TR
Hi everyone, I’d like to create a grey density chart (for testing gradation) – simply by using the slide on the cassette of my large-format camera. The steps should each be exactly one stop. It’s quite simple: I just pull the slide out a tiny bit and perform exposure. Then I pull it out a little further and perform exposure, and so on. The blacks build up additively. But blimey! I just can’t seem to work out a quick formula or something similar to guide me on how long I need to expose for each step, or how far I need to open the aperture (and, of course, my film starts to follow the Schwarzschild curve after one second). With the first two stages, it’s clear: in step one I perform exposure for time X and in step two again for the same time, which means exactly double the amount of light from the first step – so one stop more. In step three, however, things already look different. That’s where I’m stuck, unfortunately. I’m not much of a mathematician.
No one should do the thinking for me now – with a long sheet of paper, I’m sure I’d manage it eventually. But perhaps there’s a very simple shortcut here? All I need is a sheet film where each ‘streak’ is exposed in such a way that it’s exactly one stop ‘darker’ than the one before it. Or is there an easier way to get hold of a transparency grey scale quickly? A 10-stop difference in density would be great. Maybe someone’s already done something like this?
Tandemfahren
Hi Thomas, don’t worry, it’s not down to your maths skills.
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The quickest way to get a step-gray scale is via Stouffer Industries. They have all the gray scales you need.
Using just the standard darkroom equipment, it would take you a very, very long time to achieve that.
You’d have to determine the characteristic curve of the film used very precisely, and then expose each streak individually. It’s not additive; for that, you’d need a film with an absolutely linear characteristic curve without a black shield.
And then expose in thirds – not a chance!
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The Stouffer wedges go up to 3.0 log D; our materials don’t even come close to that.
Considering the effort involved and the uncertain outcome, industrial wedges cost next to nothing.
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Frank
Otto
Frank is right. One downside, however, is the shipping cost of just under US$30, which covers insurance and tracking.
Best regards,
Otto!
Tandemfahren
Oh, is it that expensive now? It’s been a while since I placed my order; it just arrived in the post. I mean, back then I’d just have given Stouffer a ring, and that worked fine. Have a chat with them!
AntiLynd
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piu58
At the time, I wrote to Stouffer and asked them to send it by post. They did just that.
TR
Hello, and thank you for your replies. It seems this isn’t as straightforward as I initially thought. It then occurred to me (as Frank also mentioned) that, of course, the way I’m developing this means it’s not possible to generate a linear greyscale. I’ve seen that the Stouffer wedge is available here in the shop too. So I might order that as well next time.
Tandemfahren
Thomas, Stouffer do, however, stock grey wedges in various sizes and in third-inch increments (the one in the shop is in half-inch increments). Just so you know.
Their website is a bit confusing; I remember that some variants only appear in the price list.
Ewald
I spent a few days thinking about it, and then I realised how to achieve 7 stops (or zones) on a 4x5" sheet film.
But explaining it in writing is too much of a hassle for me here. My method is based on those of Mr Anzinger and Mr Otto Beyer.
My sole aim was to determine how steep (i.e. what gamma value) the combination of black-and-white film and developer I tested has in my camera workflow, i.e. how I can achieve a gamma of approx. 0.7. Full stops (log 2 = 0.3) are sufficient for this
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http://www.bilder-upload.eu/show.php?file=729f33-1443906046.jpg
www.bilder-upload.eu/thumb/ec6bca-1443906736.jpg
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Best regards
Ewald
