Optical Weirdness

Some of the photos I took recently have an arc of lightness through them and I'm trying to figure out what is causing this. It is always in the same place. You can see it pointed out in the #1 pic here. The #2 pic doesn’t have the arc. Both pics were shot with the Canon 1DmkIIn/70-200f2.8L/1.4XL teleconverter @ f5.6 and 280mm. #1 had a 1/2500th shutter speed and #2 had a 1/400th. For #1 I had the sun at my back—I don’t think this could be flare, # 2 was shot much more towards the sun. I got the effect in numerous images, but it was most noticeable on shots with sky. It should also be noted that the effect rotates with the camera. A Vertical shot is attached as image #3 which was shot at f5.6, 155mm, 1/1600 with the sun to my back. Also, this proves that the effect is not focal length dependant. Thankfully, most of the images with this weirdness were pretty dull and boring but I’d like to figure out what went wrong before I actually get a good shoot. Any ideas??? Thanks!

-Alan

I've seen a teleconverter do something similar to this. The right combo of light, ISO, humidity etc. I think I first noticed it with the MkII (not n, but with a ds also).

I'll look thorugh some notes and see if I can find an image similar. I have seen TC multiply the 'reflection effect' of the sensor (even with lens coatings and the Canon TC's) to the point that it is annoying. Even with the sun to your back or a well hooded lens, on a bright day a thermal or humidity layer in the sky can reflect very similarly to direct sunlight.

Take a spot meter on a 'severe clear' day and check out for hotspots the sky. It is an interesting that some days there will be 3-10 degrees of sky arc in various places that can be a full stop or more brighter. But we don't see it. Camera does.

Hope this might point you in the right direction. Oh, and high ISO sometimes will do a trick or two, that one I haven't figured out. Probably has to do with some piece of noise control in the camera.

Were you shooting RAW or JPEGS? Shouldn't make a difference . . .

Shooting all RAW... I'm pretty sure it's the TC too, just wanted to bounce it off of some people and see what they think. I did have a hood on the lens, it's just perplexing that I had the problem facing away from the sun and not on the backlit shots... I guess this gives me more reason to get the 300 f2.8 L huh? :)