Jared, this is not a simple issue. There was a whole thread on microdensitometry a while back. Basically, a 35mm image may have as a 'line' a 1 micron wide item, but in 120 (MF) that may be a 10 micron line and in 4x5 that same line may be 100 microns in width. Lets say it represents a line between telephone poles or a tree branch.
Originally Posted by Jarred McCaffrey
Anyway, this must be reproduced with the proper edge effects for each film at the optimum magnification. Let us say 4x5 for 35mm, 5x7 for 120 and 8x10 for 4x5. (or some such keeping magnification as constant as possible)
You can see right off how complicated the film design and imaging becomes. The edge effects must be balanced to give proper edges for each film format at the 'proper' magnification ratio for that film. If you err, then the final image looks 'wrong' with halos or lost detail depending on which side you err on.
Using a knife edge exposure can work, but how do you isolate emulsion turbidity from the effect? We had to use x-ray exposures to prevent the emulsion turbidity from clouding our results. Knife edge will work, but remember that the results will vary across films, only within film type will the result be valid with visible light.
It is an interesting and complex field, designing photogrphic films.
As you noted you will see increased edge effects by doing long development in lith developers . the areas with black detail will enhance with lith the longer you keep the print in the developer.
The blacks seem to start clumping together and defining these areas dramatically.
On a side note about long development. A student here in Toronto developed out defined images 24 hours or longer in Lake water. It caused quite a stir.
I would imagine if you would want to increase edge effects in a contact print you could do a double hit on the print with the second image very , very , slightly off register.
Also I would think by using a complicated set of unsharp negative , pos , masks you could increase edge effects with double printing.
Donald Miller has a good article on how to make masks that could be the start ing point for multiple hits on a print to increase values .
Originally Posted by Jarred McCaffrey
Yes, some of us are saying that we see greater apparent sharpness in our contact prints from negatives that are developed to maximize adjacency effects. But what I understood from your initial question was, is it possible to enhance adjancency effects in the printing process, rather than the negative development process?
That's exactly my question, Sandy. Thanks for pulling us back on topic.
I'm curious if anyone has achieved the same effect at the printing stage. Enlarging and magnification aren't really the issues I was looking at, but we can acknowledge their effect on adjacency effects. To compare apples to apples, let's assume a large contact print. One can get adjacency effects on the negative by film development techniques, we know this. Why not at the time of contact printing? It would great to try different levels of adjacency effects for the same image rather than being stuck with your choice when you developed your film.
Photo Engineer may have had the best answer here when he brought up bromoidide vs chlorobromide. If paper emulsions are formulated so differently that they don't react to adjacency techniques like stand and semi-stand development, then that perfectly answers my question. Curiosity gets the best of me though....
My memory tells me that Fred Picker use to claim that Zone VI paper gave an improvement that was either due to Mackie lines or the Eberhadrt effect.
Personally, improved adjacentcy effects in a printing paper when printing 35mm for maximum sharpness is about that last place I would look fqr an improvement My own pre-judgement based on nothing but a limited experiences of 40+ years would have me looking at the light source, enlarger chacteristics, enlarging optics, specialized carriers etc for the maximum extraction of the quality contained in a negative. Equally as important to me if not far more important would be the general gradation character of the paper. More importantly I would use great care in on the choice of the camera, film,optics tripod and technique in the creation of the negative in the first place. My guess would be that a wood tripod designed for professional cinema work that weighed in the area of 25 to 50 poumds and a first class fluid head, another 20 pounds, will do more for your negative's clarity than any adjacency ehancement effects from special paper processing techniques. I suppose the fact that you and I and three others would be required to carry the $10,000 of tripod to take a photo could be a minor complication.
I recommend that use a first class film well suited for your application and dilute Pyrocat HD for stand development and call it a day.
Claire (Ms Anne Thrope is in the darkroom)
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I have been thinking about what you wish to accomplish. Here, I believe, is a technique worth trying to get maximum sharpness with darkroom work.
Use a GRADED paper. Expose and develop your negative so that they are scaled to give you good gradation while printing on a number 3-or 4 paper. Then focus your negative with white light and insert a sharp cutting blue filter such as a 47B or a blue separation filter used for tr-color printing which is either a number 98 or 99 into the light path. One of these two (98-99) filters is blue and the other is green.
The increase in local contrast from the use of a more contrsty paper is easily seen. Exposing the paper with a blue filter in the light path will, I have read, give more than a 30% increase in resolution potential with many B&W papers.
This is due to two factors. The way that the nature of light from using the Blue wavelenghts, as opposed to green, are affecting the diffraction limit and the way that a particular paper will respond to blue.
If you do this and can not sense any difference get several 8 to 10 year olds who have good vision and have them view prints in good lighting that are matched except for the use of the blue filter. See which they pick out as having the greatest clarity. It should be very informative.
Claire (Ms Anne Thrope is in the darkroom)
Fred Picker did claim that his Zone VI paper increased edge effects. His newsletter was the first place I heard the term. I don't remember the reason he gave, but if Zone VI paper was in fact "all bromide" as he claimed, perhaps the bromide is the reason.
Juan, I doubt it.
Under normal diffusion conditions, the edge would be between 100 and 1 micron as I described above. In an 8x10 held at arms length for viewing, it would be close to impossible to see that type of edge.
If the edge were in film, and then magnfied in the print, then you would be seeing the edge effect of the negative, not the print.
With bromide emulsions, edges, if any, tend to be mushy and diffuse, some extending out 1000 microns or more beyond the edge. In this case you see a softening of the image due to the blur introduced by what we call bromide drag.
A thin emulsion layer on a fine RC or Baryta, especially with an absorbing dye for AH effects will give a remarkably sharp picture with the appearance of having edge effects because the effects in the film image are more readily apparent.
The only thing that can 'prove' such a claim would be microdensitometry on a knife edge exposure to soft x-ray. Been there, done that, and neither I nor anyone I know of was ever able to show suitable edge effects in paper, just soft mushy bromide drag type effects.
A bromoiodide paper may have edge effects, but under normal viewing conditions, you would not see them due to size as explained above.
Sorry about getting a bit off topic here, but as stated above, the inherent properties of film emulsions containing silver iodide seems to imply to me that higher speed films should produce more pronounced edge effects. I don't recall anyone stating that observation. Has anyone observed that? Or perhaps the higher grain of the high speed films obscure this possible advantage?
Originally Posted by Photo Engineer
Kirk - www.keyesphoto.com
Kirk, the higher the iodide, the greater the edge effects. That is correct.
OTOH, it depends to some extent on where the iodide is located. If the iodide is mainly buried in the grain, then it is not evident at the start of development whereas if it is surface iodide it floods the system at the start of development.
In theory, a pure iodide emulsion would have unusable edge effects they would be so large. In practice, a pure iodide emulsion is virtually impossible to develop due to the huge restraining power of the iodide ion.
In practice, an even distribution of about 1% - 5% iodide will give nice edge effects in a film. In color, this is supplemented by using DIR couplers for additional edge effects.
Any inhibitor that reacts with silver halide and forms a salt less soluable than the silver halide being developed will act as a restrainer or atifoggant "and will cause edge effects if released imagewise" <- that is my addition to his words paraphrased here. (Haist - Volume I "Modern Photographic Processing", restrainers and antifoggants)
In actual practice, too much in the way of edge effects becomes very distracting and causes light and dark halos around objects. The wrong 'size' of edges becomes very unpleasant at the wrong magnification. For example, a 10 micron edge around a 10 micron object in 35mm is wider than the object and looks awful. I've seen that as well as some worse than that. The object now appears to be 30 microns in size or 10 microns with a surrounding 20 micron halo.