This post is going to dive into some fairly technical stuff so if you just want to scroll and look at the pictures I totally understand.
Here is my entry for WPPD: http://pinholeday.org/gallery/2021/index.php?id=500
This is a slightly higher resolution version.
I used Harman Direct Positive paper (DPP). I used the FB, not RC paper. The image is left-right reversed. Images are captured by film (or sensors) with the top of the subject at the bottom of the film/sensor and the left hitting the right side & vice-versa. I decided on the scanner which way is up but that doesn’t correct mirror-imaging. This isn’t an issue with negatives but since this is Direct Positive paper, both axes aren’t corrected.
WTF is direct positive
? With negative film, light makes the silver halides in the film change state and the developer converts light-struck blobs into metallic silver, which looks black. That’s why it’s negative – the more light, as in brighter parts of the picture, the more black (silver) you get on the negative. This paper develops in an opposite manner. On a negative, an overexposed image is more black. On DPP, an overexposed image is more white. I don’t pretend to know what voodoo they do to make this happen but that’s how it works in use.
About the paper
(I used 8×10″):
First, holy carp, this stuff is curly. It has a curl out of the package along the 8″ axis. I used double sided tape to load it into the camera but it was barely enough. After it’s developed, it curls every which way. The above image was taped down to dry after developing and it curled enough to peel the tape off of the backing surface. Flattening it is complex enough to warrant its own post so I’ll just say I re-humidified the paper, pressed it flat, and then scanned before it could re-curl.
Most of what I could find online from people who’ve used it suggested a starting point of ISO 3. The problem is that the paper is orthochromatic, not panchromatic. In english, it doesn’t respond much to the red end of the spectrum.
My ISO test sheet.
My ISO test:
I loaded paper with a 2-layer black construction paper dark slide.
I was going to meter for ISO 1, 2, 4, & 8 and move the dark slide so each strip got the metered exposure. The f-stop remained constant at 254. The meter app has 256 – close enough. I figured I could interpolate if neighboring strips were too light & too dark.
I almost made a big mistake. I mostly use the “Luxi” app on my phone. The app works by entering 2 of the 3 exposure variables, ISO, f-stop, or shutter. It then gives you the 3rd variable. I metered for ISO 1 and got 32 seconds. I metered for ISO 2 and also got 32 seconds. I didn’t know the app tops out at 32 seconds. If the value for ISO 1 had been more than 32 seconds but ISO 2 was less, I would have been off by however much ISO 1 was really over.
I unlocked the f-stop so it would be the calculated variable and scrolled the shutter value and sure enough, it wouldn’t go past 32 seconds.
I had deleted the “Light Meter” app because I hated the UI changes. I re-downloaded it because I had used it in the past for pinhole metering. Nope. It also now tops out at 32 seconds. Why? At least turn the speed red or something to let the user know it’s out of range.
D’oh! Now I have to meter for ISO 6 (takes 1/2 as much light to respond the same as ISO 3) and then double the shutter time.
I did make a mistake. After the 2nd strip, I forgot to move the slide so I had to do corrections as I went.
I ended up with:
ISO 8 @ 26 seconds.
ISO 4 @ 52 seconds.
ISO ~2.5 @ 130 seconds.
ISO ~1.5 @ 156 seconds.
Harman gives ISO 1-3 with lots of caveats about testing for yourself so I was in the ballpark and didn’t have to bail and start over. I decided to use ISO 3 as my baseline. It’s just a baseline because Harman DPP barely responds to the red end of the spectrum at all so it really depends on the color of the light and most meters respond fairly evenly to the entire visible spectrum.
First attempt – great exposure, bad framing.
Drove to the church and got some nice images on my phone & a digital I’ll review soon.
I used calculations from the Mr. Pinhole Pinhole Camera Design Calculator.
I’m not bashing the site at all – it’s been incredibly helpful to me over the years but…
The angle of view (AoV), which is mathematically correct, is based on the coverage of the longest axis of the film, the diagonal. A lens doesn’t care that we want rectangles or squares, it outputs a cone of light which resolves at the focal plane (film or sensor) as a circle (a conic section). So, the angle of view of the lens is the top of the triangle from the pinhole to the focal plane. The problem is that the actual film dimensions determine where the angle is cut off. The angle of view of my camera was more than enough to cover the diagonal of an 8X10″ piece of paper (12.8″). For my camera, the diagonal AoV is 65.3 degrees.
I framed the image based on 65.3 degrees. I also bumped the camera as I took off the tape/shutter but I thought I had enough field of view to cover it. Along the 8″ side of the film, I really only had an AoV of 43.6 degrees (53.2 on the 10″ side). Metering was good in the early afternoon sun with lots of blue from the reflected sky (36 seconds at ISO 3 & f/254).
I got home and processed the image. It’s something
but I had a couple of hours before sunset so I decided to try again. I re-loaded the camera (lots of double-sided tape to mount the paper and more black tape to make it light-tight and more blue tape for structural integrity and to hold the black tape in place (black console tape is expensive and blue painters tape is cheap).
By the time I got back to the church the light was beautiful. Beatiful for something that can register reds. I metered 80 seconds but added 10 more since the pre-sunset light was much more red. It was enough to get the image but it’s pretty underexposed.
Served me well for 2 years and it’s foamboard & tape.
It was my backup since I didn’t finish my more ambitious project in time for WPPD. I used it last year as my backup-backup
so I won’t go into details here. It’s a square cone with a focal length of 10 inches and a 1mm pinhole.