Bellows extension

Canna, originally uploaded by The Central Scrutiniser.

Took the Shenhao 54 out in the garden today looking for something to shoot close up. Lit on this Canna seed head.

With the 150mm Nikkor-W 1:5.6 lens I was able to achieve something approaching 1:1 size on the ground glass with a bellows extension of about 9 inches.

Now here's the thing - when the bellows is extended beyond the focal length of the lens, one must increase the exposure to compensate for light drop-off.

Lens focal length in inches = 6. Take that as an f-stop, f/6. Close enough to f/5.6.

Bellows extension measured from ground glass to middle of lens board in inches = 9. As an f-stop, f/9 is close enough to f/8.

f/8 is one stop narrower than f/5.6. So we must increase the exposure by one stop.

This was taken in full sun, using 100ISO film (Fjui Acros), so, using the "sunny 16" rule, we would expect an exposure of 1/100 at f/16 (i.e. in full sun the exposure is 1/ISO at f/16). Increasing that by one stop gives us 1/60 at f/16 - and that's what I used.

It would have been nice to stop down more and get a little more depth of field, but there was a slight breeze and the Canna was moving a little.

I processed the Acros in Rodinal diluted 1:100. I tried to achieve 18 minutes at 20ºC but the developer warmed a little during the process. At 15 minutes it was 20.5ºC so I cut the time short at 17 minutes. The perils of processing film in the sub-tropics.

I like the tonal graduation and the sharpness. Rodinal is great stuff. I normally use it at 1:50 and it gives a bit more contrast but I like this a lot and will stick with it.

Lots of good info on bellows extension factor

And lots of data on film and deevelopers at massive development chart