Focusing distortion on telephoto shots.

[euphonywho]

Hello everyone! I have a question, and I hope I've posted it in the correct place!

This weekend was the second time I really had a chance to put my 55-250mm 3.5-5.6 IS lens to the test. Similarly to my first experiences with it, I'm finding that when I am past 200mm (maybe earlier?) that my pictures come out with a strange focus distortion effect. Check this picture as an example (not the most interesting picture, but it was the best example of the effect I could find!)

Links to larger size.

The center is nicely in focus, but as you get closer to the edge it gets progressively worse.

Can anyone help? It's making using my long lens a little pointless IMO. Thanks!

[RexK_Cozumel]

what is the exif data on the shot?

[Elmo]

Are you using a filter?

[euphonywho]

Here's the EXIF:

Exposure Bias Value: 0
Exposure Mode: Auto exposure
Exposure Program: Normal program
Exposure Time: 1 / 400
Flash: Flash did not fire, compulsory flash mode
FNumber: 7.1
Focal Length: 214
ISO Speed Ratings: 200
FlashCompensation: 0
Lens Model: EF-S55-250mm f/4-5.6 IS

There is a Tiffen UV filter on the lens. I hadn't thought of that being the cause. I can try taking some more test shots soon. Thanks!

[takethislife5150]

It almost looks like an effect you can achieve by zooming while the shutter is open. But I don't think thats your problem

[dcclark]

Could be from a wonky filter.

It also could be extremely bad coma -- which is the weird lengthening of spots of light as you get closer to the edges of the frame. I've never seen it so horribly bad though!

But, I'm thinking, the most likely choice is zoom creep. You either accidentally nudged the zoom ring (just a little!), or the lens was in a position where it creeped on its own. The result is that you have a very minor "zoom" effect.

[euphonywho]

I tried it again earlier today during lunch with the filter removed, and it had the same effect. I'll try right now and make sure to leave the zoom ring alone. Thanks for the help so far everyone! I'm trying to avoid sending it in to Canon...

[Doug Pardee]

You've gotten some good advice so far, but I'm concerned about the way that the effect is diagonal rather than purely radial. That suggests to me that a lens element is tilted out of position inside the lens. I have a feeling that you will be sending the lens to Canon for repair.

[euphonywho]

Thanks for the suggestions. I'll check to make sure I've registered it (lens is only 1 month old, so everything should be okay still), and look at getting it sent in. Here's another good example of the problem, emphasizing the diagonal-ness.



This was taken with no filter, at 250mm (max for the lens), so I doubt the zoom ring was moving more as there was nowhere left for it to go!

[dcclark]

If you take a shot at a wider angle, and examine the corners carefully, is the distortion still there (but less obvious)?