Double vs Single Condenser Lens

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!


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I need more time!

On Apr 13, 4:55*pm, (A R)
wrote:
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!

Broadly, I think the objective of a condenser system is to (i) as you
said evenly illuminate the negative, (ii) pass as much of the light
through the negative as is practical and (iii) pass it through as
nearly colimated as possible.

With one lens, if the convex side is toward the negative, objective
(i) would likely be fulfilled. I have doubts about (ii) and (iii).

Peter wrote:

On Apr 13, 4:55 pm, (A R)
wrote:

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?

I need more time!

Broadly, I think the objective of a condenser system is to (i) as you
said evenly illuminate the negative, (ii) pass as much of the light
through the negative as is practical and (iii) pass it through as
nearly colimated as possible.

With one lens, if the convex side is toward the negative, objective
(i) would likely be fulfilled. I have doubts about (ii) and (iii).


But what if the lens was turned flat side towards the negative?


--

I need more time!

On Apr 13, 7:49*pm, (A R)
wrote:
Peter wrote:
On Apr 13, 4:55 pm, (A R)
wrote:
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?
I need more time!

Broadly, I think the objective of a condenser system is to (i) as you
said evenly illuminate the negative, (ii) pass as much of the light
through the negative as is practical and (iii) pass it through as
nearly colimated as possible.

With one lens, if the convex side is toward the negative, objective
(i) would likely be fulfilled. *I have doubts about (ii) and (iii).

But what if the lens was turned flat side towards the negative?

--

I need more time!- Hide quoted text -

- Show quoted text -

It should be evident if you try it.

The extent of the effect depends on the lens and the distance from the
light source and the film. For a distant light source it should the
lens should cause the light to converge. As you bring the light
closer to the lens it willl converge to a lesser degree. Measuring
the focal length and doing a bit of ray tracing with paper and pencil
should clarify the behaviour.

Since you have the lens, you can just try it (small light, dark room
and white piece of paper as a target).

"A R" wrote in
message
news:1ifcdoj.2mqs62hnrnbdN%news*NOSPAM*@ihatebosca stle2.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.


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Richard Knoppow
Los Angeles, CA, USA