Prime lens question

[Bukitimah]

There so much talk about fast lens and how well they perform under low light. Take for example the Nikon AFD 50mm f1.8. To use it, we actually lock at f1.8 and use the camera aperture to adjust the f stops.

Can someone explain what is the difference between the lens aperture and that being set in the camera? Also since we take photo at the smallest aperture as possible to achieve sharpness, would a fast lens gives sharper photo than the normal kit lens which starts at f3.5?

I took some photo with this lens without flash at f2.8 and 1.8, I find them great as compared to my kit lens. However, when I am shoot at higher f stops, I don't seem to notice any difference.

 

[Patriot]

there is no difference between the apertures besides setting it manually. I also have a 50mm prime that's AI and I always have to change the aperture myself. The camera cannot do it because those types of lens are missing the aperture control lever on the lens itself. When the lens have the control lever on the back the camera is able to choose the aperture base on the setting itself. Prime lens usually give sharper photo because they have less glass meaning less light have less to go through.

 

[KmH]

The smallest aperture possible (f/16 to f/32 or smaller) usually softens focus because of diffraction, rather than making focus nice and sharp.

Small apertures are used to get deep depth-of-field. Large apertures are use in low light, or to separate a subject from the background using selective focus (a very shallow DoF).

Prime lenses usually give sharper focus because fewer design compromises have to be met compared to zoom lenses.

Note that consumer grade prime lenses are generally not as sharp as professional grade prime lenses. In many consumer grade prime and zoom lenses some of the internal lens elements are not made from glass, and are instead made of resin (plastic).

 

[djacobox372]

At higher F-stops most lenses become equal. How they perform at larger f-stop is what you're paying for when you buy more expensive glass.

Also it's a misnomer that smaller apertures equate to sharper images, this varies on a lens to lens basis with some lenses being extremely sharp at their widest apertures and others needing to be stopped down 1-2 stops to achieve best performance. Also f11 and greater is never as sharp as lower f-stops due to diffraction.

The prime lens you have, 50mm f1.8 afd, happens to be one that is not really sharp until f2.8, but if you were shooting the new 50mm f1.8 af-s G, you would find excellent sharpness even at f1.8.

Also, modern pro f2.8 glass is tack-sharp at f2.8, and all pro f4 glass is tack sharp at f4.

 

[Markw]

At higher F-stops most lenses become equal. How they perform at larger f-stop is what you're paying for when you buy more expensive glass.

Also it's a misnomer that smaller apertures equate to sharper images, this varies on a lens to lens basis with some lenses being extremely sharp at their widest apertures and others needing to be stopped down 1-2 stops to achieve best performance. Also f11 and greater is never as sharp as lower f-stops due to diffraction.

The prime lens you have, 50mm f1.8 afd, happens to be one that is not really sharp until f2.8, but if you were shooting the new 50mm f1.8 af-s G, you would find excellent sharpness even at f1.8.

Also, modern pro f2.8 glass is tack-sharp at f2.8, and all pro f4 glass is tack sharp at f4.

Bingo.

Mark