E.L.. Shapiro Loc: Ottawa, Ontario Canada

This may sound very unscientific but unless your sharpness issues are very critical, don't knock yourself out with lens performance statistics. As a commercial photographer, I sometimes worry about maximizing sharpness because many of my images end up on billboards, giant posters on the sides of buses or on big trans-illuminated menu boards or screens in fast food outlets. Many of us, however, are viewing our photographs on a medium sized computer monitor, or making prints with a moderate degree of enlargement where slight differentials in edge sharpness may not make an appreciable visual difference.

There are a few optical issues or theories that you should keep in mind. Do not confuse depth of field with intrinsic lens performance. At smaller apertures, depth of field increases, that is, more of the foreground and/or background will appear in ACCEPTABLE focus. At smaller apertures, however, oftentimes there is a decrease in general lens performance due to diffraction. Very generally speaking, many lenses are at their best level of performance about 2 stops down form their maximum apertures.

With prime (single focal length) lenses, performance levels are usually better and more predictable than with zoom lenses where the sharpness levels can vary form one focal length setting to another. Macro lenses can be used for general photography but preform best at close distances. Lenses with APO- designations are supposedly better, however I am not sure of that still hold true.

Of course, reading test results on photo magazines and online resources can be helpful when contemplating the purchase of lenses. Much of this data is obtained by "optical bench" testing procedures which have become very sophisticated over the years. Theses tests are not subjective, that is, the results are not based on examining photographs but rather determined by electronic means.

When I studied optics, there were BOOKS written about optical aberrations- the intrinsic defects in various lens types and designs. There are zonal aberrations that occur on various sections of the image- usually on the edges. There were long lists of problems were certain objects would be distorted or misshapen and various colors could not be focused in the same plane. Optical engineers and designers, over the years, have minimized many of theses issues and with the advent of computer designed and manufactured lenses, improvement in optical glass and very stringent productions standards, many of theses issues have been circumvented, minimized or eliminated. There are now camera bodies that detect certain issues and make electronic corrections for them- that's why Hasselbald digital cameras cost a fortune.

It is rare that any of the lenses that are produced by the major manufacturers are real "lemons" but some are better than others, especially where specific usages are factored in. There are always some compromises to be decided upon. "You gets what you pays fir" sounds totally unscientific and hackneyed but, realistically speaking, in many cases it is a truism.

I am fortunate to deal with a local supplier who allows me to thoroughly test lenses before I make a final purchase. Again, I do not have optical bench test gear and I am going by stats and my subjective decision- if I like what I see and it fits the usage, I buy it.

rydabyk Loc: Florida Panhandle

Thank you, the more I think about it, I'm just going to stick with the f/2.8 that I already have. I really think that they are both very good lenses and any difference would be so small as to not have much effect on what I'm looking for.

Again, thanks to every one that took the time to respond.

Griff Loc: Warwick U.K.

jeep_daddy Loc: Prescott AZ

I would stick with the 2.8 because of the ability to be used wide open on night scenes and stars such as milky way images. If you want the best of both worlds sell your mkII and buy a MkIII. The mkIII is sharp as can be at the corners no matter the aperture setting.

Yes, it’s big bucks. That’s why I’m still shooting with the original 16-35 f/2.8

amfoto1 Loc: San Jose, Calif. USA

Compare for yourself...

https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=412&Camera=979&Sample=0&FLI=0&API=4&LensComp=949&CameraComp=979&SampleComp=0&FLIComp=0&APIComp=3

To me the f/4 lens looks much better wide open at 16mm.... especially in the corners. Although, to be fair, the difference is considerably less once you stop the f/2.8 lens down to f/4 too.

Check out other focal lengths and apertures. Top image set compares crops from the center (very good from both lenses). Next images shows mid-frame comparison (where the f/4 lens appears to have a slight edge at most settings). Third image set shows the extreme corner comparison, where the f/4 lens in most cases is sharper

In that comparison tool I used 5DS-R examples for both, since that's probably the most demanding camera. Differences might not be as apparent on other, lower resolution cameras. Feel free to change cameras, but I'd try to use the same model for both lenses, for the most accurate comparison.

The-digital-picture.com has other tools to compare distortion and vignetting (both of which might be correctable in post-processing... maybe even automatically if using a software with a lens profile).

To me the f/4 version is attractive for it's smaller size, lighter weight, lower cost and that it uses 77mm filters (which I have) instead of 82mm (which I don't have). I also have little or no need for f/2.8 for the type of shooting where I use an ultrawide zoom (landscapes, cityscapes, seascapes, architecture). Other folks might want f/2.8 (such as for astrophotography). Also, the f/4 lens has IS, which all the Canon 16-35mm f/2.8 lenses lack (I don't feel IS is a necessity on a wide angle lens.... But it certainly can't hurt either.)

boomer826 Loc: Florida gulf coast

Amen to that !!

boomer826 Loc: Florida gulf coast

LoneRangeFinder Loc: Left field

Not a side-by-side comparison, but if you like analysis that seems to be non-biased, here's a link:
http://www.slrgear.com/reviews/index.php

SharpShooter Loc: NorCal

Not only are the two lenses probably indistinguishable unless you're shooting charts, but you have one more stop of DoF to be creative with or for when you need more speed!!!
You can either double the speed or get twice the light, or 1/2 the ISO!
SS