Where's the dust?

[pvonk]

I'm new to digital photography, received a 20D two weeks ago. Yesterday, after shooting a number of pics in RAW, I noticed some "spots" when viewing on the computer. I then cleaned the lens and took more pics. Here's what I've found:

I can see some smudges throught the eyepiece, very very slight smudges. On the pictures, there is one spot, looks like a bird flying in the sky. The spot is blurry when using f/5.5 but sharper at f/20. I changed lenses and the same thing happens. So I can rule out the lens. That leaves the flip mirror or the sensor. I'm hesitant clening the sensor at this point, since I'm wondering if a sensor can "show" a slight spot on the eyepiece. Maybe it's several things at work here. Any thoughts? Thanks.

- Pierre

[ddelallata]

the smudge on the eyepiece will not affect the quality of the images. The dust on the CMOS sensor is another story. Here's a link that many here have found useful for cleaning the sensor on these cameras.
http://www.pbase.com/copperhill/ccd_cleaning

[robertwgross]

If the spots show up on the captured image, then this is likely dust on the sensor surface. If the spots show up in the viewfinder view, then this is dust either on the eyeball side of the viewfinder or else on the focus screen. If you remove the lens and look into the chamber, you will see the mirror. The reflection in the mirror is that of the focus screen.

---Bob Gross---

[pvonk]

If the spots show up on the captured image, then this is likely dust on the sensor surface. If the spots show up in the viewfinder view, then this is dust either on the eyeball side of the viewfinder or else on the focus screen.
---Bob Gross---

Yes, I suspected a spot seen through the eyepiece AND on a picture couldn't be the same one. I've cleaned the eyepiece and the mirror as well as a lens (but another lens gives the same result) but I still see several fuzzy spots through the eyepiece. I guess I haven't cleaned well enough.

Q: how sensitive is the mirror (that flips up when a picture is taken) to cleaning? Will it become uncalibrated if I clean it with a cloth (lightly) or otherwise touch it? Should I just use air/brush??

As for the spot on the picture (there's always one, same position), I'm baffled that it appears light and fuzzy at f/5.6 but sharp at f/20. I would have thought if the sensor has dust on it, that affects certain pixels and the resulting picture will always have the same spot image, regardless of f-stop setting.

Q: can someone shed some light on this issue of sharpness vs f-stop (no pun intended)?

Thanks. - Pierre

[glangston]

First use a blower, preferably a Giotto Rocket blower as it seems to be a little more capable than the little ones. I've gotten stuff on the sensor and the blower has worked for me twice. If it's still there then the Copperhill method mentioned above will be a possible next step if you feel capable of following the steps. Sending it to Canon to be cleaned is likely $50 and some varied results.

[pierrot]

As for the spot on the picture (there's always one, same position), I'm baffled that it appears light and fuzzy at f/5.6 but sharp at f/20.
No, it's normal: at f/20 light rays are nearly perfectly parallel and the shadow of the dust grain well defined.
At f/5.6 the lens pupil is far broader thus the blurriness of the dust shadow.

It's definitely must be dust on the sensor. Rocket Blower rules! :mrgreen:

[robertwgross]

Yes, I suspected a spot seen through the eyepiece AND on a picture couldn't be the same one. I've cleaned the eyepiece and the mirror as well as a lens (but another lens gives the same result) but I still see several fuzzy spots through the eyepiece. I guess I haven't cleaned well enough.

Q: how sensitive is the mirror (that flips up when a picture is taken) to cleaning? Will it become uncalibrated if I clean it with a cloth (lightly) or otherwise touch it? Should I just use air/brush??


Pierre, did you read what I wrote? "I guess I haven't cleaned it well enough," on the eyepiece?

The mirror is relatively sensitive, and it is probably much more delicate than the sensor. I will admit to having touched my mirror with a cotton swab, but that is about all.

---Bob Gross---

[pvonk]

The mirror is relatively sensitive, and it is probably much more delicate than the sensor. I will admit to having touched my mirror with a cotton swab, but that is about all.

---Bob Gross---
More delicate?? What gets me is the lack of information in the owner's manual on cleaning (at least the one I got). I also have another booklet on the 20D - it also discusses the sensor and its cleaning, but nothing on mirror or "focus screen".

So help me out - cotton swab (yes I have these - the long type for cleaning reading heads in computer tape drives, CD and DVD readers), do I just use the swab, or add some drops on the tip from a lens cleaning liquid bottle?

As always, I appreciate the help we get on forums. Isn't the Internet great!

[lancea]

I don't dare touch the mirror. If I got desperate (blower didn't work) I might stroke it with a microfiber cloth or sensor-cleaning brush, making sure I hadn't touched that part of the cloth first. No fluid at all. If it needed a proper clean I would take it to a camera technician and hope that they didn't make it worse. Being in New York state, you could at least send it to be properly cleaned.

My philosophy it that you need steady hands to do this kind of thing, and since I'd be so nervous I'm unlikely to have steady hands!

[robertwgross]

So help me out - cotton swab (yes I have these - the long type for cleaning reading heads in computer tape drives, CD and DVD readers), do I just use the swab, or add some drops on the tip from a lens cleaning liquid bottle?

Personally, I do not use the expensive sensor swabs that are so popular. I use an ordinary cotton swab, and I put a fraction of one drop of ordinary lens cleaner solution on it. I don't attempt to wash off the sensor surface. I simply wipe the sensor surface.

The focus screen and mirror should not have to be cleaned, since they do not contribute to the image. However, I have knocked off a mosquito or two that were perched on the mirror.

---Bob Gross---

[Keiffer]

I sure do wish there was a diagram or pictures for this, I'm not really sure which is which so I have cleaned everything I thought might have dust and still have some:-(

[pierrot]

The mirror in a reflex camera is much more delicate than a "normal" mirror because the silvering is not laid behind but in front of the glass (in order to avoid diffraction inside the glass blade and send a perfect reflected image to the focusing screen).
Thus, rubbing the mirror is not a good idea. But if you do it very gently with a sensor cleaning tissue and a drop of cleaning fluid, you shouldn't damage anything.
Anyway, cleaning the mirror will only affect the image you see in the viewfinder, not the picture you take.

[pvonk]

Thanks for all your input. I'm on vacation, no photo shops open, so I bought a baby's nasal asperator, nice small size but what a powerful blower! Well, it cleaned up the sensor, and the pics are now spot-free. I also used cleaning tissue (very lightly) with a drop of fluid on the mirror and that got rid of all the spots appearing through the eyepiece.

- Pierre

[kenyc]

Personally, I do not use the expensive sensor swabs that are so popular. I use an ordinary cotton swab, and I put a fraction of one drop of ordinary lens cleaner solution on it. I don't attempt to wash off the sensor surface. I simply wipe the sensor surface.

The focus screen and mirror should not have to be cleaned, since they do not contribute to the image. However, I have knocked off a mosquito or two that were perched on the mirror.

---Bob Gross---

and I assume that works fine for you? Do you do much shooting at the smaller apertures?

I'm noticing dust on my sensor and basically used your method of the cotton swap (less the cleaning fluid) and it seemed to work okay, but I still have a few dust spots as f22. I ordered one of the sensor clearning kits for $30....figured I'd try it at that price.

KAC

KAC

[robertwgross]

Do you do much shooting at the smaller apertures?

This afternoon, I had an osprey circling overhead in a bright blue sky, and I got off about 25 shots.

I'm noticing dust on my sensor and basically used your method of the cotton swap (less the cleaning fluid)

So, you skipped the fluid? Why? That was an important part of it, and it acts like a lubricant to keep the cotton from scratching anything on the surface. Now what have you done?

---Bob Gross---

[kenyc]

I was just trying to remove the worst offending dust spots. It worked fine.

KAC