Travelling: 17-40mm, 18-55mm, 18-85mm...

[neuroanatomist]

I'm actually surprised; obviously the L lenses should be superior in optics, but it appears not in this case. Not sure if that's a comparison on corner or centre, though surely the 17-40mm is at least superior centrally? ...confusion over superiority of optics...

The ISO 12233 comparisons show crops from the center, mid-frame, and corner (labeled on the left side). When comparing EF-S to L-lenses, keep in mind L-lenses are EF lenses with a full-frame image circle - the larger the image circle, the more difficult (and more expensive) the design. So, it's harder to design FF wide angle lenses than the EF-S counterparts, so for a similar price point, the EF-S lens will likely outperform the L lens, because the elements do not have to project as large an image circle. To take that to an extreme, look at lenses for medium format cameras - the 'cheap' ones (sort of the MF equivalent of the $100 Canon 50/1.8) start in the $600 range. The cheapest 'general purpose zoom' for MF is over $2K.


Even if Canon releases an EF 17-40 f/4L II, I doubt it will match the IQ of the EF-S 15-85mm when comparing them on a 1.6x crop body.
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As I suggested above, there are a few EF-S lenses that deliver L-quality optical performance. At this time, those are the 10-22mm, the 15-85mm, and the 17-55mm. So, it's not too surprising that the EF-S 15-85mm lens beats out the 17-40mm L lens, even though it has a wider range. Often, you get what you pay for, and you're comparing one of the cheapest L lenses with one of the most expensive EF-S lenses...

Looking at the comparisons between the 15-85mm and the 17-55mm, the 15-85mm definitely wins:www.the-digital-picture.com/.../ISO-12233-Sample-Crops.aspx...This remains true at least for up to f/4.

Right - wide open, the 15-85mm is sharper. But wide open is 2/3-stop faster at wide end, and 2 full stops faster at the long end. Optical design involves trade-offs, and wider aperture vs. sharpness is one of those trade-offs, especially at the wide end. So, if you're shooting at ~50mm with one of those zoom lenses, and you need f/2.8 for a high enough shutter speed to get the shot, you can only do that with one of those lenses...


Also, Bryan's statement about the 15-85mm being 'nearly equal' to the 17-55mm seems to be based on lens performance across all focal lengths and apertures, and if you look at one specific focal length/aperture combination, there may be bigger differences. Here's an example - to me, the results from the two lenses at the selected apertures (on the same body so the comparison is valid) look very similar. One of the two lenses is a Rebel kit lens that costs $100 or less with the package, the other is an L prime costing over $5K, so if you base your comparison on just those crops, it's a 50-fold price difference for the same optical performance.


Bottom line, if you're shooting outdoors or indoors with flash, and not planning on getting a FF camera soon, I think the EF-S 15-85mm would be the best choice for you.

[dsiegel5151]

Personally, I'd go with the 17-40mm. What it lacks for in image quality, it makes up for in build quality. Lots of things can happen in two months. Of course, this is coming from someone who once broke two lenses in an airport on the way to his destination. Woops!!








Canon 40D, 17-40mm, f/9, 1/500s, polarizer attached

[Gred]

the 17-55 is a great lens but your paying for the constant f2.8 aperture if this is not what you are looking for the 15-85 would be my choice, it as variable max aperture but it

[D-Lucas]

"...the EF-S lens will likely outperform the L lens, because the elements do not have to project as large an image circle."


Well yes, that

[neuroanatomist]

Anyhow, CR has it that a 17-55mm update should be coming some time next year. Apparently there are a few problems with this one.

LOL. Yep - and CR said the 24-70mm f/2.8L with IS was due out in 2009, then in Feb 2010 it was 'the source said next month, you can take that to the bank,' then it was for sure last month for Photokina. But it's ok, because CR has now positively assured us that the very next lens from Canon will be the 24-70 f/2.8L IS. Except that maybe it won't.


Last time I tried to take pictures with a rumored lens, the images didn't turn out as well as I hoped they would... [:P]


On a more serious note, I have no problems with my 17-55mm lens, and Sean (our flash guru) loves his.


You're quite correct - the 15-85mm does appear to have an edge in sharpness based on Bryan's ISO 12233 crops. If you look at the numerical comparisons on photozone.de (be sure to check the review from the same camera, i.e. the 15 megapixel ones from the 50D), you can see that the MTF resolution numbers are almost a wash - very similar across all apertures and focal lengths, and no consistent 'winner' there - but there's a mild trend for higher MTF numbers for the 15-85mm.


But, sharpness is not everything that defines 'image quality' - the 17-55mm has significantly less vignetting and handles chromatic aberration better, despite it's wider aperture (which usually makes those problems worse, but the 17-55mm is better corrected, withtwo Ultra-low Dispersion elements instead of the one found in the 15-85mm). The 17-55mm also has ~30% less barrel distortion at the wide end (usually the broader the zoom range, the worse the barrel distortion at the wide end). I suspect those characteristics, combined with the only slightly lower sharpness, are what's behind Bryan's assessment that the 15-85mm is 'nearly equal' to the 17-55mm.


Ultimately, I think both lenses are pretty similar (as in, both are excellent), and mostly it comes down to whether or not you want/need f/2.8 and can afford the price difference, or you'd prefer a broader focal length range. As you state, if you're shooting outdoors in daylight, you are not likely to need the extra 1.67-2 stops of light toward the longer end of the 15-85mm for shutter speed. Outdoors under overcast skies, even my 100-400mm does ok, and that's slower/as slow as the 15-85mm and has a less effective IS. But if you want to shootoutdoor portraits, you might want the thinner DoF that you'd need a wider aperture to achieve. Choosing lenses, like many things in life, is all about compromise. Do your research (which you have), ask for the opinions' of others (which you are), weigh all the factors, make your choice, and act on it.


Even though you have a while before your trip, don't wait until the last minute to get a new lens - you'll want some time to get comfortable with it before you get on the plane!


--John

[Kayaker72]

Lensrentals.com recently published an evaluation of the repair rates of different lenses. One of the lenses they focused on was how much better the efs 17-55 was doing lately (fewer issues with lenses purchased recently compared to a few years ago). Their suspecion is that Canon has worked behind the scenes to correct whatever problems the lens had. It

[D-Lucas]

Hey John -


Yes, I did make a mistake there, CR proposed a change for the 24-70mm, not the 17-55mm (they only speculated that there would be a very, very thin possibility of the 17-55mm update).


Nonetheless: I also noted that the 15-85mm performed poorly in the corners all throughout the lens, and particularly was rather soft at 85mm (as well as suffering other problems at that focal length too).


Regarding getting used to a lens; I

[xCalebx]

beautifull! messaged thanks for the advice even 9 months or so later

[xCalebx]

beautifully messaged! thanks for the advice !

[xCalebx]

neuroanatomist thanks for the advice!