Dirty lens?

[missc]

<p>Hello everyone,<br>

While looking over some pictures I recently took of my daughter on a snowy day, I was surprised to see a great deal of "vignetting" going on in my images. I will hereby be including an example photo as it came out of the camera (no post).<br>

I am using a fairly good quality lens (Canon EFS-17-55mm f/2.8 IS USM) mounted on a 7D. Is this normal? Does this mean my lens should be cleaned?<br>

Thanks in advance for your input!<br>

Miss C.</p><div></div>

[esfishdoc]

<p>I think you would have to dunk your lens in chocolate pudding or mud to get enough dirt to cause vingetting. The average dirt and dust on a lens never interferes with an image. The picture you are going to post might help.<br>

Richard</p>

 

[William Kahn]

<p>Were you using a lens hood?</p>

[greg_moss4]

<p>A dirty lens shouldn't cause that. Looks more like an improper hood or sunshade (Maybe it got twisted?) OR a filter that's too deep.</p>

[missc]

<p>No hood. No filter.<br>

Oh! But now that I think of it, since it was snowing I had a special plastic cover on the camera with a drawstring for tightening around the lens. That must have created the hoodlike shadowing / vignetting? I think my mystery is solved!</p>

[Marcus Ian]

<p>Since the vignetting is only noticeably strong on 2 of the four corners, I'd consider that a mismounted lens hood is a strong possibility, as (as Richard pointed out) for vignetting to occur as a result of dirt, it would literally have to be caking the corners - that would be a first...</p>

<p>Still, vignetting is one of the weak points of this particular lens, @ 17mm and WO (f2.8) it's at it's worst. Based on the image (which says it was shot at f2.8) I think it's a strong possibility that this is 'normal' for this particular lens (as there is often some unit variation from lens to lens), but that you've only noticed it here because of the white on white background. To test this out, I'd shoot a bit against a white wall or similar to evaluate the vignetting impact at some different focal lengths and f stops.</p>

 

[JosvanEekelen]

<p>Not abnormal, 24-105L does that too on full frame. It can be corrected easily in Lightroom, Photoshop or other software.</p>

[missc]

<p>I will do that testing Marcus. Thanks for the tip.<br>

Yes, I know how to correct in post, I was simply wondering why the vignetting was happening in the first place.<br>

Thank you all for taking the time to respond. You're such lovely bunch of people! Have a great day.</p>

[g dan mitchell]

<p>Vignetting is not caused by a dirty lens. It can be caused by:</p>

<ul>

<li>Normal light fall off in the corners at larger apertures. Some lenses are more susceptible than others, but all lenses will exhibit this effect to some degree.</li>

<li>Adding one or more filters or adding a screw-on hood to a filter, resulting in the filter/cap slightly extending into the corner of the frame at wide angles. (You can test for this as a possible though unlikely cause by shooting without the filter/hood.)</li>

<li>Not fully attaching the hood, either leaving it rotated slightly or else not aligned parallel to the front of the lens. This is unlikely in this case since the vignetting seems symmetrical.</li>

</ul>

<p>I suspect that you are simply seeing the normal vignetting with whatever lens this is, and that it is more visible than usual because light areas with smooth gradients are in the corners of the shot.</p>

<p>Dan</p>

[Michael R Freeman]

<p>I would agree with G Dan Mitchell. I think what you are seeing is normal optical vignetting (light falloff) in the corners as opposed to mechanical vignetting, which would be more evident at smaller apertures. Your sample photo was shot wide open (f/2.8) near the widest end (20mm) of your 17~55/2.8. That is exactly where I would expect to see light falloff on a fast zoom ... widest focal length and wide open. I can see falloff in all four corners, although it is a bit more obvious at the top corners due to the difference in brightness.</p>

<p>It's easy enough to verify. Shoot some test photos at f/2.8 at various focal lengths of an <strong>evenly</strong> lit blank wall with no filters, and no hood. I'll bet you will see even corner falloff near the wide end of the zoom range. Then shoot some test photos of the same blank wall at 20mm and various apertures. You should see the falloff retreat and then disappear all together as you stop down the lens aperture.</p>

<p>If you don't have a blank wall handy, clear blue north sky also works nicely. Basically you want an evenly lit monotone canvas to shoot.</p>

[mark_pierlot]

<p>By the way, the vignetting doesn't detract from this image in the least.</p>

<p>My interest in the photo is created by the "contrast" between the colourful, well-defined subject and the hazy monochrome background. It's nicely composed, too.</p>

[missc]

<p>Thank you for those additional comments guys. Bottom line : I will test for peace of mind but this effect is probably normal with this lens, aperture, conditions... So that's good news for me as I won't need to pay to get my lens cleaned! :)</p>

[ljwest]

<p>I have the same setup, and have experienced this also. I think it is fairly normal for this lens. It can be corrected for in the 7D (and other Canons) with<strong> Lens Peripheral Illumination Correction </strong>(page 76 in the manual). This is data that is stored in the image file about how <em>Canon</em> lenses perform at the corners regarding light falloff. The camera comes with some 25 EF and EF-S lenses already programmed into the body, but I'm pretty sure the 17-55 is NOT one of those. For JPEGs, the correction is applied in camera, for RAW files, DPP will make the correction.</p>

<p>You enable this feature in the first Red menu, bottom item "Peripheral Illum. Correct.". You can also see here if data for the mounted lens is available, as this screen will say "Correction Data Available" if the lens is attached, and the data is stored in the body. If not, you will need to use EOS Utility to connect the camera to your PC to load the data for the 17-55 lens. You can only see all the lenses that your body is programmed with from EOS Utility, not on the camera. You can add lenses, or delete lenses you never expect to buy or rent or borrow. I think the body can hold info for about 40 lenses or so.</p>

<p>As an aside, you may be interested to know that the APS-C sensor is not mounted with the same center point as the full-frame sensor would be! I'll try to post a picture tomorrow (I won't be home until late tonight...), but here's how I found that out, and others can try it too:</p>

<p>I have the EF-S 17-55 f/2.8 and I also have the EF 100-400 f/4.5-5.6L They both use different lens hoods, but are from the same series, the EW-83J for the 17-55, and the ET-83C for the 100-400, so they mount up the same. Just for the heck of it, and to see if there were any creative possibilities, I put the 100-400 hood (basically a 3-4" long tube with a slight taper) on the 17-55. I knew I would get significant vignetting, but I fully expected it to be even at all corners. Not even close. As I recall, the lower edge of the frame was still sharp all the way across, but I now had an 'arch' occupying much of the frame, a lot like looking out of a tunnel!</p>

<p>Here I am thinking that an APS-C camera is getting illuminated by the center "sweet spot" of my EF lenses, when it isn't! My 7D still takes great photos, so I'm not really worried about it. But I was quite surprised!</p>

<p> </p>