need help deciding between canon 17-85 vs 15-85 II have a canon t1i and want to upgrade to a better lense. I tried the 18-135 but was not impressed with the optical quality. Should I spend 450 for the 17-85, or 740 for the 15-85. Is the 15-85 really worth the extra $$$. Is the 17-85 a bang for the buck. And what does UD glass do ?
[UPDATED] asked by canon newbie on May 1, 2010
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"Why would one choose the 15-85 over the 24-105?"

Its just a matter of usefulness on a crop camera. The 24-105mm L costs about 50% more than 15-85mm but just isn't very wide at all on a crop camera - 38mm vs. 24mm equivalent focal length respectively. That's a huge difference when you want to capture a landscap, etc. The sheer versatility of the 15-85mm makes for an excellent travel lens on a crop camera without the need for also carrying an ultra-wide.
Technology Guy answered on December 15, 2010

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For the most part in lenses, you get what you pay for. So, if you want better image quality then the Canon EF-S 15-85mm f/3.5-5.6 IS USM UD Wide Angle Zoom Lens is your choice. Depending on the focal length of most of your photographs, the Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens might be a budget choice to upgrade your image quality.

edit: Learning how to read MTF charts which Canon provides for their lenses will help you choose the best lens.

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml

Remember lenses like the EF 28-135mm are designed for full frame cameras, so when comparing their MTFs for lens designed for APS-C cameras, you have to make sure you are comparing equivelent portions of the MTF.

http://www.canon.com/camera-museum/tech/room/hotaru.html

'When parallel light rays are refracted by a prism, a rainbow-hued spectrum comes out. This phenomenon is called "dispersion". In case of photographic lenses, the dispersion causes color fringes at the edge of subjects, which is called axial chromatic aberration, and as a result, deterioration of image quality of photography. There is a limit to the correction of chromatic aberration, using regular optical glass lens elements only. Some aberrations not corrected by optical glass are called secondary spectrum or residual chromatic aberration or secondary chromatic aberration. The artificial crystal fluorite lens element, featuring very low optical dispersion index, was developed by Canon to eliminate secondary spectrum. Canon succeeded artificially crystallizing calcium fluoride (CaF2) into fluorite at the end of 1960s. Canon EF lenses are the only interchangeable lenses for 35mm SLR at the time that employ fluorite lens elements. In the late 1970s, Canon also developed special optical glass lens elements with very low dispersion index called Ultra-low Dispersion (UD) glass lens elements, and in 1990s an upgrade version of UD glass, called Super UD glass, was developed. Fluorite, UD and Super UD glass lens elements are widely used in EF lens series, for super-telephoto L series lenses, as well as in telephoto zoom and wide angle lenses.'
Tom Martin answered on May 1, 2010

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Yes, EF-S lens focal lengths are NOT 'pre-adjusted' for APS-C sensored cameras, so, the 35mm film camera equivelent focal length is 24mm-136mm, which is a very useful range.
Tom Martin answered on May 2, 2010

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thanks tom. took your advise bought the 15-85. all i can say the image the quality is superb for a non l lense. thank you for recommending this lens.
canon newbie answered on May 8, 2010

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Agreed with Tech Guy. 24mm on a crop (effectively 40mm) is just not wide enough for a general walk-around lens.

That said, I do wish that Canon would have made the 15-85 a constant aperture lens like the 24-105 f/4L.
JB answered on August 8, 2011

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one more question. If I get the 15-85 efs lense do I still have to multiple the 1.6X crop factor to get the true range for the lense , just like I would have to do for ef lens on a rebel t1i?
canon newbie answered on May 1, 2010

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Sounds good! I'm buying my first digital camera for my daughter and her family. I've locked in on the t1i and 15-85. I really like my 24-105 lens and think that the 15-85 should be a great match for the camera.
Mark H. Gary answered on November 30, 2010

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http://www.photozone.de/Reviews/overview#canon_aps
Bob answered on November 7, 2012

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Check out the problems that the 17 - 85 is having. It appears that after 5 years or so it needs major repairs. I have a 17 -85 and am facing $250.00 in repairs right now and my experience is not unusual. When I called the repair shop, they knew what the problem was as soon as I told them which lens I had.
Gerhard Stavney answered on January 25, 2014

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Why would one choose the 15-85 over the 24-105? Despite the relative ratio differences it seems as though the 24-105 is so much more of lens for not much more money. Any thoughts?
Brett Turner answered on December 13, 2010
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