Dealing with fall-off?

[Ian Leake]

I want to make some copy negatives by contact printing from the original 8x10 and 11x14 film negatives. I'm planning to use an old enlarger as the light source. Unfortunately with the enlarger head as high up the column as it will go, I get about 1 stop in fall-off between the centre of the film and the corners.

What is the best way to deal with this? I've never done much small format / enlarger printing so I don't know the tricks of the trade. Is this what 'edge burning' is all about?

Thanks in advance for your advice.

 

[RobC]

A centre filter would be the ideal solution for producing copy negs if you are contact printing on baseboard but if head is fully up then you would only be using central portion of projected light circle so I doubt fall off would be an issue at all unless you are making bigger negs in which case I think center filter would be a must have.

But won't you be making a postive and then a negative so that fall off cancels itself out through the process?

 

[wy2l]

Suggest you use what's available: Expose the contact print by turning on the room lights for a second.
If that's too much light, hang a single bulb above the contact print. Vary light bulb wattage, distance from the light bulb to the contact printer, and time of exposure as needed.

I have successfully used this technique in the past with fixed-contrast paper that did not require dodging or burn-in.

Improvise, adapt, overcome.

 

[Ian Leake]

Thanks both. I hadn't thought that the positive/negative would cancel out.

 

[Doremus Scudder]

With your enlarger head all the way up, and a suitable lens, there should not be so much fall off... Are you adjusting everything properly? Make sure your light source is even (condensers adjusted or diffused correctly). You should try to project a much larger circle than the size of the contact print you are trying to make and then use a negative carrier or mask to get it down to size. That way, you'll only be using the center of the projected image circle and light fall-off should be minimal.

If you still have significant fall-off, then there are a couple of approaches. If you're making a negative and then contact printing that again with the same set-up, then the fall-off will cancel itself out for the most part, as Rob mentions above. You'll have to try and see if the results are acceptable.

I shoot a lot of black-and-white negative film with wide-angle lenses and no center filter. I compensate for this when printing by doing what I call a "center burn." I have a card with a lens-size hole in it. I start the exposure with the card almost resting on the paper and with the hole centered over wherever the optical center of the image is (with view-camera movements it isn't always the center). I then lift the card slowly toward the enlarger lens over a few seconds till the hole is close to the lens and the entire sheet of paper is being illuminated. I then whisk the card out of the way. For various lenses with various amounts of fall-off, I come up with a percentage of the total base exposure time for the "center burn." I've also learned that the movement of the card has to start fast then slow down. I've had good results with this technique. I do this at the beginning of the exposure, but it would work just fine at the end as well.

If you have a filter drawer above the negative stage on your enlarger, then you could experiment with diffusing materials either stacked in concentric circles or drawn on with soft pencil, etc. effectively making your own center filter for the light source. Many use a similar technique above the negative to "dodge" shadows (masking).

FWIW, edge burning does the opposite of what you want to do. You need an "edge dodge," which is essentially what my "center burn" does.

Best,

Doremus

 

[Ian Leake]

Thanks Doremus, that was very helpful.

 

[ic-racer]

I want to make some copy negatives by contact printing from the original 8x10 and 11x14 film negatives. I'm planning to use an old enlarger as the light source. Unfortunately with the enlarger head as high up the column as it will go, I get about 1 stop in fall-off between the centre of the film and the corners.

What is the best way to deal with this? I've never done much small format / enlarger printing so I don't know the tricks of the trade. Is this what 'edge burning' is all about?

Thanks in advance for your advice.

If you have the lens on the enlarger (you should) then you need to stop down to f8 or so. Nearly all enlarger lenses have a hotsopt when wide open. If it is a condenser enlarger, make sure the condensers match the lens and the lens is focused on a negative in the negative stage, then remove the negative. The lens and condensers have to be a certain distance apart for even illumination.
Hope that helps.

 

[Ian Leake]

Thanks, that's also very helpful. I had the lens wide open to get the most light out. I'll try with it stopped down and focuses.

Thanks again!

 

[Jim Jones]

Suggest you use what's available: Expose the contact print by turning on the room lights for a second.
If that's too much light, hang a single bulb above the contact print. Vary light bulb wattage, distance from the light bulb to the contact printer, and time of exposure as needed.

I have successfully used this technique in the past with fixed-contrast paper that did not require dodging or burn-in.

Improvise, adapt, overcome.

This is much better than bumbling around with an enlarger. If this method was good enough for Edward Weston's prints, it is good enough for our interpositives. You do need to improvise a contact printer, but solutions to this have been offered here frequently.

To make copy negatives, you'll have to copy your diapositive again unless you can find some reversal film.

 

[DREW WILEY]

If you don't want to habitually edge burn, you'd have to custom grind a diffuser below the light source which equalizes the illumination center
to edge. A different one would have to be made for each respective enlarging lens you intend to use. Center filters over the lens are not
practical because usually the lens has to be stopped down to around f/22 for them to work as intended - fine for general shooting but not
for enlargement where much wider lens opening are routine.