The first thing I purchased after buying my Rebel XT in August 2006 was a longer lens. The 18-55mm kit lens was roughly equal to the lens on my p&s and it was time for something way longer. After doing a ton of reading I noticed that a particular lens kept being mentioned as a great beginner (read cheap) telephoto zoom lens. This would be the Sigma 70-300mm f/4-5.6 APO DG Macro lens. Supposedly it was the sharpest lens under $500 and with a street price of about $220, I could actually afford it.

I had taken some pretty good photos after nearly 8 months of use but I had two big complaints, the focusing system and the lack of sharpness. I had been willing to accept these weaknesses until a recent trip to the zoo where it became apparent that I needed something better. Time to get out the credit card.

The choices
With the task of finding a new and better telephoto zoom lens at hand, I enlisted the help of the DPC forums. Most people suggested one of two lenses, the Canon 70-300mm f/4.5-5.6 IS or the Canon 70-200 f/4L. The IS lens is a tiny bit cheaper and has Image Stabilization but is slow, lacks ring type USM and lacks the sharpness of a L lens. It would be an somewhat lateral move in terms of image quality but it had IS. The L lens is way sharper, a little bit faster and has ring type USM, but is not as long as the other lenses. I had pretty much decided on the L lens when I stumbled onto a used IS lens at a local camera shop. I had found a 75-300mm f/4-5.6 IS lens, the previous version of the 70-300mm IS lens. The shop was selling it on consignment for $350 and it was in great shape both cosmetically and mechanically. It also came with the optional lens hood. This would work fine as a stepping stone to the nearly $600 L lens. I bought it.

The lens itself
The 75-300mm looks almost exactly like the newer 70-300mm model except for one difference, the older model only has "Mode 1" IS and doesn't have a mode switch. This means that IS works in both horizontal and vertical directions all the time. "Mode 2" allows IS to only effect one direction for using it while panning. The casing is all metal and feels solid. The zoom and focus rings move smother than the Sigma bit are not L quality. Unfortunately the barrel does turn wile focusing.

Using the lens
The 75-300mm lens focuses much faster and accurately than the Sigma, but can not come close the speed and accuracy of the L lenses. IS seems to do a good job but time will tell if really helps as much as people say. One annoying aspect to the lens is the placement of the zoom ring. When you have the hood turned around backward and attached to the lens, it totally covers the zoom ring. So in effect every time you want to use the lens, you have to flip the hood around. This was not the case on my Sigma. I find this irritating but I am sure I will get used to it soon. After taking a hundred or so photos with this lens, I have to say I like it very much and that it is much better than I ever expected.

Comparing the Canon to the Sigma
This would be my first lens comparison and as such I am only going to compare the lenses in one way, shooting the same subject using both lenses at 300mm and varying the aperture. The subject is the top of a power line pole near my house and is roughly 100 yards from my front porch, where I have the tripod set. These crops are 100% and unedited except for the text. The took photos with the IS both enabled and disabled on the Canon lens and found both sets of photos to be extremely similar. I will be using the IS-off photos in this comparison.

Click each pic for larger view

Conclusion
Here are the results as I see them

• The Canon shows more color saturation.
• The Canon has slightly more magnification at the 300mm setting.
• Wide-open both lenses lack sharpness with the Sigma being very soft.
• At f/8 the two lenses are very similar in terms of sharpness.
• At f/11 and f/16 the Canon is the clear winner.
• Stopped down to f/16, both lenses start to lose sharpness with the Sigma becoming very soft.