Background

I am very happy with my 28-135. It's a fine lens, with a very useful zoom range, and image stabilization is wonderful. So why did I buy a 50mm lens? Partly because I expected that it might be sharper than the zoom, and partly for its extra speed (for low light use, extending the range of flash, and shallow depth of field). Also, because I have an addiction to looking in the used lens cabinets at local photo stores, and the 50/1.4 (which is quite rare on the used market) was sitting there, begging me to take it home for a really good price. I figured that if I didn't use it much, I could probably sell it on eBay for about what I paid for it.

I used a similar testing procedure to the one I used in my zoom lens test. I drew a 3:2 rectangle on a two-page spread of a broadsheet newspaper, taped the newspaper to the wall, set up my Elan II on a tripod (relatively low to the floor), used the two-second mirror prefire and a corded remote release to try to minimize vibrations, and took pictures at a variety of apertures. No filters were used.

The flaws in this procedure are basically the same as the flaws listed in the other test. The main difference is that this time, I used the film that happened to be in the camera already (Kodak Ektapress PJ100). It's a sharp, fine-grained colour negative film, but it's not as sharp or fine-grained as the TMX I used for the previous test; therefore, it can't reveal smaller differences in sharpness that TMX would show. However, since PJ100 is the sharpest, finest-grained film I usually shoot, the results should reflect how I'll use the lenses in real life. I have repeated this test with TMX, but have not had time to write up much in the way of results except for some minor editing of my earlier findings.

Test Results

At f/1.4, the 50 is very soft, even in the center; this aperture is pretty much unusable unless you want soft results. At f/1.8, it is much sharper in the center; in fact, there's very little difference from f/1.8 to f/8 (TMX shows that sharpness continues to increase as you stop down). Corner sharpness gets somewhat better when stopped down. At the same aperture (f/4.5, f/5.6, and f/8), the results from the two lenses are almost indistinguishable. This goes to show you just how good the 28-135 is.

The 50 has slightly more barrel distortion than the 28-135. Both lenses are pretty good, though.

I have not taken any pictures to test this; this comment is just from looking through the viewfinder. Both lenses show strong veiling glare from bright lights within the field of view. The 50 is more resistant to flare from outside the field of view because its front element is somewhat recessed (the 28-135's front element actually sticks out in front). The 50 has a larger advantage if you use the lens hood, since its lens hood is designed for a 50mm lens' field of view whereas the 28-135's hood is designed for 28mm. A proper test of flare would involve taking pictures and reviewing the results; I hope to do this sometime.

Which lens is better?

That depends on your criteria.

• Low light: Use the 50. Wide open, it's not sharp, but at f/1.8, it's quite sharp and it's three stops faster than the 28-135. The IS in the 28-135 can make about a two-stop difference if the subject is stationary; that means the 50 has a one-stop advantage. In most cases, that's not a big deal, but sometimes it may make the difference between getting the shot and not getting the shot. (On the other hand, if depth of field is a concern, the 28-135 with IS wins - to get the same shutter speed with the 50 requires a much wider aperture and gives you much less depth of field.) If the subject is moving, you'll need to turn off IS (because it doesn't work properly when panning, and it won't give you a higher shutter speed to freeze action), and now the 50 truly has a three-stop advantage. What you might shoot with the 28-135 at (say) 1/15 @ f/4.5 you chould shoot with the 50 at 1/45 @ f/2.8, or 1/90 @ f/2, or even 1/125 @ f/1.8.
• Selective focus: The 50 wins, easily. At f/1.8 (the widest aperture that gives usable sharpness), you'll have much less depth of field and a much blurrier background than the 28-135 at its widest aperture of f/4.5. I'd also expect the 50 to have better bokeh - it has very little astigmatism, and more diaphragm blades (8 vs. 6).
• Longer flash range: The 50 wins, easily. At f/1.4, it gives you over three times the flash range of the 28-135; stop down to f/1.8 for better sharpness and you still have over 2.5 times the flash range. This is particularly useful with the relatively weak pop-up flash on many cameras, and also useful for bounce flash in rooms with high ceilings.
• Size/weight: The 50 is much smaller and lighter. Personally, I don't mind the 28-135's size and weight, but I know many people find it too bulky for their tastes. The 50 is also not going to block a camera's built-in pop-up flash; the 28-135 may, depending on focal length and focus distance.
• Price: The 50 is significantly less expensive. Also, due to its smaller filter size (58mm vs. 72mm), filters cost less.
• Convenience: The 28-135 is much more convenient, because it doesn't restrict you to one focal length. I used to be quite happy with my old camera, which had a 50mm f/1.8 (and a 2x teleconverter); if 50mm is all you have, it's amazing how you can manage to compose scenes to fit. But it's so much better to have a choice of focal lengths without having to mount and dismount lenses.
• Filter use: Both lenses score top marks here - they both have non-rotating front elements.
• Focusing speed: No clear winner. You'd expect the 28-135 to focus more quickly - it has a better focus motor (ring USM vs. micro USM) and it focuses by moving only smaller internal elements (the 50 focuses by moving the entire optical formula - seven elements plus the diaphragm - in and out). But it doesn't have a marked advantage. Sometimes the 28-135 seems to focus more quickly, and sometimes the 50 does. My only guess is that the body's AF system can determine focus more quickly with the faster lens, and that may offset the 50's mechanical disadvantages.
• Viewfinder brightness: The 50, but not by as large a margin as you'd think. On my Elan II, there is little if any difference in viewfinder brightness from f/1.4 to f/2.8; only at f/3.5 does a slight difference in overall brightness become noticeable.
• Depth of field scale: No winner. The 28-135 doesn't have one, and the 50 does. But the 50's scale is almost useless. It only shows DOF for one rarely-used aperture (f/22), and even for that, it's not very useful. The scale is quite small, and the seven distances marked in the focus distance window (0.45m, 0.6m, 0.8m, 1m, 1.5m, 3m, and infinity) are fairly far apart so the DOF markings don't usually match up with the distance markings. For example, if the lens is focused at its hyperfocal distance at various apertures, what are the points of closest acceptable focus? The only answer on the scale is that at f/22, the closest acceptable focus is somewhere between 1.5m and 3m. Whoop-de-doo. The 50mm f/1.8 for my old Miranda is much better; it has seventeen different distances marked, and markings for six of the seven apertures shown on the aperture ring, so I can tell you the points of closest acceptable focus for f/4, f/8, and f/16, and give pretty good estimates for f/5.6 and f/11. Thank goodness that most EOS bodies have an automatic depth-of-field mode.
• Ease of manual focusing: No outright winner. The 28-135 feels better; with the 50, you can feel play in the gearing. The 28-135 has a shorter throw, which means it takes less time to go from one extreme to another; however, the 50's longer throw makes it easier to get to precisely the distance you want.

So which do I prefer?

That's easy. The 28-135 will be the one that lives on my camera, and the 50 will sit in the camera bag most of the time, despite the 50 having won most of the categories in the list above. If the 50 were significantly sharper, it would stand a better chance of being a general-purpose lens, but the 28-135 is just as good for practical purposes, and wins on convenience. The 50 will be a lens that I save for times when I really need the larger aperture (shallow depth of field, low light, or when I need every last bit of flash range).

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