Lens problem. Help me diagnose.

[SSonnentag]

I have a really nice Canon 70-200 f/2.8 IS lens, but it's consistently giving me a bright streak across the top of every frame, or across the left side when in portrait mode. Has anyone seen this before? My other lenses don't have this problem, so I know it's not likely a camera issue.

Thanks for any insight.
Shawn

[SSonnentag]

Here's a 100% crop from the top right corner.

[SSonnentag]

I can tell you that the washed out streak doesn't change based on zoom. It looks the same at 70mm as it does at 200mm.

[lightwrangler]

I know that you don't have an issue with other lenses ... but this does look like a shutter problem to me ... curtain sticking. Why it doesn't occur with other lenses I can't explain. Good luck.

Cheers,
Adrian

[Swampy]

I know that you don't have an issue with other lenses ... but this does look like a shutter problem to me ... curtain sticking. Why it doesn't occur with other lenses I can't explain. Good luck.

Cheers,
Adrian

With a film camera, I can see this. Digital however, will bring up, does the sensor turn on and off for the specified shutter speed or is it turned on before the shutter is open and/or turned off after the shutter is closed?

Or is the shutter speed actually controlled by the "shutter" in digital?

I wonder - Shawn - do you have another lens that overlaps the 70-200 that you could try? Does it happen at certain apertures by chance?

[Tom V]

I bet that it is the camera, but probably not the shutter (for the usual shutter reasons anyway).

The fact that it is straight and not round or arced, make me think it is a camera rather than lens gremlin.

The rear element on the fast f/2.8 lens is probably pretty large, and that large opening is letting light bounce around inside your sensor box. The lens is designed to cover a full frame of film, or at least a full-frame sensor. Not all the light that goes through a lens ends up on the sensor - some bleeds off the edge (unsensored), and some even bounces around the areas that film wouldn't even get. The image projected by the lens is, for the most part, round. It may be masked by a frame at the back of the lens, baffled by baffles, or absorbed by black paint or flock inside the mirror box. I bet some of that non-image forming light is hitting something inside the camera, near one side of the sensor, and reflecting onto the sensor.

If the rear elements of the lens move during zooming or focusing, you would see differences in the light band resulting from those moves. Shooting at different apertures might make a difference, but maybe not. Even when you shoot at f22, light is going in the entire front element, and exiting out the entire rear element (not just a tiny center portion of it). The aperture blades are near the optical center of the lens, like the pinch in an hour glass. The ends of the hour glass get sand in them, no matter how tiny the aperture is.

I wonder what it looks like inside your camera's mirror box, or around your sensor.

Maybe a shutter curtain is hanging up, and the edge of it is reflecting some light in. If it was caused by the shutter during travel, you would see variations of the band by doing a bracket of equivalent exposures - raise the shutter speed while lowering the aperture and visa versa. It would be less prominent on a long exposure if it was related to shutter blade travel.

Try the lens on a different model camera.

Has the sensor been cleaned often or hard enough to rub some black paint off an edge somewhere?

[SSonnentag]

I have 50, 85, 135, 24-70, 17-40 and 100-400 lenses that all work perfectly with the camera, so I highly doubt it's the camera body, but I've been known to be wrong before. :) The affect shows up at various apertures, but only when the subject is light toward the top of the frame. If I shoot dark objects such as trees, indoors, etc the light band doesn't appear or isn't noticeable. Take a look at my latest Yellowstone album and go through the various EXIF values (available by clicking on the like to the right of each photo). See if you can figure out any correlations. I only took two lenses on the trip, the 17-40 and the 70-200.

I think I've only cleaned the sensor twice, both times very lightly with a sensor brush....compressed air over the brush and then single swipe across the sensor, repeat 2-3 times.

Thanks again for any input.

http://photos.sonnentag.net/album/408235#imageID=26030143

Shawn

[SSonnentag]

One other thing...I don't have another body to test the lens on, I wish I did. Maybe I can find someone locally with a camera.

[Tom V]

I have 50, 85, 135, 24-70, 17-40 and 100-400 lenses that all work perfectly with the camera, so I highly doubt it's the camera body, but I've been known to be wrong before. :) ... [clip]...

Shawn

I wonder if the rear element of your 70-200 is larger than the rear element of any of those other lenses. The wider the source of light into the sensor chamber - the rear element - the more possible light reflection angles there could be. Even the fastest aperture wide angle lenses will have a small rear element, while long and fast lenses have wide rear elements.

Your 50, 85, 135 lenses might have wide rear elements if they are very fast versions.

Since the band shows up more pronounced depending the subject matter brightness/contrast, it seems to me that it is a reflection of non-image forming light. The mystery is what is that light bouncing off of to make the band on the sensor. Internal guts of the lens? Internal guts of the camera?

Since the band is so straight, I tend to think that the reflector is close to a straight edge near the sensor. Things closer to the lens tend to be rounder.

It could be something in the lens related to IS or a possible framing mask.

It could be something on the underside of the mirror, that may not be raising enough to get entirely out of the way of the light pouring out of the lens's rear element.

It could be something surrounding the sensor, such as a frame, edge of the filter, etc.

Or I could be wrong.

[SSonnentag]

The 50mm is f1.4 and the 85 is f1.2.

[Tom V]

The 50mm is f1.4 and the 85 is f1.2.

Those are fast, and do have large rear elements.

I would think that if any of your lenses would give you trouble with internal reflections, it would be the awesome 85mm f1.2. The rear element looks like it is as big as the lens mount will allow. (Are you sure you never get the band when shooting with this lens?)

[SSonnentag]

I'll shoot some with the 85 after work today. The sun will still be up, so I can duplicate the light sky conditions with various f.stops and apertures.