Everyone is probably tired of me asking questions but here goes another. When using a yellow filter in front of the pinhole to reduce contrast, does that apply to all scenes or just scenes in which you want to keep the sky from blowing out?
Be aware that any speck of dust or dirt on a filter used in front of a pinhole or between the pinhole and film will be as well-focused as everything else in the field of view.
Lee
A filter's effects will depend on the color sensitivity of the emulsion, as well as the colors of the subjects of the photo (including any colors caused by the color temperature of the light in which you are shooting).
However, VC printing paper is a special exception, as there is more going on. A VC printing paper has a high-contrast layer that is sensitive to one color, a low contrast layer that is sensitive to another, and the entire paper is not sensitive to red. There is a change in over-all contrast with a change in filtration. Specifically, the yellow filter would lower the over-all contrast, like Vaughn sez, and a magenta one would raise it. You do the same thing in the darkroom when you move to a lower filter number; you add more yellow filtration in relation to the magenta. This makes it so that the low-contrast layer of your VC paper gets more exposure than the high-contrast layer, causing it to dominate the picture more, resulting in lower over-all contrast.
With a panchromatic film (unlike photo paper in that it is not VC, and in that it is sensitive to all the primary colors of light), the filter will simply darken opposite colors and lighten its own in relation. The change is in how specific colors are rendered tonally, not in over-all contrast.
So, to answer your question, with a VC paper in the camera, the yellow filter will lower contrast in all situations. With a panchromatic film in the camera, the over-all contrast is not changed, but the apparent color sensitivity of the film is; this means a change in the tonal relationships that certain colors produce.
You can also use VC filters on your camera, of course. They are actually designed specifically for altering the contrast of photo paper, so you will get more predictable results with them as opposed to using your common Wratten-numbered filters.
IMO, it is better to think of filters' effects in terms of the colors of subjects, not in terms of specific subjects themselves. For instance, think of it as the yellow filter darkening things that are blue, as opposed to it darkening sky. Sometime the sky is more or less blue than at other times, and sometimes it isn't really blue at all (overcast days, warm light, etc.).
I believe the data sheet that comes in most papers lists ISO speeds of the paper with different Ilford Multigrade filters. However, that is for tungsten illumination TMK. The papers might be more sensitive in daylight. So, yes, I would say some tests at first are the way to start.
I would not recommend using a 00 as a matter of course, but using the filter that will best give you what you want for each shot at hand. To pick this, you will need an eye for the luminance range of your composition (or a spot meter), and trial and error.
Vaughn said:Pinholes with VC papers -- no need to over-think it, just go out and do it! It is pinhole photography after all! Check the pinhole sites for their recommendations for starting points, but there are so many other factors (size of the pinhole, how far from the pinhole to the film, etc) that one might as well just jump into it with both feet. You have reciprocity failure effects, too. So forget about "tests" and go out and burn some paper! Try different filters! Keep notes so that you can repeat the successes and hopefully not repeat too many of the "failures".
Go out and have fun!
You also get a very useful extension of dynamic range of the paper negative by pre-flashing. I pre-flash my Ilford VC so that when I develop it, a sheet that has not been exposed in camera would develop so there is just a fraction of darkening compared to an area covered during the pre-flash. I spent quite some time characterising Ilford VC and many other VC papers seem to be similar. I meter using a digicam (not through any filters) and then rate my pre-flashed paper as EI 20 if I am not using filters, or EI 6 if I am going to use a yellow filter (the reduced paper speed also takes any filter effects into account). The paper ratings are assuming you are developing the negative to completion and not pulling it early from the developer. In daylight and without the yellow filter, the paper will capture plus/minus 2.5 stops relative to the metered shade and with the yellow filter, plus/minus 4 stops are usable, however the highlights are going rather non-linear.
For very long exposures, you will also need to correct for reciprocity failure. e.g. if 30 sec metered, use 40 sec; 1 min goes to 1min 30; 2 min goes to 3:20; 4min goes to 8 min; 8 min goes to 20 min; 17min goes to 1 hour; 33 min goes to 2 hours. I regularly make multi-hour exposures, but you do get higher contrast results.
Best regards,
Evan
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