The exposures start to appear uneven at 1/200, 1/500, & 1/1000. At 1/200 the uneven exposure is slightly noticeable. But, at 1/500 & 1/1000 the frame is exposed only on one side. I did the "television test" for 1/100 through 1/1000 and the "sliver of light" looks even for each speed. I was curious if there might be another quick test to reveal the actual culprit here. Thanks in advance.