[rollei_list] Re: couple of ignorant lens design questions.

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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