Lens focusing difference??

Hello,
I am having a problem with my Tamron 28-200mm lens. It doesn't focus very sharply. I took a couple of pictures the other night on a tripod, one with my 50mm f/1.8 and the other with my 28-200mm f/3.8-5.6, but both pics were at very similar settings. i.e. they were both taken at 50mm, ISO 100, 1/60 sec with flash and both were at f/4.5. Both of them focused on the middle AF point and the camera did not move (it was on a tripod). Anyway, there was quite a difference in sharpness between the two images and I am wondering what may cause this, as the 50mm lens was MUCH sharper?

Is the problem with the 28-200 just having too much stuffed inside the lens to produce as clear of a picture as the 50mm, or can a shop adjust the lens so that it focuses better? I'll post the two pics as soon as I can so you can all see the difference and maybe give me some pointers. Thanks in advance!

PS, the 28-200 is much older than the 50mm however, could that have something to do with it?

Here are the pics completely untouched, just cropped.

28-200mm

CBass,

bear in mind, that any 'hyperzoom' (i.e. a zoom with a very large zoom range, like 28-200) will always have a very hard time to be sharp at all apertures ans focal lengths.

On the other hand, a prime (and especially a 50 mm prime) is very easy to construct so that it gives sharp and contrasty pictures.

I'm afraid it's not so much a focus problem, but rather the lens is just not as sharp as the other one (at least not wide open). This would be consistent with everything I've heard about the lens so far.

Check out this article, it gives an example by comparing shots of the Tamron 28-300, the Canon 70-200/2.8L and the Canon 70-300 DO.

You will notice that the difference in image quality is very pronounced at wide apertures and tends to diminish if you step down the lens (hence the saying "F 8 and you're there" )

So try stopping it down to f/8 and see if you get better results...

Best regards,
Andy

Thanks for the explanation Andy. I'll try that and see if I get some better results. That's kind of what I was hoping though.

If there is something wrong with the AF on the lens, is there any way for a shop to correct it by chance?

I'd suggest manually focussing the 28-200 and see if you can get it better. Then, test auto focus and see if it will stop at optimum values.

I have my 20D using ONLY the center focus point. That way, I have much better control of the camera's brain when using auto focus. Try it and see if it helps.

If the focus is off, it normally can be calibrated.
That means sending the lens in to Tamron - sometimes they also ask for your camera

Do a focus test ... search the forum for this!

Best regards,
Andy

Here is another thing to consider... aperture.

Most lenses are not at their sharpest when they are wide open or very near wide open. Most are the sharpest when they are at least two stops up from wide open, or somewhere around the middle of the entire aperture range.

Your f/1.8 lens, used at f/4.5, is more than two stops up from wide open. The f/3.8 lens, at f/4.5, is almost wide open.

If you repeated the test at f/8 or something, the results would be closer.

Still, a single focal length lens tends to be sharper than a wide-range zoom lens.

---Bob Gross---

Also something to consider, How close were you? The 200mm might need alittle more room to focus. Unless ofcourse if it's macro. Just my thought. But I also agree about trying to try it outside both at F8 and see what you get.

That would be my first suggestion, too. Choose a fairly distant subject with details rather than something right at the close end of your lens' capabilities so you can be sure it's able to focus on it. A bare tree, picket fence, or brick wall would be good; for that matter, so would a chain-link fence.

Thank you all very much for the information, it's been cery helpful and educational

I tried it again on a subject a little further away with f/9.0 on both lenses and the 28-200mm was MUCH better, it still wasn't as sharp as the 50mm, but it was a kind of soft focus that I imagine to be desirable in certain settings. And it is definately acceptable with the aperture closed down a bit more (in my eyes at least).

I had already searched for the Auto Focus test, I just haven't had time to print a page out and try it. That's the next step to decide if I need to send it in to Tamron. Once again.... THANKS!!