fst lens question

[RalphLambrecht]

is a fast lens, stopped down, just as good as a slow lens at the same aperture?

[Chan Tran]

I thought you know the answer Ralph. Now to think about it, if a fast lens stopped down isn't as good as a slow lens at same aperture then I would never buy fast lens. The reason that I would never use the large aperture because the shallowed DOF. I was hoping that having fast lens when stopped down to medium aperture it's sharper than the slow lens at the same aperture.

[BMbikerider]

The chances are that a fast lens, shall we say a Nikon F1.4 is made to the same standard as a Nikon 1.8 so the difference will be well nigh on impossible to distinguish except on an optical bench. We are really into straw splitting territory here.

If you are going to stop down the former to say F8 and the latter to the same apperture, whats the point of paying extra cash for the wider apperture lens.

[Newt_on_Swings]

It depends... I remember reading lens tests comparing lenses to their faster counterparts and at f8 some of the slower lenses were just as good or slightly sharper. But say going from a 2.8 vs a f4 or 5.6 there is a larger difference of sharpness in favor of the faster lens when shooting stopped down.

I personally favor using the faster lenses because of the latitude they afford me in various situations and the brighter image in viewfinder.

[jnanian]

yes,

but the larger the format, the more you have to stop it down ( or so i have been told ) ..

[David Brown]

Whichever lens cost more, has to be better ...

[Mustafa Umut Sarac]

No , faster lens is faster but quality is lower , MTF Graph , Color MTF Graph is like crazy. American media publishes weak reports but German magazines are amazing. I was followed them for years at Goethe Institute and faster is worser , impossible to reach some quality point , impossible to control the aberrations.
Buy a 75 year old Elmar and buy a new Nikon f:1.4 and compare if you are knowing what to look for.
Fast lenses are similar to ultrawide angle lenses and they bump somewhere on the road.
Even for Noctilux.

Umut

[benjiboy]

It depends on which lenses you're testing, I doubt if there is law of the universe that aperture for aperture faster lenses are better or vice versa, I can't say I ever lost any sleep over the subject, speaking personally I have always bought marque Canon FD lenses with the exception of two independent ones I own, and I know they are better optics than I'm a photographer, and the same applies to the the marque lenses of the other major manufacturers, Nikon , Minolta etc.

[philbed]

Following my experience, fast lenses are optimized for full aperture i.e Nikkor 1.4 35mm has no distorsion and no aberration at full aperture. It is at its best at f/2 and then the quality is constant. A f/2.8 35mm must be stopped down f/5.6-8 to achieve its best quality. There is also a difference in the corners. The 1.4 is better than the 2.8 in the corners. But I prefer the color rendition of the 2.8, a little warmer than the 1.4

[E. von Hoegh]

One area the fast lens when stopped down might not show as good performance is in contrast. A 50mm f:1.2 lens has much more area of internal reflecting surfaces than a 50mm f:2, regardless of the actual working aperture. Multicoating helps, but no matter what you do, more area equals more internal reflection. There are also optical tradeoffs when designing a large aperture lens.