[rollei_list] Re: couple of ignorant lens design questions.
- From: Aaron Reece <oboeaaron@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 10 May 2007 13:46:03 -0400
On May 10, 2007, at 1:05 PM, dpurdy@xxxxxxxxxxxxxxx wrote:
#1 Why is it not possible to add coatings to your lens by adding a
coated
filter? Or why can't Rollei come out with a plain glass with HFT
coatings
on it that you can put on your older lenses? I know that at least
some
filters are coated. Does it have the affect of adding a coating to an
uncoated lens if you use one? My guess is that you can't put
mulitple
coatings on a single surface of glass so you have to coat multiple
elements with different coatings to get all the HFT.
No. I will leave the technical explication to others more qualified
in this field, but no, it won't work. Flare results from reflections
between the air-glass surfaces in the lens, which will not be reduced
by the filter. The additional air-glass surfaces on the filter will
even add a slight amount of flare. GIGO.
A music professor recently asked me if recording a scratchy old LP
onto a recordable CD would take away all the surface noise and pops
and make it sound like a commercial CD.
Stupid question #2 Is contrast always good in lens performance?
Or is
there some way of designing shadow detail into a lens? Or if one lens
gets better shadow detail than another lens of the same focal
length and
speed and size then the one with more shadow detail is really just
getting
a boost from flare. And that extra shadow detail should always be
of low
contrast.
In some situations flare can act to boost shadow density in a manner
similar to pre-exposure, but it is more difficult to predict and
control.
Stupid question #3. How much of the affect of super multiple
coatings can
be duplicated by just using a good quality polarizing filter?
None; they are completely different effects. The polarizing filter
will only reduce the light that is already polarized, which may not
be the light causing the troublesome flare in the first place. If you
want to minimize flare, the best advice is to use a good quality lens
hood which extends forward far enough to block any light from outside
the image area, and try to exclude any strong light sources from the
frame. The resulting pictures may be very boring but there won't be
much flare.
thanks.
No, thank *you* for the opportunity to procrastinate even further on
my paper which is due tomorrow.
Best regards,
Aaron
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