Topic – Exposure again

Today I made an series of exposures with the GA645Zi. It was mounted on a tripod and had  some sunshine from about two o’clock. It was not shining directly into the lens. Before the actual exposure run was started I metered the scene with a spot meter. To avoid erroneous readings I went real close to the spot I wanted to measure. This way there is no chance stray light could have entered the meter. The film was Fomapan 200. It was developed for 8 minutes in HC-110 1+60 at 20C. Before first shot the internal exposure meter of the camera was read (1/30 f/8, =”exposure +-0″ below).  The full series was then from 4 stops under this exposure and up to 6 stops over  in 1 stop increments. Actual settings were:

Pic # Time Aperture Exposure
1 1/60 f/22 -4
2 1/30 f/22 -3
3 1/30 f/16 -2
4 1/30 f/11 -1
5 1/30 f/8 +-0
6 1/15 f/8 +1
7 1/15 f/5.6 +2
8 1/8 f/5.6 +3
9 1/4 f/5.6 +4
10 1/2 f/5.6 +5
11 1s f/5.6 +6

Leaving the highlights out of the question for now, lets concentrate on the dark areas. The first picture is clearly too dark and under exposed. Relative to the camera’s exposure meter of the scene this in under exposed four stops. The same goes for all under exposures, they really are under exposed! (Jump to ** for next text).

#1 Exposure: -4 dens1 #2 Exposure: -3 dens2 #3 Exposure: -2 dens3 #4 Exposure: -1 dens4

** The cameras internal meter averages this to normal exposure. The round black disk on top of the arrangement is however not only pitch black but also without any trace of texture. Thus still under exposed!

#5 Exposure: +-0 dens5

At +1 the disk gets a bit lighter but still there really are no traces of the marks in the disk.

#6 Exposure: +1 dens6

At +2 some very minimal texture of the disk starts to appear. It is still too little for my scanner to discern really.

#7 Exposure: +2 dens7

This is where it all happens! At +3 the disk is not a black blotch any longer but emanates as something with a surface.

#8 Exposure: +3 dens8

With more over exposure one can quickly see that not much more texture appears on the disk, it only gets lighter and lighter. Beyond this exposure the experiment does not say anything useful about the disk. The rest of the series is left below for reference.

#9 Exposure: +4dens9 #10 Exposure: +5 dens10 #11 Exposure: +6 dens11

Discussion

The spot meter metered the black disk as having a light value of 10 EV. In the “#8, Exposure +3” shot above, where the disk’s texture is just beginning to appear, this EV-value would correspond to the scene’s Zone III. For the disk, which now is placed in Zone III, this exposure is the correct one.

The exposure meter reads +3 and the Zone III lands where it should. To permanently set the camera to +3-exposure one could change the ASA to 1/4th, i.e. ASA 50 instead of ASA 200 (200->100->50).

Zone V is, by definition, be what the camera and spot meter meters (the famed “18 % grey”). The scale on the Soligor spot meter tells me that 10 EV @ ASA 200 corresponds to 1/30 f/8 (which incidentally happens to be exactly the same exposure the built in meter suggests for the entire scene).  Now, if 1/30 f/8 should be stopped down two steps, to place it in Zone III, this translates to 1/30 f/16. This later value corresponds to picture “#3 Exposure -2” and is too dark! As it turned out it would be better to stop up the spot meter reading by 2 to get picture “#7 Exposure +2”.

Zone V is, per definition, 2 stops above Zone III and is be what the camera meters for the average of the whole scene. In this case the camera would better have metered 2 stops above it. Here the camera reading should over-expose by 1 stop to place the shadows in Zone III. By this reasoning another way of seeing this is to reduce the film’s speed from ASA200 to ASA100 as this would off-set the internal meter by +1.

Conclusion

Lots of numbers to and fro here. I have not really managed to get them together in a consistent way. They always seem to be one f/stop off. One conclusion must be to not to be too concerned with quite large amounts of plus-exposure. Another conclusion would be that setting the camera for ASA 100 or even 50 for Fomapan 200 is preferred.

Finally: The best exposure (#8) has its highlights washed out so development time must be reduced somewhat.

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