On Wednesday, March 12, 2003, at 03:34 PM, Moose wrote:
I just did a little measuring and research.
First, to whoever posted saying that Hoyas have brass threads, the
info I found says they are anodized aluminum. That's what a worn one I
have is.
I compared 2 49mm UV filters, Oly and Hoya:
Hoya Oly
Front thread 2mm 2
Shelf to hold glass from front 1 0.5 Glass
2 1.8
Glass to rear 1.7 1.4
Total 6.7 5.7
The Oly uses a shelf half as thick to hold in the front of the glass,
a thinner snap-in retention ring on the back and slightly thinner
glass to save 1mm of thickness. I suppose it may use a stronger mount
to maintain the same strength, shich may, slong with the thinner
glass, mean greater production cost. I don't have a Hoya thin filter,
but the spec says it is 3mm thick, whereas the Oly without the front
thread would be 3.7mm, so they do a little more "thinning" than on the
Oly.
Hoya does make what you want, filters using 1mm thick glass with front
threads and overall thickness of 3mm, but only in UV and 1A. They are
called Hoya Pro 1 and are SMC coated.
Just 'cause it was sitting here, I now know a B+W 72mm UV filter is
8.7mm thick.
Moose
Doesn't Oly primarily make the thin filters for the 21mm lens? Then
they have calculated how thick it should be to prevent vignetting
considering the relationship between the glass and the filter ring. So
I think the filter should be at least that thin, but probably only need
for that lens or any that they specific a thin filter for. I suppose
you could get ordinary filters and not worry about thickness so much if
you did the step up adaptor like Oly does for the 18mm.
Winsor Crosby
Long Beach, California, USA
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