Sunday, October 8, 2023

Pinholes as recommended by Lord Rayleigh.

The 4x5 Pinhole Lab Camera has four settings for the distance from pinhole to image plane, ergo angles of view. From stupidly wide 118° at 38mm to almost normal 55° at 120mm. The pinholes, one on the axis and 20mm above it in both dimensions, can be changed for the size with minimal diffraction Lord Rayleigh would recommend with his equations.

As a practical matter, the sizes appropriate to the different settings were the size I first succeeded in drilling three matching pinholes, in the range I was looking for. I've been using .28mm pinholes for the 60mm setting, which is a bit smaller than .32mm that the equations specify. (I also used them for the ultra-wide 38mm setting, because what's optimal when the distance to the pinhole ranges from 38mm at the center to 75mm at the edges?) For 90mm, I made a set at .36mm, again a little small and for the 120mm slot, .45mm holes, closer to the .46mm Lord Rayleigh suggests are the best for that distance than the other sets.

One day rummaging around for something else in my messy pinhole supplies, I encountered an envelope of .40mm Gilder Electron Microscope Apertures from a long ago deal with League of Upper Midwest Pinholers comrade Earl Johnson. I think he still does this for a buck apiece ($) with appropriate postage added. You can only get them from Gilder in quantities of 100.

When you ask Mr. Pinhole, the optimal size for 90mm from the pinhole is exactly .40mm.

It seemed appropriate to my course of studies in Antique Film Large Format Pinhole Photography to see if those mathematically perfect holes, a little smoother than I can drill myself, in a bit thinner metal, make any difference. My assignment is to expose a couple developer-tanks worth of my elderly sheets of Plus-X at moderately-wide 90mm with the repurposed consumable scientific supplies using photons instead of electron beams.

My first encounter was with the metal maze of the backlit shiny bleachers of the softball fields in Menomonee Park.

Along the shore of Lake Winnebago, I passed this fellow with his guitar, playing for no one within a quarter mile. He agreed to my photograph and followed my direction to just go about it as if I wasn't there. After apologizing for his somewhat hoarse voice, he performed a spirited rendition of "Guadalajara." I confessed that I hadn't played guitar much lately, but maybe the solution was to try doing it sitting by the lake shore. 

The haul from the Farmers' Market. After I opened the shutter for the hour long exposure, I realized the ingredients for lunch were in the picture so we ate a little late.

The annual cabbage report.

Perhaps as a student attempt at a new take on a rephotographic project or a desparate measure by an old dude, I've started photographing scenes I've done before, but from the opposite direction.

This image reminds me so much of an early 1900's postcard photograph I'm surprised there's not a hand written "Oshkosh Public Library" etched into the lower left hand corner of the negative.

This is the South Side Branch of the Oshkosh Public Library. Oshkosh's population has always been divided by the Fox River, with the earlier settlers from the east on the north side and the laborer immigrant population south of the river. When they expanded the Main Library and closed the South Side Branch, there was much comment about how the North Side was lording it over the South Side again. 

The curved southwest-facing collonade of the Horizon Village apartment-style residence hall at the University. I tried and failed to shade the pinhole from the sun which is just outside the frame, but it looks like some flare added to the complexity of the lighting situation.

The grand facade of The Waters, originally the Oshkosh Yacht Club, facing Lake Winnebago in the morning sunlight.

I seem to have an obsession with Neo-Federalist architectural details lately.

That's a good enough test of the Gilder Apertures. Switched to the ultra-wide 38mm distance and the .28 pinholes in order to feature the modified-to-meet-code stair railings on the newly restored front porch, done by Metalverse, two guys whose shop is only a few blocks away. All the rest was done by Jacobson Home Repair, one guy who lives four blocks away in the other direction.

These all seem pretty darn sharp, especially the uncropped full-frame ones. (Not sayin' which ones those are.) Looking at them at full resolution I really can't tell if they're better than the smaller hand-drilled pinholes I have been using.

The 4x5 Plus-X was semistand developed in Rodinal 1:100.

No comments:

Post a Comment