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Canon 5d mark iv strange artifacts on images

lnlposner
Apprentice

I have a new 5d mark iv, and have mostly been shooting in my studio.  I have begun to notice some strange artifacts on some images.  They look like a small squigly wire and show up in different places on the image.  A little like a letter M.  Weird thing is that my older Nikon D7000 had these too.  Mostly shooting with the Canon 105 macro.  Brand new lens.  Anyone know what these are?

8 REPLIES 8

ScottyP
Authority

If it is in focus it is on the sensor. A piece of thread or dust etc. get the rocket blower out and go to town. 

Scott

Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?

TCampbell
Elite
Elite

This does indeed sound like dust on the sensor.

 

When you swap lenses dust can get into the camera.  The shutter is technically closed at that time, but when you attach a lens and take a shot, the reflix mirror swings up very quickly creating wind inside the camera as the shutter opens and the dust can settle on your sensor.

 

An easy test is to take a photo of a plain white wall ... or plain blue sky.  You need something with no contrast and the lens doesn't even need to be focused.

 

But take TWO different exposures... one at wide-open and the other stopped down (to say... f/22).  If the issue is well defined at f/22 but less noticeable at wide-open then you have dust on the sensor and it'll need to be cleaned.

 

 

Tim Campbell
5D III, 5D IV, 60Da


TCampbell wrote:

This does indeed sound like dust on the sensor.

 

When you swap lenses dust can get into the camera.  The shutter is technically closed at that time, but when you attach a lens and take a shot, the reflix mirror swings up very quickly creating wind inside the camera as the shutter opens and the dust can settle on your sensor.

 

An easy test is to take a photo of a plain white wall ... or plain blue sky.  You need something with no contrast and the lens doesn't even need to be focused.

 

But take TWO different exposures... one at wide-open and the other stopped down (to say... f/22).  If the issue is well defined at f/22 but less noticeable at wide-open then you have dust on the sensor and it'll need to be cleaned. 

 


I may be missing something obvious, but I'm confused by that explanation. You seem to be suggesting that the problem is at least partly a DOF effect. But if the contamination is already at or very near the focal plane, won't it be unaffected by the focus of the lens? In fact, I'd almost expect it to be more noticeable at a wide aperture, because it might tend to stand out more from an unfocused image than from a focused one.

Bob
Philadelphia, Pennsylvania USA


@RobertTheFat wrote:

@TCampbell wrote:

This does indeed sound like dust on the sensor.

 

When you swap lenses dust can get into the camera.  The shutter is technically closed at that time, but when you attach a lens and take a shot, the reflix mirror swings up very quickly creating wind inside the camera as the shutter opens and the dust can settle on your sensor.

 

An easy test is to take a photo of a plain white wall ... or plain blue sky.  You need something with no contrast and the lens doesn't even need to be focused.

 

But take TWO different exposures... one at wide-open and the other stopped down (to say... f/22).  If the issue is well defined at f/22 but less noticeable at wide-open then you have dust on the sensor and it'll need to be cleaned. 

 


I may be missing something obvious, but I'm confused by that explanation. You seem to be suggesting that the problem is at least partly a DOF effect. But if the contamination is already at or very near the focal plane, won't it be unaffected by the focus of the lens? In fact, I'd almost expect it to be more noticeable at a wide aperture, because it might tend to stand out more from an unfocused image than from a focused one.


Just to make sure that you're thoroughly confused.  Light does not always behave as one would expect.  It is not a DOF issue. It is a quirk of light itself.  Light dows strange things at times.  Like the famous dual slit experiment.

 

https://en.m.wikipedia.org/wiki/Double-slit_experiment

 

In the case of the lens aperture, we are dealing with a single round slit, instead of narrow vertical ones.  

 

The really weird part of the dual slit experiment is that if you introduce instruments to measure the number of photons traveling past the slits on the multiple paths, the multiple paths will suddenly disappear and all that you will see be two slits of light!

--------------------------------------------------------
"The right mouse button is your friend."


@Waddizzle wrote:

@RobertTheFat wrote:

@TCampbell wrote:

This does indeed sound like dust on the sensor.

 

When you swap lenses dust can get into the camera.  The shutter is technically closed at that time, but when you attach a lens and take a shot, the reflix mirror swings up very quickly creating wind inside the camera as the shutter opens and the dust can settle on your sensor.

 

An easy test is to take a photo of a plain white wall ... or plain blue sky.  You need something with no contrast and the lens doesn't even need to be focused.

 

But take TWO different exposures... one at wide-open and the other stopped down (to say... f/22).  If the issue is well defined at f/22 but less noticeable at wide-open then you have dust on the sensor and it'll need to be cleaned. 

 


I may be missing something obvious, but I'm confused by that explanation. You seem to be suggesting that the problem is at least partly a DOF effect. But if the contamination is already at or very near the focal plane, won't it be unaffected by the focus of the lens? In fact, I'd almost expect it to be more noticeable at a wide aperture, because it might tend to stand out more from an unfocused image than from a focused one.


Just to make sure that you're thoroughly confused.  Light does not always behave as one would expect.  It is not a DOF issue. It is a quirk of light itself.  Light dows strange things at times.  Like the famous dual slit experiment.

 

https://en.m.wikipedia.org/wiki/Double-slit_experiment

 

In the case of the lens aperture, we are dealing with a single round slit, instead of narrow vertical ones.  

 

The really weird part of the dual slit experiment is that if you introduce instruments to measure the number of photons traveling past the slits on the multiple paths, the multiple paths will suddenly disappear and all that you will see be two slits of light!


As it happens, I'm not quite the novice at theoretical physics that you probably have a right to expect, so I'm less than thoroughly confused by discussions of the wave/particle duality exhibited by light and matter. But we're talking here about objects several orders of magnitude larger than a photon or even a buckyball. I think it's hardly necessary to introduce quantum mechanics in order to explain how to recognize a hair or dust particle on the surface of a sensor. I accept Tim's explanation of how, at least in principle, shadows are enhanced when illuminated by a smaller light source. but I'm not sure I altogether accept that it makes a significant difference in the context of this discussion.

Bob
Philadelphia, Pennsylvania USA

"As it happens, I'm not quite the novice at theoretical physics that you probably have a right to expect, so I'm less than thoroughly confused by discussions of the wave/particle duality exhibited by light and matter. But we're talking here about objects several orders of magnitude larger than a photon or even a buckyball. I think it's hardly necessary to introduce quantum mechanics in order to explain how to recognize a hair or dust particle on the surface of a sensor. I accept Tim's explanation of how, at least in principle, shadows are enhanced when illuminated by a smaller light source. but I'm not sure I altogether accept that it makes a significant difference in the context of this discussion."

 

--------------------------------------------------------------------------------------------------------------------

 

The slits in the experiment are hardly the size of sub-atomic particles, and neither are the dust paraticles on an image sensor.  Just as in the slit experiment, the measurement process of the light dramatically changes what the image sensor records.  The sensor records what we expect to see, although what it records isn't what is actually occurring. 

 

The sensor records the result as a sharper blob, or as a fuzzier blob.  You mentioned DOF.  As Tim pointed out, DOF has nothing to do with it because the lens elements have no impact, just the size of the aperture.  Ask yourself this.  Why would changing the aperture cause a change in what image sensor records?  All you're doing is changing the amount of light striking the sensor.  Right?  Shouldn't you get more, or less, the same recorded image as you vary the amount of light?

 

If all that you're doing by changing the aperture is equivalent to raising and lowering a window shade, to change the amount of light passing through a window, then why would that change the apparent focus?  The apparent variation in sharpness isn't due to the lens, it is due to the quantum effects of light passing through a smaller, or larger, aperture!

 

Changing the aperture size does MORE than vary the amount of light striking the image sensor.  It also changes how the light behaves as it travels between the aperture and the image sensor!

--------------------------------------------------------
"The right mouse button is your friend."

You stop down you get light exiting the lens from a very tiny area... like a pin-point of light.  The shadows are well-defined.  When you shoot wide open, you have light exiting the lens from a very broad area and the shadows are very gentle.

 

You can detect dust spots much easier at high f-stops and if you vary the f-stop (by an extreme amount) and it makes a noticeable impact on the definition of artificacts then you've confirmed it's a an issue with something on the sensor.

 

The lens focus doesn't actually matter because you're not trying to take an image of anything in front of the lens... just looking for a shadow on the sensor.

 

Tim Campbell
5D III, 5D IV, 60Da

TCampbell
Elite
Elite

I'm not sure why the double-slit experiment was brought up.  That experiment works because of the wave nature of light and to really make it work requires that all the light have a common wavelength (which is why the experiment is typically conducted using a laser).

 

 

My comment about dust showing better at high f-stops than at low f-stops had nothing to do with the wave nature of light.  It was a much simpler idea.

 

If you imagine holding a pencil in front of movie screen... and shine light at the pencil using a pin-point source of light, you'll get a well-defined shadow of the pencil on the movie screen.  But if you shine a light originating from an extremely broad source then you'll get a shadow with very fuzzy edges (and depending on how broad the source is, the shadow may even be difficult to notice.)

 

The idea is that simple... wide-open f-stops result in dust shadows with fuzzy edges that may be so diffuse as to escape notice.  But hight f-stops (small aperture opening) results in dust shadows with strongly defined edges which makes the dust much easier to spot.

 

If an "artifact" on the sensor can be changed just by varying the f-stop, then you're almost certainly dealing with something resting on the sensor surface (technically there are a few filters in front of the sensor... so it's really resting on the outermost filter.)

 

 

 

Tim Campbell
5D III, 5D IV, 60Da
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