Focus issues: 400D or my kit lens?

[2069]

Today, i shot this poster for some office work. I was shocked to see that the

focus was off in the corners. I noticed this when i compared the same image shot

by a typical sony digicam. I was astonished to see that sony digicam image

appeared to have better focus, and therefore sharpeness.

 

This was despite:

FAST Shutter speeds 1/125 to 1/1000.

CLOSED DOWN Aperture, 7.1 to 11.

 

Here are the crops, shot as JPEGs and resized in ps.

 

 

 

Can someone tell me what's going on? If this is what i should expect from a SLR

then its quite demoralising....

 

regards,

anurag<div></div>

[2069]

Center and corner crops:<div></div>

[2069]

left upper corner<div></div>

[2069]

Lower right corner<div></div>

[2069]

Let me add, that this is one of the better examples. Here the focal length is 18mm.

Same shot taken at 55mm is very bad. Please remember that the shutter speed was optimum.

Is it the cameras' fault or the lens's fault?

Unable to understand what's going on...:)

[JosvanEekelen]

Perhaps your expectations are too high. At a focal length of 18 mm you must have been quite close to the poster. You can't expect a perfectly flat field of focus for this lens. To achieve that you'd need to use a macro lens. And the kit lens is probably not overly sharp in the corners. You can't compare this picture to that of a digicam since that has a smaller sensor and thus a greater depth of field at the same angle of view.

[2069]

Jos van Eekelem,

 

Your comment suggests that this is normal result from a kit lens. Is it? I have seen many pictures from the kit lens that are sharp and well-focussed.

 

I shot these at 50mm also...that's much worse...the field of focus is flat there, still you have soft corners...also, when comparing with a digicam, i am not bothered about the hazy/soft/not-sharp look of the pictures, which can be corrected perhaps in photoshop. My discomfort was about "focus".

regards,

[2069]

Also...my submission is that at such high shutter speeds and F11, shouldn't an (almost) flat subject come out completely in focus?

regards,

[sam_thompson2]

It's mostly the lenses fault. Kit lenses have lower corner performance.

 

You see many pictures from kit lenses but alot of them take advantage of the soft focus so while the center is sharp your corners are not so sharp but you don't notice it.

 

Focusing only happens on one spot in a picture. You can't have total focus at the entire range unless the subject is completely flat. In this case it looks like you are shooting this at an angle. A point and shoot with its great depth of field will look sharper than the DSLR. This is probably why you are getting worse results at a longer focal length.

 

That is the gift and the curse of the DSLR you can use focus blur to get rid of distracting elements and at the same time not as forgiving when shooting things close up.

[athinkle]

I agree that it's most likely the lens's fault due to the overall corner performance of the optic. However, I doubt the problem has anything to do with depth of field. Granted, it looks like you were at a very slight angle when you shot this. However, at 18mm and f11 the depth of field should be more than sufficient to make up for the small difference in flatness caused by the camera position. Long story short: If you're doing this on a regular basis consider a macro prime lens like the 50mm f2.5. Lenses like that are sharper from corner to corner. Also, Use a tripod with a bubble level on it to help with postioning. Finally, I think you might be being too critical. I'm sure that for whatever purposes you're using this image the small difference in corner sharpness won't be noticed.

[charles_stobbs3]

Many lenses are made to be curved field, not flat field.

[wandern]

<i>"If this is what i should expect from a SLR then its quite demoralising...."</i>

 

<p>

It has nothing to do with your camera; it's merely that the $50 lens you have has (unsurprisingly) poor quality. A P&S lens is only a few mm across, and can potentially still be reasonable quality even within severe cost constraints. I've tried several kit lenses (18-55mm f/3.5-f/5.6), and I've found that the rabid fans of the lens notwithstanding, it's horrible optically, regardless of the aperture or focal length you're using. The colors are poor, the sharpness is poor, the edge performance is miserable, it suffers from chromatic aberration, and the focus plane exhibits significant field curvature.

 

<p>

At f/9, you're certainly compensating for the field curvature (focus) issue, but everything else still applies. Here's a random sign with a corner crop from a Tamron 17-50mm f/2.8 lens.<div></div>

[wandern]

Corner crop<div></div>

[JosvanEekelen]

I meant to say that depending on the actual circumstances there may (or may not) be a significant difference in subject distance between the camera/sensor and the centre respectively the corners of the poster. I assume you can still measure or guess the actual distances. Use a DOF calculator to see whether that can be of influence. Other than that the kit lens is not stellar. Keep in mind that most tests with this lens are done with a certain object distance that is probably larger than in your case.

[jcuknz]

Obviously it is the ket lens which is pushing things to get the 18mm focal length so to get the shot I suggest using mid or long end of the zoom and eventually get a better lens ... else stick with the digicam like I do ... at least pro-sumers anyway :-)

 

Using a longer focal length should help you to get square on to the poster which you are not in the first shot. If the softness is the small print in the LRC then probably you are expecting too much resolving power from the sensor.

[wandern]

It's _not_ sensor resolving power. This is why one hears, over and over, that with the quality of modern DSLRs, it's the lens that counts, not the camera.<div></div>

[wandern]

100% unsharpened crop from middle of image.<div></div>

[wandern]

100% unsharpened crop from extreme lower left of image.<div></div>

[JDMvW]

It looks like the lens and perhaps somewhat grand expectations for a decent, but not incredible $100 lens . See http://www.photo.net/equipment/canon/efs18-55/ to get a better idea of what to expect and how to work around it (stop down more, use tripod, etc.)

[2069]

Brian Pape

 

At f/9, you're certainly compensating for the field curvature (focus) issue...

 

PRECISELY. IN WHICH CASE THE SOFT CORNER FOCUS SHOULDN'T BE THERE, ISN'T IT? ALSO, DOF AT 18mm SHOULD BE LARGE FOR SUCH A FLAT SUBJECT.

DOES THAT MEAN, IS THERE A FOCUS PROBLEM WITH THE LENS?

 

JC uknz

 

I suggest using mid or long end of the zoom and eventually get a better lens ...

 

I DID, AND THE RESULTS WERE MUCH WORSE THAN THIS, EVEN AT 1/1000

 

Andrew Hinkle

 

Finally, I think you might be being too critical.

 

TOO CRITICAL?

 

I had gone to shoot this poster with a friend (an art director) who also shot it with his Sony digicam. After we saw the results, he said let me check out what i have. And the digicam image was what he used eventually for a small magazine artwork that we're doing. Obviously i felt very bad.

 

I HAD A G2 (F2-F2.5) AND I SHOULD EXPECT BETTER THAN THAT FROM MORE $$$$ I SPENT.

 

regards,

[2069]

Hi, just a small thing...

 

Do you think that the poster is in focus?

 

regards,

[sam_thompson2]

"DOES THAT MEAN, IS THERE A FOCUS PROBLEM WITH THE LENS?"

 

No focus is always at a particular point. If there is a focus problem then your focus will be at all different point or your poster would not be in focus at all. Only way to figure it out would be to use a tell whether or not it is a camera problem or a lens problem different camera with similar lens and do the same tests so you can see what kind of problem you have.

 

If there is a problem it might that the lens is not stopping down all the way to f/9.

 

Yeah you are too critical. You are missing that the guy is an art director and he probably has more skills. Aside from the focus problem which won't be noticeable in print your poster is shot at an angle and is little bit crooked and has some distortion.

 

Image quality isn't the reason why people get DSLRs. Any camera can take similar pictures in a bright environment and in some cases compact digicams are better. People get DSLRs because of the short shutter/focus lag, interchangeable lenses, higher ISO performance.

[2069]

Hi all,

 

yesterday, i got this new lens.

i hadn't gone to buy it, but i asked for it and it was there.

i was completely surprised when i saw this lens cause' i was expecting it to be the same crappy kit lens plus IS. But it seems much better than that. To sum it up:

 

1

Nice broad rubber zoom grip with vertical lines.

Min focussing dist 0.25 (it was 0.28 with kit lens)

Front element proudly announces "made in japan" vis a vis sheepish "made in china" hidden on the rear of earlier kit lens.

focus ring slightly broader.

zoom ring is smooth, and overall the lens gives cues of better quality than the decidedly cheap looking kit lens.

 

2

but the best part is this: i shot few pics while coming back home. i could handhold at 0.6 seconds from a moving taxi. The shot was tack sharp.

 

Overall image quality seems to be positively improved. May be its just IS thats making me feel like this. But i am very happy that the shots are much much better.

 

3

I had gone to exchange my 400D for a new one because i was getting soft pictures plus very dark shots. I posted to this effect few days back.

 

Guess what. All these problems are gone. I believe that all my problems were actually the kit lens problems.

 

My camera is not giving dark pictures now (based on yesterday and today morning shooting).

 

Shots are not soft. They are crisp with focus bang on.

 

Will post few pics later.

 

Thanks a lot.

 

regards,

--

anurag

[2069]

Here is an image taken at night, from a cab, at 0.6 seconds:<div></div>

[2069]

This is a 100 percent portion of the same image:<div></div>