Well, I guess if you want it done, you have to do it yourself, eh? While I do not have Lee filters, I do have a Cokin 2-stop grad ND filter and I wanted to see how much image degradation occurs by putting that piece of plastic in front of your lens.
Purpose: To evaluate how much image degradation occurs when using a cheap Cokin filter in front of a nice lens. Contrast can be evaluated within the constraints of the subject matter. Flare is not evaluated at all.
Setup: I took a drug insert which has nice small writing and taped it to the wall. I used a tripod, wireless remote, and flash with my 180mm f/3.5L Macro. The working distance was not at the extreme of the lens, but was somewhere close to it.
Method: I took 3 shots using the filter and 3 shots without it, refocusing with the autofocus each time. Instead of using the ND portion of the filter, I merely shot through the clear portion so as to evaluate the plastic alone. Shooting through the ND portion would be a good second experiment. The pictures were shot in RAW, simply converted, and then sharpened with one pass of 300/0.3/2 using USM.
The shot:
[thumb]606463[/thumb]
The results (100% crops):
With Cokin filter:
[thumb]606460[/thumb]
Without Cokin filter:
[thumb]606461[/thumb]
Conclusion:
It appears to me that some image degradation occurs, but the effect is small. However, if massive enlargements are required (say 30x40), it may be noticeable. That, however, is speculation. Contrast seems to be minimally affected. I do think that stacking filters would produce a poorer image, but I have not gotten in this habit as of yet (I will stack a Cokin on top of my polarizer though if I need extra ND stops).
Now, it would be nice if someone with Lee filters would do the same and see if using a Lee results in just as much degradation. Any volunteers?
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