Condenser vs diffusion enlarger - film flatness requirements?

tomfrh · May 25, 2017

Is one more tolerant of non-flat negs than the other?

From what I hear diffusers are better at not showing dust, which makes me wonder they're also not as good at getting wonky film in focus?

Paul Howell · May 25, 2017

Light source will not improve an image from a warped negative, it has to do with the lens, saying that some say that a cold light is not as likely to cause a negative to buckle. I have both and have not any problems with negative buckling under the condenser head.

tomfrh · May 25, 2017

Thanks.

To clarify I'm talking about already warped film, eg film with some curl in it, mounted in glassless holder.

MattKing · May 25, 2017

tomfrh said:
Thanks.

To clarify I'm talking about already warped film, eg film with some curl in it, mounted in glassless holder.

The diffusion light source would make using a glass negative holder less of a challenge.
So if you have a choice of acquiring and using a glass negative holder for those of your negatives that are warped, then you may prefer using a diffusion source with that glass carrier.

tomfrh · May 25, 2017

I have glass holders however strongly prefer glassless.

MattKing · May 25, 2017

tomfrh said:
I have glass holders however strongly prefer glassless.

Me too!

Photo Engineer · May 25, 2017

AFAIK, the depth of field does not change with light source.

PE

tomfrh · May 26, 2017

If depth of field is the same how come dust etc isn't as much a problem with diffusers?

What's going on optically to obscure the dust with diffuser?

MattKing · May 26, 2017

The dust which creates the most in the way of problems is the dust pushed right up against the emulsion by the glass!
Followed up by the dust pushed right up against the substrate by the other piece of glass!
The accentuated appearance of dust is due to the nature of the light from the point or condenser source. Being "hard", it reveals the edge detail most clearly.
And dust has lots of edge detail.

tomfrh · May 26, 2017

i really need to get my head around the optics of condensers vs diffusers...
So confused right now.

AgX · May 26, 2017

tomfrh said:
If depth of field is the same how come dust etc. isn't as much a problem with diffusers?

It is not a matter of DOF but a matter of contrast.
See: Callier Effect

Doremus Scudder · May 26, 2017

tomfrh said:
i really need to get my head around the optics of condensers vs diffusers...
So confused right now.

Simple answer: with a condenser, the light is all coming from one direction, aligned by the condenser lenses. This creates a very sharp and large shadow of any dust particles. With a diffuse source, light rays are coming from all directions and, therefore, some sneak around the edges of dust particles. This creates a large penumbra to the dust-speck shadow, softening the edges and reducing the size of the darkest area.

Best,

Doremus

tomfrh · May 26, 2017

AgX said:
It is not a matter of DOF but a matter of contrast.
See: Callier Effect

Thanks, I will read up on this.

Doremus Scudder said:
Simple answer: with a condenser, the light is all coming from one direction, aligned by the condenser lenses. This creates a very sharp and large shadow of any dust particles. With a diffuse source, light rays are coming from all directions and, therefore, some sneak around the edges of dust particles. This creates a large penumbra to the dust-speck shadow, softening the edges and reducing the size of the darkest area.

Thanks, I think I understand that! Is this also why people say a condenser gives a much sharper image? Because you start with parallel rays which traces sharper sillhoettes of the grains which make up the photo?

Doremus Scudder · May 26, 2017

tomfrh said:
... Thanks, I think I understand that! Is this also why people say a condenser gives a much sharper image? Because you start with parallel rays which traces sharper silhouettes of the grains which make up the photo?

Prints made with condensers are not inherently sharper than those made with diffusion light sources. The negative is focused on by the lens and projected onto the paper in both cases; no difference there. What is different is the contrast. Collimated light from condensers results in more scattering away from the direction of the lens when the light hits the silver grains. With diffused sources, light is coming from many directions and the scattering effect is less. Result; more contrast from condensers.

See here about the Callier effect: https://en.wikipedia.org/wiki/Callier_effect

As far as depth of focus at the negative goes: this is a property of the lens and the chosen aperture and has nothing to do with the light source (would a cloudy day have a different depth of field than a sunny one?) DoF is relatively shallow at the negative, which is why curled negatives can often cause problems. Stopping down helps a little, but if you stop the lens too far past the "sweet spot" of two stops from wide open, you risk degrading the image due to diffraction and lens aberrations. A glass negative carrier comes in handy for problem negatives. However, if your glassless carrier holds the negatives flat (and popping is not a problem), then that makes things easier in terms of dust. I use both glass and glassless carriers depending on the negative and the enlarger I'm using (condensers = more heat at the negative = more chance of popping).

Best,

Doremus

Ronald Moravec · Jun 24, 2017

Condensers give more contrast in shadows, Diffusion gives more in highlights. Small and you have to perfect prints side by side to see it and the neg has to be processed to higher contrast for the diffusion so #2 paper can be used in both. You can not use the same neg in both because the curve of the different papers , 2 & 3, change results.

I have a nice neg that got a scratch. It shows on Leitz Focomat sharply and Leica V35 not at all. But diffusion has little to no effect on dust.

Omega enlargers have heat absorbing glass that helps. But no glassless carriers hold the neg flat hot or cold. Top glass helps significantly, two sides resolve the issue perfectly. There is no other way to get corner to corner sharp as possible.

Leigh B · Jun 24, 2017

tomfrh said:
If depth of field is the same how come dust etc isn't as much a problem with diffusers?
What's going on optically to obscure the dust with diffuser?

Incident light in a diffusion enlarger comes from many different directions.
Only the light from a particular direction is obscured by the dust.

Light in a condenser enlarger is collimated, incident from a single direction.
A shadow is a shadow.

- Leigh

klownshed · Jun 24, 2017

Condensers can produce images that appear sharper as they accentuate edge contrast (and therefore perceived sharpness or accutance) for the reasons already mentioned above.

This is also why dust and scratches are more pronounced with a condenser. The scattering of light from a diffuser source softens the edge contrast compared to the condenser light source.

Disclaimer. I'm tired! I have 3 kids (each of which has in turn halved my IQ) and the youngest is 7 weeks old so I get too little sleep. This results in my addled brain getting confused and results in me being able to make statements which are the polar opposite to what I already know to be true (and fully understood before child 1). Apologies if I've done it again! ;-)

cliveh · Jun 24, 2017

Photo Engineer said:
AFAIK, the depth of field does not change with light source.

PE

Don't you mean depth of focus?

RalphLambrecht · Jun 24, 2017

tomfrh said:
Is one more tolerant of non-flat negs than the other?

From what I hear diffusers are better at not showing dust, which makes me wonder they're also not as good at getting wonky film in focus?

as long as the neg is sandwiched between glass, the light source is of no consequence

etn · Jun 24, 2017

Doremus Scudder said:
Simple answer: with a condenser, the light is all coming from one direction, aligned by the condenser lenses. This creates a very sharp and large shadow of any dust particles. With a diffuse source, light rays are coming from all directions and, therefore, some sneak around the edges of dust particles. This creates a large penumbra to the dust-speck shadow, softening the edges and reducing the size of the darkest area.

Best,

Doremus

Out of topic here, but if you also shoot digital, you probably noticed that dust on the sensor is more visible when the lens is stopped down. Same effect as described here.

etn · Jun 24, 2017

tomfrh said:
I have glass holders however strongly prefer glassless.

How do you manage film flatness? At some point I moved to glass holders, as my films were generally too warped for best results in glassless mounts.

Gerald C Koch · Jun 24, 2017

In his book Controls In Black And White Photography Dr Richard J Henry determined that contrary to common opinion there is no difference between properly made prints using either type of enlarger.

tomfrh · Jun 24, 2017

etn said:
How do you manage film flatness? At some point I moved to glass holders, as my films were generally too warped for best results in glassless mounts.

I try to start with flat negs, and I use mount which clamps the neg fairly hard along all edges. I use glassless slide mounts sometimes. There's still some bend though of course.

I main print 35mm and 645.

tomfrh · Jun 24, 2017

As follow up to this thread, I am using a diffuser now. I prefer it. Tidies up scratches/defects, and the color controls are handy.

I understand now the concept of the grains being illuminated by diffuse vs collimanted light, and see my original question was based on faulty assumptions that scratch hiding ability was somehow related to depth of field.

Photo Engineer · Jun 24, 2017

cliveh said:
Don't you mean depth of focus?

Probably.

Condenser vs diffusion enlarger - film flatness requirements?

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