Contact printing...misinformation?

Discussion in 'Contact Printing' started by ic-racer, Oct 22, 2007.

  1. ic-racer

    ic-racer Member

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    I was a little upset today because I spent a few hours going over posts on APUG contact printing forum (up to page 14 of prior posts) and did not find what I need to know to get a good 8x10 contact print.

    So, here we go, I have to re-invent the wheel.

    Lets start with the basics of light sources . 1) Collimated and 2) Diffuse.

    Lets start with a collimated source. The first and obvious question to me is 'do you need an overlay glass' with a collimated source. I believe it is intuitively obvious that a glass is NOT needed if the light source is perfectly collimated (ignoring diffraction around the edge of the silver grains). However, I don't have a perfectly collimated light source available to me for printing.

    The closest I could get to a collimated source in my darkroom would be to crank my enlarger to the top of the column and use a very small exit pupil for the light source. Realistically I can get 90mm of column elevation, and I measured an exit pupil of 4mm on a 50mm lens stopped all the way down. Lets assume that the negative won't sit flat on the paper. It is 0.5mm above the paper at the worst area. The question is mathematically illustrated in the JPEG. The solution with these real-life numbers indicates that the circle of confusions formed by the above setup will be 0.022. Thats 10 times smaller than they need to be for most "8x10 at 'normal' viewing distance" calculations (0.2mm).

    So, mathematically, you do NOT need a glass when using the enlarger as a light source. In fact using a glass would be quite detrimental in this situation because of the way collimated light would render all the imperfections in the glass.

    Now lets consider diffuse light sources. The goal with a diffuse light source would obviously be to minimize scratches and dust on the film base and on the overlying glass. To test the efficacy of diffuse light on the elimination of these pesky scratches I made a simple empiric observation. I took my very scratched and dusty contact printing glass and compared the shadows the scratches made with different light sources. I used my own eyes for the observation. First I observed the shadows cast by the scratches onto a piece of paper just below the glass. The shadows were very obvious!

    Then I brought my small light box over the glass and observed the shadows as the light box got closer. When the 8x10 light box was just a few cm from the glass, all the shadows from the scratches and dirt on the glass disappeared! Like magic! (In this observation most irregularities were on the TOP of the glass).

    To see how flat the film needs to be pressed against the paper I repeated the above calculations using these values: Exit pupil 300mm, Distance from light source 50mm and circle of confusion of 0.2mm. The gave a result of 0.03mm. (as a comparison I measured some hairs on the back of my hand and got 0.04mm)

    So, to answer the question of "how does one contact print an 8x10 negative onto VC paper" I have an answer:

    1) Use an enlarger as a light source without an overlying glass
    or
    2) Use a diffuse light source (like a translucent white plastic suspended a few CM above the negative, with the enlarger shining on this) and use an overlay glass that can oppose the film and paper to a maximum separation of 0.03mm.

    Questions, comments, math errors??
     
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  2. JBrunner

    JBrunner Moderator Staff Member

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    While the amount of thought and figuring that went into this is commendable, it's a bit over done. Allot of math breaks down when it hits real world conditions. Diffuse source for contact printing is fine, but you can't see or control dodging or burning. The glass is there not just to press for sharpness, but to assure absolute contact, to prevent Newton rings, which is what you will get, sooner or later without the glass, depending on the negative, humidity, and other factors. An enlarger makes a wonderful light source for contact printing, particularly a dichro head, for split printing. The lens aperture matters not a wit, with a good frame, and a miniscule aperture would do little except give unbearably long exposure times. Use a good quality contact printing frame with clean scratch free glass, and strong springs, throw away the slide rule, and print away. :smile:
     
    Last edited by a moderator: Oct 22, 2007
  3. Vaughn

    Vaughn Member

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    "Realistically I can get 90mm of column elevation, and I measured an exit pupil of 4mm on a 50mm lens stopped all the way down."

    And how long of an exposure does that translate into for Azo paper?

    Interesting study, but I'll keep using a contact printing frame...though I suppose that using a bank of UV tubes 3" from the neg is not too dis-similar to your #2...which is how I print my platinum prints (and explains why only big chunks of crap sitting right on the neg shows up, but rarely any thing on top of the glass.)

    Vaughn
     
  4. lee

    lee Member

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    you are way over thinking this. Just lay your neg on top of a piece of paper and lay glass over that. Either light source will work just fine. Mr. Brunner has a good handle on the technique.

    lee\c
     
  5. John Bartley

    John Bartley Member

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    Wow ... that's an awful lot of work .... my brain is hurting.

    For a light source I use a 10watt halogen bulb in a desk lamp about 30" above the frame and for filtration I use coloured plastic report covers above the frame. I use a digital watch for a timer.

    I use this setup for both VC and AZO - they just have different exposure times and AZO doesn't need filtration

    cheers
     
  6. Robert Hall

    Robert Hall Subscriber

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    Don't suck the fun out of this, Jason and Lee know what they are talking about. :smile:

    This reminds me of my college days when my professor told me that I always seem to find the hardest way of doing things.

    The only caveat I can warn against is I use an anti-reflective glass on the side that touches the film to prevent newton rings.

    Best of luck!
     
  7. ic-racer

    ic-racer Member

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    Thanks for the comments but are you shure this is what you intended to say? How can Newton rings form without an overlay glass? I can't imagine they would form between the two emulsions.

    I guess another way of thinking of things in the OP is that I think enlarger light is "TOO COLLUMATED" and acts like the proverbial "point source" enlarger light used for projection printing. I have heard of a few souls who use this type of light for projection printing, but the reason I use a diffuse light, when projection printing, is minimization of dust and scratches.

    I agree with you that I need to make some prints, but my darkroom is only dark during the night so I need to do something while waiting for it to get dark:tongue:

    In practical terms I think I will buy the Bostic-Sullivan 8x10 frame, but unitll it arrives I want to test the two scenerios from the OP.

    That is, make a contact print WITHOUT an overly glass (ie just negative sitting ontop of the paper) with the enlarger high up.

    Then try using my heavy dirty scratched glass over the negative with a diffuse light source.

    I have already used the dirty scratched glass with the enlarger as a light source and it was possibly the worst print I ever made (in terms of dust and scratches, and thus the reason for the original post) Though If I were to go for a Joel-Peter Witkin look it might be OK:D
     
  8. Alex Hawley

    Alex Hawley Member

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    The traditional light source for contact printing has always been a plain, ordinary light bulb of sufficient intensity. That was all that was needed in the days when we had silver chloride contact printing paper such as Azo. No collimation or diffusion necessary.

    Now that those papers are gone and we are printing on enlarging paper, the light intensity has to be much, much lower, hence, more widespread use of enlargers as the light source. I recently measured the light intensities I frequently use just for trivia's sake. For Azo printing, I used a 120 watt bulb, four feet above the frame. Intensity was 70 foot-candles. Under the enlarger using enlarging paper, a typical intensity is 0.43 foot-candles. That's three orders of magnitude less intensity.

    But, other than the inherent tonal characterisitcs of the respective papers, my negatives haven't cried one tear about being printed with a bare light bulb or the collimated condenser enlarger source.
     
  9. JBrunner

    JBrunner Moderator Staff Member

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    Newton rings can form between any two surfaces that are not in complete contact with each other. Glass to neg, or neg to paper. You most often hear us whining about the glass ones, because that's what we have the most trouble with, as the paper to negative contact is seldom an issue in a frame, because of the give of the paper, and felt. Glass to negative are two fairly hard surfaces, and more prone to the problem in a frame, even under the spring pressure, especially if there is the least bit of moisture on the glass to push a curve in the neg and paper. Roberts anti glare glass is a solution, but I haven't gone that route yet.

    Since the negative contacts the paper, as long as the light hitting the paper is even, it's all the same to the paper, except, of course, in the case of dirty, or scratched glass, where a point source light creates shadows because of the problem glass. But again, no dodging or burning. Glass is cheap. Many if us print with condensor enlargers. There is debate (of course, it's photography), but many persons will tell you they are sharper, and have better contrast. Those of us who use them, know the condensors have to be clean, and scratch free, just like an enlarger lens, camera lens, negative, glass carrier, or the glass in a contact printing frame.

    The best contact prints in the world have been made in various closets and darkened workshops with a contact frame, or just a piece of glass, and a bare light bulb, with no math beyond the exposure. The methods for outstanding contact prints won't be found in calculations. You'll find it it your negative, brought out by your practice, patience, persistence, and experience. But all means, experiment, nothing wrong with that. Thats how we get good, but you'll probably find the old wheel still rolls pretty good.

    Best,
    J
     
    Last edited by a moderator: Oct 22, 2007
  10. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Weston used a light bulb with some cloth tied around it--probably just a handkerchief. He could adjust the height of the bulb to vary the exposure.
     
  11. mcfactor

    mcfactor Member

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    If you are using fiber paper, isnt glass needed to kept it flat?

    If the paper curls, the negative will be much more than .5mm away from the paper. There is also a higher probability that the negative will shift, especially if you are waving your hands above it to dodge or burn.

    You also mention the circles of confusion will be "10 times smaller than they need to be for most "8x10 at 'normal' viewing distance"" Isnt the entire point of making 8x10 contact prints to have the sharpest and most tonally beautiful print possible, not merely sufficient for a certain viewing distance? After all, when i view prints in a gallery i like to get as close as possible and study every detail, especially with a smaller print.
     
  12. Alex Hawley

    Alex Hawley Member

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    Yeah, that's why a contact printing frame becomes necessary.

    Ditto what Jason already said.
     
  13. Curt

    Curt Subscriber

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    Paper, negative, glass, in a contact printing frame to make it easier, a bulb overhead and a watch or timer. Turn on the light, make the exposure, unload the frame and develope the paper.

    :munch: Or get a degree in physics to prove mathematically that it's all impossible.:munch:
     
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  15. dslater

    dslater Subscriber

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    Just a couple of comments. First, I don't disagree with those of you who state the OP should use a contact printing frame - you have given good reasons such a holding the paper flat, avoiding newtons rings, etc.
    However, I find it interesting that whenever someone posts some kind of mathematical derivation here, there a bunch of people who chime in saying "you're over thinking this". I just don't buy into this - there are actually some of us who enjoy carrying out a good derivation to see where it leads.

    Jason, math does not break down when it hits the real world - it simply becomes more complicated. One of the truly remarkable things about this universe we live in is that it can in fact be very accurately described by relatively concise mathematical equations. Indeed, this leads into a great philosophical question. Is math something humans discover, or is it something we invent?

    mfactor - I a COC of 0.022mm is smaller than you can detect no matter how close you get.

    ic-racer - In your diagram, I see that you computed your COC for the special case of a point directly under the edge of the exit pupil. However, when you making a contact print - say 8x10, most of the image points will be further off to the side so you will no longer have right triangles to work with - I believe they will be obtuse triangles. Did you try computing the COC for these?
     
  16. JBrunner

    JBrunner Moderator Staff Member

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    I don't disagree with this at all. What should have said is that all variables are not accounted for. And yes, doing the math is fun for some persons (thank God, or we wouldn't have much in the way of photography, or other technology) so I'm not, and haven't tried to knock the OP in any way, just pointing out the variables, and that the combined experience of the contact printers here isn't "misinformation" :smile:

    The real issue of the OP seems to be scratched/pitted/ or dirty glass. He has found that large source illumination gets under the imperfections in the flawed glass, and eliminates them, but this is of course at the expense of any further control over any specific area of the print. #2 solution is to simply lay the negative on the paper, sans the offending glass, and hope for the best, because the math, absent any paper curl, negative curl, humidity, vibration, bump, or draft, says it works. (and it very well might, now and again)

    I say get some glass that doesn't suck. :smile:

    Contemplating the vectors of the photons probably isn't much use in the real world pursuit of a fine contact print, which is, as I understand it, the goal. Time spent doing is the way, and plenty of more accomplished and eminent foreheads have beat the walls before us. Contact printing is as simple as it gets, and brutally reveals any deficiency in the negative or the process. You can't calculate around that. Get some good glass, and clean the printing area- that's the problem, and you can figure all the day long, but it won't change until you do something about it.

    I don't think any photographic pursuit, mathematical or otherwise is a waste of time, but I honestly don't see the application here, when what's needed are the proper tools, and attention to the details that matter.
     
    Last edited by a moderator: Oct 23, 2007
  17. garysamson

    garysamson Subscriber

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    Ice-racer,
    Are you attempting to produce a photographic work of art via the contact print process? If so, a contact printing frame with a scratch-free glass and an even light source should be all the tools you need. You do not need to engineer the process to death - you just need a good negative that has the printing characteristics that match the paper you are printing on and your personal vision as an artist to guide you to a finished print. You should also be having some fun in the process!
     
  18. Chris Breitenstein

    Chris Breitenstein Member

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    Whoa!!! You are making this so much more difficult then it needs to be. If you are contact printing all you need is a voltage regulator (a good suggestion when enlarging as well), a simple light source (ie. a light bulb), a frame, and some sort of timer, Ansel Adams recommended a metronome. This is a rudimentary setup and it is capable of producing the highest quality prints you will EVER see, look at the works Edward and Brett Weston. When printing this way you will need graded paper, which is no big deal.

    always remember the words of Albert Einstein "everything should be made as simple as possible, without being made more simply." Words to live by.

    Yours;
     
  19. ic-racer

    ic-racer Member

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    For my tests I just put the negative/paper unit in a conventional 8x10 easel. (see results http://www.largeformatphotography.info/forum/showpost.php?p=285139&postcount=90)

    In terms of the circles of confusion, you are so right. In fact I discount most dissertations on circle of confusion because it all depends on viewing distance (as you point out) and a good print (in my opinion) DRAWS the viewer IN to examine it closely.

    Looks like I ran out of space to post prints, so check out the LF forum link above for the results. I need to think about it some before I decide the next step:confused: .

    In case it wasn't clear in the first post, using a piece of glass over the paper and the enlarger as a light source produced too much artifact (ie dust and shadows from scratches) that my prints were a waste:sad: . Thus the need to sort things out and find a better way of doing it.

    I don't WANT to be doing this testing:mad: , I'd rather make prints, but they are not turning out. The calculations in the initial post were just to get an idea of WHAT to test as the next step.

    Anyway, check out the link above and see what you think.
     
    Last edited by a moderator: Oct 23, 2007
  20. ic-racer

    ic-racer Member

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    Excellent point, though I think they would probably still be "similar" triangles and the same A, A prime, B, B prime, C, C prime in the diagram would still be equal.

    Anyway, the results were a little 'blurrier' then expected. Probably OK at safe viewing distance, but I want to make out all the leaves and pebbles:tongue:
     
  21. JBrunner

    JBrunner Moderator Staff Member

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    :rolleyes:
     
  22. ic-racer

    ic-racer Member

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    I was just upset and had too much coffee when I wrote that title and didn't mean to insult anyone. Anyway it got you all to read it:surprised:

    But the thing I was upset with was reading suggestions (mostly in the archives, and not neccessarily by those 'in the know' on these topics) that were not applicable to someone who wants to use VC paper. NOT AZO, NOT ALT process, NOT graded paper. So suggestions for UV light, standard light bulbs, etc are pretty useless. So that leaves 'enlarger' light and its inherent collimated character which clearly shows any little dust spec or glass imprefection that gets it its way. I did not come across any posts in the archives that address this issue other than 'clean the dust off' which is a somewhat useless comment, as not all the dust can be removed in my environment.

    The experiment where I show the complete elimination of dust specs and glass scratches and smudges by the simple placement of a diffuser between the enlarger light and the contact assembly was not suggested in any post that I came across in the archives or in this thread (if I missed them, my fault).

    Anyway I hope you all will just understand I am just venting a little anger because I am not getting good results right off the bat after the extensive time and energy that went into restoring this 8x10 camera. I mean, one night I stayed up untill 4:30 AM to finish the bellows and frankly I am exhausted(http://www.largeformatphotography.info/forum/showthread.php?t=29267).

    Anyway I look forward to any comments and suggestions on the test results (http://www.largeformatphotography.info/forum/showpost.php?p=285139&postcount=90) and hope to start making awesome 8x10 prints soon.:wink:

    PS anyone know what I need to do to be able to post more pictures on this forum, will 'subscribing' do it, it didn't find anything about it in the 'subscription benefits' area.
     
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  23. JBrunner

    JBrunner Moderator Staff Member

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    No offense taken. Get some rest, get up fresh and have some fun. There is not much more rewarding than a good LF contact print. I promise it will be worth the headaches.

    It's the glass, not the light source. (Also, you can print and filter VC paper with a regular tungsten globe, you just have to rig the filters up.) Take the lens out of your enlarger, board and all, and you will have a larger source, but not, of course as large as a diffuser placed directly on the frame, you will still have nearly the same problem. You will see that the source has to be nearly as big as the frame before the imperfections disappear. Now that is fine for straight printing, however, eventually, when you want to dodge and burn you will want to get between the light source and the print, so you will have to go to some kind of harder source. You gotta have good clean glass. I suspect you live in a dry climate, since dust seems to be a problem. A humidifier in your work area will go a long way to holding down the dust level, as will an air purifier in addition. I have a big Honeywell that I have on a timer, runs for several hours at night, every night. Cheap, compared to wrecked prints. Long ago, in a galaxie far far away I fought the dust/scratch thing at first too. Had an old antique contact frame, weak springs, bad glass, dusty darkroom. I tried to work around it, but in the end, I found it just had to be done right.

    PS I've seen dust in Ansels skies. Don't forget that spotting is part of the process. You just want to minimize how much. Rarely will you ever make a print that is perfectly free of any imperfection. It is a watermark of the process.
     
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  24. Ian Leake

    Ian Leake Subscriber

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    If you've got dirty or scratched glass then of course you'll get defects in your prints. It stands to reason. If you want to use a sheet of diffuser (which in effect turns your enlarger into a softbox) then that’s great, do it. But there’s really no need.

    It’s well established by many, many master printers that a sheet of glass is necessary to keep the negative pressed flat against the paper. In my own experience I’ve seen soft spots on a print where there hasn’t been complete contact – and that’s when I’m using a printing frame. In fact the third scan you posted on the LF forum shows exactly what I’d expect if you’re negative doesn’t have glass (and as an aside the middle “glass & diffuser” scan suggests to me your negative isn’t completely flat under the glass anyway). I expect that your diffuser will actually be making the blurriness worse in this case (softer light). And removing the glass is not going to eliminate dust/hair defects (e.g. the right hand defect in your first scan) because that stuff is just as likely to settle on your negative or your paper.

    Using a clean and unscratched piece of glass that’s either heavy enough to flatten the paper on its own or is clamped to the paper in some way (e.g. a contact printing frame) will fix the blurriness because your negative will be flat against the paper. It will fix the shadows because there will be no scratches to cast shadows (remember I said “clean and unscratched”). And if you clean the paper, negative and glass before you make the sandwich then you’ll only have to worry about dust on the surface of the glass (which you’d have to worry about anyway without the glass).

    What I don’t understand is why you reject using glass when most of your problems seem to be caused by the specific piece of glass you’re using. And I don’t understand why, after having the patience to restore a large format camera you don’t have the same patience when it comes to learning how to contact print. My suggestion is that you should do what countless others have done before: find out how the master printers do it and then copy their process. That’s the quickest way to creating the stunning prints you’re aiming for.
     
  25. haris

    haris Guest

    I am in process of thinking (which model and how) and preparing to buy LF camera, and I will go 8x10, because I don't have space for 4x6 or 5x7 enlarger. That lead to contact printing. I use for now 35mm/6x7

    So, after readings, lookings and thinking, for me it is clear: Get a good glass (I have Paterson's 24x30cm contact printer, so first will try that), enlarger (with proper lens/mixing chamber or condensor combination, focused lens) as light source, and I will start with multicontrast papers and will see for further.

    Afer that I belive it is all in practice and adjusting process acording "real life" situation.

    Regards
     
  26. Ian Leake

    Ian Leake Subscriber

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    Good luck. In my opinion contact prints are the richest, most "true" print medium. (Of course others will disagree with me, but life would be so dull if we agreed all the time :wink:)

    One thing I did when I started Pt/Pd was to buy some prints from people I considered to be master printers. These became my reference prints. Not only do they look good on the wall, but they're inspirational too. When I struggle and get frustrated, I can get them out and remind myself what's really possible (and how much I've improved since I started :smile:). Good prints from top printers are not cheap but they're worth the investment.

    I'd recommend this to anyone who is thinking of starting contact printing (or any kind of printing I suppose). Just make sure they're in the same medium that you want to work in. Obviously there's no point in comparing a master printer's Azo print with one made on enlarging paper, or a pt/pd print with a silver print. They're different media, so are unlikely to be very helpful as educational tools.