Very soft image - Canon 50mm, 1.4, USM

[qqqavi]

Hi everyone, 

I own a Canon 50mm 1.4, USM lens and even though I already knew the image was a little bit soft at aperture like 1.4, 1.8 , in a recent test the image actually look terrible. I don't know if this is normal or it is because the lens is damaged.

I attached you an example at f1.8.

At f2.5 looks a little better, still with a lot of fringe on edges. 

Thank you. 

[kvbarkley]

Assuming that this is a crop frame camera, and that the subject is .3 M away from the camera, A DOF calculator shows that the acceptable depth of field ranges from .299 to .301 m, so very little of the subject will be sharp even under ideal conditions.

Questions:

What were you focusing on?

Is this on a tripod?

If you were handholding, did you keep the camera from shifting back and forth less than 2mm? I doubt it. I would guess that you were handholding and the camera shifted slightly back so that none of the subject is in focus.

[qqqavi]

1. If you look closely at the first image you'll notice that that look like an optical issue (looks like smearing) not shallow depth of field, nor motion blur.

2. I was focusing on the center of the ball and I was 1 m away.

3. if again look closely at the first image, you'll notice that it doesn't really matter what area I was focusing on since the entire image is smeared (not out of focus), more noticeable at the edges. 

4. At f1.8, f2.0, f2.5 I've never achieved a sharp image. I have also tested it by using the lens set to manual focus in video mode. Trust me, it's impossible to get the ball in focus at 1 or 2m away. 

5. I can get an acceptable sharp image at f4

Thank you. 

[kvbarkley]

What camera?

Are you handheld?

If you can't focus with a tripod and liveview there is something wrong with the lens.

[qqqavi]

Tripod, liveview, canon 7d

[diverhank]

There are two things I'd try before declaring there's something wrong with the lens, if I were you.  I'd use a tripod for all tests to eliminate user's error.

1. Manual focus, using live view @ 10X magnification.  I find that in low light the Auto-focus is lacking and that may not be the lens fault.

2. Try it outdoors where the light is good, with AF and MF.

[qqqavi]

The camera was mounted on a tripod, shutter 1/200 in daylight conditions. I tried both manual and automatic focus in liveview at 10x. The more I look at the pictures the more I believe that is an optical issue since there was no motion blur and that look like smearing, not out of focus.

[diverhank]

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@qqqavi wrote:
The camera was mounted on a tripod, shutter 1/200 in daylight conditions. I tried both manual and automatic focus in liveview at 10x. The more I look at the pictures the more I believe that is an optical issue since there was no motion blur and that look like smearing, not out of focus.

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In that case, there is indeed something wrong with this.  Mine doesn't do this, even at f/1.4.

[ebiggs1]

Let me ask two more questions.

First are you perpendicular to the ball?  If you are at an angle the DOF can be worse.

Second how big of a crop is the example?