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.

 

[removed account4]

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.

 

[summicron1]

the newest leica book has lens test data on every leica lens and while i haven't had a chance to ponder the charts all that much, the feeling i get is that lens performance is more a function of construction than maximum lens opening. Most of the Leica lenses seem to perform best when stopped down a bit, even the smaller aparature ones.

 

[narsuitus]

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

It depends on the lenses and the situation.

For example…

At f/16, I see a significant difference in image quality between my fast normal lens on my small format camera and my slow normal lens on my medium format camera. The medium format image is so much better.

At f/16, I see very little difference in image quality between my high-priced 50mm f/1.4 lens and my low-priced 50mm f/1.8 lens.

At f/16, the close-up images produced by my high-quality 55mm f/3.5 macro lens are so much better than those produced by my high-quality 50mm f/1.4 lens.

At f/5.6, the close-up images produced by my 105mm f/2.8 macro lens have more image detail than those produced by my 105mm f/2.5 lens. However, the portrait images produced by my 105mm f/2.5 lens are better than the portrait images produced by my 105mm f/2.8 macro lens.

http://www.flickr.com/photos/11336821@N00/6012452194/

 

[RalphLambrecht]

thanks. i was looking for an easy answer, but you are right. There is none,have to study the mtfs in question.

 

[Jim Jones]

. . . At f/16, I see a significant difference in image quality between my fast normal lens on my small format camera and my slow normal lens on my medium format camera. The medium format image is so much better.

At f/16, I see very little difference in image quality between my high-priced 50mm f/1.4 lens and my low-priced 50mm f/1.8 lens. . . .

At f/16 any decent 50mm lens on a 35mm camera should be noticably diffraction limited. A good MF lens should be conspicuously better at f/16.

 

[laser]

Diffraction limit

There are many optics books and websites that provide information to answer this question. For example:
http://en.wikipedia.org/wiki/Diffraction_limit

The old rule of thumb: "The best definition is obtained 2-stops down from wide open" still holds for modern lenses.

Larger apertures are subject to aberrations (coma, spherical etc.) that can be eliminated by stopping down a couple of stops. The exceptions are lateral chromatic and distortion.

Stopping down beyond this degrades the image by diffraction. This point is called the diffraction limit. Further stopping down causes increased degradation because of diffraction.

The smaller the physical size of the aperture the greater the diffraction caused degradation. The wave length of light is constant so focal length, format etc come into play.

So stop down 2-stops for the best definition. Stop down more if you need the depth-of-field but you will lose some sharpness at the focused subject plane.

Photography is simple, don't make it complicated.


www.makingKodakFilm.com

 

[laser]

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

To clearly answer:

It is unlikely they will be equal.


Lateral color and distortion will not be corrected by stopping down.

Depending on the structure and materials used the contrast and color may not be equal.

In order to get the speed in the faster lens other performance characteristics are compromised.

 

[Alan Gales]

I used to shoot Contax. The slower Zeiss lenses were said to have tested a little sharper than their faster counterparts.

In real life shooting I doubt you would tell a difference.

 

[TheFlyingCamera]

The reason(s) for buying a faster lens vs the slower lens, even though it costs more, in response to someone else's comment earlier in the thread:

• The faster lens is easier to focus in low light
• The faster lens can let you use a faster shutter speed in low light, enabling you to capture an image you couldn't with the slower lens
• The faster lens may have a more aesthetically pleasing appearance at or near wide-open than the slower lens does
• The faster lens will let you blur out backgrounds and foregrounds more than the slower lens does (see item above)

and then there's always, perhaps the most important reason of all-

• the faster lens proves you're a better photographer because you can afford more expensive equipment, and gives you an excuse to toss around terms like bokeh, circle of confusion, and diffraction limited... (cough cough)

 

[RalphLambrecht]

At f/16 any decent 50mm lens on a 35mm camera should be noticably diffraction limited. A good MF lens should be conspicuously better at f/16.

all mts, i've seen so far verify this statement!