Is it possible for a lens's internal dust to appear in an image?

**Tonytee** · 01-03-2020, 03:07 AM

A very long story short, after cleaning the sensor on my Pentax K-7, I decided to take a few more test shots with my Pentax-M 80~320mm Lens. Once the images were

up on the monitor, I was aghast at the amount of debris in the form of black specks of various sizes. I went after the sensor again, took more shots and the situation improved

but not my much. There again was the bunch of specks and what appeared to be hair in the lower right corner. I decided to change lenses and these artifacts were not there.

To prove that the problem was in fact the lens, I placed the 80~320mm back onto the camera and took shots of another area, only this time on the wall. Low and behold the

artifacts were there. I had never heard of this before and so now I know what folks mean when they say, "This lens I have for sale has internal dust but does not affect image

quality." Any other possibilities besides internal dust? I did use a flashlight to see what I could see and I could not tell if there was any dust in there or not. However, the proof

is in the pudding, it is showing up in the images. Thanks very much for any feedback.

Tonytee

Last edited by Tonytee; 01-03-2020 at 03:09 AM. Reason: Grammar Correction.

**PJ1** · 01-03-2020, 04:48 AM

Could you post some images? This sounds rather strange. The specs (or hair) would only be identifiable if they were in focus. I can't see how internal dust could be in focus (others might be able to explain why). I assume that the impact of dust would only be noticeable if it had an effect on light transmission. That is why a small amount of dust in a lens is usually not an issue. I have seen images of lenses with enormous cracks in them, and the images are still very good because the crack is not in focus (although there may be flare issues).

zapp · 01-03-2020, 05:12 AM

It is a common eBay lie that dust in lenses has no effect on image quality. Typically you don’t notice the effect, the more dust, the more it effects image quality. To see particles in focus they should sit at the very back of the lens or even on the sensor.
Dust moves around, the camera shakes the sensor, ... you should see the evil dust by using a flash light.

**aslyfox** · 01-03-2020, 05:18 AM - **1 Like**

I claim no expertise but this article is either wrong or something else is going on ?

Quote:

The Apocalypse of Lens Dust
By Roger Cicala Published August 2, 2011

. . . .So what did we learn today?

The biggest surprise I got (it shouldn’t have been, I just didn’t think about it) was putting a fairly large foreign object on a rear element may keep the camera from autofocusing. Does it have real world implications? I don’t think so, although perhaps heavy rear element dust could interfere with autofocus accuracy.

Individual dust particles have to be HUGE before they can show up under almost any conditions. By HUGE I mean bigger than dust. Think an insect part or a small screw (I’ve seen both of those in lenses. It happens.)
Even something large probably won’t show up at wide apertures (f4 or wider probably).

A wide angle lens shows front element objects more than a moderate telephoto.

The moderate telephoto showed rear element objects more dramatically.

Remember, though, that what we really did here was look at big objects on the front and rear element of the lens. Internal dust might behave a bit differently if it was near the focal plane of the lens internally, or perhaps just in front of or behind the aperture. I’m not so curious that I’m going to take a lens apart and put a sticky note on an internal element and reassemble it to take test shots. Not yet anyway. Maybe in the winter when things are slow.

Does any of this have any real world implications? Nah. Unless you get a bug inside your lens there’s not much need to worry about dust. Until there’s so much dust that it interferes with contrast or light transmission. When is that? Well sounds like another article coming up, doesn’t it? But it would be a lot of dust.

Roger Cicala

Lensrentals.com

Lens Rentals | Blog

gatorguy · 01-03-2020, 05:57 AM - **1 Like**

Originally posted by aslyfox

I claim no expertise but this article is either wrong or something else is going on ?

Lens Rentals | Blog

I consider Roger to be a pretty reliable source. Thanks very much for his comments about lens dust.

aaacb · 01-03-2020, 06:02 AM

Did you have both lenses at a small aperture (f16-f22), when dust didn't show with the other lens? It's very unlikely to have debris in focus and not be on the sensor, especially since you don't see much of it inside the lens when looking with a light. Good luck figuring this out.

**jatrax** · 01-03-2020, 06:07 AM - **1 Like**

Originally posted by Tonytee

I went after the sensor again, took more shots and the situation improvedbut not my much. There again was the bunch of specks and what appeared to be hair in the lower right corner.

When you made your test with a different lens what aperture were you using? The visibility of dust can be dramatically different at different apertures. Test both lenses again using a neutral wall or better a clear blue sky at f/16 and see what happens.

It has been my experience, though I am certainly not an expert, that dust in a lens will not be visible on an image unless it is huge and easily visible to the naked eye. Dust can affect the image by causing scattering of the light, but you won't see actual spots unless they are on the sensor. I have quite a collection of vintage Takumars and Pentax-F lenses and all of them have some internal dust. And the dust does not show in images.

**Lowell Goudge** · 01-03-2020, 06:32 AM - **3 Likes**

Start with a shot of a blue sky. You could do a second shot with the lens rotated slightly (I.e. partially unlocked) if the spots move it is the lens, if they stay fixed it is the sensor.

But as others have said, sensor spots show up much more than lens dust

**BigMackCam** · 01-03-2020, 06:49 AM

It really depends on the optical formula as to where within the lens a large, individual piece of dust or debris might be noticeable in certain images. I would certainly be more concerned about debris at the rear element than elsewhere in the lens, and largely unconcerned with dust or debris at the front group.

For dust and/or hairs to be clearly visible in images, they will almost certainly be on the sensor rather than in the lens - and they may be difficult to see on the sensor with the naked eye.

The best test would be to take two photos of an unpatterned white or light-coloured wall, or else a clear, light blue sky, at a small aperture such as f/22, with two separate lenses. If the debris is visible in both photos, it's on the sensor, not in the lens.

**clickclick** · 01-03-2020, 07:31 AM

I've been amazed on sensor dust showing up when stopping down and shooting at a blank surface. I feel it's been more apparent when I've done it with telephoto lenses. Worth a few shots. Even a white wall can work. Move where you're aiming the camera, and if the spots don't change position, you know it's sensor or perhaps lens in your case. What happens as you zoom this lens? Do they change in any way? If it's on the lens side, I'd expect that to occur.

**AstroDave** · 01-03-2020, 07:56 AM

A few more comments: use a clear sky! Walls and other smooth surfaces (such as a piece of white paper) almost always have some variations in surface texture/features, which might cause confusion. You can go out of focus to help with that, but with the sky focus doesn't matter (as long as it is really clear sky - NO clouds!). Use daylight WB (not really very critical, though). Use a small aperture (f16 or f22) as noted by several folks above.

As to sky: aim as straight up as possible; at lower elevations there will be brightness variations across the sky. Get your histogram in the middle.

Now, go to your favorite post-processor. Convert to gray scale. This should result in a quite narrow histogram. Then, slide the brightness sliders in from both ends. This will really zoom in on any specks anywhere in the frame. In fact, you may be appalled at what you see! Fortunately, most of that crap doesn't have much effect on your images. Repeat this process after sensor cleaning until you are happy.

Neat idea above to rotate the lens slightly between frames.

swanlefitte · 01-03-2020, 08:43 AM

I always use a white wall in low light. I move the camera slowly over a 5-10 second exposure at f/22. This ensures only the lens/camera combo can have anything with an edge because everything else has motion blur.
Definitely redo the test with 2 or more lenses to be sure.

gatorguy · 01-03-2020, 08:55 AM - **1 Like**

Originally posted by AstroDave

A few more comments: use a clear sky! Walls and other smooth surfaces (such as a piece of white paper) almost always have some variations in surface texture/features, which might cause confusion. You can go out of focus to help with that, but with the sky focus doesn't matter (as long as it is really clear sky - NO clouds!). Use daylight WB (not really very critical, though). Use a small aperture (f16 or f22) as noted by several folks above.

As to sky: aim as straight up as possible; at lower elevations there will be brightness variations across the sky. Get your histogram in the middle.

Now, go to your favorite post-processor. Convert to gray scale. This should result in a quite narrow histogram. Then, slide the brightness sliders in from both ends. This will really zoom in on any specks anywhere in the frame. In fact, you may be appalled at what you see! Fortunately, most of that crap doesn't have much effect on your images. Repeat this process after sensor cleaning until you are happy.

Neat idea above to rotate the lens slightly between frames.

100% agree on testing against a clear and BRIGHT blue sky. Empty walls do not work as well, often having some teeny shadow spot or texture.

gatorguy · 01-03-2020, 10:02 AM - **1 Like**

Originally posted by Bassat

My 3 cents. Using a clear, even sky is a bad way to do this. You need to MOVE the camera around during a several second exposure. Five seconds of clear, bright sky will blow the entire frame, resulting in nothing at all being visible. Use the smallest aperture on each particular lens, lowest ISO available, and uniformly lit, light colored, blank wall. As mentioned above, using this method will show nothing but sensor dust and lens (mush less likely) dust. Any spots that appear in 2+ tests with different lenses are on the sensor.

It is extremely overcast in northern Indiana right now. I set my camera to ISO 100, f/32, and pointed it at blank sky. Metered exposure is 1/4 second. That, my good friend, is not going to get you the image you desire.

Then it's certainly not a clear blue sky is it?

I've never had an issue with seeing sensor dust against a bright blue cloudless sky, and never have blown out the entire frame either. Why move the camera around and use a long exposure? Infinity focus (heck autofocus the empty sky works about as good) and fire away. There's zero question that it works, and works well. Under an overcast sky? Well heck no.

Now if you can't wait for a better sky then perhaps your method is the only good option. Thanks for sharing it as some will find it useful.

**clickclick** · 01-03-2020, 10:54 AM

Regrading not using walls etc., while perhaps not ideal, it may be the easiest option. I'm in a highly wooded area, and it can be a real pain trying to get the perfect piece of sky. Take multiple shots and see what moves and what doesn't. I've found it pretty easy to figure out what's dust on my sensor versus a blemish on my test background.

01-03-2020, 03:07 AM	#1
Tonytee Loyal Site Supporter Join Date: Jul 2012 Photos: Gallery \| Albums Posts: 21,452	Is it possible for a lens's internal dust to appear in an image? A very long story short, after cleaning the sensor on my Pentax K-7, I decided to take a few more test shots with my Pentax-M 80~320mm Lens. Once the images were up on the monitor, I was aghast at the amount of debris in the form of black specks of various sizes. I went after the sensor again, took more shots and the situation improved but not my much. There again was the bunch of specks and what appeared to be hair in the lower right corner. I decided to change lenses and these artifacts were not there. To prove that the problem was in fact the lens, I placed the 80~320mm back onto the camera and took shots of another area, only this time on the wall. Low and behold the artifacts were there. I had never heard of this before and so now I know what folks mean when they say, "This lens I have for sale has internal dust but does not affect image quality." Any other possibilities besides internal dust? I did use a flashlight to see what I could see and I could not tell if there was any dust in there or not. However, the proof is in the pudding, it is showing up in the images. Thanks very much for any feedback. Tonytee Last edited by Tonytee; 01-03-2020 at 03:09 AM. Reason: Grammar Correction.

01-03-2020, 08:55 AM - 1 Like	#13
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	Originally posted by AstroDave A few more comments: use a clear sky! Walls and other smooth surfaces (such as a piece of white paper) almost always have some variations in surface texture/features, which might cause confusion. You can go out of focus to help with that, but with the sky focus doesn't matter (as long as it is really clear sky - NO clouds!). Use daylight WB (not really very critical, though). Use a small aperture (f16 or f22) as noted by several folks above. As to sky: aim as straight up as possible; at lower elevations there will be brightness variations across the sky. Get your histogram in the middle. Now, go to your favorite post-processor. Convert to gray scale. This should result in a quite narrow histogram. Then, slide the brightness sliders in from both ends. This will really zoom in on any specks anywhere in the frame. In fact, you may be appalled at what you see! Fortunately, most of that crap doesn't have much effect on your images. Repeat this process after sensor cleaning until you are happy. Neat idea above to rotate the lens slightly between frames. 100% agree on testing against a clear and BRIGHT blue sky. Empty walls do not work as well, often having some teeny shadow spot or texture. Last edited by gatorguy; 01-03-2020 at 09:01 AM.

01-03-2020, 10:02 AM - 1 Like	#14
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	Originally posted by Bassat My 3 cents. Using a clear, even sky is a bad way to do this. You need to MOVE the camera around during a several second exposure. Five seconds of clear, bright sky will blow the entire frame, resulting in nothing at all being visible. Use the smallest aperture on each particular lens, lowest ISO available, and uniformly lit, light colored, blank wall. As mentioned above, using this method will show nothing but sensor dust and lens (mush less likely) dust. Any spots that appear in 2+ tests with different lenses are on the sensor. It is extremely overcast in northern Indiana right now. I set my camera to ISO 100, f/32, and pointed it at blank sky. Metered exposure is 1/4 second. That, my good friend, is not going to get you the image you desire. Then it's certainly not a clear blue sky is it? I've never had an issue with seeing sensor dust against a bright blue cloudless sky, and never have blown out the entire frame either. Why move the camera around and use a long exposure? Infinity focus (heck autofocus the empty sky works about as good) and fire away. There's zero question that it works, and works well. Under an overcast sky? Well heck no. Now if you can't wait for a better sky then perhaps your method is the only good option. Thanks for sharing it as some will find it useful. Last edited by gatorguy; 01-03-2020 at 10:15 AM.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Image review - colours appear washed out	learner50	Pentax K-3 & K-3 II	5	04-03-2016 08:17 AM
PentaxnFA 43 F1.9 Ltd with internal dust	Kootenayrider	Pentax SLR Lens Discussion	4	07-02-2012 02:37 AM
Some part of my image does not appear on focus, How can i get it all in focus?	rustynail925	Photographic Technique	11	09-08-2010 07:24 AM
Internal Dust & Cleaning - Pentax-M 50mm/1.4	ManhattanProject	Pentax SLR Lens Discussion	3	08-16-2010 12:17 PM
SMC 85mm f/2 internal dust?	Dealchzr	Pentax SLR Lens Discussion	10	06-03-2009 11:55 AM

01-03-2020, 04:48 AM	#2
PJ1 Loyal Site Supporter Join Date: Jul 2012 Location: Toowoomba, Australia Photos: Gallery \| Albums Posts: 5,484	Could you post some images? This sounds rather strange. The specs (or hair) would only be identifiable if they were in focus. I can't see how internal dust could be in focus (others might be able to explain why). I assume that the impact of dust would only be noticeable if it had an effect on light transmission. That is why a small amount of dust in a lens is usually not an issue. I have seen images of lenses with enormous cracks in them, and the images are still very good because the crack is not in focus (although there may be flare issues).

01-03-2020, 05:12 AM	#3
zapp Pentaxian Join Date: Jul 2011 Posts: 2,385	It is a common eBay lie that dust in lenses has no effect on image quality. Typically you don’t notice the effect, the more dust, the more it effects image quality. To see particles in focus they should sit at the very back of the lens or even on the sensor. Dust moves around, the camera shakes the sensor, ... you should see the evil dust by using a flash light.

01-03-2020, 05:18 AM - 1 Like	#4
aslyfox Seeker of Knowledge Join Date: Aug 2016 Location: Topeka, Kansas Photos: Gallery \| Albums Posts: 24,581	I claim no expertise but this article is either wrong or something else is going on ? Quote: The Apocalypse of Lens Dust By Roger Cicala Published August 2, 2011 . . . .So what did we learn today? The biggest surprise I got (it shouldn’t have been, I just didn’t think about it) was putting a fairly large foreign object on a rear element may keep the camera from autofocusing. Does it have real world implications? I don’t think so, although perhaps heavy rear element dust could interfere with autofocus accuracy. Individual dust particles have to be HUGE before they can show up under almost any conditions. By HUGE I mean bigger than dust. Think an insect part or a small screw (I’ve seen both of those in lenses. It happens.) Even something large probably won’t show up at wide apertures (f4 or wider probably). A wide angle lens shows front element objects more than a moderate telephoto. The moderate telephoto showed rear element objects more dramatically. Remember, though, that what we really did here was look at big objects on the front and rear element of the lens. Internal dust might behave a bit differently if it was near the focal plane of the lens internally, or perhaps just in front of or behind the aperture. I’m not so curious that I’m going to take a lens apart and put a sticky note on an internal element and reassemble it to take test shots. Not yet anyway. Maybe in the winter when things are slow. Does any of this have any real world implications? Nah. Unless you get a bug inside your lens there’s not much need to worry about dust. Until there’s so much dust that it interferes with contrast or light transmission. When is that? Well sounds like another article coming up, doesn’t it? But it would be a lot of dust. Roger Cicala Lensrentals.com Lens Rentals \| Blog

01-03-2020, 05:57 AM - 1 Like	#5
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	Originally posted by aslyfox I claim no expertise but this article is either wrong or something else is going on ? Lens Rentals \| Blog I consider Roger to be a pretty reliable source. Thanks very much for his comments about lens dust.

01-03-2020, 06:02 AM	#6
aaacb Pentaxian Join Date: May 2016 Photos: Gallery Posts: 3,724	Did you have both lenses at a small aperture (f16-f22), when dust didn't show with the other lens? It's very unlikely to have debris in focus and not be on the sensor, especially since you don't see much of it inside the lens when looking with a light. Good luck figuring this out.

01-03-2020, 06:07 AM - 1 Like	#7
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by Tonytee I went after the sensor again, took more shots and the situation improvedbut not my much. There again was the bunch of specks and what appeared to be hair in the lower right corner. When you made your test with a different lens what aperture were you using? The visibility of dust can be dramatically different at different apertures. Test both lenses again using a neutral wall or better a clear blue sky at f/16 and see what happens. It has been my experience, though I am certainly not an expert, that dust in a lens will not be visible on an image unless it is huge and easily visible to the naked eye. Dust can affect the image by causing scattering of the light, but you won't see actual spots unless they are on the sensor. I have quite a collection of vintage Takumars and Pentax-F lenses and all of them have some internal dust. And the dust does not show in images.

01-03-2020, 06:32 AM - 3 Likes	#8
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,886	Start with a shot of a blue sky. You could do a second shot with the lens rotated slightly (I.e. partially unlocked) if the spots move it is the lens, if they stay fixed it is the sensor. But as others have said, sensor spots show up much more than lens dust

01-03-2020, 06:49 AM	#9
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,670	It really depends on the optical formula as to where within the lens a large, individual piece of dust or debris might be noticeable in certain images. I would certainly be more concerned about debris at the rear element than elsewhere in the lens, and largely unconcerned with dust or debris at the front group. For dust and/or hairs to be clearly visible in images, they will almost certainly be on the sensor rather than in the lens - and they may be difficult to see on the sensor with the naked eye. The best test would be to take two photos of an unpatterned white or light-coloured wall, or else a clear, light blue sky, at a small aperture such as f/22, with two separate lenses. If the debris is visible in both photos, it's on the sensor, not in the lens.

01-03-2020, 07:31 AM	#10
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,903	I've been amazed on sensor dust showing up when stopping down and shooting at a blank surface. I feel it's been more apparent when I've done it with telephoto lenses. Worth a few shots. Even a white wall can work. Move where you're aiming the camera, and if the spots don't change position, you know it's sensor or perhaps lens in your case. What happens as you zoom this lens? Do they change in any way? If it's on the lens side, I'd expect that to occur.

01-03-2020, 07:56 AM	#11
AstroDave Loyal Site Supporter Join Date: May 2007 Location: Flagstaff, Arizona Posts: 1,637	A few more comments: use a clear sky! Walls and other smooth surfaces (such as a piece of white paper) almost always have some variations in surface texture/features, which might cause confusion. You can go out of focus to help with that, but with the sky focus doesn't matter (as long as it is really clear sky - NO clouds!). Use daylight WB (not really very critical, though). Use a small aperture (f16 or f22) as noted by several folks above. As to sky: aim as straight up as possible; at lower elevations there will be brightness variations across the sky. Get your histogram in the middle. Now, go to your favorite post-processor. Convert to gray scale. This should result in a quite narrow histogram. Then, slide the brightness sliders in from both ends. This will really zoom in on any specks anywhere in the frame. In fact, you may be appalled at what you see! Fortunately, most of that crap doesn't have much effect on your images. Repeat this process after sensor cleaning until you are happy. Neat idea above to rotate the lens slightly between frames.

01-03-2020, 08:43 AM	#12
swanlefitte Pentaxian Join Date: May 2015 Location: Minneapolis Photos: Gallery Posts: 4,068	I always use a white wall in low light. I move the camera slowly over a 5-10 second exposure at f/22. This ensures only the lens/camera combo can have anything with an edge because everything else has motion blur. Definitely redo the test with 2 or more lenses to be sure.

01-03-2020, 10:54 AM	#15
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,903	Regrading not using walls etc., while perhaps not ideal, it may be the easiest option. I'm in a highly wooded area, and it can be a real pain trying to get the perfect piece of sky. Take multiple shots and see what moves and what doesn't. I've found it pretty easy to figure out what's dust on my sensor versus a blemish on my test background.