Reciprocity problems with Portra and Ektar

Ektagraphic · Mar 23, 2010

Hello- I am going to be heading to Washington DC and I will certainly want to shoot at night. I was wondering what results people have gotten out of Portra and Ektar for exposures from 2 seconds to 20 seconds. I have gone up to 4 seconds so far and the films are okay for me. I have been extremely sucessful with E100G at night up to 30 seconds so I'll bring some of that along. Hopefull, I can do some tests of my own before I go.

Thanks,

Patrick

nickandre · Mar 23, 2010

The new slide films are very good. I would just not worry about it. The worst that will happen is some slight color shift or underexposure. If you're worried, overexpose 1/3rd stop or something.

Ektagraphic · Mar 23, 2010

I have been sucessful with the slide films but rumor has it that Ektar is aweful after 4 sec.....

nickandre · Mar 23, 2010

I did some pinholes at 11 seconds and they looked fine, although I did overexpose them...

Ektagraphic · Mar 23, 2010

With which film?

nickandre · Mar 23, 2010

Ektar 100. Sorry.

hrst · Mar 23, 2010

Ektagraphic said:
rumor has it that Ektar is aweful after 4 sec.....

Rumors are rumors. Ektar is fine after 4 seconds. I've shot it at 1 minute. It will require some additional exposure, of course, but not much at 4 seconds.

hrst · Mar 23, 2010

Someone posted results of a quick reciprocity test of Ektar 100 here at APUG; I can't find the post anymore but I have a copy of it.

Pardon me for quoting without the source. Here;

----- ----- -----

"I ran a quick test for reciprocity using a 120 second exposure with a 10 stop ND filter, but it was the end of the roll, so I didn't have room for proper bracketing. My estimated speed loss was about 1.3 stops. That would yield the following adjusted times in seconds.

metered time -- adjusted time
1 ----------------- 1.4
2 ----------------- 2.9
4 ----------------- 6.3
8 ----------------- 14.1
15 ----------------- 29.7
30 ----------------- 68.4
60 ----------------- 159.0
90 ----------------- 261.2
120 ----------------- 371.7
240 ----------------- 871.5"

----- ----- -----

And remember that with color negs, it's usually on the safe side to overexpose rather than underexpose! Exposure latitude and reciprocity law failure together make exposure at night quite simple; you can't easily overexpose too much; just expose as long as you can!

Ektagraphic · Mar 23, 2010

How bad is the color shift?

2F/2F · Mar 23, 2010

I have got poor results out of both with long exposures, as far as reciprocity maintenance is concerned. Looks like someone posted a chart for Ektar, however, and you can experiment with that.

FWIW, I would say that Ektar is a film that will exacerbate some of the big "problems" with night photography: high contrast, and color shifts. The film is a high contrast, high saturation film. It will black out your blacks, white out your whites, and increase the intensity of color shifts. If you want that, have at it. If not, pick another film.

If you have the money, I'd get some Fujichrome T64 and/or Provia. They have some of the best reciprocity characteristics ever, and T64 is color balanced more closely to some of the lights in the city than is a daylight film. I would overexposed them two to three stops and pull to match in most night shooting scenarios, to lower contrast. If you want a neg, cross processed Astia is decent. Try to overexpose it a few stops and pull 1/2 stop to 1 stop in C-41 processing to lower contrast and make color correction easier.

Lee L · Mar 23, 2010

hrst said:
Someone posted results of a quick reciprocity test of Ektar 100 here at APUG...

That was me, in this thread: (there was a url link here which no longer exists)

Lee

hrst · Mar 23, 2010

My (currently quite limited) experience is completely the opposite! I find Ektar 100 a superb film for night photography. I get moderate contrast and nice, enhanced colors. Color shifts? I haven't seen them. Best film for night photography IMO! If you could ever even consider chrome films, Ektar100 should be able to deliver you much more dynamic range.

hrst · Mar 23, 2010

Examples.

Exposures ranging at 15 - 60 sec.

Direct film scans with very minor adjustments. I've RA-4 printed two of them, no problem.

Lee L · Mar 23, 2010

hrst said:
Examples.

Exposures ranging at 15 - 60 sec.

Direct film scans with very minor adjustments. I've RA-4 printed two of them, no problem.

It's very difficult to tell with mixed artificial lighting from outdoor fixtures (the colors of which vary widely by type and age of the lamp) and interpretive printing, but it looks to me like you're getting some color crossover, cyan in the shadows and magenta in the highlights.

In the thread I referenced, others seemed to think it was pretty decent for wide field astrophotography with a correction for a slight color shift. I have been working on finishing off my Kodachrome, so haven't really shot Ektar since that post. I have some more in shipment now, so I'll have more experience with it in a few weeks, but no long exposures planned at this point.

Lee

2F/2F · Mar 23, 2010

The compositions one will most likely shoot in Washington are much higher in contrast than what you shot, HRST. Additionally, your exposures were only 60 seconds, which are very brief in the world of night photography, so it is no wonder your color shifts were somewhat correctable (though they are there, for sure). I am thinking of exposures well in excess of that. Of course color neg materials are ideal for night shooting, in theory, in terms of how much of an SBR they can capture. However, practically speaking, in looong exposures, the reciprocity and color shift issues are huge compared to something like T64, and T64's dynamic range can be increased a good deal by doing what I recommended. Properly exposed and developed T64 is way more accurate in color and exposure calculation, and will not leave you sitting there twiddling your thumbs nearly as long (a VERY important consideration, especially in cold weather). I understand the benefits and the amazing quality of color neg films today, and they are both good tools for the task, but there are definite reasons I suggested trying some Fujichrome. Additionally, I suggested cross processing, because if color is not of import, this gives you the best of both worlds. I suggested cross processing a low contrast, low saturation film (Astia) by overexposing it and pulling it a bit. Overexposing is a good trick to reduce contrast when cross processing. You have to get a dense neg to do it, but it works. This is why I generally overexpose at least two stops when cross processing. In some recent tests of Astia and EPP, I found that overexposing two stops when cross processing adds about a stop of dynamic range in a straight proof print to the EPP, and about a stop and a half to Astia.

Ektagraphic · Mar 23, 2010

I have had great experiences with slides at night but the only reason I am looking into a neg option is so that optical prints are less expensive to have made than Ilfochromes.....

hrst · Mar 24, 2010

2F/2F said:
The compositions one will most likely shoot in Washington are much higher in contrast than what you shot, HRST. Additionally, your exposures were only 60 seconds, ----However, practically speaking, in looong exposures, the reciprocity and color shift issues are huge compared to something like T64, and T64's dynamic range can be increased a good deal by doing what I recommended.

Okay, I understand. Thanks for your insight! I really was thinking of 60 second exposures and less, and was really answering to rumors that Ektar cannot be used after 4 seconds.

Some Fujichrome films indeed have very good reciprocity characteristics.

Ektagraphic · Mar 24, 2010

Would Portra be any better? I need to find a good subject to try this on......

dainmcgowan · Mar 24, 2010

i cant remember the exposure details, but i used the numbers supplied from Lee L.
many thanks Lee.

Lee L · Mar 24, 2010

dainmcgowan said:
i cant remember the exposure details, but i used the numbers supplied from Lee L.
many thanks Lee.

You're welcome. Glad some folks are finding the info useful.

Lee

Josh Harmon · Jul 6, 2010

Been browsing this post and decided to take the data from hrst's post and interpolate a function.

(x)=-5.5391+2.5568x+.0046x^2

This is helpful for long, astrophotographical exposures. Hopefully it follows the function.

Cheers,

-josh

Tom Taylor · Jul 6, 2010

What's x in the above equation? Time of exposure?

Lee L · Jul 6, 2010

Tom Taylor said:
What's x in the above equation? Time of exposure?

x = metered exposure time in seconds
f(x) = exposure time in seconds adjusted for reciprocity

Josh's polynomial works decently (and well within any realistic margin of error), but the original post: (there was a url link here which no longer exists) and the exposure adjustment table that was copied from there to this thread uses another form of equation.

f(x) = a*x^b+x

were
x = metered exposure time in seconds
f(x) = exposure time in seconds adjusted for reciprocity
a = 0.423779032413281
b = 1.33325705621286

(serious overkill on significant digits, don't confuse precision with accuracy)

If you look for Gainer's posts on APUG about reciprocity failure, you'll see that he's adopted this same form of equation to describe reciprocity failure, but set b as a constant, so that:

f(x)= a*x^1.62+x

Because I make adjustment tables to carry with me in my camera bag, I find it just as easy to let the value of b 'float' when making up my tables.

Lee

Tom Taylor · Jul 6, 2010

Then if the metered time is 5 seconds, then ƒ(x)=-5.5391+2.5568x+.0046x^2 =18.44 seconds if my arithmetic is correct. Which is way too much compensation for both Tmax 100 and Fuji Acros.

If a*x^b+x then f(x) = 8.62 seconds then, according to the manufactures data sheets TMax is overexposed by 1/3 stop and Acros is overexposd by 2/3 stops.

If a*x^1.62+x then f(x) = 10.75 seconds.

Thomas

Lee L · Jul 6, 2010

Tom Taylor said:
Then if the metered time is 5 seconds, then ƒ(x)=-5.5391+2.5568x+.0046x^2 =18.44 seconds if my arithmetic is correct. Which is way too much compensation for both Tmax 100 and Fuji Acros.

If a*x^b+x then f(x) = 8.62 seconds then, according to the manufactures data sheets TMax is overexposed by 1/3 stop and Acros is overexposd by 2/3 stops.

If a*x^1.62+x then f(x) = 10.75 seconds.

Thomas

TMX and Acros would have very different polynomial coefficients than Ektar and different coefficients and exponents in the case of the second equation.

Gainer's coefficient a would be different from my number, given that the exponents are different, and in any case, those numbers would still be different for TMX and Acros than for Ektar or Portra. And TMX and Acros wouldn't share the same coefficients or exponents.

There may be a couple of useful general forms of equations for reciprocity failure, but films vary widely and consequently so do the exponents and coefficients for any given form of equation.

You can't randomly apply the solution for one film to another film.

Lee

Reciprocity problems with Portra and Ektar

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