Getting max contrast out of litho film without litho chemicals

[BetterSense]

I need to make some optical encoders for a robot. I plan to print out a pattern onto white paper with my inkjet printer, then shoot the pattern with my speed graphic and use litho film. The black areas should be as infrared-opaque as possible and the clear areas should be as infrared-trasparent as possible. I understand that for max contrast litho film is designed to be used with special developers, but all I have is Dektol, D23, HC110, Rodinal, and Arista II ortho litho film. Any suggestions on developing for maximum contrast with these chemicals?

 

[David William White]

Develop to completion, and you don't necessarily need to use litho film for this application. Think of the soundtrack coding on motion picture prints. Your application sounds similar.

 

[BetterSense]

It's very similar. I would rather use regular sheet film since the base is a lot thicker. However last time I tried using some Delta 100, the base fog in the clear areas was substantial, indicating that my black ink-on-paper wasn't quite pure black, and the density of the dark areas was not all that dense. I would like more overall contrast. I plan to meter the white paper with my spot meter, then increase exposure about 4 stops.

 

[richard ide]

A litho neg developed in lith developer should give you a density of 4+ with a clear base. I think the maximum density of Delta 100 is around 2. Bleaching with ferricyanide would clear the base fog without affecting the maximum density too much. You could also try developing in Dektol or equivalent. Try scrounging some film from a graphic arts business with an imagesetter. Develop in Dektol or equvalent as well. The graphic arts films today are Rapid Access and develop to a high density. I used these films for years. Base fog near 0 and Dmax of 5+ over less than a 2 stop range

 

[BetterSense]

I shot my target and developed. My spot meter said that the subject brightness range between the black areas of my target and the white ones is at max 3 stops. I bracketed my exposures and developed them in dektol, HC110 and water mix for about 4 minutes or so. The density on the dark areas of my pattern is not as dense as the film I exposed to room light, but the light areas are starting to show density. I suppose I could expose one for a bit more, then bleach the density out of the highlights as suggested. Or, I could try contact printing to another sheet of litho film. I heard that that can increase contrast.

 

[2F/2F]

If you can't use A+B, try using an ortho copy film, such as one of the two Rollei emulsions that are available.

I'd think it easier to get the cheap A+B chemicals rather than a whole box of film, unless you will be doing this often. There must be a place to get A+B somewhere in Dallas.

 

[BetterSense]

My impatience knows no bounds.

 

[2F/2F]

My impatience knows no bounds.

Then find a new hobby!

 

[dancqu]

Without Litho Chemicals? Do You Home Brew?

A very few standard Home-Brew chemicals
will make a lith developer. Hydroquinone,
sodium sulfite, sodium carbonate and
perhaps a little potassium bromide
are all that is needed. Dan

 

[BetterSense]

Do you know the proportions? I have everything but the potassium bromide.

Anyway, duping my highest-contrast negative to another sheet of litho film and developing in the same brew worked really well. Basically perfect contrast now; I can't see the ceiling lights through the dark areas and the light areas are perfectly clear.

 

[dancqu]

IIRC

Do you know the proportions? I have
everything but the potassium bromide.

Not knowing so I concocted a lith developer.
I was experimenting with a carbonated low sulfite
hydroquinone mix. I found out later that the mix
was indeed a lith developer and of the Wall's
Normal Hydroquinone type. My mix is for
one-shot use.

I'll need to dig through my notes. Ratios of 1:1:2
hydroquinone : sodium sulfite : carbonate may put
you in the ball park. Shoot for 8 - 18 minutes. Use
a least solution volume. Rich browns on one paper
but two others flunked. Dan