[photodan]

Share with my bad experience in a local water goods store for my 70-200L f4 lens.

I discovered the problem that it's sharpness is not excellment from about 100 photos on the first day. I then tested out in my home with a very simple method. I took a photo with auto-focus and then followed by another one at the same point but turning the manual focus ring for 1-2cm after the AF confirmation light is on. I repeated the test for around ten times. I got the second image sharper in all the cases. It's not easy to see on the 1.8LCD but definitely distinguishable on 100% crop on my 15' PC LCD. I would suggest is the problem of back focus.

The sales person in the store take another test with the lens box on an inclined angle in the shop and refused the return because of the followings:

The first shot of the test shown something behind the focus point but he believe it's may caused by his handshake. The setting of the photo is 70mm 1/500s 2 meters away. Does anyone suggest his comment is making sense?

The second shot having two printed zeros and a cross line, one zero was located 2 cm away from the other, focus point on the closest cross line. The behind one show sharper than the first one. He claimed the DOF is across the whole testing point but DOF means gradient that it's normal to have two zero even with the DOF with different sharpness. It's out of my believe that DOF means all length covering the depth is sharp. How would you comment this?

Besides, he also claimed the below and sent me out of the shop then...

1. AF is only possibility and that's no way you can confirm the exact point. It even not possible to definitely focus on one's eye. (Learnt so much about protrait photography to focus on the eye of the target!)

2. 300D and 20D sensor size is large. The target of the above test case may already over the single sensor of the two DSLR. (70mm 2 meters away on a target of 3 cm.)

3. There no way to callibrate a lens. When callibrating the 70mm side, the 200mm suffer. (But Canon services center have the callibration service and it cost $600)

4. Canon quality control is quite loose. He claimed 7% AF accuracy out of factory is acceptable. (For my 'L' grade lens? Anyone here would buy for the cost?)

I took my lens to local Canon services center to be the judge. And result will be clear after a week. Any comment on my thoughts is welcome.

I would say the shop is the worst in HK for my couple of lens. It's located in Tung Ying Building with a orange logo. The sales person is Mr. So.

Unhappy Dan.

Canon 50mm f1.8 II
Tamron 28-75 f2.8 SP XR DI
Canon 75-300 f4-5.6 III
Canon 18-55s kit lens

[photodan]

Just received the call from Canon services center that the lens did show back focus problem and it cost me 400 for the callibration.

Nice to confirm my through on the problem. Angry with the sales person Mr. So just to persuate the customer that the AF of the lens is not reliable and is normal.

I suggest who get this lens to do a simple test before shooting important event.

Don't buy anything from the UR***** in TungYing Buildings except you think you're lucky enough.