How safe is my safelight?

Testing the sensitivity of Direct Positive Paper to my darkroom safelight.

In my previous post, The Bin-cam pincam, https://donaldtainsh.wordpress.com/2019/10/09/the-bin-cam-pincam/ I created a pinhole camera from a redundant food-waste caddy and exposed a sheet of Harman Direct Positive Paper (DPP). The resulting image was fogged and I subsequently set out to discover the source of the problem.

The paper had been loaded in my darkroom under the glow of my red safelight. It is an AP ‘Dark Red’ light, basically a mains powered 15W lamp with an appropriately coloured plastic cover. I have previously found that DPP can be fogged by over exposure to the safelight but have never attempted to quantify the ‘problem’.

Furthermore, the plastic of which the food-waste caddy is constructed is well weathered and I wanted to assess if and by how much the opacity of the plastic had been affected by the weathering.

I started with a 10″x8″ sheet of DPP from the same pack as had been used for the original image. In total darkness I cut it into approximate 5″x4″ sheets, two to be used for testing, one as a control and one as a spare.

My first test was to expose one sheet in the darkroom as a test sheet at five-minute intervals. The safelight was positioned 2 metres away, just above the level of the test strip gadget. When developed, I was surprised at how sensitive to the red light DPP was:

It may not show too clearly here but just five minutes was enough to visibly fog the paper!

In complete darkness I placed a second sheet inside the Bin-cam pincam and put the camera outside in bright autumnal daylight for three hours. The lid and shutter remained closed for the duration of the test. This sheet was developed and compared against the above test strip and the third sheet which was developed completely unexposed.

Again, it may not show clearly here, but there is visible fogging of the ‘exposed’ sheet compared to the unexposed control sheet, comparable with the 5-minute test strip.

The paper of the original Bin-cam image was exposed to the safelight for two to three minutes while being loaded and the exposure was made in bright sunlight. From my tests, the paper would have been fogged to some extent both by the safelight and the less than perfect opacity of the camera.

With the knowledge I now have, I can take steps to minimise fogging in future, primarily in loading the paper but perhaps also making some alteration to the camera with paint or lining paper.

… Or I can live with it and find pleasure in serendipitous imperfection!

The Bin-cam pincam

How I recycled a redundant food-waste caddy as a pinhole camera.

My local council recently made some changes to our waste recycling collections. Food waste would no longer be collected separately but would instead be put in the garden waste bin. However, residents were told that the redundant food-waste caddy would not need to be returned.

I couldn’t not recycle it and let it go to waste!

The food caddy is a simple moulded plastic design with fixings for the handle and the hinge for the lid being part of the moulding. So apart from the lid opening, there are no holes in the container. Furthermore the lid, which is locked in place by the rotation of the handle, closes over a raised lip on the container’s top edge. The construction is perfect for adaptation as a pinhole camera and the internal size just about right to take a 10″x8″ sheet of photo paper.

I reckoned it only needed a hole to be drilled over which a pinhole could be fitted, something to ensure the top lip would function as a light seal, and a shutter mechanism fitted.

With a piece of paper taped in place I worked out the best position to drill a 25mm diameter hole in the front of the bin. Once drilled, I measured the projection distance and used Pinhole Assist to calculate the ideal pinhole diameter.

The optimal pinhole diameter of 0.72mm is a bit wider than my pin cams usually require (0.3 to 0.5mm) and needed a wider pin than I am accustomed to using. However I found a larger pin and punched first-time a clean hole which measured 0.79mm, checked by high resolution scan, in aluminium cut from a beer can. The pinhole was fixed in place inside the bin with glue and electrical tape, later reinforced with duct tape.

I stuck strips of sticky-backed black foam to the inside of the lid where it would close on the moulded lip of the container. Initially, I had intended to use black electrical tape as a shutter but the tape wasn’t adhering well to the plastic surface of the bin. I decided to craft something more elegant from offcuts of plywood and sticky-backed black felt. A handle moulded as part of the front edge of the container provided a pivot point that I could drill through without going through the container wall.

All that was left to do was to test it. My favourite location for testing new cameras is Queensferry and the Forth Bridge. I took advantage of a convenient brief sunny interlude and with the help of Pinhole Assist, gave a sheet of Harman Direct Positive Paper a 7min 36secs exposure.

Here’s a straight scan of the result. There’s some fogging but the image is well exposed and pleasingly sharp (I never expect or look for sharpness in a pinhole image!). I’ve had issues with fogging DPP in the past and need to work out whether this was due to over exposure to red safelight when loading, to less than perfect opacity of the (well weathered) plastic from which the bin is made, or a combination of the two. There’s nothing in the image to suggest light leaks which I would expect to see as specific areas or streaks of over exposure.

With the benefit of scanning and thus having a digital file to play with, this is what a little tweaking of the histogram produced.

In my next post, How safe is my safelight, https://donaldtainsh.wordpress.com/2019/10/09/how-safe-is-my-safelight/ I try to find the source of the fogging.