I am making a front filter for my 400mm Takumar. You might wonder why I'm doing this considering there is a threaded area in the rear of the lens for a 77mm filter. Using the rear filter, especially a polarizer, is a real problem. The lens must have the body removed to be able to turn the filter to check the amount of polarization needed. Rear filters also change the focus points so that the DOF scale on the lens barrel becomes almost useless. So, I'm building a 115mm linear polarizer to fit over the lens hood just like the lens cap does. I could not find any companies that would sell me any unmounted, glass covered, polarizing film, so I bought some polarizing film without the glass. I bought a 4 inch black plastic pipe adapter and cut it to size. I will mount the film between two rings of this modified plastic pipe. I'm not done with this project but will inform as to its success when complete. SR

-- Steve Rasmussen (srasmuss@flash.net), September 23, 2000

Answers

Roy, the difference in image quality between using a front filter VS a rear one is vey slight. It is proven optically that a plane parallel plate in the optical path will introduce aberrations. Why a front filter would degrade the image on a 300mm ED telephoto does not make sense unless the flat surfaces are not flat. The reason I'm building this filter is for ease of use when using a polarizer. SR

-- Steve Rasmussen (srasmuss@flash.net), October 01, 2000.

After using my newly made polarizer and shooting many test shots, I have made a conclusion about using it. It seems that the plastic coated polarizing film that I used is not of good optical quality. The resulting images are soft and similar to using a soft filter. In fact, it is better suited for portrait work when turned to the non polarized position. Anyway, it was a good idea that just didn't pan out. I will go back to using the rear filter. SR

-- Steve Rasmussen (srasmuss@flash.net), October 21, 2000.

I have used the 400mm EDIF with the 67mm rear filter and it appears to have no effect on image quality. It has been my experience with long lenses, e.g. the 300mm EDIF F.4 Nikor, that a front filter will seriously degrade image quality. Please advise if you find the image quality degraded by this setup.

-- Roy L. Jacobs (rljacobs@pipeline.com), October 01, 2000.