Something in my lens / Question

I have 7 lenses. Some I use once or twice a year. Such is the case with my 100 F2.8 L.

Did a shoot this weekend and every shot has what looked like dust in the same place in every shot. Not sensor dust. I figured something got on the front element of my lens, but nothing there. BUT, some is inside the lens that does not move. Almost looks like black plastic.

So to Canon it goes. And I'm sure they will charge me to fix it, but should they? After all, equipment very well cared for and a filter since day one. If something is inside the lens, it would seem to be a manufacturing defect, not a fault of mine.

Where is my thinking wrong?

~Bob

I think you are right, but I am not Canon
The first question they'll ask is why you realized that only now.

How do you know it's not sensor dust?

rrblint wrote in post #18238389
How do you know it's not sensor dust?

This is definitely the question, since it is generally practically impossible to see any "object" that might be within a lens system as a spot on the final image. To see that in effect you only have to look at a Catadioptric telephoto lens, more commonly known as a mirror lens. You can even, depending on the size of the front element, put a 1/4" to 1/2" square bit of post-it note on the front element of a lens and take test shot, you won't see it as a mark on the image, although it will have a dramatic effect on the Bokeh. Also on a digital sensor, because of the sensitivity of the sensor design to the angle of incidence of the ray paths you will get uneven exposures, but across a very large proportion of the image, and it would have to be a very large area to have an observable effect. If it looks at all like a sensor dust spot, then it is on the sensor, well actually the OLPF in front of the sensor, but that is being somewhat pedantic, and not in the lens.

Alan

rrblint wrote in post #18238389
How do you know it's not sensor dust?

It's easy to know for him using one of the following methods:
1) Shoot the 100/2.8 prime on both cameras and compare the results.
2) Shoot the 70-200/2.8 set at 100 mm f/2.8 and compared the results with the prime.

Dust will eventually get in all lenses. Fungus can grow in there too. The manufacturer cant be responsible for maintenance of everyone's lens at no cost. It's not a manufacturing defect. There are lots of tips on the net explaining how to help prevent getting dust in there. Probably some tips on here as well.

rebop wrote in post #18238278
I have 7 lenses. Some I use once or twice a year. Such is the case with my 100 F2.8 L.

Did a shoot this weekend and every shot has what looked like dust in the same place in every shot. Not sensor dust. I figured something got on the front element of my lens, but nothing there. BUT, some is inside the lens that does not move. Almost looks like black plastic.

Bob, you need to do a simple test to prove that the "problem" is actually inside the camera.

Use two or three different lenses. Take photographs of a solid-color wall or a cloudless sky at f/16 or more (higher f-numbers). I suspect you'll see the same sort of spots and, particularly, they will be in the same positions in your images with all the lenses you try.

As mentioned above, dust or even large particles of debris on or in a lens will not show up in focus in your images even though they may reduce the image quality a bit.

SkipD wrote in post #18238592
Bob, you need to do a simple test to prove that the "problem" is actually inside the camera.

Use two or three different lenses. Take photographs of a solid-color wall or a cloudless sky at f/16 or more (higher f-numbers). I suspect you'll see the same sort of spots and, particularly, they will be in the same positions in your images with all the lenses you try.

As mentioned above, dust or even large particles of debris on or in a lens will not show up in focus in your images even though they may reduce the image quality a bit.

I agree. You can shoot forever at small numbered f-stops & never see sensor dust. But as soon as you go to f/16, there it is!
Look at this: Some personal views on Sensor cleaning.

Again, the OP has 2 cameras. There is no need for complex tests to understand if the dust is in the sensor or in the lens.

The tests are very easy and more definitive in their results when you first test for sensor dust. Any other test at wide open apertures on different bodies with different lenses isn't quite as definitive, and you will almost certainly end up back to testing your sensor. Why not just get that out of the way now with a simple shot taken on each camera at f16+?

I can see it in the lens. And just noticed because it showed up on a gray object. Must have been masked by more complex images. And I only use this lens twice a year.

I can see this in the lens. Period. Looks like a small piece of maybe black plastic. Trust me. Not sensor dust. Not lens dust.

can you post a pic with exif?

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Perhaps you can just shake the lens back and forth, real hard. The object might "settle out", and work its way down out of the line of sight, so to speak. Sometimes problems are really easy to solve it you take an aggressive approach and don't worry over what you are doing too much.

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rebop wrote in post #18239404
I can see this in the lens. Period. Looks like a small piece of maybe black plastic. Trust me. Not sensor dust. Not lens dust.

The point we are all trying to make is that if you can see something in the lens, you won't see it causing a visible spot in the resulting image. To cast a shadow on the sensor that is visible as a spot the offending debris, be it a spot of oil or dust/dirt must be in contact with the surface of the sensor. this is because rays from any point on the focal plane will strike every point on the surface of the lens, and then be brought to focus at the focal plane. So from the point of view of the sensor the light is coming to any point on the surface of the sensor from every point on the lens, so it is like being outside on a cloudy day, when the light is coming from all directions, and you can't see any shadows. In fact because the light is coming from such a relatively wide area it is even hard for the dirt sitting on the "sensor" to cast a shadow. The sensor is actually a stack of many layers, with the sensor at the bottom, there are the microlenses, UV and IR filters, normally an OLPF, AKA the AA Filter, and the Bayer Colour Filter Array all sitting above the sensor itself which is also a 3D object. This is why it is always recommended to point the camera at a plain light coloured wall, and stop right down to the minimum aperture, usually f/22 on most DSLR lenses. This reduces the area that the light is coming from, and so maximises the shadow cast by the sensor dirt. Having a long exposure time is actually helpful, as is allowing the camera to move about, while pointing at the plain surface. This removes detail from the image, so that all you are left with is the sensor dirt. Even this process will not show up foreign objects or dirt/dust in the lens in the image.

I don't doubt that you can see something loose in the lens, however it will not be causing a spot to appear in the final image. Spots like this that show up especially well in areas of constant mid tones, such as the sky, are always caused by sensor dirt. Having the item in the lens is just coincidental. Dirt/dust and other debris in the lens tend to contribute to an overall lowering of image contrast, and may also increase the lenses susceptibility to flare. The other effect it may have is to change the shape of out of focus highlights. I have a 500mm catadioptric telephoto lens, and the half inch mirror mounted in the center of the front lens element definitely reduces the contrast of the image, and you get the classic donut shaped OOF highlights associated with this lens design. You definitely don't see it as a spot on the lens. With a digital sensor, which have issues with ray paths that come from off center out at the periphery of the sensor, due to that 3D nature of the sensor, Catadioptric lenses can also suffer more with vignetting when used on a digital sensor as they would have done when used with film. Perversely this makes the outside of the sensor darker, while the obstruction is in the center of the lens.

Alan