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Rebel XTi: Why are my pictures so blurry?

Responses


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Sarah Fox , Mar 25, 2009; 01:36 p.m.

It's a bit hard to tell much from the photo posted, as it's small. A 100% crop would help.

I assume you 18-55 is the non-IS version. That's one of Canon's least sharp lenses. (The IS version is actually quite good, BTW.)

With all due respect to Dan, who knows a whole lot more about lenses than I do, diffraction limits are a relative thing. For your particular lens, which is somewhat soft, diffraction doesn't "worsen" the optical quality of the lens until maybe f/16. You'll probably get your best sharpness at f/8 and f/11. If you had the IS version, you'd start noticing the degrading effects of diffraction starting at f/11 or so, with f/5.6 and f/8 being your best apertures (in general). The same is true with your 60/2.8, which is a pretty sharp lens.

It's hard to debug your problem with the info given. You're going to need to do some well-controlled testing. Try this: Disable in-camera sharpening. Mount up your 60/2.8, with no filters on it. Put the camera on a good tripod. Enable the mirror lockup, and set the camera to the self timer mode. Set aperture to f/8 and exposure mode to Av. Put a ball or other object in your back yard, perhaps 20 ft from the camera, and focus on it. Take a test shot, and post a 100% crop here. This test will rule out camera shake and filters and will test focus accuracy. Also a 100% crop will allow people here to see if the sharpness is all that it can be. That's a start.

Josh A , Mar 25, 2009; 02:11 p.m.

Wow. Thanks for the great responses, all around.

Here is the actual RAW file:
http://tinyurl.com/cxlqgb


@ G Dan Mitchell:
Yes, I am shooting in RAW. I did not know that post-process sharpening was so important to be labelled as a 'must'. Why is that? Shouldn't it be naturally capable of sharp images? Post-process sharpning adds a bit of noise and messes with various characteristics of the photograph such as contrast, no?

I am using Apple Aperture as the RAW processor. The images in the original post were exported as PNGs from Aperture.

@Rob Bernhard:
I haven't changed any in-camera sharpening settings from the factory default but I'll look into those. Thanks.

@Michael Lawson:
My camera bag stocks the following lenses:
EF-S18-55mm f/3.5-5.6
EF-S60mm f/2.8 Macro USM
EF28-90mm f/4-5.6
EF75-300mm f/4-5.6

Yes, this happens to me on my 75-300mm, too. I assume you notice the same on yours, then?

I usually always hand hold unless shooting below 1/30ish or so.

@Dan Ferrel:
Just a UV filter. My 60mm macro doesn't have anything on it and I still notice the blur.

G Dan Mitchell , Mar 25, 2009; 02:30 p.m.

Regarding diffraction, I'm not necessarily saying that the primary "issue" that the OP sees in these photographs is due to diffraction blur. As I wrote, I did not have all of the information about the images (including access to a 100% magnification crop that would be a bit more definitive) - and that is why I provided a list of potential issues that might be related to the question.

Regarding diffraction blur and 1.6x cropped sensor cameras, there is no question that image sharpness decreases due to diffraction blur at apertures such as f/11 or f/16 on these cameras. It doesn't matter what lens you use - the most expensive L prime or the kit lens - whatever the resolution qualities of the lens for other reasons, diffraction blur has a negative effect on resolution at these apertures on cropped sensor cameras.

It is reasonable to ask "how much of an effect" and "is the negative effect balanced by other positive effects of the small aperture" when it comes to a specific photograph. For example if you are shooting a subject with the intention of creating a soft image and you need a longer exposure or larger depth of field, giving up some sharpness to get those things is a reasonable choice. I've made this choice when shooting, for example, long exposures of seascapes in which I wanted a diffuse effect from motion blur by means of a long exposure... and where maximum resolution wasn't important.

However, in this case, we have a shot of a flat subject that is more or less parallel to the sensor, made at f/11 and ISO 400 and 1/200 second. In just about every way it would make a ton more sense to shoot this at, for example, ISO 200, 1/100 second, and f/5.6. 1/100 should be enough to control camera motion blur with good technique, ISO 200 would provide better noise performance on this camera, and f/5.6 would give sufficient depth of field for the subject and would not negatively affect sharpness through diffraction blur.

I won't argue with the idea that many people might not notice the difference in a 4 x 6 inch print or in a web image. (I thought this one looked fine on the screen.) But the OP asked specifically about sharpness, and in that light recommending a larger aperture than f/11 on crop is a good recommendation, especially in light of the details of the specific photograph and how it was made.

Dan

BTW, if the OP is using the non-IS version of the 18-55 kit lens, it will be limited as to sharpness. IQ is only "OK" with that lens. If the OP is using the newer IS version of the kit lens, it can produce quite decent results if everything is done correctly.

Michael Lawson , Mar 25, 2009; 02:46 p.m.

Josh, I do notice it on both the kit lenses (18-55mm and the 75-300 both non-IS), but it can be controlled with good technique and a good post processing work flow. I used to shoot mostly hand held, but purchased a monopod last year and it has made a noticeable difference in the quality of my shots and the number of keepers I get. I would certainly consider getting a nice monopod to use for walk around shooting when possible, and a tripod for the macro lens. Here is an article about the sharpening work flow you should consider reading: http://www.pixelgenius.com/tips/schewe-sharpening.pdf . It will explain better than I can why sharpening is a must.

Michael Lawson , Mar 25, 2009; 02:54 p.m.

G Dan Mitchell , Mar 25, 2009; 03:34 p.m.

Yes, if you are shooting RAW you MUST sharpen your images in post. If you do not do this, they will always look blurry and will never be as sharp as in-camera jpgs - which ARE sharpened in-camera.

If you are using Photoshop, try the following as a starting point: Without sharpening in ACR (Adobe Camera RAW) during conversion, apply one layer of smart sharpening and one USM (unsharp mask), best as smart layers.

Smart Sharpen at 150, 1.0 (but think about lowering the second number to taste)
USM at 12, 50, 1

Dan

Rob Bernhard , Mar 25, 2009; 03:38 p.m.

[[Regarding diffraction blur and 1.6x cropped sensor cameras, there is no question that image sharpness decreases due to diffraction blur at apertures such as f/11 or f/16 on these cameras]]

[[and that is why I provided a list of potential issues that]]

You stated, immediately, that you "would avoid apertures smaller than f/8 on a cropped sensor camera as a general rule." This is a strong statement and one that does many new photographers an extreme disservice, IMHO.

Discussion of diffraction issues in this context are about as useful as talking about adding the right amount of air to the tires of a car that is missing its engine. Great information, but not helpful in actually getting the car up and running. In fact, I'd go so far as to say it is distracting to the point of being a disservice.

G Dan Mitchell , Mar 25, 2009; 03:58 p.m.

Rob, you are welcome to your opinion, but I disagree that pointing out that diffraction blur at small apertures is be among a set of issues that could affect sharpness is "an extreme disservice" to new photographers. I did not suggest that it is the only issue, and I went on to discuss several others that could also be important.
In the context of the OP's broad question and in the context of my overall response, I think my reply was appropriate and relevant.

Ross Murphy , Mar 25, 2009; 04:21 p.m.

"I would avoid apertures smaller than f/8 on a cropped sensor camera as a general rule - though there could be exceptions in unusual situations. The issue is diffraction blur that sets in as you stop down - and it sets in about two stops sooner on a cropped sensor camera than on a full frame camera."

this is misleading at the very least, when I shot a 40D I never had problems with diffraction at f11.

Ross

G Dan Mitchell , Mar 25, 2009; 04:42 p.m.

Folks, please do a bit more reading about diffraction blur before you dismiss what I write out of hand - and not just one post that agrees with your current notion.

I'll leave it at that.

Dan


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