I recently got a new 7D and was experimenting with different lenses and high speed sync on the flash. I noticed that any picture taken with my 200mm lens looked a bit blurred, but the pictures from the 24 to 70 were pin sharp. Initially I came to the conclusion that I just couldn't hand hold with the 200mm.....old age!!. Then I tried 1/3200 on flash and the images were still blurred. after a lot of experimentation using a tripod.I traced the problem to the UV filter on the lens and realised it had been a recent purchase and I hadn't actually taken any pictures using the new filter.
The filter is a 7DayShop 'professional' grade filter. Optically it looks perfect and I use a similar filter on the 24-70 with no problems. I tried using a Hoya polarising filter and the image was pin sharp. I tried the filter from the 24-70 (also 7 day shop)... image was pin sharp. I tried manual focus using live view and it was a lot better, but still not perfect, which tends to suggest it is the optical quality, however when I use auto focus, the blurring is so bad that is cannot simply be due to the optical quality of the filter otherwise it would be obvious. Everything was repeatable using my 40D, so it's not camera dependent.
The only thing I can think is that there is some curvature on the filter which is throwing the focus off and even though the filter looks perfect, it is screwing up the focus. I checked the curvature using a laser and it wasn't obviously off. I tried projecting a light through the filter over a long distance to see if I could form an image of the light, but both good and bad filter performed identically. I'm baffled, perhaps someone can come up with an explanation?
Sandy
The filter is a 7DayShop 'professional' grade filter. Optically it looks perfect and I use a similar filter on the 24-70 with no problems. I tried using a Hoya polarising filter and the image was pin sharp. I tried the filter from the 24-70 (also 7 day shop)... image was pin sharp. I tried manual focus using live view and it was a lot better, but still not perfect, which tends to suggest it is the optical quality, however when I use auto focus, the blurring is so bad that is cannot simply be due to the optical quality of the filter otherwise it would be obvious. Everything was repeatable using my 40D, so it's not camera dependent.
The only thing I can think is that there is some curvature on the filter which is throwing the focus off and even though the filter looks perfect, it is screwing up the focus. I checked the curvature using a laser and it wasn't obviously off. I tried projecting a light through the filter over a long distance to see if I could form an image of the light, but both good and bad filter performed identically. I'm baffled, perhaps someone can come up with an explanation?
Sandy