noticable differences - A muse on lenses.

I'm wondering just how much difference is really noticable between cheaper and more expensive lenses.

For example, is the Tamron 28-75 noticibly worse than the Canon 24-70L?

I do know that the Tamron 28-75 is a lot better than the equivalent Vivitar if my old 35mm days are anything to go by. In fact, back then zooms were so poor that I kitted out solely with primes.

Are the brands: Sigma, Tamron, Tokina noticably different in quality from the Canons?

I hear a lot of "this lens is sharper", "I had a bad copy", "the manufacturer fixed it for me" all of which could very well be results influenced by one's perception of the lens and or the repair. Certainly all lens analysis is by its very nature subjective.

How many people have tested their lenses extensively alongside similar lenses?

For example, I have the Tamron 28-75 which I feel is sharper than my Canon 18-55 although I do notice I can get tack sharp photos from the Canon when it's on a tripod and focussed correctly. Is it perhaps that people don't get correct focus and blame the lens for being poor?

I put my 28-75 on a tripod and aimed it at my wife's bra as it hung from a doorknob. I shot two photos. One was in focus and the other was slightly out of focus. Everything was the same except the camera focussed in a different place for both shots. The difference was only an inch or two but at 5 feet, it was noticable. That, I feel, is more the nature of the AF beast than a fault with the camera or the lens. I notice the same kind of thing with other AF systems - none seem focus with pinpoint accuracy every time. There's always a degree of slack in it.

This degree of slack brings me to another issue: if we agree that there is a degree of slack that shows demonstrably at f2.8 then what does that say about f2.8 and faster lenses? Perhaps it says that cheaper f4 lenses are better bargains?

opinions?

I have a Sigma 28-70/2.8. At f/4, it's no less crisp than the 24-70L that I tried out in the store (I take my DSLR into the store and shoot my own test shots in the store).

At 2.8, the difference is more noticeable, even focused manually.

But there's one place where my Sigma lens (and your Tamron) offer no hope of competing, and that's at a 24mm focal length. When 28 represents a normal lens as it does with a small sensor, the 28-70 is no longer a wide-to-tele zoom. I can use the 24-70 on my 10D at a wedding, but I can't use a 28-70. Thus, they are hard to compare. In fact, I hardly ever pull the Sigma out of the bag any more--a good zoom range in the 24x36 format doesn't work well at 15x23.

I sometimes miss shots from my 50 and 85mm lenses because they are not perfectly focused. That's been true for every short tele I've ever owned going back to the 135mm lens on the Mamiya C-3. Focusing requires skill, even when we delegate the responsibility to our camera on those occasions when it's easy.

So, I would modify your final statement: If we aren't going to focus our lenses accurately, we should use small apertures to hide our focusing errors. It doesn't sound so good in those terms, does it? But even if I only get half my f/2.8 shots focused accurately, that's more good f/2.8 shots than I'm likely to get from an f/4 lens, isn't it? I just need to make more images to improve my chances.

Rick "acknowledging the need for better manual focusing aids" Denney