Gast
Hello,
Have you also noticed that Efke films yield about 3–6 DIN more in flash photography than other black-and-white or colour films of the same speed?
(I’m aware of the ‘true/double’ speed thing, but, for example, a Plus X film developed at 19 DIN doesn’t suddenly yield 22 DIN again in flash photography, does it?)
Specifically, Efke KB 50, correctly exposed to 18 DIN in daylight according to the light meter and developed accordingly, yields around 21–24 DIN for me in flash photography.
In this regard, old photography literature often mentions that black-and-white films can be exposed two stops less than colour films of comparable speed.
However, that doesn’t explain why this is the case, and secondly, I wonder why this is no longer the case with other black-and-white films.
What could this be down to – a lower short-time effect or a different sensitisation?
Roland
PS: Even if I don’t understand the technical side of it, it’s obviously an advantage to have double the flash sensitivity with almost the same film speed.
zensusa
Hello Roland,
Here’s a brief note suggesting one possible reason why Efke films, among others, might be more sensitive to flash photography.
Generally speaking, there are three main categories of black-and-white film:
1. Receptan films, or films with similar characteristics (e.g. Maco PO 100c; Efke 25 and Efke 50)
2. Panchromatic films (the vast majority, e.g. Agfa, Delta, HP5, etc.)
3. Superpanchromatic films such as R3, Cube 400, Classic Pan 400, etc.
Receptan films, such as Efke 25, have a spectral sensitivity below 400 nm (i.e. extending into the UV range) but cease to be sensitive at a wavelength of approximately 630 nm. This means that their speed increases towards ‘blue light’ and decreases towards ‘red light’. Consequently, for example, receptan films render shadows (which naturally have a higher blue component) significantly better than other films in landscape photography. On the other hand, they are less suitable for sunset scenes or even incandescent lighting, as their red spectrum speed is greatly reduced! As flash light itself has a high blue light component, theoretically all Receptan films should have an advantage here, i.e. they react more sensitively. This could be one explanation, as there can be up to 2 stops more speed.
Just for the sake of completeness, super-panchromatic films behave in the opposite way. That is to say, their speed only really begins at around 430 nm but extends to around 730 nm. In practice, this means they are ideally suited for use in sunset light and incandescent lighting, i.e. conditions with a high red component. Their weakness, accordingly, lies in their lower speed in the blue region.
‘Normal’ panchromatic films start with a speed above that of Receptan films but end below that of superpanchromatic films; in other words, they are ‘average’.
Anyone wishing to gain practical insight into the characteristics of these films should simply photograph a colour chart in daylight using a Receptan, a Pan and a Superpan film respectively. It is astonishing how differently the films will render the respective colours in grey tones. Anyone who has tested this for themselves will then be able to determine very quickly, if they have a specific idea of how grey tones should be rendered, which type of film is ideal for realising those ideas.
Until then, best regards
Gast
Sorry,
I’ve made an embarrassing slip-up: of course, it should be Rectepan. Please do forgive me :unsure:
Best regards, Lo van de Renne
