In article <4ft646$av8@nntpb.cb.att.com>, rma@clockwise.mh.att.com says...
>In article <3122136E.499E@mtgbcs.mt.att.com>,
>d.galensky wrote:
>>> Should I buy one for protection? As the 39mm L37C is included,
>>> should I take the 39mm one away if I use the 82mm UV front filter?
>>no no no no!!!! the filter in the drawer is 'designed into'
>>the optical path and must remain in place at all times.

>While you are quite correct, I did some tests a while ago with a rear
>filter in and out of a Canon lens. Suprisingly little difference, in
>fact hard to see any difference at all. It does cause a focus shift,
>but just refocus. I can't see any reason to remove the rear filter,
>but, for example, should you drop and break it, don't pack up and go >home!

I found the same thing with a Nikkor 400mm f3.5. While checking the effects of using/not using the front filter, I did the same with the
rear filter -- no difference but the slight focus shift.
Hope This Helps