Lens sharpness woes

[Hub]

I have a Canon 500d with EFS 15-85mm lens. These aren't cheap and are supposed to be really sharp - so do I have a duff one? The truth is I have had this a couple of years, so it is out of warranty, but I have never been happy with it: it has always been really inconsistent - some pics reasonably sharp, but lots more not, and in different parts of the frame too. I just didn't get around to doing anything about it earlier (you always think, is it me or the lens?)

I got around to doing a bit of testing as, if anything, it seems to be getting worse if that is possible!

Camera on a tripod aimed at brick wall, IS off, ISO 100, 2 sec timer and Aperture Priority shows it is worse wide open and at the wider end of the focal range.

None of the edge of frame is sharp, but the worse seems to be bottom left corner, from where these crops are taken. 15mm is really bad, but these were all from 35mm where you'd expect it to be ok?

f4.5


f7.1


f14

(sharpest but unusably slow shutter speed for hand-held use)

The problem is with this lens for hand held it seems to need to be wide open to get a fast enough shutter speed most of the time in all but the brightest sunlight. I use this as a walkaround lens for travel, family, landscapes and everything - but I feel disappointed with it. Wide angle landscapes are particularly bad.

Here's another crop from a row of people ISO 100, F9, 1/160sec and from towards the right end of the frame - the faces are similarly blurred!



So the question is - should it be like this or is it defective? And if so what can I do now? I bought it at a local camera shop but over a year ago so out of warranty.

Anyone else had experience of this lens, and was it like this?

[Hub]

mike80 said:

Is it like this at all focal lengths? Sometimes wide lenses can be like this. Might be worth sending it off to be looked at though, something could've worked loose.

All focal lengths up to about 50mm I guess, not so bad then and a bit worse right at the end of the zoom again (85mm)

GetCarter said:

Techie term for this... it's fked.

Well that answers that one!

Next question then - rough cost and timescale for repair?

(Or stick it on eBay and buy a new one?!)

Edited by Hub on Sunday 14th June 16:52

[Hub]

One shot focus, single centre focus point.

I have the original 18-55 kit lens that, while I have not directly compared under the same conditions, does not produce the same issue and feels more consistent to me.

Will try a 45 degree test when I have time. Thanks.

[Hub]

Actually - I should have done this first! Dug out the old 18-55 for direct comparison with the same settings and focal length on a test chart I printed:

Bottom left corner area:
15-85:



18-55:



None of the edge of photo is great, but it seems the whole left hand side is worse, with bottom left particularly bad.



Canon!

[Hub]

OK, so I decided to send this lens off for repair - to Fixation UK, a Canon authorised repairer with a decent reputatation.

It was repaired for a not insignificant sum, and came back today. I have not had time to do any significant testing, but a quick setup in the office with exactly the same settings to compare with previous test chart has this result:

Before and after:

The crops haven't come out the same size and the room was a bit darker before, but to my eyes it doesn't look any different in terms of the poor sharpness, and in the same part of the frame too. Again at 35mm I would expect better, and compared to the kit lens above still awful.

So what does this mean?
Either
-They haven't repaired it and I have to send it back again?
-It is an issue with the camera (or camera and lens combination) itself?

I'll do some more shots, but it seems the same to me. What now?

[Hub]

AndyS2 said:

I'd be giving them a call tomorrow, I have the same lens on a 450D and it's been nothing but pin sharp.

That's useful - so if you shot at 15mm and f3.5 would it still be reasonably sharp in the corners? (Or even any focal length but wide open?)

[Hub]

LongQ said:

Horrible.

Did you send examples of the problem?

Have they offered any information about what work was done?

I would say it is still disappointingly dodgy.

Extremely dodgy - but I have no idea what the margins for tolerance might be according to the service criteria.

I printed some samples on paper with an explanation similar to the above.

They sent an estimate with no detailed notes but listing parts and work to the focus system and optics as well as a recalibration, clean and service!

I'm depressed! I'm going away in 4 weeks and wanted it sorted, but it is just a rubbish lens.

Edited by Hub on Wednesday 1st July 20:42

[Hub]

Not scientific, but I did actually briefly compare (hand held) a second hand one in the local camera shop before sending it off for repair:




I have noticed in fiddling around that the AF points on the left hand side hunt a lot more and fail to focus more than the centre or right side - could that have any significance?