Just a little background. I shoot landscapes but have been managing to get by with telephotos and using a Rokinon 24 f/1.4 (fully manual) when I need a wide. My widest Full Frame AF lens is a Canon 28 f/1.8 which I have had since I started photography. As most people, I started out in the crop sensor body world, when I had a Tokina 11-16 f/2.8 which I loved, however when I moved up to FF, this lens wasn’t as useful to me anymore.

That being said, this initial impression is targeted at a quick study of performance at 28mm to determine where my 28 prime would fall in my lineup, if it even needs to be there anymore.

I did comparisons at 28mm on the 16-35 and compared them at f/4 with the same ISO. I used A mode because I did not feel the shutter speeds would have varied much at matching apertures anyway. IS was left on for the 16-35 and my 28 prime does not have IS.

For these tests, I have used Lightroom’s compare feature and with the exception of the first image, all will be at 1:1 or 100% zoom

This first one is 28mm f/4 on both lenses and at first glance looks indistinguishable.

f4-comparison

Lenses are usually sharpest at the center so the next set does not show much. Equally sharp on both in my eyes.

f4-center

The next two are right middle edge and left top corner

f4-edge f4-corner

To me these are both appropriately sharp and there is no distinguishable difference.

The next set, I decided to test the 16-35 f/4 vs 28 at f/1.8 wide open. Most lenses are always a little soft wide open so I will then follow up with a f/2.2 test to mitigate the inherent softness wide open. The 16-35 will remain wide open at f/4 with IS on however.

Here are the f/1.8 images. Compared at similar zoom points. The Left is the 16-35 zoom and the Right is the 28 f/1.8

f4-vs-1-8-center f4-vs-1-8-corner f4-vs-1-8-edge

As expected, wide open, the f/1.8 is significantly more soft on edges and corners. The center remains usable however which is the only reason I have held on to this lens as an AF alternative on my FF camera. The added stops of light make this still a fairly usable night photography camera especially once you stop it down to f/2.2 as seen in the following set. f4-vs-2-2 f4-vs-2-2-corner f4-vs-2-2-edge

As you can see, f/2.2 is still softer however the added stop of light allows for faster shutter speeds and a shallower depth of field.

In conclusion, I will continue testing the 16-35 f/4 L IS as my new wide angle FF AF lens. I believe the IS will allow me to take images at slower shutter speeds, potentially 1-2 stops more than I was with my 28 f/1.8. This in turn should compensate for the loss from f/1.8 to f/4. I have yet to test this in real world situations though.

I will have to determine whether or not the f/4 is able to perform in low light settings. If the lens struggles to focus in darker settings or the IS is unable to compensate the slower shutter speeds needed at a maximum aperture of f/4, I will have to continue holding on to the 28mm f/1.8 as a primary AF wide angle night lens or continue to use the Rokinon 24 f/1.8 MF lens. The Rokinon is sufficiently sharp at f/1.8 however the limitation of it being a manual focus lens makes it highly impractical for day to day usage.

Canon 16-35 f/4 L IS

  • Pros
    • Wider
    • Covers a wider range as well, including 28mm
    • Sharp wide open
    • IS
  • Cons
    • f/4
    • Difficult to focus in low light due to f/4
    • Limited bokeh at f/4

Canon 28 f/1.8 II

  • Pros
    • f/1.8
    • Smaller and cheaper
    • Equally sharp to the 16-35 f/4 at matching settings
    • Decent bokeh at f/2.2
    • $ half the price of the Canon 16-35 f/4
  • Cons
    • Softer wide open f/1.8 and still soft at f/2.2
    • Prime lens, no zoom range
    • Flares significantly

Recommendations: I would still consider the 28mm as a cheaper sufficient wide angle lens. I have countlessly shot 3 photo panoramas on the 28mm to create a higher resolution wide image and have been happy with the results. With this method you also reduce distortion on the edges. The 16-35mm f/4 may be sharper however I foresee difficulty creating any panormas if needed due to distortion on the edges. Also depending on the photography you are doing, I do not see significant differences between the two lenses even with the 28mm f/1.8 wide open at a web/online resolution. The artifacts and soft corners are only noticeable at full scale and only until about 10% from the margins. The centers remain sufficiently sharp in comparison to the 16-35mm f/4.

I did not purchase the 16-35 f/2.8 II due to the sharpness issues that have been well documented online and did not purchase the f/2.8 III for cost. As an occasional portrait and predominantely landscape photographer I did not feel a wide f/2.8 lens would be used as much to make it worth purchasing (will rent if needed only).

Addendum: This lens is perfectly capable in low light. The IS compensates sufficiently and allows for sharp photos without pushing the ISO to compensate for faster shutter speeds. You lose quite a bit of bokeh at f/4 but in my experience this is more noticeable because of the wider focal length, not so much the aperture limitation.

Photo by: Kevin Ly www.facebook.com/kevinlyphotography

Canon 6D 16mm, ISO 1600, f/4, 1/15sec

Purchase links for lenses discussed. Disable adblocker if they don’t appear.
   

Canon 28mm: http://amzn.to/2gSKCG0

Canon 16-35 f/4 L IS: http://amzn.to/2gN7xzW