Lens sweet spots

Rocketman766

Is there a general rule of thumb about where a lens' sweet spot is to get the sharpest shots? As an example, If I am shooting with a 135mm f/2.0, is there a certain aperature that gives the sharpest shots? I am assuming that shooting wide open will not be the sharpest. Also, after writing this, I am also guessing that it is lens/brand specific and also that the camera body might affect this? The magical answer might be if a chart exists that shows every lens' sweetest spots, where would I find it? Guessing it doesn't exist. Just trial and error?

Tim Kamppinen

Often times reviews of specific lenses will do tests on this and report on how much you have to stop down to get maximum sharpness. As a general rule however, you should be good at f/8 even on lower quality lenses. Typically the better the glass the wider you can go and still retain sharpness. Cheaper lenses tend to be very soft wide open while pro glass is still going to be softer but not show such a drastic difference.

Of course, the best thing to do would be to experiment with your own lens to see exactly how it behaves, since there is no other lens exactly like it.

Tee Why

Looking at Photozone. The center is sharpest at f4 and the corners at f5.6.

http://www.photozone.de/canon_eos_ff/430-canon_135_2_5d?start=1

Having said that, I have this lens and IMO, in real world shooting and printing situations, it's pretty much sharp regardless of the aperture (unless you really stop the lens down to like f22 or something).

I would set the aperture based on the dof and shutter speed yhou need rather than some minute difference in sharpness.

General rule of thumb is that the lens is sharpest 2-3 stops down from max. which holds true here.
Good luck.

ziggy53

Tim and Tee Why have it right. Professional reviews are the best way to understand lens properties.

Do understand that "sharpest" can refer to both the center of the image and the edges/corners of the images. Sometimes you may want a particular attribute for the center and a different attribute for the edges.

A case in point is a lens like the EF 50mm, f1.4 USM. This lens can be reasonably sharp in the center, even at f1.4, but the sharpness rapidly tapers to the edges which are fairly soft at that aperture. This may be exactly what you want to help draw the viewers eye to the subject or to help seperate a subject from the surroundings.

By f5.6 that lens is very sharp, even to the edges. By f8 the center and edges are equally sharp, but the center sharpness has started to drop just a bit (still very good however and more than suitable for most tasks.) By the minimum aperture of f22 diffraction has softened the lens accross the board, but DOF is maximized and the sharpness still may be suitable for the task.

Good lens review sites:

http://www.photozone.de
http://www.the-digital-picture.com (Canon only)
http://www.slrgear.com/reviews/index.php
http://www.photodo.com
http://old.photodo.com (old version of the above)
http://www.dpreview.com/lensreviews/
http://www.dyxum.com/lenses/index.asp (Minolta/Sony Alpha)
http://www.fredmiranda.com/reviews/ (peer reviews)


These are the sites that I refer to for reasonable accuracy and impartiality. Some other (notable) sites tend toward opinion and conjecture.

Try to find concensus in the reviews. If the professional sites say something that generally has more weight than the peer based sites, but they can both be useful.