It is early in the morning at this reading, but I don't see mention of what format you are using, simply “multiformat.” If you are using a view camera you may need to add a bellows factor. Search here and the large format forum if you are not familiar with “bellows factor”. If you have a large bellows you may need to add more exposure, several stops.
When experimenting with night photography in any format, or even work in deep shadows, it is money well spent to bracket your exposures. By that I mean add at least two stops to the exposure you think addresses all of the above, including reciprocity. It is reasonable to assume that you can make a pretty usable print one stop on either side of the correct exposure. If your bracket is two stops more than the maximum exposure you think you need, this will give you a six stop range for your experiment.
If this is not enough exposure then reconsider how you are metering. Consider a gray card, consider an Incident Light Meter which measures the light that hits the subject. It all boils down to the old standard “metering for the shadows, printing for the highlights.” If your first experiment doesn’t give you the detail you want, shoot it again with much more exposure and then bracket with two more stops (yes, doubling the time for each stop).
The joy of experimenting in the neighborhood is that it gets dark every night. You experiment close to home, learn what you need, so that you know what you are doing when you go on an expensive trip. I hope this helps.
John Powers
