Hi all:
I was off at Stellafane (an amateur telescope maker's convention in
Springfield, VT) for the weekend, so am just catching up on mail. Joel
wrote:
>A while ago I asked whether MC filters might not be a solution to flare in
>SC lenses. Lee Hawkins responded without explanation that it would make
>flare worse. Since I am an erstwhile academic, I accept statements of
>authority readily. Taking the hint, I assumed that the MC coating passes
>more unflared light, and this aggregate of light causes the SC lens to go
>into a worse state of flare. Of course, as an academic the only thing I
>really know about light is that Book Three of _Paradise Lost_ begins "Hail,
>holy light, offspring of heaven first-born." A nice definition of "Zuiko,"
>but I need a physicist!
>
>My attempt to explain this to myself takes as a given a state or situation
>in which a MC lens would not flare "*because* it is MC but a SC lens would
>flare because it *is* SC. But SC lenses most of the time are not in a
>state of flare. Would an MC filter *induce* flare or just exacerbate it
>when flare going to happen anyway?
Some comments:
1) Any filter will pass less light than a filterless lens, MC or
SC.
2) Adding an MC filter to an SC lens introduces one more element
in the flare equation. The MC filter will pass perhaps
98-99 0f the incident light, but the SC element behind it
will reflect at least 2-3%, which will the be reflected again
off the back side of the MC filter.
3) If the filter is used in a situation when the SC lens is
is not in a flare condition, it certainly won't cause
flare. MC filters can't "make" extra light.
4) If the filter is used in a situation where the lens will
flare, the filter will certainly not reduce flare, and
might make it worse because of 2) above.
>
>Are there any circumstances in which a MC filter would be either neutral or
>perhaps an improvement over a conventional uncoated filter with an SC lens?
A multicoated filter is always preferred to an SC filter. It just can't
magically make a lens that will flare not flare.
Cheers,
--Lee
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|