Focus Test Chart with Canon 70-200mm f/4 L USM (no IS) problem?

Ciphershot · Mar 11, 2011

Hi everybody,

First post ! ;-)

I just bought the Canon 70-200mm f/4 L USM (no IS) from Amazon to use on my 50D after reading so many positive reviews of this L lens.
The last few days I tested the lens, but I was not really happy with the results. According to most reviews on the net, this lens is supposed to be very sharp, which however I could not confirm on my pictures.

So I searched the net and found this focus test chart. I set everything up and tested the lens. You can see the results on my photostream.
Here is the picture taken at f4.0 from a distance of 1.2m.

If it doesn't show, you can see it here on Flickr : Focus Test Chart with Canon EF 4L 70-200mm USM on Canon 50D @ f4.0 | Flickr - Photo Sharing!

While the the center point where the focus lies is mostly sharp, the front (left side) is way more blurred than the back (right side).

Is it normal to get such a difference in DOF? Or did I get a bad lens?

I will probably send the lens back in a few days, but I wanted to hear some opinions before ordering another one...

Thank you !

Robin Usagani · Mar 11, 2011

???

You shot it from really close with F/4.. yes your DOF will be shallow. That is what you want. Make your aperture f/8 or f/11 i bet everything will more in focus.

The fuzzines of something that is closer to you will be different than something that is farther from you. For example a line that is farther should be thinner, line that is closer should be thicker.

Drake · Mar 11, 2011

I don't have the lens and I am no expert in optics, but I think the left-right side difference might be a result of the lens not being at 45 degrees from the test chart. It's also not lined up perfectly so the top and bottom is also blurred a bit differently.

Ciphershot · Mar 11, 2011

The rest of the pictures can also be seen on Flickr : Focus Test Chart - a set on Flickr

The chart was positionned at 45°.
Even at f/16, the front 3 doesn't seem sharp to me... :-S

Robin Usagani · Mar 11, 2011

If you are shooting that close, its hard to get more depth of field. You have to be farther.

Ciphershot · Mar 11, 2011

Well actually I'm not looking for more DOF in this case... But shouldn't the focus scale be sharp throughout, front and back, at f/16? I still see a blurry 3 in front at f/16... That is why I'm doubting the quality of this lens...

Robin Usagani · Mar 11, 2011

Depth of field relates to focus. Whatever within the depth of field should be in focus. On your sample the 3 is not in the depth of field. The moral of the story is, there is probably nothing wrong with your lens.

rehab · Mar 11, 2011

Dont forget you DOF wont be exact both in front and behind your focal point.

Thats why the left side has more blur than the right.

gsgary · Mar 11, 2011

Just go out and take photos instead of wasting your time with those silly focus charts the 70-200 is a great lens

Ciphershot · Mar 11, 2011

That was my plan for tomorrow... ;-)

Btw, do you use a UV-Filter on this lens ?

gsgary · Mar 11, 2011

I have one on only because it get abuse when shooting events and sport

Here's a few taken with it

Derrel · Mar 11, 2011

Drake said:
I don't have the lens and I am no expert in optics, but I think the left-right side difference might be a result of the lens not being at 45 degrees from the test chart. It's also not lined up perfectly so the top and bottom is also blurred a bit differently.

Diz-actly! You do not have the chart lined up properly to test side-to-side sharpness. What you are seeing is normal depth of field. The lens is fine. It is the testing procedure that is wonky.

mikehaugen · Mar 11, 2011

^ Wonky?

Derrel · Mar 11, 2011

mikehaugen said:
^ Wonky?

wonky adj. Chiefly British , -kier , -kiest . Shaky; feeble. Wrong; awry

Overread · Mar 11, 2011

Actually the test looks pretty well done setup wise - the only problem is that the OP has slightly miss interpreted the results and the specific effect that the test is trying to achive. In this focus test the idea is that the auto focus (middle point) is used to focus the shot and the you take the photo - the idea being to ensure that the point you set the AF to focus upon is in focus and that the point of focus isn't infront of or behind the point you've focused upon. This then ensures that lens and camera are focusing correctly (and provided AF was used this looks to be the cast with this lens).

The depth if field of the shot is (in this case) neither here nor there (as has been said). Far as I can tell then from this test is that (like the others) I can't see anything wrong with this lens at all - now go forth and shoot!