Reciprocity factors for Kodak Ektar 100 beyond 5 min exposures?

[J 3]

Has anyone made a reciprocity table for Kodak Ektar 100 that goes beyond 5 min by chance? Also are there any filtration requirements with Ektar pushed out into the hour range?

I'm hoping for the factors on exposures from 15 min to about 2-3 hours for large format moonlit photography. The table at this site puts the factor for 4 min at a little above 2x, but I've seen nothing that extends beyond that - https://www.jasonrobertjones.com/journal/2018/2/5/velvia-reciprocity-chart

Charting in Excel one would get for an exposure metered at an hour, a correction factor of about 18x if it's linear (metered time to exposure compensation ratio) and about 3.2x if a power series is a better model. I'm expecting it's probably closer to 4-6x in reality but it's hard to know.

Thanks much in advance.

 

[thuggins]

I have opined in the past that "reciprocity" is as much a philosophical construct as a scientific one. The structure of our eyes is such that we do not have color vision in low light (A fact immortalized by the Moody Blues). Since you are taking a photograph of something that you cannot see, how can you judge whether the film has "properly" rendered it?

I have taken a number of nighttime shots with my OM's which use Off The Film metering to determine automatic exposures in low light. The OM-4 goes up to a four minute exposure. These are invariably with slide film, so there is not a whole lot of room for error. In every case the shots come out beautifully. Are they rendered "correctly"? That question really doesn't have any meaning as what my eyes saw and what the photograph records are fundamentally different. Since the film type is not a variable with the OM's, there is no concept of reciprocity with these exposures. Yet the OTF exposure process (along with Olympus' multi-spot metering) was widely recognized as the most sophisticated metering method of any film camera.

 

[brbo]

Charting in Excel one would get for an exposure metered at an hour, a correction factor of about 18x if it's linear (metered time to exposure compensation ratio) and about 3.2x if a power series is a better model. I'm expecting it's probably closer to 4-6x in reality but it's hard to know.

It doesn't really matter with big format (slow lenses) and slow negative film with a big reciprocity failure and long exposures. It's more of a seasonal thing - either is the night long enough or it is not...

Anyway, I have a Reciprocity Timer app on my phone and it gives the following times (for 10min and up, if you need shorter times too just let me know):

10' --> 45:24
12' --> 57:02
15' --> 1:15:27
30' --> 3:00:31