Night photography with Portra 400 / reciprocity failure

I've been using Portra for daylight pictures for a while now, and want to try it our for night pics as well. I have a blue correction filter with a filter factor of 1.5 and a handheld light meter. I read about reciprocity failure online, but am not entirely sure how I should calculate the correct exposure. Can someone explain how to do this?

Each film is different, and the best advice I can offer is to look up the film sheet which Kodak produces for each film; these almost always give the necessary info re reciprocity failure. FWIW in most cases the issue comes into play when exposure times exceed one minute in length.

I've been using Portra for daylight pictures for a while now, and want to try it our for night pics as well. I have a blue correction filter with a filter factor of 1.5 and a handheld light meter. I read about reciprocity failure online, but am not entirely sure how I should calculate the correct exposure. Can someone explain how to do this?

 

My data Kodak Data Sheet for Portra 400 (release February 2016 E - 4050) states

 

 

This type of instruction has become more common, especially when the negative development can vary.

 

The three key elements that you need to ensure are:

 

> have a consistent negative development process

 

> use film from the same batch and all having been stored the same

 

> for each one typical EV, make a series of initial test exposures, I suggest bracketing in half stops on TIME, plus two stops and minus one stop.

 

Then, after negative development, evaluate the negatives, mainly looking for: optimal density; acutance; shadow and highlight detail; and tonal range.

 

WW

It's hard to overexpose Portra, so err on the side of a generous exposure.

 

This is what I'd do personally, without wasting whole films on test exposures:

 

Between 2 seconds and 10 seconds; give half a stop more, or 1.5 x the metered time.

Between 10 seconds and 60 seconds; open up one stop or double the exposure.

1minute upwards - bracket from 2x plus, or use digital!

 

In any case, metering night exposures is always a bit hit or miss. With cityscapes containing artificial light sources, you'll nearly always get an image - even if it's not quite what you had in mind.

Thank you! What I'm gathering from your response is that making photographs at night is not an exact science. I guess it's time to experiment then!

Many years ago I did moonlight photography at a lake, full moon and Ektachrome 200 in about 10 minutes.

 

Since my meter doesn't go that far, that was mostly a guess, but they came out well.

 

With ED, a little underexposure is better than a little overexposure, and I didn't worry much about it.