Drop in 52mm Filter for f/2.8 300mm - Screw vs Gel II

BigBen08 wrote:

I also have the 300 f2.8 IS II. Because I shoot aircraft at slow shutter speeds to capture prop blur, I needed to add a ND filter. At first I used the gel filter holder that comes with the lens. Later, I bought the screw filter. With the screw filter holder I use the Heliopan Digital ES 52 ND filter. With either filter holder used, I cannot see any optical difference or degradation. None at all.

However...about 4 or 5 years ago, on another photography web site, an aviation shooter advised me against using the screw-in filter holder. He owned the 300 f2.8 also. He claimed the screw-in holder diminished IQ in some manner. It has been so long ago that I can't remember the details. But when I use the screw-in holder, I experience no problems.

MY thought is that the lens was designed with specific tolerances between the sensor, first lens and then the lens and their elements.   I don't know how smart it is to change what Canon designed as optimal.  There are clear differences between the Screw in and Gel filter.  Both in size and distances from the sensor.

I'd like to read what the person stated about IQ and loss of IQ using the Screw Filter to see if it warrants changing back.  I say this as I would have to buy another. My original that came with the lens has a frozen latch.  I think constant shooting sea/ocean sports has the latch all gummed up and it won't stay closed. Can't risk water getting in there!!!

Thank you