A question regarding fast glass.

[greg]

If the same camera is used with the same setting, shooting the same subject under the same conditions -

Is there any benefit to having an f1.2 lens set at f4 compared to an f2.8 (or any other slower speed lens for that matter) lens set at f4(or any other lower f stop)? In other words, is the benefit of an f1.2 lens only that it can shoot at lower light levels, or does it actually perform better when stepped down to identical f stops? I am speaking in general terms, I am not looking for a Zeiss versus Tamron versus so forth answer.

[William]

I believe that it is usually the case that faster lenses perform slightly better in image quality when stopped down to the same f-stop that's used on another similar yet slower lens. It would be interesting to hear a more thorough explanation on the matter.

[hinnerker]

The 1.2 Lenses are mostly better corrected on the optical formula to bring useful results in low light conditions. Its a higher complexity to math an build such a lens.. so in most cases, the error correction is higher/better ..

So my fast lenses, especially the 1.2 are very soft wide open and hard to handle in sunlight.. better stop down 1 or 2 f/stopps.

If you stopped down the lens, for me it gives the same if not better results as a f/2 lens at the same f/stop..

As i did say.. mostly!! Not absolut each of the faster ones.

LG
Henry

[ManualFocus-G]

Remember though that a 50/2.8 might have smoother bokeh at f2.8 than a f1.2 or f1.4 lens stopped down, because of the rounder circle. This isn't always the case though.

[no-X]

That depends really on many factors.

Faster lenses has typicaly more optical elements for corrections. But these corections sometimes aren't focused on sharpness/resolution - e.g. the 55/1.2 Tomioka. This lens was corrected for astro-photography, so primary target was reduction of optical aberrations like coma.

So, Tomioka 55/1.2 at f/4 isn't sharper than e.g. Tessar 50/2.8 at f/4. And S-M-C Takumar 50/1.4 at f/4 beats them both

Some slower short-tele lenses were built on Ernostar/Sonnar formula, which can offer better bokeh, than faster Planar-based tele-lenses.

With a bit of generalization, the sharpest M42 lenses are typically:

35mm: f/2.8-f/3.5
50mm: f/1.4-f/1.8
135mm: f/3.5

[martinsmith99]

Way too many variables when making comparisons like that.

If you have 2 exact optical formulations, both built to the same standards with one lens being an F2 and the other being a a faster F1.4, then both when stopped down to F4 should be the same.

[cooltouch]

The premium f/1.2 lenses may perform better at f/4 than their more pedestrian counterparts, but this will be due to better correction of chromatic aberrations than "mere" f/1.4 through f/2 optics, for example. Otherwise, the slower optics will perhaps deliver better optical performance.

For many years the old Nikkor 50mm f/2 was considered Nikon's sharpest 50mm. The old pre-war Leitz 50mm f/3.5 Elmar is one of the sharpest 50mm lenses ever made, period. And with great contrast to boot.

In general terms, it is easier to correct for optical aberrations with a slower lens, so really it makes a certain amount of sense that, if anything, the slower optical formulas have a natural advantage.

[ChrisLilley]

[ManualFocus-G]

[no-X]

[cooltouch]

Okay, here's a specific example: a Canon FL 55mm f/1.2 vs a Canon FD 50mm f/3.5 Macro. Which do you think will be sharper at f/4?

It's rather obvious, isn't it? So it really depends a LOT on the optical formulas of the two lenses being compared.

Now, if I were to compare an FL 55mm f/1.2 against an FL 50mm f/1.8, the results might not be as clear-cut. I own an FL 55/1.2, and while I don't own an FL 50/1.8, I do own an FD 50/1.8. So I would be able to make this comparison test, if only I had my DSLR -- which is STILL at Canon being repaired . . . <sigh>.

But I have done some testing of the 55 FL not too long ago, and it behaves probably like most "ultra fast" lenses of its era (mid-to-late 1960s), in that it is rather soft wide open, and improves to acceptable levels beginning at f/4, but isn't really what I'd call sharp until about f/8.

So using the early 1.2s like the FL Canons and probably the Minolta Rokkors and maybe even the pre-AI Nikkors as examples, I would suspect that a pedestrian f/1.8 or f/2 normal lens would outperform them at f/4, both in terms of sharpness and contrast.

[Orio]

I add +1 to what Chris said.

[francotirador]

It depends on the lens and I think the main advantage is to shoot in low light ..
One example, the super Takumar f3.5 is sharper than the F2.5.
Talking superficially.
The objectives are optimized to sharpen or faster. But I prefer the Rokkor 58 1.2 to 1.4 by the Bokeh.

Another example is the Micro Nikkor lens

Each objective should be studied to know where their strengths are.

I think many members have already written something.

Greetings.