Archived posting to the Leica Users Group, 2000/02/15
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on 15/2/00 3:41 pm, Julian Thomas at mimesis@btinternet.com wrote:
>
>> Moreover they are on the rear element, which I feel slightly more
>> comfortable about than the front. Less blazing light flying about.
>> --
> I always thought that the rear element was more important than the front -
> don't know why.
> Julian
>
Since a lens is a symmetrical device (ie same resolution no matter which way
the light goes) they should be of equivalent importance, optically, I think.
However, my point was that the front element, even with a good hood, is
still subject to off-axis illumination which could theoretically cause
flare, or at least lower contrast, if it fell on cleaning marks which
scattered it into the lens. At least the rear element should only be
transmitting on-axis light.
My experience with even quite heavily marked glass is that the effects are
hard to see, certainly compared with fungus or fog.
- --
John Brownlow
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