by Joe Farina » Mon Aug 13, 2012 3:46 pm
Film thickness in MBDCG (and regular DCG) opens up a lot of questions, and I got even more confused after following the "film thickness" thread. That's why I decided to use a variety of Mayer bars for my first tests. With a given winding on the bar (and a given gelatin concentration), the thickness should be quite repeatable. So far, I have tried the 14 and 17 micron coatings, and didn't see any difference (but that was only a 3 micron variation).
I constantly re-read my collection of papers on MBDCG looking for common observations by the authors. If the goal is to get a narrowband recording on MBDCG, then I get the impression that a thicker coating is favored, in the range of 18 to 25 microns. My objective is narrowband, because I'm working on two-color MBDCG. One paper by Rimpler et al. on MBDCG (SPIE 2333, "Influence of some parameters on grating structure and diffraction efficiency in red sensitive DCG") showed a relationship between diffraction efficiency and film thickness, with the thicker coatings being brighter than the thinner ones (around 25 microns appearing to be best, according to them). But of course there are a myriad of other variables involved such as gelatin type, MB concentration, hardening methods, etc.
Zhu and the others (who needed a narrowband result for full-color MBDCG) seem to prefer something in the 18 to 25 micron range, but they are not explicit about it, and I may try to duplicate their coating method to get a handle on how thick their coatings were. I would need to mix their exact film formula, and spread 8ml over an area 8 X 24 cm (this is what they specified) and let set by gravity. Then measure using a micrometer.
Not many papers discuss narrowband MBDCG except Zhu et al. One big difference between the Chinese formula and the original one by Blyth (and also Cristiano Perrucci's formula) is that it uses a much smaller amount of TMG, about 14% of what Blyth specifies. I'm assuming they used this smaller amount because they didn't want too much to wash out during processing, which would cause a color shift to the blue. Blyth states (and I certainly believe him) that more TMG causes better sensitivity, yet Zhu and the others claim very good sensitivity for their emulsion, 60mJ for 633, while Jeff's was said to be 50mJ. It's just possible they were getting good sensitivity due to the 18 micron film thickness, while I think Jeff's film was much thinner.
Film thickness in MBDCG (and regular DCG) opens up a lot of questions, and I got even more confused after following the "film thickness" thread. That's why I decided to use a variety of Mayer bars for my first tests. With a given winding on the bar (and a given gelatin concentration), the thickness should be quite repeatable. So far, I have tried the 14 and 17 micron coatings, and didn't see any difference (but that was only a 3 micron variation).
I constantly re-read my collection of papers on MBDCG looking for common observations by the authors. If the goal is to get a narrowband recording on MBDCG, then I get the impression that a thicker coating is favored, in the range of 18 to 25 microns. My objective is narrowband, because I'm working on two-color MBDCG. One paper by Rimpler et al. on MBDCG (SPIE 2333, "Influence of some parameters on grating structure and diffraction efficiency in red sensitive DCG") showed a relationship between diffraction efficiency and film thickness, with the thicker coatings being brighter than the thinner ones (around 25 microns appearing to be best, according to them). But of course there are a myriad of other variables involved such as gelatin type, MB concentration, hardening methods, etc.
Zhu and the others (who needed a narrowband result for full-color MBDCG) seem to prefer something in the 18 to 25 micron range, but they are not explicit about it, and I may try to duplicate their coating method to get a handle on how thick their coatings were. I would need to mix their exact film formula, and spread 8ml over an area 8 X 24 cm (this is what they specified) and let set by gravity. Then measure using a micrometer.
Not many papers discuss narrowband MBDCG except Zhu et al. One big difference between the Chinese formula and the original one by Blyth (and also Cristiano Perrucci's formula) is that it uses a much smaller amount of TMG, about 14% of what Blyth specifies. I'm assuming they used this smaller amount because they didn't want too much to wash out during processing, which would cause a color shift to the blue. Blyth states (and I certainly believe him) that more TMG causes better sensitivity, yet Zhu and the others claim very good sensitivity for their emulsion, 60mJ for 633, while Jeff's was said to be 50mJ. It's just possible they were getting good sensitivity due to the 18 micron film thickness, while I think Jeff's film was much thinner.