Richard Knoppow wrote:
> "A R" <news*NOSPAM*@[EMAIL PROTECTED]
> wrote in
> message
> news:1ifcdoj.2mqs62hnrnbdN%news*NOSPAM*@[EMAIL PROTECTED]
>> I've started taking 6x6 photos. Instead of buying a new
>> enlarger, I'm
>> adapting my trustworthy MPP condenser to take 6x6 negs.
>> This has
>> involved fabricating a new lens board, fabricating a new
>> neg holder,
>> purchasing a new enlarging lens and replacing the
>> condenser.
>>
>> Now, I have a pair of spherical condenser lenses but
>> unfortunately I
>> have no cell to mount them in. A single lens on its own
>> fits snuggly in
>> the enlarger head and seems (by eyeball) to give a uniform
>> illumination
>> across the easel.
>>
>> I know some enlargers use single apsherical lenses but
>> what
>> advantage/disadvantage do I have using a single spherical
>> lens?
>>
>> Come to think of it, I'm not to sure why condenser lenses
>> come in pairs!
>>
>>
>> --
>>
>> I need more time!
>
> Symmetry corrects coma, lateral color, and geometric
> distortion. The improved coma and distortion probably
> results in better uniformity of illumimation and lateral
> color will reduce color fringing from the condenser system.
> The symmetry does not correct spherical aberration but the
> plano-convex shape of the condenser reduces it. Actually,
> the spherical of the two halves of a symmetrical lens add.
> Some enlargers use only a single condenser but, since
> most condenser enlargers also use light sourses of
> relatively large area and diffuse surface the aberrations of
> the condenser have less effect.
> Ideally the condenser should focus the source on the
> entrance pupil of the enlarging lens but the focus is not
> too critical where a large lamp with a diffuse surface is
> used.
>
>
Wooops..... my reply was based on dimly remembered things (like symmetry
canceling stuff, but not spherical I guess. Please disregard the wrong
info in my previous post!
gr
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