Re: Double vs Single Condenser Lens

Richard Knoppow wrote:
"A R" <news*NOSPAM*@ihateboscastle2.demon.co.uk> wrote in message 1ifcdoj.2mqs62hnrnbdN%news*NOSPAM*@ihateboscastle2.demon.co.uk">news:1ifcdoj.2mqs62hnrnbdN%news*NOSPAM*@ihateboscastle2.demon.co.uk...
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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