Have I gotten a Lemon?

[ehwhatthe]

Hi fellow CS-ers

Need your expert advice on an issue i realized with my lens. I'm using a 24-70 paired with a 7D

The lens focusing is rather irregular and it gives soft images every once in a while.

Did a quick test.

Here are some examples (all shots on tripod with timer release and focusing point always on center) These are around 79% to 85% crops

1. F2.8 - 1st shot ISO100 70mm

2. F2.8 - 2nd shot ISO100 70mm

3. F4 ISO100 70mm

4. F5.6 ISO100 70mm

5. F8 ISO100 70mm

As you can see, the first F2.8 shot and the second F2.8 shot vary in sharpness significantly. The 2nd was shot only after all the shots from F2.8 - F8 were made. They're just put side by side for ease of comparison.

F4 and F5.6, the shot at F4 seemed sharper. Shouldn't the shot at F5.6 be sharper?

F8 seems fine.

It troubles me as the performance is not consistent and every 3-4 shots, i get 1 OOF

Is this normal ? Should i send it in for servicing/calibration?

Thanks guys appreciate it.

 

[catchlights]

you shot that with camera mounted on tripod?

 

[allenleonhart]

you shot that with camera mounted on tripod?

i think so... at least looking from the spots of white light, they all look like they at same place.

try changing the material? the reflective surface might be a reason why the lens isnt sharp. camera might be trying to choose between the words vs the reflection to focus

 

[jukebox19]

TS stated that he was using tripod and timer release

you shot that with camera mounted on tripod?

 

[Rashkae]

FYI, the Canon 24-70 is NOT known to be a sharp lens anyway. Lots of sample aberrations and decentering/focus issues. The Canon CSC is very busy with 24-70 lenses. Best to bring it to them and let them fix it.

 

[catchlights]

my bad,
if already taking the trouble to set up a tripod, that shouldn't be any trouble to download and print a lens focusing test chart.

 

[Turboredbean]

i think so... at least looking from the spots of white light, they all look like they at same place.

try changing the material? the reflective surface might be a reason why the lens isnt sharp. camera might be trying to choose between the words vs the reflection to focus

I agree on this one, try changing the material. Lets see if its the same...

 

[ehwhatthe]

Thanks for the input guys.

Below is what i've taken with a test chart. Wondering whether I did it correctly in the first place. Place my camera facing approximately 45 degrees, focusing on the middle black line.

Again, these are 75-85% crops of the original. Taken on tripod with timer release.

1. F2.8 ISO 100 70mm

2. F2.8 - 2nd shot ISO 100 70mm

3. F4 ISO 100 70mm

4. F5.6 ISO 100 70mm

5. F8 ISO 100 70mm

Shooting wide open, its not as sharp as I'd hope it'd be, or am i expecting too much?

Thanks again people!

 

[ehwhatthe]

one more.

6. F2.8 ISO 800 70mm

Does the iso performance seem a bit down?? i.e. too grainy for ISO800?

 

[shaoken]

Can the position of the item and the camera play a part too? Also, the focusing points?
I experienced this situation before so not sure does these affect the image?

 

[LFC25]

What's the subject distance? The DOF for f2.8 at 70mm is very narrow.

 

[allenleonhart]

to be honest, i think it is tolerable, after a little USM

even my camera+lens never gets me close to a perfect sharpness... there is a certain level of unsharpness i can tolerate, based on the viewing size i'm working with...

may i ask if this is auto or manual focus? if manual focus, the "maximum" sharpness at each aperture is liddat, i think can send to servicing.

if its AF, some possible factors

-lowlight
-material
-contrast area

etc etc. these are just my own personal experience when dealign with AF, and what seems to influence it. different people may have different observations

 

[tecnica]

seems like a severe case of back focusing.

 

[ehwhatthe]

What's the subject distance? The DOF for f2.8 at 70mm is very narrow.

The subject distance is slightly shorter then a meter.

Can the position of the item and the camera play a part too? Also, the focusing points?
I experienced this situation before so not sure does these affect the image?

That i'm not too sure. Just took a quick read through and found that i had to place the camera 45degrees to the paper.

to be honest, i think it is tolerable, after a little USM

even my camera+lens never gets me close to a perfect sharpness... there is a certain level of unsharpness i can tolerate, based on the viewing size i'm working with...

may i ask if this is auto or manual focus? if manual focus, the "maximum" sharpness at each aperture is liddat, i think can send to servicing.

if its AF, some possible factors

-lowlight
-material
-contrast area

etc etc. these are just my own personal experience when dealign with AF, and what seems to influence it. different people may have different observations

Its AutoFocused. I didn't use manual on this. Lighting wise, for this test i had turned on all the lights in my room. Not sure whether it helps.

seems like a severe case of back focusing.

..... i'll go google back focusing first haha =)

Edit: ok i get it now and yea i agree. Seems the back is always in focus compared to the point at which the AF point is pointed at.

 

[LFC25]

The subject distance is slightly shorter then a meter.

For f/2.8, the DOF is only 2cm for max 1m subject distance. Worse still if the distance is less than 1m.

Suggest you try back off to 2m for the f/2.8 setting.

 

[ovaltinemilo]

I believe there's af micro adjustment on 7D. you can try if it helps on front/back focus issue.

 

[ehwhatthe]

i actually read about it but still don't understand :/

 

[tecnica]

I believe there's af micro adjustment on 7D. you can try if it helps on front/back focus issue.

don't think the microadjustment can save such a massive BF issue.

even if it's possible, you will prolly waste a lot of shutter count in doing so.

not worth the effort, leave it to CSC to fix it.

 

[David Kwok]

Yeah, there seems to be an obvious back focus. If still in warranty, bring down to the service centre for a check.

 

[ZerocoolAstra]

Thanks for the input guys.

Below is what i've taken with a test chart. Wondering whether I did it correctly in the first place. Place my camera facing approximately 45 degrees, focusing on the middle black line.

Again, these are 75-85% crops of the original. Taken on tripod with timer release.

1. F2.8 ISO 100 70mm

Shooting wide open, its not as sharp as I'd hope it'd be, or am i expecting too much?

Thanks again people!

'10mm' and '14mm' texts look quite sharp. My guess is that your lens is back-focusing.
If under warranty, bring to CSC for a check-up.
If not, then see if your AF micro-adjustment can overcome this problem.

Last check: You didn't select the AF point that is above the center spot, did you?