IS, sharpness, or stops

[ddr]

With the new lenses coming out, I'm kind of stumped upon some ... basic photography theories. I currently own the tamron 17-50 f/2.8 on a t1i, and I love it as my walk-around. Tamron recently announced the VR version of that lens, and Canon also came out with the new 15-85 IS lens.

If the new Tamron is anything like the one I own right now, I know I'll be happy with it even more. But I'm reading reviews of the Canon 15-85 IS and that it's sharp at all corners throughout its range; even comparable to "L sharpness" at certain focal lengths and f-stops and "better than canon 17-55 f/2.8 IS".

I know that the f/2.8 VR (IS) would give me more light than the f/3.5-5.6 IS, but let's pretend that the canon is as sharp as some of the reviews say. Which would you pick?

[sybren]

I'd pick the Canon. I've used third-party lenses in the past, but I wasn't too fond of them.

Originally Posted by ddr

"better than canon 17-50 f/2.8 IS"

There is no such lens. I guess you mean the EF-S 17-55 f/2.8 IS USM. I own that lens, and it's amazing. If the new lens is even better, there is no doubt in my mind as to which one you should pick.

[ddr]

thnx

i'm more curious about the question as to a sharper lens + IS vs. lens with more light

[Saralonde]

It's a tough one to answer. If I was comparing two equal lenses, both Canon, both covering the same range, with the only difference being one was 2.8 non IS and the other was IS 3.5-5.6, I'd go with the 2.8. For me the lower light capability would be more useful. However, IS is always tempting, which is why, like Sybren, I got the Canon 17-55 f/2.8 IS.

Given the choice of these two lenses, I might go with the Canon. I'd like the extra range. The IS would allow for a stop or two.

Read some more reviews of the Tamron as they come out since it's still pretty new. BTW, I own a Tamron and I'm very happy with it, but it does not begin to match the sharpness of my 17-55.

[ddr]

Thanks for the breakdown

I'm just trying to wrap my head around the logic behind these choices. If i didn't care so much for corner sharpness, the 17-55 would be better since it has IS and is f/2.8. Then it'll depend on how much the new Tamron is, how much better it is with VR over my current Tamron, and how it fares with the canon 17-55 IS.

Another idea I'm contemplating is keeping my lenses and upgrading the t1i to a 7D. The low light performance from reviews are amazing. It seems like an overall upgrade when you consider the shots I can do without IS at higher ISOs.

[n_mazur]

Another thing to think about when comparing IS to a larger aperature is that no matter how good IS is it won't get you a good sharp image of that animal scurrying across the ground, or someone running around. The larger aperature will allow you to shoot at a faster shutter speed so you can freeze the action. I don't know what kind of scenes you prefer shooting, so if you're more into still subjects you can go ahead and throw what I just said out the window.

[ddr]

i do shoot more still stuff, but what you said is very true and an important point. thnx

still torn between the 15-85 and 17-55. sharpness vs. larger apeture

[TerryMC]

Originally Posted by ddr

still torn between the 15-85 and 17-55. sharpness vs. larger apeture

Have you considered f/2.8 is better in getting a focus lock? What is so good about image stabilization and sharpness when the lens is still hunting and you miss the best moment.

[jdepould]

The corners improve as you stop down. So it really depends on your shooting style. If you're shooting available light wide-open, then yeah, corner sharpness is pretty important. If you're shooting portraits at f/8 all day long, you could probably get away with a kit lens.

[n_mazur]

I think I'd go with the lens that has the f2.8. Like TerryMC said: "What is so good about image stabilization and sharpness when the lens is still hunting and you miss the best moment." I'd rather be able to get a shot that's a little less sharp at the corners (or less sharp overall) then not get the shot at all. Have you ever looked at the National Geographic best images coffee table books? At least half (I'd be willing to bet more like at least three quarters) of the images aren't really that sharp. It's all about composition in the end anyway. I could teach my five year old how to shoot sharp images, but I doubt they'd be very interesting (although maybe I'd be surprised....).
I do mostly available light shooting, since I don't have an external flash and the built in flash isn't the greatest, so I tend to shoot in aperture priority in darker situations, stop down, and use higher ISO's. Do you primarily shoot handheld or with a tripod?