the sharpest aperture setting.  The "best" f-stop of each lens is just one of many elements to keep in mind.

[Mr. Lips]

Most lenses perform best in the F/8 to F/11 range.  Or, at least, that was true 30 years ago when I was really into photography.

Most of the time I shoot at f/11 in aperture priority.

I can't see shooting at F/1.4 very often, due to extreme lack of depth of field, but I could see shooting at F/3.5 in really low light.

I guess what I was getting at is whether it's worth it to pay the extra money for the faster lens if you probably aren't likely to go past f/3.5?

[Pieter]

54 minutes ago, Mr. Lips said:

Most lenses perform best in the F/8 to F/11 range.  Or, at least, that was true 30 years ago when I was really into photography.

Lens technology has improved a LOT in 30 years. Most modern lenses perform best at around f/2.8 to f/5.6. In fact, they perform much better wide open than they do at f/11, where resolution is significantly hampered by diffraction.

Have a look a this typical MTF chart for the Sony 50mm f/1.4 GM: center performance is diffraction limited from f/2.8 onward.

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56 minutes ago, Mr. Lips said:

I guess what I was getting at is whether it's worth it to pay the extra money for the faster lens if you probably aren't likely to go past f/3.5?

Like all here have basically said: don't let your generalized assumption guide you in your buying decisions. Check reviews of the options you're considering to compare them at your relevant aperture settings.

That being said, if I only ever shot at f/3.5 and smaller, I would never consider an f/1.4 lens if only for the extra weight and bulk it would bring.

[Phormula]

Diffraction is more critical for APS-C sensors than for full frame.

On the  other side, depth of field is opposite.

With my Sony APS-C lenses I end taking most of my shots at /f 5.6 and /f 8, which gives me the best compromise between depth of field, ISO and diffraction. In my film days I would had chosen /f 8 - /f 11 for the same reason. Of course, if I want to do handholding close to dusk or I need a small depth of field, I need to open up. I tend not to go past /f 11 because every small piece of dust on the sensor or on the rear element of the lens is likely to bounce out as a spot in the picture. I have also a few relatively fast primes and I use them exactly because they are fast. Although stabilisation can do miracles, when shooting moving subjects a fast enough shutter speed is mandatory.

Actually, as pointed out by Pieter, fast lenses are more and more performing better close to their maximum aperture. The reason is simple, people buying these lenses are more likely to use them wide open. For example, the official photographer at the last conference I attended to was using Nikon Z gear, two bodies, one with a fast normal zoom and the other with a fast telephoto zoom, shooting all of them wide open, except when shooting the whole audience in the room.

That said, there is no general rule, each lens has its own gold spots. And sometimes, especially for cheap or aged (the lenses could have misaligned a little because of bouncing around) there is also a big chunk of sample variability.

 

[XKAES]

I'll add into the soup that lenses, whether new or old, have more glass elements in them the faster they get -- to TRY to adjust for aberrations.  That doesn't mean they succeed completely.  Usually a lowly f2 lens will do just as well or better than an f1.4 or f1.2 lens at the same f-stop -- not that you will notice the difference in a typical picture.

Edited December 18, 2024 by XKAES