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Discussion in 'Exposure Discussion' started by Regular Rod, Oct 7, 2013.
Can anyone point me in the right direction for an EKTAR 100 reciprocity table please?
I am not so sure there will be one, but if there is There will be someone along with some sort of reply
For a starting point, longer than 1 second, add 1 stop. Longer than 1 minute, add two.
I don't think that there is an "official" table. Kodak suggests that you run your own tests with exposures longer than 1sec.
Have you searched for people's results on this? I had a quick look and there is a fair bit of anecdotal information out there (including on this site).
Yes but what if the stop is pre-decided for the exposure and the indicated exposure is more than a minute?
ILFORD provides a useful graph for customers. Kodak it seems does not. Maybe they don't test their products. It's okay for Kodak to say "Make your own tests..." They aren't the ones buying the film!
I'm really looking for a graph or table as per ILFORD's customer service. Kodak could learn from the once smaller company...
The Ilford charts are pretty loose IMO. You're still guestimating times when the X and Y don't intersect on a given time combination. For instance, how long is the required exposure with an indicated 2 second exposure on this chart?
Run some test. You don't need to use much film; strip tests using the dark slide will give you a pretty good starting point. Ektar's pretty forgiving, so your results might not be as varied as you currently think they'll be.
That would be 5 seconds. You simply look across to the numbers on the right hand side. You can make the chart easier to use by printing it off with a grid.
I have used the ILFORD charts for a long time and they have never let me down.
The EKTAR 100 film and processing is far too expensive for me to squander on testing that Kodak should have done for us, the paying customers, in the first place.
What did you do when you were finding out that EKTAR 100 was pretty forgiving?
An f-stop in this context is a quantity of light. It can be achieved by opening the lens further or it can be achieved by adding time. I prefer adding time when dealing with long exposures. So if the indicated time is more than one second but less than one minute, double the time. If the time is more than one minute, double it and double it again - i.e. if the meter says 1 minute, then give it four. if it says 15 seconds, give it 30 seconds. This is a fairly stable formula for most color negative emulsions. This is probably why Kodak has not provided a chart for Ektar. Besides, once you get into these extremely long exposures, precision becomes a relative thing and is fairly irrelevant. What you get is largely a matter of taste and need, not a matter of accuracy.
Thank you. I will give that a try.
I get it at 4 seconds. Or 6. Or 5, as you wrote, depending on where I decide 2 seconds lies and where the intersection point is. Hardly accurate. At best, it is an indicative graph.
I avoided rubbish graphs and shot with it. I also looked at dark locations shot on Ektar Google Images and explored the Shooters' descriptions.
It is easier to read the graph if you print it with a grid. I can send you a file if you like.
I like the idea of looking on Google at images and seeking the information from there.
Thanks for the offer; I've moved on to an App that gives me Reciprociy, though, so shouldn't need it.
Speaking of that App, it has Ektar on it, so I'll run a spreadsheet of its data, convert to a graph and PM you with it if you'd like?
The difference between 5 versus 4 or 6 seconds is only 20%. Insignificant especially with color neg. Always err on the side of more exposure with color nef so give it 6 and don't worry about it.
It's for HP5+.
And it is more than 20%, as you have reciprocity failure on reciprocity failure.
But my point was, it is not an accurate graph, particularly for shorter exposures.
I like long exposure photography and I have practice it quite long. I have to say that in my experience Ilford films have generally much worse reciprocity failure than any Kodak emulsion I have used. I am not a big fan of Ektar, to be honest I don´t like it at all, but I expect Ilford table to give overexposed results, when used with for it. The best way is to make tests and check the exposure and the color rendition. It seems like Ektar tends to shift more to cyan when used for very long exposures.
Here is a link for an old APUG thread:
What's the App. called? That could be the answer...
Well ok - lost that in the thread I guess. But no matter, I'd bet (a small amount) of money that one could barely tell the difference visually between 4, 5 and 6 second exposures.
One of the problems with nite photog is that the film speed depends a lot on the light source. You get all kinds of artificial sources potentially mixed into the scene. Then if there's is corrective filtration in play,that has to be factored in. So maybe Kodak just decided to play it safe and say nothing. But if I get around to experimenting myself, I'd probably follow a game plan similar to that already posted.
Woah. That's true, but only when reciprocity holds and we're specifically talking about the regime where it does not. A stop is a factor of two and for long exposures, it matters where you apply that factor of two, because time and aperture are no longer equivalent.
If you give something a stop more aperture, you are increasing the luminous flux on the film, which will reduce the effects of reciprocity failure. If you give something a stop more time, the luminous flux is unchanged and you're still in the realm of reciprocity failure. Fixing RF through additional time requires a larger correction than fixing it through larger apertures because the latter actually helps to solve the problem.
Secondly, RF causes a contrast increase. Because RF is worse at lower fluxes, the shadows are affected more severely than the highlights. If you want to maintain not only an appropriate exposure but also an appropriate contrast, you will need to pull the film (overexpose+underdevelop). This means that there are now effectively three parts to correcting your image:
- additional exposure sufficient to bring your shadows up off the toe
- a reduction in development time in order to tame the contrast increase
- yet more exposure to deal with the loss of speed arising from the reduction in development
When you read a reciprocity table and it says "add X extra", it matters where you add it. 90% of the time they will recommend a (much?) longer time but sometimes, the corrections list a larger aperture. Using the aperture correction is NOT sufficient if applied to time, using a larger aperture is basically a cheat and may well not be possible (max aperture limits) or artistically desirable (DOF). If you could possibly get away with a larger aperture, you would have done that for yourself and started your reciprocity calculations from a different (less severely affected) point on the curve.
It's all too hard? Go shoot some Acros or Provia