Sigma Telephoto - Great Price, Doesn't Stop!

Am I nuts for thinking I can make this work? I'm optimistic, but the used Sigma 170-500mm APO is coming on Thursday and I'm trying to decide on a few quick tests that will show if I need to immediately return it. (Thank goodness for an accommodating seller!)

Because this is an older lens, my T2i won't be able to change the aperture from it's f/5.6 wide open setting. I'll be using the lens primarily for casual surfing photos. (That's casual photo-taking, not casual surfing). My "kit" 55-250mm IS does a half-way decent job so there's no sense in having the longer zoom if the end product is no better than a similarly cropped photo from the 55-250.

My main concerns are image quality with the lens wide open and whether it's going to be possible to focus on a moving object with the resultant thin depth of field.

So, I'm thinking that I'll do two tests:
First, I'll put my camera on the tripod and take a few shots down the street at various focal lengths. I'll take the same shots with the 55-250 and maybe even with my friend's new 70-200 f/2.8. Then I'll look at the results side-by-side.

Next, I'll go down to the beach and try shooting some birds in flight, surfers, or whatever else is moving around down there. I'll do that with all three lenses and compare the results.

I'm really anxious for this lens to work for me (a 500mm zoom for $390!) and I won't return the lens unless it's completely impractical to focus or unless the images are far inferior to my current lens. If this lens doesn't work out, I'm pretty sure I can find a 70-200mm f/4 for about $100 more, plus another $150 for a tele-converter.

Any advice here? I'm within my budget but feel like I might be out of my league in terms of expertise.

that lens doesn't seem that old, i'm kinda surprised you can't change the aperture at all...and i'm guessing it'll be f6.3 at 500mm...that makes me kinda wonder if the lens will be able to trick the camera into focusing still...

I'll definitely be reporting back. Looks like you have the 150-500 OS model. A friend has that one and has taken some very good surfing shots with it.

Any other tests I should run the lens through?

The 170-500 is quite old. I had one for sports photography in the days of film -- up to about 12 years ago. I had it on a Canon EOS 5 and it worked like a charm - no problems at all.

I tried this lens in the past, and I wasn't overly impressed with IQ. I ended up selling it and moving to the 50-500 Bigma at the time, I was much happier with that lens over the 170-500. I might have had a bad lens though, not sure.

Darn you TeamSpeed!!! Now that I've learned about micro-adjustments I'm not going to get a good night's rest until I upgrade my T2i to a micro-adjustable body.

It sounds like your free micro-adjustment tool might be a good way to compare lenses. I could put one far enough away so that it fills the frame at 500mm and then compare that image with the cropped image from the 55-250mm and the 70-200mm lenses. While I'm at it, I probably ought to move it in to where it fills the frame at 400 and 200mm focal lengths.

Just wondering if I also need to compare shots of a distant building. Would there be a difference in lenses at increased distance from the subject? I'm guessing yes, because it would affect the depth of field.

And now, thanks to your signature line, I have a half-hour's worth of reading to sort out the difference between Sigma's Stigma, Bigma, Bigmos, Sigmos, and Bigmos-ma.

If you really believe you need OS (and it is always a wise thing when you are considering that these are slow lenses at 500mm), just concentrate on the 150-500 OS or the 50-500 OS. You could look at the 120-400, but why go that range, you might as well look at the 100-400L used too then.

Good options for long telephotos under $1500:

Canon 100-400L + 1.4x Kenko
Sigma 50-500 OS
Sigma 150-500 OS
Sigma 120-400 OS (but I would prefer the Canon over this)

Remember that bing cashback ends in July, so if you are going to buy one off ebay to use the 8%, you have a month and a half.