Serene Life

by garik

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Recently, I've been doing a lot more photography, particularly with my 100-400mm telephoto and 16-35mm wide. I am skilled enough that I can capture the shot mostly as I want with just the camera gear, requiring minimal post processing. I'm a huge fan of ETTR now, so most of my shots are overexposed to support more shadow DR and improve the noise performance of my el-chepo 450D body.

I've noticed quite a bit lately during post processing in lightroom that my sky's or any other lighter areas of my shots tend have spots on them. They are soft and dull to one degree or another (seems to depend on the zoom factor), so probably something either on the sensor or the lens. I'm having a hard time figuring out exactly what they are, as I try to use my lens pen brush before any shoot, yet I still have them. I am having to make quite a few healing corrections post-process to get rid of them.

Is there an easy way to identify where the spots are on my lenses? Once identified, if a quick brush of the outer lens element with a lens pen (or soft camel hair brush) doesn't do the trick, does that mean the spots are on my sensor? Is it possible there is particulate inside the lens body (all of my gear is less than a year old outside of my 450D body, and its all Canon L-Series gear, so I would home that I don't already have detrimental particulates floating around inside my lenses messing up my shots. :|)

Here are a couple examples. The spots are harder to see on screen, and I first noticed them when I printed a few of my more recent shots. There are quite a few, and the shot the examples below were taken from, where the sky took up about 30% of the top edge of the photo, there were probably 10-12 different spots, some of them darker, many of them lighter. The darker ones are the ones that are very visible in prints, where as the softer ones are not as visible, but still apparent enough to ruin an expensive print.

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I keep having the same problem: yankeepotroast.org/image/spritespot.jpg whoaaaa... I'm sorry. –  BBischof Sep 24 '10 at 18:58
    
@BBischof: HA! Funny. :P –  jrista Oct 26 '10 at 19:05
    
since you didnt respond for a while, I was worried that you were angry with me for making this joke. :P –  BBischof Oct 26 '10 at 20:17
    
@BBischof: No, no. Not at all. :D (I just didn't see it before.) –  jrista Oct 26 '10 at 22:48

4 Answers 4

up vote 18 down vote accepted

Some dust spots on the sensor will absolutely not shift with air-pressure (blowing) alone. To shift them you need to wet clean the sensor.

I was nervous the first time I did this as I can understand most people would be. But it is not that difficult or risky, basically it involves wiping the sensor assembly with a soft rubber "wand" with a cleaning fluid dampened wipe attached to it. At this point it's worth stressing:

You are not cleaning the sensor microchip itself you are cleaning a toughened piece of glass (the low pass filter) that sits on top of the sensor.

The only damage you can do (when using the correct fluid) would be to the delicate shutter curtains, so make sure the shutter is open and will remain open for long enough to clean the sensor. This usually means ensuring the camera's power source remains uninterrupted.

Eclipse fluid has been tested on all sensors and determined to be safe. It's basically just alcohol and will evaporate without residue. See:

http://www.photosol.com/guarantee.htm

Likewise PEC PADs are highly recommended to go with it. I suggest you get a kit that includes the basic rubber wand, fluid and pec pads, then replace the fluid and pads as they run out. This is a very cost effective solution compared to all in one wet cleaning solutions. All you have to do is wrap the pads round the wand and tape them each time.

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This sounds like the solution. I really don't like the idea of blowing anything into my camera body, as that is just as likely to bring more particulate in, perhaps more likely, than when switching lenses. I know that there is a series of filters in front of my sensor. What I am not sure about is how to get at the sensor. Would just using a cable release in BULB mode be enough? –  jrista Sep 24 '10 at 18:25
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There's a dedicated sensor cleaning mode on the 450D (available through the second yellow spanner menu) which will flip up the mirror and open the shutter for you, you just need to make sure you have a decent amount of battery before you start. –  Matt Grum Sep 24 '10 at 18:31
    
Another liquid/wipe combo that works really well are good-quality lens wipes, like the ones in sealed packets for cleaning eye-glasses or binoculars. Test them on a house mirror first to make sure there's no smearing. I keep some of the ones from CostCo in my camera cases for the times dust gets out of control. A quick wipe or two across the filter seems to get it done 90% of the time. I've had a couple occasions some dust wouldn't come off and took a couple wipes, but I live and shoot in Arizona and dust can get really bad here. They'll sometimes leave a fiber behind but a puff will fix that. –  Greg Dec 22 '10 at 6:31

I have an Olympus 1030SW Digital camera and have been getting round ghostly circles in some of my photos. I just spoke to Olympus customer services and was advised it has to do with light reflection from dust in the air particularly when using flash. Nothing wrong with the camera but the downside of some digital cameras because of settings. His advice was to move a few steps to the right or left when taking the picture to get a different angle to the light. I did and have got some perfect pictures after dreadful ones of the same scene a few minutes earlier. He said I could also increase shutter speed - a bit too technical for me.

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I did try moving the camera. I've taken enough shots now to know for a fact that the spots are on the sensor. I get the same spots in the same location in my pictures every time I take a photo. Sometimes they don't show up if the location they are at is complex...but in solid colors or smooth gradients, they show up like beacons. I have to find a cleaning system for my camera and clean the sensor. –  jrista Oct 26 '10 at 19:06

That is definitely not from anything on or in the lens, it's from dust on the sensor. Or rather, dust on the filter in front of the sensor. If the dust was actually on the sensor itelf, it would always be sharp and only a few pixels big. As it's on the filter in front of the sensor, it's slightly out of focus, and appears as a blurred dot.

Dust on the lens is never visible on a photo. When the light passes through each lens element in the lens, the entire image passes through every point of the lens surface. So to have dirt on the lens being visible, it would have to cover a large part of the lens surface. On a mirror lens a large part of the front lens is actually covered by a mirror.

I regularly get dust on the sensor, and clean it with a brush and an air blower when there is too much.

A few spots can easily be removed using the healing tool in the post processing. As few as 10-12 spots is barely worth cleaning the camera for.

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Well, healing 10-12 spots on every photo I keep after a shoot (which could be 20 or so) is a LOT of work. If it was only 1 or 2, that wouldn't be so bad, but there are quite a few. They don't show up much on the landscape, but in the sky, which tends to be lighter, they show up quite well. Its gotten to the point where it is rather annoying, and very time consuming. –  jrista Sep 24 '10 at 18:07
    
@jrista: It of course depends on what you count as a spot that would need editing. Smaller dust particles show up as more faint spots (but with the exact same size), so if you have a lot of those in addition to your 10-12 darker spots, then it's of course a lot. I'm a bit too thorough, and tend to edit out also the more faint spots down to where they are barely visible, so I would perhaps be able to find a lot more spots in your images. :) –  Guffa Sep 24 '10 at 20:20
    
I basically only edit out the stuff that shows up in print, the rest I leave alone. If I tried to fix everything, I'd spend weeks just cleaning up spots on all my images. :P Even 10-12 spots on 20 images, though, is up to 240 spots. Thats a lot, and I have to adjust the healing brush in LR to accommodate large and small ones. Even with only 10-12 per image, I still have a lot of cleaning to do. –  jrista Sep 24 '10 at 20:33
    
@jrista: You generally don't have to adjust the healing brush more than once, as all dust spots in an image are the same size. It's the aperture that determines the spot size, not the size of the dust itself. –  Guffa Jul 28 '11 at 19:19
    
Yes, for a single image, thats true. But I usually don't keep my focal length and aperture the same for every single shot, so I have to adjust the brush for each new shot I correct. –  jrista Jul 29 '11 at 19:32

I'm willing to bet that that's dust on your sensor, not on the lens.

If you stop down to f/22, that can help to confirm that assertion, one way or the other. My sensor dust would really show up at the smaller apertures.

If they are indeed on the sensor (and they really look like the dust spots I got on my d70 and d200), you can try some of the Visible Dust products to clean it. Before I got the d300 (with the dust-shake on startup), one of their brushes was like American Express or a polarizer, I never left home without it.

I would stay away from any liquid-based solution, however-- I once tried one of those, and it ended up mucking up my d200 sensor glass.

Also, do not blow on the glass with your mouth, use a blower or something like that. Your mouth has spit, and once that's on the sensor glass, you're in for a much harder cleaning job.

Edit to address the comments below (because my comment was longer than the allowed number of characters):

@jrista, @Reid-- The lens has two places where it's in focus, on either side of it. There's the side outside the camera, and then there's the focus on the detector (the eyepiece or the film/digital detector). Stopping down increases the 'thickness' of the focal plane, which is still generally outside of the lens itself-- I can't imagine an optical configuration that would allow focus inside the lens, but maybe they could exist. If there's nothing in the focal plane outside the camera, then the only place for the dust is on the sensor. Stopping down just brings the dust into focus, so that when the light is collected by the sensor, you'll see the dust.

Incidentally, I can see dust on the light path to my eyepiece that isn't on my sensor using this trick. Since that dust is just annoying but doesn't affect my process significantly, I just leave it be.

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It definitely shows up at f/22, and the worst spots are barely visible at f/2.8. Does that mean its definitely on the sensor? –  jrista Sep 24 '10 at 1:01
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Correct. Almost certainly on the sensor based on your aperture tests. Also, if you're eyeballing the sensor looking for them, the spots will be reversed location-wise on the sensor; i.e. if they're at the top of your images, they'll be towards the bottom of your sensor. –  Conor Boyd Sep 24 '10 at 1:19
    
Here's Thom Hogan's (extensive) take on sensor cleaning: <bythom.com/cleaning.htm>;. However, I'd do a bit more googling on sensor spots vs. dust in the lens, etc., to identify where exactly the goober is coming from. –  Reid Sep 24 '10 at 1:21
    
@Conor, not disagreeing necessarily, but wouldn't goobers anywhere in the light path be more obvious with a smaller aperture? –  Reid Sep 24 '10 at 1:22
    
I'm curious about the same thing that Reid asked. Why is it that stopping down the aperture make spots on the sensor more visible, but not those on the lens? –  jrista Sep 24 '10 at 2:16

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