corner sharpness

Started Jan 18, 2012 | Discussions
tukatu Junior Member • Posts: 27
corner sharpness

Bought 7D + 17-55 recently. did come shots and notice when using off-center focus , the photo is not sharp where the focus was used.

so did some test shots below using center focus. notice the corner of the photos are not sharp. is this normal?

Canon EOS 7D
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Flapshots Regular Member • Posts: 213
Re: corner sharpness

Focus is a distance value so if your test sheet doesn't move, no matter which focus point you take, your focus will still be on the test sheet.

This is not a focus problem if your center point is always sharp.

Lenses are never as sharp in the corners as they are in the center for maybe a very few fixed lenses..

I don't own the 17-55 so I can't say if the amount of sharpness loss in the corner is what is expected from this particular lens although photozone.de had this to about the lens

"The center resolution is very good to excellent throughout the range and neither the borders nor the extreme corners showed a significant weakness during the tests. There's only a very marginal weakness at 35/50mm @ f/2.8 but even so the lens remains perfectly usable here."

OP tukatu Junior Member • Posts: 27
Re: corner sharpness

these sets of photo are taken using Canon 10-22mm (bought 2nd hand)

am not sure if its consider ok. I know the center is very sharp. but is the corner consider ok?

Martin Ocando
Martin Ocando Veteran Member • Posts: 6,525
Re: corner sharpness

I think they are. Very few lenses are sharp across the range. And even the better lenses have a resolving power that is better on the center than on the corners. Also, I can see you tend to shoot wide open, which is not usually the sweetest spot for many lenses. Only stopping down a half stop make a big difference.

Redo the tests, but this time at different apertures, and you'll see the difference.
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OP tukatu Junior Member • Posts: 27
Re: corner sharpness

Do you those building shots?

I've done 10mm and 22mm with F4.5 and F8.

Martin Ocando
Martin Ocando Veteran Member • Posts: 6,525
Re: corner sharpness

Yeah, but even at f:8, the building shots are not very good to judge raw sharpness. I can see some softness on the last image, left corner, in the trees. Try to do the tests with your test charts again at f:8 and f:11

tukatu wrote:

Do you those building shots?

I've done 10mm and 22mm with F4.5 and F8.

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Marc de Vries Contributing Member • Posts: 856
Re: corner sharpness

None of these building shots is suitable to judge corner sharpness.

The reason for that is that the corner has no objects that are on the plane of focus. They are either further away from that plane or closer. So the unsharpness you see in the corners is caused by the shallow depth of field.

The first test shots you did were better.

You could compare your shots we the test chart shots here:

[url] http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=398&Camera=474&Sample=0&FLI=4&API=0&LensComp=0&CameraComp=0&SampleComp=0&FLIComp=0&APIComp=0[/url]

OP tukatu Junior Member • Posts: 27
Re: corner sharpness

thanks for the info regarding the corner sharpness.

What about the below test shot? using a 10-22MM shot at F11 22mm. you can see that right corner sharpness bad comparing to the 3 corner. possible lens issue?

Flapshots Regular Member • Posts: 213
Re: corner sharpness

Like we've mentioned before, you're not going to get top sharpness across the range.

Everything looks sharp in that last test and you have some softness in one corner.

Be happy and shoot!

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