[Dean]

I am sure one of you learned guys will be able to answer this.
If I take a photo using a F2.8 lens closed to F5.3 and compare it with an image taken with a F5.3 lens fully open, assuming all other conditions are equal, what difference would I expect to see?

[EnglishBob]

I might expect a little more sharpness, especially in the corners in the 2.8 stopped down, though if all other things are equal it should be minimal. If chromatic aberration is present, I would expect it to be less in the lens that is wide open.

[MrB]

You should see a better quality image with the f/2.8 lens at f/5.3. As a generalisation, lenses usually perform best at an f-stop two or three stops smaller than their widest aperture.

As an example, refer to the following linked page of data for a Nikon lens, and scroll down to the MTF values, which give an indication of the sharpness of the lens at four different focal lengths and five different apertures:
http://www.photozone.de/nikon--nikkor-ap...dx?start=1

The numbers don't matter, but the trend does. You can see that the highest values on the MTF graphs for that lens occur at around f/5.6, which is two stops smaller than its maximum of f/2.8. If you were to look at other lenses on the web site, you would find similar trends.

Hope that is helpful.

Cheers.
Philip

[Jocko]

Nothing more to be said. I agree with these two gents. entirely.

[Dean]

Thanks for the responses.
Dean