Here’s the Sunpak auto 25SR Flash Manual — A Piece of Forgotten Photography History from the Past
Looking for the scanned PDF manual? Here it is. And it’s free.
Film photography is very much a thing these days, and I started to shoot film (again) since 2014. My first camera is the Nikon EM, for which my father bought in Hong Kong airport in 1980.
Along with three lens and some UV filters, there is also a electronic flash unit — the Sunpak (サンパック) auto 25SR. Very little is known about its manufacture date, but presumably in late 1970s and is the predecessor of B3000S. You can still find these flashs on market today, along with countless Sunpak vantage siblings. In Japan they are often referred as ストロボ (strobe).
The auto 25SR uses four AA batteries and has GN (guide number) 25 at ISO 100. The head is turnable and can clip on a wide angle adapter/diffuser. The flash can be triggered by hot shoe or a PC sync cable (useful for older cameras with no X-sync hot shoes). I’ve used it on my modern cameras, Canon EOS M and Fujifilm X100S, without apparent issues. Someone in Japan had mentioned that the flash trigger voltage is 8V.
The flash features an “auto” mode, which means under a certain distance it can cut off itself as soon as the body sensor receives enough reflected light, although in my own test there was not much difference from the manual mode. You can set the setting on the side of the body to see what range you can operate the flash.
Anyway, I found the original manual some years ago while we were renovating our apartment, hidden and forgotten in a drawer. No one else ever shared this manual on the Internet, not even butkus.org (yes; I did try to email the website owner with no replies). I’ve posted an earlier version — not scanned but photographed with a camera — on Flickr and was amazed that quite a few people actually asked for access permissions. Later I tried to post this on Reddit, but sadly it is not searchable anymore.
So hopefully this manual finds you well and can help you learn more about how to work with this old flash.
How to calculate aperture: f value = GN ÷ distance (meters).
For example, when the flash is GN 25 and the subject is 3 meters away, then the aperture is 25 ÷ 3 = 8.3 (roughly f/8).
Be reminded that this is at ISO 100. At ISO 200, GN is equivalent to 25 × 2 = 50, and at ISO 400 is equivalent to GN 100, and so on.
You can simply set the shutter speed to anything under 1/1000s and ideally above 1/30s while handheld. Look up slow sync flash if you wish to expose both subject and background properly while using a flash.
