Making diapositive

Discussion in 'B&W: Film, Paper, Chemistry' started by NDP_2010, Jul 21, 2011.

  1. NDP_2010

    NDP_2010 Member

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    I have been reading a darkroom book and alot of the printin techniques require making a diapositive. I was wondering how you go about doing this. I assume there is a special type of film required for this?
    If anyone could explain, that would be great.
     
  2. Diapositivo

    Diapositivo Subscriber

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    A diapositive is a slide. From Greek "dia" = "through" and Latin "positive" = "positive" :smile: i.e. a transparent positive. Your book might refer to a printing technique known as "unsharp mask" which - I am not a printer and only go by theory - involves making a slightly out-of-focus "negative" of the negative you are printing, which means you have to do a positive.

    Somebody else here will certainly give you a better answer anyway, have faith :wink:

    Fabrizio
     
  3. holmburgers

    holmburgers Member

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    An unsharp mask for a negative would actually have to be a positive. That's how it attenuates the negative tones, affects contrast and enhances edges.

    What do you need the diapositive for? Does it need to be enlarged or the same exact size?

    From what I've learned, the tailor-made "copy" films, or internegative films, are all gone. The key is to have an upswept shoulder I think. In all cases, copying a negative will lead to an increase in contrast on the new diapositive. So, you might have to employ some contrast controlling techniques of some sort.
     
  4. NDP_2010

    NDP_2010 Member

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    the book says it is needed for making relif prints and high contrast images. The neg and pos is enlarged at the same time i think.
    The book refers to 'line film', im not sure if this is needed?
     
  5. holmburgers

    holmburgers Member

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    You might have trouble finding a line film these days (though some exist), so you might just try some normal films in high-contrast developers (paper dev's?) or use inherently high-contrast film.

    A neg + pos will lower contrast in the final image though.
     
  6. grahamp

    grahamp Subscriber

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    Line film (when you could get it) had a clear base and a a rich emulsion that was opaque when fully exposed and developed. Typically used for bas-relief (where you would have a positive and a negative on line film printed as a sandwich slightly offset), posterization (several negatives of different densities printed in contact in sequence to produce a print with a few distinct grey steps between white and black, or sometimes just to get a high contrast tone drop out effect.

    If you start with a conventional negative and enlarge onto film, you will get a positive. Contact print that and you get a negative. For graphic arts purposes the contrast increase is often useful. When I was doing posterizations I would often use process black paint to fill in any areas I didn't need.

    Line film is typically ortho, and needs either a red safelight, or full darkness. Using something like Ilford Ortho might work, but I am not sure that you could get the contrast step you need even with very strong print developer. Line film was sensitive to small exposure changes and the steep gradient gave an 'on/off' response.
     
  7. NDP_2010

    NDP_2010 Member

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    thanks for the reply. How do you go about enlarging the neagtive onto film? What sort of exposure is required? I assume it would be quite short?
     
  8. tj01

    tj01 Member

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    I find that you get higher quality if you make a positive via enlarging, then contact printing this positive to negative. You will need an enlarger for this as it's almost like making a print, but the paper is another negative.
    The exposure times depends on the ISO of the negative and the size. But as benchmark, you could be using F22, 3 secs ( at 65cm enlarging height on a very slow neg ).
    Goodluck
     
  9. Neal

    Neal Subscriber

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    Dear NDP_2010,

    If I read your posts correctly, I think you are trying to make an unsharp mask. Here is a decent description online. My apologies if this is not what you are looking for.

    Neal Wydra