Sunday, May 29, 2011

Importance of Proper Contact Printing

Dewi,
A long time between drinks I’m afraid. Sorry. There’ve been a lot of problems to sort out up here, mostly of my own creation.
I want to get into the issue of what I call ‘proper’ contact prints. It’s something that is done a lot easier by demonstration but the theory has be laid out first. In essence it boils down to using a simplified version of Ansel Adams’s zone system with a disciplined method of making contact prints.
Without going into great detail I’ve zoned many films for their correct speed. More to the point I’ve had somebody do it for me as I don’t have a densitometer. My conclusion is that films (with the exclusion of Agfa film) all zone out to a correct working ASA/ISO close to half the manufacturers rating. Therefore a 100 ASA film will be close to 50, a 400 close to 200 etc. We’re talking B&W here of course.
That said and done we need to have a system which gives us control, or indicators at least, of a correct exposure/ processing combination in different lighting situations.
About 40 years back, using a system of basic logic, I concluded that the only thing we know about a piece of film is that if we don’t expose it to any light, then process and fix it normally, we wind up with a sheet of ‘clear’ film. 
We can make only one assumption now. That is if we  make a good print from that ‘clear’ film it should be a beautiful black image with no detail whatsoever.
I have said ‘clear’ - not clear. Because as we know the film is not totally clear. When it is processed and dried it has a base fog which will vary from film stock to film stock. 
As I said before the only thing we know about this film is that it will print to a black tone.
We also know that if we expose and process a film correctly and make a good print we will have a fine print with a full range of tones from highlights through to shadow detail. We can also take into account some personal style here. Some photographers prefer more contrast in prints, some fuller tone prints. Nevertheless, we do need to have some control and not depend totally on guesswork.
So, given that we have our technique under control we should get a good print.
But we’re still in the position of having only one controlled fact - the black print.
This is where the technique of PROPER contact printing comes into action.
Many photographers will make contact prints several times in order to get one which looks good - often to keep a client happy.
However, a contact print can tell us an enormous amount about how good our basic technique is. But first we need to make a very simple test to help with the production of a proper contact print:
We have to assess the MAXIMUM PAPER BLACK WHICH CAN BE OBTAINED WHEN PRINTING IN THE MINIMUM EXPOSURE TIME NECESSARY TO ACHIEVE IT.
Then, given that you have chosen the correct paper grade and have a perfectly exposed and processed negative, you will automatically get a perfect contact print given the correct enlarger exposure time. And this is a technique which, with very little practice, can give you a near perfect print on the first effort. Test strips are a thing of the past, both time wasting and a waste of paper and chemistry.
This is where the proper contact print becomes your only guide.
Here’s how we obtain the perfect contact. We can talk about other aspects of this technique later but the basics are simple.
We first have to use a negative which has been processed but NOT exposed to any light. I’m writing this on the assumption that you use 4x5 most of the time but it works on all formats.
  • First set up the enlarger so that it throws a pool of light on the baseboard which is sufficient to cover about 12x10 inch paper (we’ll be using 8x10 for this exercise).
  • Focus the frame edges of the film carrier on the baseboard.
  • Measure the height of the enlarger above the baseboard and note the height. (I measure from the lens panel)
  • Set the lens aperture to a normal aperture that you are likely to work with. This is to ensure even light coverage. A good enlarging lens will usually be operated at 1 to 2 stops down.
  • Choose a sheet of paper from the type you normally print with and set the enlarger or filter to a normal contrast. eg Grade 2.
  • Place a sheet of 8x10 paper on the baseboard and keep it flat with a sheet of clean glass or use a contact printing frame but strip from it those plastic film holding guides. They don’t let light through and make neat white lines all over the place. We DO NOT WANT ANY WHITE ON THE PAPER. It makes any dark grey look black by comparison. We need to compare black to black.
  • Now place the negative in the centre of the paper and make a normal step wedge, exposing, say, 1cm strips of the film at a time for a short exposure. You’ll know your enlarger better than, me but 5 second intervals will work well on a bright enlarger.
•When the step wedge is completed process it right out for about 2-3 minutes, depending on paper stock.
  • Fix wash and dry the paper and then examine it under the light you would normally examine your prints under in the darkroom.
  • The trick now is to look for the first point where you see the difference in black between the paper’s black and the negative’s edge disappear. You will see the grey tones becoming increasingly dark. Until the negative black and the paper black match. That point will represent the MAXIMUM PAPER BLACK IN THE MINIMUM EXPOSURE TIME NECESSARY TO ACHIEVE IT. 
  • Make a note of everything you have done to achieve this and keep it with that enlarger:
Enlarger height
Aperture
Paper type
Paper/filter grade
Exposure time as well as making sure that processing times/temps for the print are in reasonable control.
Every time you make contact prints simply set up this system.
Now here’s the rub. If you have this contacting system under control and you’re not happy with your contacts for one reason or another they will help you sort out the problem. For example, if you find the images made with one particular shutter speed are looking over or under exposed it indicates a problem with the shutter. It’s not necessary to send the shutter off to the workshop, simply learn to compensate when using that speed. If images look too contrasty or flat it is a problem with basic exposure and processing control.
You will be surprised at how quickly you come to read the contacts and fine tune your whole technique.
While I’m a believer in the Zone System I find that this is a very useful, simplified, technique for putting it into practice. 
Here’s another advantage of the system. You should never have to make a step wedge test again. When you have got your contact printing technique under control try this little test. Simply take a negative and without changing anything on the enlarger at all put the neg into the carrier. You may need to fine focus it. Now slip a sheet of 8x10 paper in a frame and make an exposure identical to the one you used for the contacts.
It will obviously only be a cropped image (because you’re covering about a 12x10 area). Process it and you should find the image is a very close match to the contact. So close that it will be an acceptable print. You may only need a tiny change in exposure or paper grade to put you in the realm of a perfect print.
Slight variables do cause slight changes - that the image is now projected through glass is one of them. But with very little practice you will find your print technique will expand beyond recognition. 
But what happens if you want to make a smaller or larger print? That’s quite simple and it’s worth putting in a bit of practice. A simple law of physics (almost) applies. Check this. It looks complicated and is best demonstrated:

Inverse Square Law, Light
As one of the fields which obey the general inverse square law, the light from a point source can be put in the form
pastedGraphic.pdf
where E is called illuminance and I is called pointance.
pastedGraphic_1.pdf
The source is described by a general "source strength" S because there are many ways to characterize a light source - by power in watts, power in the visible range, power factored by the eye's sensitivity, etc. For any such description of the source, if you have determined the amount of light per unit area reaching 1 meter, then it will be one fourth as much at 2 meters.
The fact that light from a point source obeys the inverse square law is used to advantage in measuring astronomical distances. If you have a source of known intrinsic brightness, then it can be used to measure its distance from the Earth by the "standard candle" approach.
And it only applies to a point source which, in relation to the Law, is infinitely small. Your source will be 4x5inches. Again, is is a simple matter to make a note of the difference in exposures necessary. And the arithmetic is simple. For example if your enlarger is set to make a 12x10 print and you need an exposure of 20 seconds and you then want make a print of 16x20 inches which entail the enlarger lens to baseboard distance increasing from 15 to 30 inches your exposure will need to increase  by a factor of 4. That’s 80 seconds. (I’d stand to be corrected on that - my maths is B-).
Either way you will find that with very little practice you will be able to make very accurate exposure compensations.
A lot can be read from the contacts, not only equipment faults. If for example you find your negs are consistently too contrasty or too flat it means that your exposure/processing needs a minor tweak. It may be that the film zoning just needs a small adjustment. Eg from 50 to 64 asa.
Also, as you know, different lenses have different transmission characteristics. However, all of these things become apparent when you have the contact printing under control.
It’s also important to know the difference which occur with different enlargers, paper grades, processing times etc. So it is necessary to make tests for different enlargers. I don’t bother with tests for different enlarger lenses though, mainly because I use  different ones for different neg sizes. It’s possibly to pick up variations simply with a ‘feel’ through experience.
I’d like to make sure we go through this system in a practical way when I get down there.

2 comments:

  1. Interesting and detailed description of your theories on printing here Roger, one I've never heard of despite my obsession with traditional printing and its history.

    Not sure what your procedure tells you however other than what film base plus fog density on a particular film stock is when processed and exposed by a consistent standard. It tells you nothing about the exposed negative.

    Also using traditional practice I expose the print for highlight required modifying dmax through contrast control. Your method determines print exposure time according to lowest print values.

    Perhaps the critical issue here is that one never achieves 'the perfect negative' you mention, the notion of a perfect negative is itself debateable I think.

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  2. You have a nice blog
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