Condenser vs diffusion enlarger - film flatness requirements?

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.

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Managing film flatness starts with film storage. There are advantages in a film file system that stores all film with the emulsions facing only one direction. However, this does not control the tendency of film to curl. A system where the negatives are alternately stored face to face and back to back under modest pressure counters film curl. The long discontinued 35mm negative wallets from Print File, Inc. in Orlando FL do this to such a degree that the negative strips tend to slip out of the wallets if one is not careful. Perhaps similar negative wallets are available somewhere.

Heat in the enlarger can cause negatives to pop out of focus. My former Omega B22 had a small lamp housing that could become quite hot in long printing sessions. To counter negative popping I left the lamp on. When not actually exposing the print, reducing the voltage with a variable transformer prolonged lamp life.

tomfrh said:

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

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So, it is actually a geometry problem. One way to think about the difference between a condenser and a diffuser light source is as the perceived size of the light source that any single point on the negative 'sees'.

From a condenser light source each point on the negative sees a very small light source, much the same as we see from an incandescent bulb across the room. From a diffuser it's more like seeing a large fluorescent fixture from across the room.

When you look across the room you can hold up a single finger a foot from your face and that finger will block all the light coming straight to one of your eyes directly from that incandescent source, that covered eye will be completely in shadow, you can't keep the finger at the same distance from your eye and do the same for the fluorescent source.

Similarly a speck of dust on top of the negative illuminated buy a condenser source casts a sharp shadow on the emulsion, the shadow of that dust particle on the negative will look like a sharp black area to the lens below. With a diffuser source the shadow of the dust particle on the negative is diffuse rather than sharp because the light is coming from many directions rather than 'just one', the lens below sees a more evenly lit negative.

cliveh said:

Don't you mean depth of focus?

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I thought you might have picked up on my answer.

There is depth of field (depth of image being taken which is in focus) and depth of focus (depth of image in focus to be projected on the film or paper). In this case, we are talking about the image being taken which might have some curvature. This is depth of field. The depth of focus is what is projected on the paper or film.

At least, that is what I have been taught.

PE

Photo Engineer said:

I thought you might have picked up on my answer.

There is depth of field (depth of image being taken which is in focus) and depth of focus (depth of image in focus to be projected on the film or paper). In this case, we are talking about the image being taken which might have some curvature. This is depth of field. The depth of focus is what is projected on the paper or film.

At least, that is what I have been taught.

PE

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I thought we were talking about the image being printed, but I may have miss-understood the OP.

Non-flat negatives, and that is what I said what I did.

PE

I do not see much need for rocket science here. If the negative is not flat enough one must do something to get a good print.

1. Can you get it flat enough without a glass negative holder?
2. If not, will a glass negative holder work without newton rings?
3. If not, get a glass negative holder with appropriate newton ring glass.

Gerald C Koch said:

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.

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I believe that's also what Ctein has said in the past.