B+W Filter question

[Richard_Miami]

I am going to order a B+W MRC circ polarizer.. but when reading the description of the Kaesemann 77mm.. I came across this paragraph:

"Another advantage of the new F-Pro filter mount is its modified retaining ring, which is no longer threaded in from the front, but holds the filter glass in place from the back. This prevents the retaining ring from being accidentally loosened during the removal of an additional filter or a lens hood that has been screwed in too tightly.

For the life of me I can't picture in my head what they are trying to say? I believe all screw in filters are threaded frm the back of the filter - allowing them to screw into the front of the lens. Is that not the case with this filter?? Does this take a regular lens cap? (It is NOT the slim version). Am I totally wrong about how to mount this lens?

or.. is it because I am up at 6 am and researching polarizers on the web? :rolleyes:

Thanks to anyone who can translate that paragraph for me.

[Jon]

What they're saying is that the retaining ring which holds the glass into the filter is threaded from the back, not the front. Filter retaining rings have a lip against which the glass rests. It's held in place by a ring (screw-in for better brands, snap-in for cheap ones) which could conceivably work loose. In this case, they're saying that even if the ring comes loose, the glass won't fall out since the ring will be between the lens and the filter frame. It has nothing to do with how the filter mounts. I don't have Kaesemann filters but my regular B+W CPs all have front threads while the slim one doesn't.

[Richard_Miami]

Thank you very much Jon. You have explained it very well.

The price difference for the Kaesemann is very small. Given some of the extreme conditions I encounter down here and shooting in the tropics, I thought I would go the extra little bit. Any thoughts?

[Jon]

I've never seen a polarizer that delaminated or got moisture inside, but I don't go out in extremely humid conditions with them. If you don't mind paying the difference then I'd say to go for it.

[rwong2k]

I've owned both filters. I've notived the 'Kaesemann' colours to be slightly different (stronger contrast). I'll have to do a better comparison (that's just from memory) but I believe it's only $10 ~ $15 difference so I went with the more $$ (after researching, that
the Kaesemann one is 'sealed'

[Richard_Miami]

Jon -- or anyone really - do you think this CP will vignette on a wide open 17-70mm on a 5D?? or should I go to the slim version?? Thanks in advance.
-- Richard

[Jon]

A 17-70 without filters will vignette on a 5D. It's designed for the smaller sensors of the 30D and Digital Rebel family.

[Richard_Miami]

Sorry Jon.. my bad.. its a 17-40mm L Darn fingers can't type any more!

I have not used the lens a whole lot, but I have used it wide open on my 5D and have not noticed any vignetting... I will take a few test shots tonight.