Need a technical review

prairieboy · August 4, 2006

Hi all,

I am looking for some expert opinions as to what could be the problem here (lens? camera?). Canon has indicated they believe there is a fault with the L class lens and that it should be repaired.

Basically, every shot taken of flesh tones in the shade (not deep black shadows, just a normal "outdoors in the daytime" kind of shade) with this L class lens on a Canon 20d produces these results - low contrast, grainy, virtually no image detail.

If you look at the subjects t-shirt and face are you'll see they are in equal shade (the sun is high and to her right). if you were to zoom in (even to 50% or more) and look at the writing on her shirt - it is stellar how crisp the lens is. There seems to be no issue with light quality/quantity or with resolution in the shade. Now, move up to her face and have a look - it is grainy and missing anything that resembles detail - it is horrible.

Thoughts? Opinions as to root cause?

Here is a (corrected) link to the shot:
http://www.snapdrive.net/files/31029/Shots/IMG_3307.JPG

Here are the shot specs (taken using a Manfrotto monopod):
1/400 Sec, F/5.6, ISO - 100 ASA, Metering - Evaluative,
Exposure Compensation - 0, Flash - Off, White Balance - Daylight,
Color Space - sRGB, Parameters - none added, RAW

Thanks everyone!

Nikolai · August 4, 2006

Link does not work

prairieboy wrote:

Hi all,
Here is a link to the shot:
http://www.esnips.com/nsdoc/24f3a5e4-3455-4d74-abad-6754ad623ebb

I mean: it requires signup. Please provide a direct link or attach the image in question...

Thanks!

Bob Bell · August 4, 2006

I love Fxif for firefox

Camera Make: Canon
Camera Model: Canon EOS 20D
Image Date: 2006:07:29 17:03:25
Flash Used: No
Focal Length: 70.0mm
CCD Width: 14.43mm
Exposure Time: 0.0025 s (1/400)
Aperture: f/5.6
ISO equiv: 100
White Balance: Manual
Exposure: aperture priority (semi-auto)

Anyway, those are pretty tough lighting conditions. High contrast background. Their face is in shadow and there is a pretty wide dynamic range in that shot plus its not exposed for the face, looks like its exposed for the tshirt.

Have you taken side by side shots with other lenses?

L Class lens is funny. Just say the lens. What exactly did Canon say? I am curious what they recommend since focus seems fine.

I think your DoF is causing that but others might disagree. If you put center spot on her face and had AF kick in, it would be a very different shot I believe.

gluwater · August 4, 2006

I think you're asking a lot from a backlit shot like that.

prairieboy · August 4, 2006

Bob Bell wrote:

I love Fxif for firefox

Have you taken side by side shots with other lenses?

L Class lens is funny. Just say the lens. What exactly did Canon say? I am curious what they recommend since focus seems fine.

Yes, I can take a 17-55 (the new F/2.8, not the cheap plastic one) and using the same conditions I will not get results this poor. I can post 20 more shots - they all exhibit this effect but, only when using this lens, and, only (always) in skin tones.

Both Canon USA and Canon Canada did not indicate what they felt the problem was, only that they felt it was the lens needing service not the camera. I of course, would like to make sure.

Why would the shirt be so crisp (the writing on her t-shirt is 1/2" lettering) and the details be so poor on skin?

ziggy53 · August 4, 2006

prairieboy,

Some observations,

It would appear that you interpolated this to 3MPix. We need the full resolution original image to make an accurate assessment. Some interpolation methods can exagerate the problem.

The shot is rather "busy" with detail, except for the skin tones. JPG is designed to be rather compressive in smooth tonal areas. Since the skin regions are rather small, compared to the entire photograph, the skin shows the problem more.

Did you shoot this as a high compression JPG? If you did, and then you interpolated down to 3MPix and resaved as a JPG, you double compressed an already compromised image.

For difficult lighting, like this photo shows, shoot RAW, and only save as JPG for the last stage of processing as the delivery or presentation format.

To sum, this looks like JPG artifacting, exagerated and compounded by interpolation and JPG recompression.

I'm not sure how anyone would relate this to a lens problem?

Please shoot some more samples under similar circumstances, but use RAW and only save as the best quality (least compressed) 8MPix JPG, and let's see what your system is capable of.

Thanks,

ziggy53

prairieboy · August 4, 2006

ziggy53 wrote:

prairieboy,

It would appear that you interpolated this to 3MPix. ...

For difficult lighting, like this photo shows, shoot RAW, and only save as JPG for the last stage of processing as the delivery or presentation format.

To sum, this looks like JPG artifacting, exagerated and compounded by interpolation and JPG recompression.

ziggy53

Thanks for the reply:

This was shot as RAW not JPEG (please see initial post of this thread for shot specifics). I can place the CR2 image on the file hosting web site but that would force everyone to download it (I didn't want to be a pest!)

So it isn't JPEG interpolation since the "trouble" appears in the RAW image (using Canon's Digital Photo Pro vsn 2.1.1.4). I did a no frills added "save as" using D.P.P. to create the JPEG for the hosting site.

Does this help shape your thinking?

prairieboy...

ziggy53 · August 4, 2006

prairieboy wrote:

Thanks for the reply:

This was shot as RAW not JPEG (please see initial post of this thread for shot specifics). I can place the CR2 image on the file hosting web site but that would force everyone to download it (I didn't want to be a pest!)

So it isn't JPEG interpolation since the "trouble" appears in the RAW image (using Canon's Digital Photo Pro vsn 2.1.1.4). I did a no frills added "save as" using D.P.P. to create the JPEG for the hosting site.

Does this help shape your thinking?

prairieboy...

Thanks prairieboy, I see the "RAW" now. (

)

You have a legitimate problem, so don't worry about being a pest, you're not. You may not be alone in the problem, so it is worthwhile trying to resolve this.

I do see a kind of skin "mottling" which could be a compression algirithm issue, or it could be the way certain skin reacts to different light. My own skin, for instance, has a similar effect when UV gets mixed in.

I am surprised to see such sharpness on the left side of the image and then the glasses frames are so soft at the right. For 70mm at f5.6 I would have expected more DOF. Perhaps that is a centering problem internal to the lens?

Is it possible we are looking at two different problems?

ziggy53

prairieboy · August 5, 2006

ziggy53 wrote:

I am surprised to see such sharpness on the left side of the image and then the glasses frames are so soft at the right. For 70mm at f5.6 I would have expected more DOF. Perhaps that is a centering problem internal to the lens?

Is it possible we are looking at two different problems?

ziggy53

Perhaps there is more than one problem, I'm not sure. I was also surprised at the way sharpness trails off, but I was more surprised to notice it occurs mostly on skin tones - very strange.

As an FYI, I selected a single focus point for this shot - I chose between her ear and eye, just above and to the right of her ear so if anything, her face should have been bang on.

Here is another sample. The sun is high and just behind the subject.

http://www.snapdrive.net/files/31029/Shots/IMG_3242.JPG

The single focus point I selected is right on his nose. You can see that the vegetation all around him is in focus. Yet look at the very poor reproduction on his face. I doubt anyone would pay for that quality which means this lens won't earn it's keep.

Every shot I take using this lens, where the subject exists partially or completely in the shade, exhibits this very poor quality.

I'm perplexed...I have been shooting semi-professionally for just over 20 years but with a digital SLR for only 1.5 years. If I am doing something wrong I want to correct my bad behaviour, not send a lens away for nothing.

But my other lenses do not do this in these conditions.

Thoughts anyone?

Sot Specifics:
Aperture-Priority AE, 1/200, F/8.0, Center-Weighted Average Metering,
100 ASA, Lens@200.0 mm, RAW, Flash Off, White Balance - Daylight,
Parameters Settings - all at standard, Color Space - sRGB

pathfinder · August 5, 2006

In your second image, there is nothing really sharp in the image - the sharpest area is lower left on the vegetation which seems to be closer than the subjects face. Both of your shots are back lit, but my first concern is whether the focus is correct.

I think I would tape some newprint to a vertical wall, put the camera on a tripod, and shoot a few frames at various apertures with a cable release and mirror lock up, with the newsprint sunlit and then shaded . You might also see if AF gives the same focus setting as manual focus. Your second shot just does not look in focus anywhere. The first shot is in focus, but under exposed in the shaded areas due to the backlighting . Just my opinion.

If Canon says the lens needs repair, why do you doubt them??

prairieboy · August 5, 2006

pathfinder wrote:

I think I would tape some newprint to a vertical wall, put the camera on a tripod, and shoot a few frames at various apertures with a cable release and mirror lock up, with the newsprint sunlit and then shaded . You might also see if AF gives the same focus setting as manual focus.

If Canon says the lens needs repair, why do you doubt them??

Good suggestions for elimination - I will give that a try sometime today.

I'm not doubting something is wrong, in fact, I agree with Canon's position. I'm just looking to make sure the correct error is being addressed (between camera, lens, and, dare I say it, operator :photo )

Bodley · August 7, 2006

prairieboy wrote:

But my other lenses do not do this in these conditions.

Thoughts anyone?

Why not duplicate the shot with multiple lenses and compare apples to apples.

Set up the camera in MANUAL mode on a tripod. Position a somewhat backlit (patient) subject on a basically flat surface (flat from tripod to subject). Shoot the subject exposing for the scene and then for the subject at f5.6, f8, f16. Then repeat the process with a lens or 2 which has given you the results you wanted using the same manual in-camera settings. With varying focal lengths the tripod will need to be moved closer or further from the subject to maintain the same scene (hence the flat surface).

Then compare all the shots. If the camera in manual mode (same shutter, fstops, white balance combinations) and the scene remains the same then the main variable would be the lenses.

prairieboy wrote:

Sot Specifics:
Aperture-Priority AE, 1/200, F/8.0, Center-Weighted Average Metering,
100 ASA, Lens@200.0 mm, RAW, Flash Off, White Balance - Daylight,
Parameters Settings - all at standard, Color Space - sRGB

Seems to match sunny 16 but you may want to expose for your subject (shade) not the scene. This will blow some highlights but will improve your subject detail. Digital cameras can handle only so much range.

Blurmore · August 7, 2006

I'm just throwin my 2 cents, I'm no techie. I shot 2 weddings this weekend, and one setting was with subjects in heavy shade with a backlit highly reflective water scene as the background. White boats, windows, just the right sun angle to get hot reflections on water. I have noticed (after 2 years of shooting a 20D and 30D) that Canon metering is uber sensitive to overexposure, and evaluative ETTL is even worse. I was minus my second light because the chruch had a no lightstands no tripods policy, and I found myself in the described outdoor shade scene riding the FEC to +2 1/2 to +3 stops. It was not that the shots with neutral FEC were UNDER exposed TECHNICALLY there was some detail in the black suits, but the skin tones lacked the POP to give them life. I don't usually see this problem because the second light I use is non TTL and if the sunlit part meters at 1/250 @ f11 I put the light on blue and it blasts um, the on camera flash then operates more like fill. When ETTL gets a hold of the situation it neurotically tries to walk the line between blowing the highlights of a boat 100 yards distant blowing the bride's dress and giving some detail in the leg of the groom's suit pants. The result is in my opinion underexposure, because I could give a crap about the boat's highlights. Obviously this applies more to using P or AV than M, but the ETTL thing still effects flash exposure in M. In your shots i think I know what the camera was thinking...."Can't blow the leaf reflections" this throws the the skin into a 1 to 1 1/2 under exposure. To get decent detail and skin in this situation you would have to blow not just the leaf reflections but other parts of the backlit scene, and I do not believe this is unique to Canon or even to digital. 100-400 speed portra looks like this in backlight with no fill flash as well. So far as the age old problem of reception halls/mirrors/ETTL goes I have found the Average ETTL rather than evaluative is less sensetive to hot reflections, and under exposed subjects.
Once again these are only the observations of a run down wedding photographer recovering for 18 hours of weekend wedding coverage, not from an informed or technically knowledgeable person.

I just checked out the second one, and again it is HARSH backlight. The face in is shade, so this might also be suffering from the WB being derived from the scene which is in full sun. I still do not really understand how this could be the fault of the lens.

Need a technical review

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