EF-S 15-85 vs EF-S 18-135

[KeithB]

Any reason for the 18-135 to be $100 cheaper? Is it just build quality, or is that bottom three mm really tough to design?

Any comments on these two lenses?

[Bob Atkins]

One obvious difference is that the 15-85 has a full ring USM AF motor, while the 18-135 either has the new STM drive or a conventional motor. That should make the AF of the 15-85 faster and allow full time manual focus (which both the 18-135 lenses lack).

The extra 3mm on the wide end also probably do contribute to additional cost and design complexity. The 15-85 has 1 UD and 3 aspheric elements, while the 18-135 STM has 1 aspheric and 1 UD and the 18-135 has just 1 aspheric.

The 15-85 also has a distance scale, which the 18-135 lenses lack.

When it comes to optical performance, I've never had the chance to shoot the 15-85 and 18-135 lenses side by side.

[KeithB]

Thanks Bob-
I already have the 70 - 300 so, I don't need the extra on the long end, the wide angle is very interesting to me though. I will save my pennies for the 15-85.

(My 17-85 died, and I already sent it in once, so I am saving up for a new GP lens - I am making do with my 18-55 right now.)

[Bob Atkins]

The 15-85 may well be the best choice for a general purpose lens. It's better than the 17-85 was, especially at the edges and corners at wideangle settings, but it's also a tad sharper at 85mm.

There's not much else that covers that range and the extra few mm on the wide end does make a difference over the 17-X and 18-X lenses.

[rixtix]

I realize I am late to the party on this topic.  However, I shoot the 15-85 everyday.  I have owned it for a year and 3 months and its performance is excellent.  IMHO it is the go-to lens for any crop sensor Canon.   You will not be disappointed. 

[deemery]

I had the 17-85 EF-S, and (after it broke, I got it fixed, sold it and) replaced it with the 15-85 EF-S.  As Bob pointed out, that 2mm makes a big difference on the wide end!  With the 17-85, I shot at 17mm a lot, and had the expected limitations with the lens at its limits.  With the 15-85, I'm still shooting a lot at 17mm, but that's not the very edge of the lens so I get better quality. I'm a huge fan of the 15-85 lens.  About the only time it comes off the camera is when I need a really wide angle, and then I go for my Tamron 10-24.  I haven't done enough comparisons to see how those two compare at 17-20mm, if I want that focal length usually I'll keep what's on the camera.  (Unless it's low light, then the 15-85's image stabilizer is a big advantage.)

On a more technical note:  Is there a reason why we're not seeing image stabilization on ultra-wide zooms?  

[Bob Atkins]

I guess that there are a couple of reasons why we don't have superwide lenses with IS. My guess at a technical reason is that it's hard to make an IS system that can stabilize at long times. For example let's say we have a 10mm lens and let's say that you can probably handhold that lens at 1/15s on an APS-C body and get sharp images (a reasonable assumption). If we add a 3-4 stop stabilization system, then we'd expect to be able to hand hold it at 1/2s to 1s.

Keeping the lens stable using the IS system for almost a second could be quite difficult. It's probably outside the bandwidth of the IS system that's used on longer lenses (i.e. at lower frequencies than current IS systems normally operate at). In fact it's advised to turn the normal IS system off for long exposures on a tripod because the IS system will cause the image to slowly drift under those conditions. I do note however that a few of the new STM lenses for video are said to have an IS system that stabilizes the image when the videographer is walking while shooting, so they may well be able to stabilize at lower frequencies than the normal IS does. Even so, they still don't need to keep the image stable for seconds, since video frame rates are 24fps and faster.

Another reason may be that IS is less important for wideangles since the required shutter speeds are slower and so they can more easily be handheld than longer lenses. Handholding a 20mm lens is pretty easy. Handholding a 500mm lens is next to impossible.

That being said, Canon have put IS in the new 24/2.8 IS USM, so they are moving to IS even on fairly wide lenses. It may be a long time before we see an EF-S 10-22 IS though.

[KeithB]

Just an update, I did get the 15-85 and so far, it is a great lens. It is a bit bigger and heavier than the 17-85, so my wife prefers the 18-55, but it is my camera. 8^)