Optimum aperture

[nickfrog]

Hi,
I am very new to photography so please excuse the naive question. I recently got a 400d and bought a second hand 24-85 USM. I have 1 question : the best photos I have taken in terms of sharpness/quality/resolution have been when the aperture is at around f11. Is this a coincidence ?

 

[Tiberius]

Each lens has a different point where its optimal sharpness and difference between light falloff and vignetting hits. For that lens, F11 sounds about right.

 

[Big Mike]

Welcome to the forum.

I've always believed that each lens has a sweet spot...which usually starts a few stops down from fully open. A photo instructor of mine believed that F8 is the best aperture for any lens.

If F11 works for you...then stick with that.

 

[Don Simon]

Hi there. It's a very good question, and it's good that you're experimenting enough to notice this. In short the answer is no, it's not a coincidence. Lenses are sometimes said to have a 'sweet spot', the point at which you have optimum sharpness and resolution (not the same as greatest depth of field). This tends to be a few f-stops down from wide-open, but not stopped down fully either. Relatively slow (in terms of maximum aperture) zooms like the 24-85 may perform best stopped down to f/11. Faster or more expensive zooms and primes tend to have their 'sweet spot' nearer to wide-open, though rarely do lenses perform best fully wide-open.

Btw this is in no way a technical or comprehensive explanation, hopefully someone less tired than me can provide that!

Edit: I got beaten to this one... twice! You should probably just read the previous two posts... they explain it better and in fewer words!

 

[Sw1tchFX]

All of my lenses's sweet spots are at f/8.

My 35-70 at 50mm at f/8 is just as sharp as the 1.8 prime, it's CRAZY!

 

[fmw]

Some lenses, like the big, fast, expensive super telephotos are designed to peak wide open. This is the way they are used most of the time and why the images in Sports Illustrated are so crisp. Most fixed focal length lenses are designed to peak around 2 f stops down from wide open. So the typical f 2.8 wide angle would be really comfy at around f5.6. Many zooms peak at 3 f stops down because of the changing focal length or even more if they are particularly long. So I would guess, that, if your lens does its best at f11, the maximum aperture is likely around f4. That's a guess on my part. I don't know much about Canon lenses.

 

[fmw]

All of my lenses's sweet spots are at f/8.

My 35-70 at 50mm at f/8 is just as sharp as the 1.8 prime, it's CRAZY!

That would be a little crazy on your 35mm. On a digital, where your 35mm lenses have a larger image circle than the frame needs, then every lens should be about the same in terms of sharpness and at about any aperture, but not in terms of contrast. The fixed lens should display more contrast than any zoom.

Every lens is best at the center with image quality declining as you go toward the corners of the frame. The nice thing about using 35mm lenses on a digital is that you never get very close to the corners.

 

[Sw1tchFX]

That would be a little crazy on your 35mm. On a digital, where your 35mm lenses have a larger image circle than the frame needs, then every lens should be about the same in terms of sharpness and at about any aperture, but not in terms of contrast. The fixed lens should display more contrast than any zoom.

Every lens is best at the center with image quality declining as you go toward the corners of the frame. The nice thing about using 35mm lenses on a digital is that you never get very close to the corners.

I'm not talking about contrast, i'm talking about crispness. You're right on the contrast. But look at this: this is straight from the camera, no PS except for cropping:

Nikkor 35-70, 1/20th, 58mm, f/8, 100% crop.

EDIT: You can see the obvious photobucket compression, but you can still get the idea.

 

[nickfrog]

wow, thanks for the replies guys. Great site.
fmw, the max aperture is f3.5 so you're not very far off...
There is soooooo much to learn at my humble level...I ought to maybe purposely ignore some of the parameters until I have fully come to terms with 1 or 2...LOL.

This is the kind of quality at f11 that I am really happy with.
This was shot at the full 85mm, f11, 1/40s, ISO100. No PS work, no crop.
This is at the Brighton Marina in England. I was interested in the repetition of the blue/yellow pattern on several parts of the composition.

 

[myopia]

what would the sweetspot be on my minolta md 50mm f/1.4 be?

 

[fmw]

I'm not talking about contrast, i'm talking about crispness. You're right on the contrast. But look at this: this is straight from the camera, no PS except for cropping:

Nikkor 35-70, 1/20th, 58mm, f/8, 100% crop.

EDIT: You can see the obvious photobucket compression, but you can still get the idea.

And to what am I comparing it?