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G35Guy Jun 14, 2005 3:46 PM

I've had my EF-S17-85 mm IS lens for about a week now and I've yet to take single shot with it that I feel is focused correctly. The lens feels a little soft overall, but what really worries me is that the things I want to be in focus don't seem to be.

Here are two images I took today. In the deer image, the focus was on the deer, yet it's not very sharp (at least not viewingthe RAWat 100%). In the bridge image, it appears as if nothing is really in focus very well (except the leaves on the left), howeverthe bridge itself was the focus in this image.

Do I have a bad copy of the lens or am I really just not used to the lens yet? Is there a more definitive way I can tell if my lens isn't performing up to snuff? I have the raws if anyone cares to see full size versions.

Shot settings and picture links follow:

Deer pic (handheld with IS on):
shutter: 1/160
85 mm
ISO 200

Bridge pic (handheld with IS on):
shutter: 1/200
38 mm
ISO 200

peripatetic Jun 15, 2005 4:05 AM

G35Guy wrote:

In the deer image, the focus was on the deer, yet it's not very sharp (at least not viewing the RAW at 100%).
The best way to test front/back focus issues is to shoot a newspaper on a tripod at a 45d angle in good light. Use centre-focus and focus on a particular word. Check the picture - is that word the sharpest or not? The DOF will normally extend 1/3 in front and 2/3 behind. I suggest you do this for your own edification and to prove that there is most likely nothing wrong with the camara or lens.

What is far more likely is that you have hit the DSLR learning curve, this is your first DSLR after moving up from a P&S - maybe you were disappointed with the 18-55 kit lens and decided to get the 17-85 because everyone raves about how sharp it is, but you're still very disappointed because you can't see much if any difference between the 2 lenses.

Viewing RAW at 100% you will never get a sharp image from any lens on any Canon DSLR camera, the fact that you expect to suggests you are fairly new to the DSLR world. 95% of the time this is the correct explanation.

There must be 100 threads here about this issue - mostly people who have just dropped a load of cash on a lens that was supposed to be sharp and they're looking at 100% magnification in PS and can't see it.

Remember - if you're shooting RAW you have to sharpen your images yourself. Otherwise switch to JPG and bump up the in-camara sharpening. A RAW file is a "digital negative" and must be processed to get the correct output.

Here's my question for you:
With appropriate sharpening of the file what does your final OUTPUT look like? How big are your prints? 6x4, A4, A3? How big is your web graphic? 800x600, 1024x768, 1600x1200?

If your prints or web jpg files are sharp enough then you don't have a problem.

There is one caveat however, which accounts for the other 5% of complaints: you are an experienced DSLR photographer, you've had your DSLR for months or years and you have other lenses that give significantly sharper pictures. If that is the case then I suggest you take your current lens back to the shop and ask to test another one - if you can see a clear difference between the two lenses then you've got a dud. Alteratively you could get the camera and your lenses calibrated by Canon.

G35Guy Jun 15, 2005 6:44 AM

I've had my first DSLR for a couple months now, but I've used a 35mm Nikon SLR for years. The digital is definitely different and you're probably right about me just not being used to it yet. With my film SLR, getting the things you want in focus consistently just seemedeasier. Themain reason I wasworried was that the images I was taking with the new lens were generally not as good as with the kit lens. I wasn't expecting a huge improvement, but I certainly wasn't expecting a step back. I just need to keep playing with it and I'll do the newspaper test just to set my mind at ease.


peripatetic Jun 15, 2005 8:24 AM

In my experience the 17-85 is noticably sharper than the 18-55, so if yours isn't then either you have a very good copy of the 18-55 or a poor copy of the 17-85.

Either way there seems little point in keeping the 17-85 that you have, sounds like it needs to go back to the shop.

G35Guy Jun 15, 2005 4:08 PM

I have a small favor. At the link below is an image of a printed paper that I used as my test image. The center focus point was used on the line of text indicated by the purple slash.

Settings were ISO-200, 1/200th, f5.6 @ 61mm. The image is a standard sheet of copy paper with 14 pt. type. It was taken with default large fine jpg settings of +1 sharpness, contrast and saturation.

To my eyes, it looks like the focus is a line or two behind the purple line and drops off in front of it faster than I would have expected.

Anyone agree? Or am I just being a little paranoid here? :?

barthold Jun 15, 2005 4:44 PM

Taken on a tripod?

On the 10D, and I presume the 20D as well, Canon only guarantees that the focus will fall somewhere inside the DOF.

Your picture looks ok to me.


G35Guy Jun 15, 2005 7:43 PM

ok, that's cool. Thanks. I'm going to put this issue to rest in my mind and chalk it up to me.

peripatetic Jun 16, 2005 3:24 AM

Hmm, I dunno - it does look a little off to me, not awful but it does seem to be front-focusing just a tad.

Can you try the same shot with the lens wide open to reduce DOF as much as possible?

Overall though I remember when I got my 28mm f1.8 - at first I was getting tons of OOF pictures. I did the "text test" and realised it was just down to me working with a lot less DOF than I was used to. Now I don't have any problems with it.

btw - I believe there is a firmware upgrade for the XT - and I vaguely remember that it may address this issue?? At any rate upgrading the firmware isn't going to hurt.

Did you buy online or at a store? If the latter then there can be no harm in going down and asking to try another copy of the lens.

NHL Jun 16, 2005 6:56 AM

IMO this lens has too much DOF to conduct a meaningful front/back focus - At least try it at the 85mm! :idea:

The AF focusing algorithm is in the camera (a lens is passive and just does what it has been told by the camera): a 50mm f/1.4-1.8 would be a better candidate and also the lighting affects the AF. I believe the Canon test method also calls out the minimum lighting required - check some older D30 AF test forums for example (the camera decides when it thinks the focus is good enough for that amount of lighting) ;)

G35Guy Jun 16, 2005 8:01 AM

Ok, here's two final images.

This one is f/4 at 17mm -

This one is f/5.6 at 85mm -

Both usingcenterpoint focus on the purple line from a tripod. 85 actually looks pretty good, but 17 looks off to me, but that could also just be the softness of this lens zoomed all the way out.

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