Are the black blobs on these pictures indicative of shutter failure?

Question

Are the black blobs on these pictures indicative of shutter failure on my Canon 5D (mark I)?

They started to show suddenly, ie. I saw nothing resembling that before on my pictures and starting from certain photo they are always there. They are only visible on photos taken at shutter speeds faster than 1/250 sec: these photos (of the sky) were taken at increasingly higher shutter speeds: at 1/250 it’s still ok, at 1/320 grey shadow starts to appear in the lower right corner, turning into black blob at around 1/640 and reaching almost maximum at 1/2500. Please, ignore the upper right corner, it was difficult to get a clear shot of the sky in the middle of the city and the slight shadow there might be a nearby tree.

Other photos taken at different apertures and with different lenses (or without a lens), with a mirror lockup, with synchronization on 1st or 2nd curtain look more or less the same.

I raised the mirror up (using 'Clean sensor' option) and there's nothing obviously wrong, ie. no parts of the shutter are sticking out and sensor looks reasonably clear.

Any ideas what this could be? And if so, is there anything reasonably simple that could be done "in the field"? (I'm NOT a photo technician!): I still have around one month of travelling in Laos/Thailand to do and probably will only be able to send 5D for professional repair once I' back in Europe.

Answer 1

Yes, I am almost absolutely certain that this is shutter failure. The reasons are as follows:

1. The phenomenon is dependent on shutter speed.
2. It is not observable below the x-sync speed.
3. The phenomenon gets worse the faster the shutter speed is set.
4. The light blockage is independent of lens--indeed, independent of the presence of any lens.
5. The reflex mirror is not involved.

It should not be assumed that shutter failure always manifests as horizontal bands of uneven exposure: the curtain leaves can become bent or misaligned, or they can stick in a way that causes light blockage in an unexpected way. The curtains move so fast that it can be impossible to detect a problem through mere visual inspection.

In any case, any problems with the shutter will involve the replacement of the entire shutter assembly, and in some cases, a replacement mirror box.

Answer 2

It initially looked to my eye more like it might be something else in the mirror box that is not moving out of the way fast enough, most likely a part of the secondary mirror assembly. The secondary mirror sits behind the main reflex mirror and reflects light into the AF sensor. But if you are experiencing this problem even when using mirror lockup then that possibility is eliminated.

At slower shutter speeds the offending part is clear of the field of view for most of the exposure time. At speeds above flash sync speed the transit time of the shutter curtains is pretty much the same, the only difference between 1/500 and 1/8000 is the width of the slit between the first and second curtain - when things are working as they should. The shape of your "blob" looks a lot like one of the arms that connects the drive mechanism of the shutter to the pieces of each curtain. It seems to me that something in the shutter mechanism may be dragging just a bit, perhaps a part of the first curtain.

Here's a link to a high frame rate video of a Canon 5D Mark II shutter in action.

Answer 3

I can't find details about the sensor read out on the 5D, but the only way this could be a shutter problem is if the sensor read out is top to bottom then left to right (which is not the way it is generally done on newer models, but I'm not sure how they may have done it on older models.) Even then, it would seem a bit odd that it spends so long with the bottom of the image blocked. If the shutter was lagging, I would expect it to continue to lessen the amount of black at the end.

My best guess (though it is still a guess) is that this is not shutter related. At least not in the traditional shutter lag way. A more drastic shutter failure could still be to blame potentially, but it would be an unusual mode of failure.

Best bet would probably be to see if you can send the images to Canon and get feedback from their repair people. They would be far more knowledgeable about the rarer failure modes.