Well, this is a difficult question, but you said it in your post Michael. Edge effects vary so much with emulsion and developer that it is impossible to say anything definitive about anything here! I can have a 3% Iodide emulsion in D76 and the edge effects will vary based on the placement of the Iodide during precipitation. So, emulsion is a factor. Then comare D76 with (a reach but an example) Dektol with one emulsion and you see something else.
I can design 5 or 6 developers to maximize any factor, but which is best. This is what the old timers found. There is no magic bullet.
I'm trying to design an HA developer right now myself. Wish me good luck! :D
Haven't had a chance to participate in this thread, since I don't study these effects. But your question brought to mind something I think is worth sharing...
A variable that I think affects the access of fresh developer to an image being developed, and which I think might impact the edge effects...
Using D-76 on TMY-2 I once made a mistake and flipped one sheet over in the developer. I had image artifacts on a pictorial negative developed in contact, emulsion-to-emulsion, with a step wedge exposed test sheet. There was a ghost image of the step wedge on my pictorial negative. I assume this is because the high density patches exhausted the developer locally.
So I would say developing stacks of sheets in trays - might - enhance edge effects.
It could have been a form of bromide/iodide drag or transfer. But those negatives must have been in close contact!
They were. One pair out of a stack of 6 or 7 sheets, were emulsion to emulsion because I flipped one sheet over. Sure I shuffled the sheets, but the pair stayed together the entire time in developer.
Originally Posted by Photo Engineer
Could have been bromide/iodide... Is that what Todd-Zakia mean by "reaction products"?
Like a quasi-diffusion transfer :laugh:.
There are all sorts of reaction products depending on the emulsion and developer constituents, but bromides are fairly typical. Iodide can be there too.
PE: How do you plan on testing your HA dev along the way? What methods will you use? I'm assuming for example you don't have a microdensitometer handy - unless you've been holding out on us!! Also if there is any way I can help you with this project let me know.
By the way, following my mention of the reference to a patent of yours in Haist I wanted to provide more detail for anyone interested. It is on page 467 of volume II in the Color Photographic Systems chapter, The Nature of Color Development section, Color Developing Agents subsection. "In a 1972 patent Richard L. Bent and Rowland G. Mowrey claimed certain p-phenylenediamine derivatives produced image dyes of superior stability to prolonged exposure to light, heat, or humidity. ...". The reference indicates "Color Photographic Processes," U.S. Pat. 3,656,950 (1972).
I quick question for everyone/anyone regarding copyright etc. If I reference Richard Henry clearly am I allowed to scan and post say a table of results from his book in this thread? Sorry if that is a dumb question but I have no idea what we're allowed and not allowed to do and we all remember that recent insane thread (now deleted) with the guy who was trying to make a formula book.
My main point is that stack developing in trays might surprise you with edge effects that you don't get in rotary or tank processing...
I think a diagram and discussion of what it means would be appropriate, but a page copied outright is less appropriate.
The references in my book are all made with permission of the original authors. For example, I talked personally to Grant Haist and Bruce Kahn and got their approval. In fact, Bruce gave me a CD with his entire outline for his GEH course.
The reference is to CD6. I had forgotten that Grant referenced that. It was planned for RA4 but missed the boat. It was used for Kodachrome.
I will be testing my HA developer with a set of evaporated metal high definition negative and positive images that cost about $500! And a friend of mine has build a micro densitometer! :D :D :D No problem with testing!
So, there you are!
What are your guiding principles in designing the developer? In other words what are you trying for when you say HA? Low solvent action? Maximum edge effects? What characteristics or components of image definition/information are you favouring? How will R G Mowrey determine if he is successful in generating "high acutance"?
Is Holmburgers helping you with this?
And how do I get access to this microdensitometer :whistling:
For the Henry tests I will put together a summary rather than lifting a page via scan.
I'm also attaching my summary of the Altman/Henn study again (was discussed in another thread some months ago).
My benchmarks will be a family of films tested aganst HC110 and D76. The film will have to have the same contrast and speed in the HA developer with better grain and sharpness. We will see what we will see. And no, Chris is not working with me on this. Our work is strictly emulsion work. I'm working with others on this.
I do not have use of the microdensitometer, I just know he has one. I have yet to ask for its use.
Could a scanner be used for a microdensitometer? I have used a scanner for a densitometer before... seems at a modest scale it could be useful.