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[OM] Re: E-1 bits & parts advice

Subject: [OM] Re: E-1 bits & parts advice
From: Moose <olymoose@xxxxxxxxx>
Date: Sat, 05 Jan 2008 01:58:48 -0800
Philippe Dambournet wrote:
> <snip>
>
> Thanks for the filter tip. Anything good enough not to degrade the 
> performance of the 14-54 is perfect.
Philippe Dambournet wrote:
> <snip>
>
> I guess B&Ws are the filters that do not degrade optical performance... ouch.
>   
You appear to be operating under a misunderstanding. All filters degrade 
the image. Most will not do so to an extent that you will notice, but 
the simple act of passing the light through two parallel, flat, 
air/glass surfaces has an optical effect, separate from the issue of 
coatings. You are in effect adding an unnecessary element to the lens so 
much time and effort was spent in designing.

If you find it necessary to have a filter on the lens, there is no 
excuse with digital to avoid taking identical shots with and without the 
filter at a few different focal lengths and apertures and checking them 
carefully against each other. Some filters have defects that may 
seriously degrade image quality but are not noticeable to the eye. 
According to Gary Reese's tests, this can happen even with the top brands.

A few years ago, we had a fellow on the list who whined on and on about 
the poor image quality of one of his Zuiko lenses. We proposed all sorts 
of possibilities until one day the light dawned and I suggested if he 
had a filter on it (which he had never mentioned) that he should remove 
it. Problem solved.

With digital, the plot thickens. The front surfaces of sensors and the 
filters in front of them are very flat and shiny, much more so than 
film. This occasionally causes problems with lenses designed for film 
with element surfaces that are relatively flat. Lenses designed for 
digital try to avoid that and use even stronger AR coatings than before. 
However, a filter has two perfectly flat surfaces, and even with those 
specially coated for digital, there are occasional odd effects in night 
shots. I've seen a few examples where weird looking things in images 
turn out to be a result of using filters.

So sure, if you are clumsy or paranoid, use a filter. But test it when 
you get it and be aware it can cause odd image effects.

Moose

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