As I noted under "MGD May Challenge #2" I have a question about Reciprocity Failure
while shooting to get a comparison between the 4 Kodak Portra emulsions.

I want to shoot all 4 rolls under the same lighting conditions and same 4 scenes.
I'll shoot 3 shots for each scene to bracket the exposures.
For most of the shots I plan, there is no direct sunlight and with the slower emulsions,
I may have to use a long exposure ... say 2-4 seconds, perhaps longer.
For artistic reasons, I'd like to keep the f/ stop fixed for each scene and get
a consistent DOF ... but I don't know if this will cause reciprocity failure in the film.
I will have to shoot all 4 rolls in close sequence to get fairly consistent light.
If I pick an overcast or mostly cloudy day, I won't be too rushed.
OTOH, On a bright day, I would have to shoot between 9 and 11, or 2 to 4 to avoid
extreme lighting changes between shooting the first and last roll.

MGD

Attached Link: http://www.kodak.com/global/en/professional/support/techPubs/e31/e31.pdf

Reciprocity failure is the films decrease in light sensitivity with increased length of exposure time... when it is pushed beyond the limits of it's exposure range.... Generally one only has to worry about this at night... I can't imagine that you would have a problem with this shooting during daylight hours. Unless you are shooting waterfalls, why would you need 2-4 second exposure times? Shoot at a moderate apertures (as opposed to f/22 or f/32) and you should be able to obtain shutter speeds of reasonable time. Reciprocity failure usually occurs at shutter speeds below 1/10 of a second. The rule of thumb (always best to consult the films data sheets) is a doubling of exposure time. So if you were shooting at 2 seconds you would want to double your exposure time more to say 4 seconds..... 4 seconds to 8 seconds..... of course as I already said this is just a generalization.... consult the film manufacturers website, or do a google search... you may come up with some charts or recommendations.

One person's failure is another's success. Long exposures make interesting colors! Sounds like an ambitious plan... What do you hope to learn? So many variables... So difficult to interpret the results...

Thanks for the responses ...

@DHolman - I'll take the printout with me today to study.

@Michelle -

I can't imagine that you would have a problem with this
shooting during daylight hours.

Shooting in the Adirondacks (20 years ago), dense forest
canopy gave even subdued light, extreme macro (Canon
70-210mm, f/4 plus FD50 extension tube) and with bracketing,
I had maximum exposure times in the range 90 to 120 seconds.
And got OK results in the prints.

Some images on the 120 roll I shot for the May challenge had
exposure times in the 2-4 second range -- f/4 lens.

Do you think there will be any color shifts because of the
range of exposure times? On the other end of the scale,
f-stop and resulting shift in DOF might prevent comparisons
among the 4 emulsions that I will be testing.

IOW, for purposes of comparison between emulsions, should I
constrain shutter speed or f-stop?

doubling of exposure time

Good rule of thumb -- no heavy book to carry along.

MGD

@Misha

One person's failure is another's success.
Long exposures make interesting colors!

LOL

Sounds like an ambitious plan...

Not too bad, just 48 images -- the pain is that I might
have to position the tripod 16 times.

What do you hope to learn? So many variables...

I have just begun to use Kodak Portra films ... I need to
see the color differences between NC and VC ... I need to
see what I can expect from 160 v. 400 for the type of
pictures I take. It might let me do all of my outdoor
shooting in one emulsion/speed.

So difficult to interpret the results...

What ... aren't we all consultants?

I expect some opinions.

MGD

PS ... Misha, I think Tedz wanted to talk to you. LOL

I am not talking to Misha anymore....phooooooooooooy! I am still convinced it was He/She that stole My Home Page and Happy Pills :[

Shooting in the Adirondacks (20 years ago), dense forest canopy gave even subdued light, extreme macro (Canon 70-210mm, f/4 plus FD50 extension tube) Now that makes sense... extension tubes will cut down a good 2 stops on available light.... You may want to do without extension tubes, for this test, make it as normal (if there is such a thing) a shoot as possible. for purposes of comparison between emulsions, should I constrain shutter speed or f-stop? Not sure about that one MGD.... FWIW.... f/16 @ 1/10 is the same as f/8 @ 1/20 ..... I really don't think that DOF by changing aperture will effect color as both of those settings above are letting in the same amount of light. You're just creating a more shallow or narrower DOF, but then again I could be wrong. shrug

@Michelle -

without extension tubes, for this test,

I wasn't planning on extension tubes of macro work -- just indicating how R/F could happen

normal

Aaaaahhhh, I love normal ... and seek it every waking moment.

DOF by changing aperture will effect color

I was thinking that changes in DOF within a scene or between
2 emulsions would affact our evaluation of color.

IOW, consider two shots of a scene made with 2 different
emulsions and therefore 2 different exposures ... If I use 2
different f/ stops, the out of focus areas will be different
and therefore harder to compare than if I keep the f/ stop
constant and vary the shutter speed.

But, how much would that (different f/ stops) affect our eyeball evaluation?

MGD

Hmmm well, sounds like your getting all the advice you need. Reciprocity also occurs during extemely short exposures as well. Shooting outside for long exposures can create a colour shift regardless of the film your using. This can be corrected in the printing stage with filtration and a colour anyliser. i realize not everyone has access to one but if you have a custom lab nearby, you can let them know about the exposures and they will compensate. batch processing at most labs doesnt give proper results when deviating from the "norm". I'm a little luckier than most being able to access my lab at work and through the custom lab we use on other projects. the 160 film should be more then adaquate to do the job you want and i find its colour shift to be minimal. the more sensitive faster films tend to be more unstable in regards to colour shifts over long exposures and can cause bleeding. hope that helps.

as for constraining shutter speed versus aperature, depends on what you want out of your picture. just remember the faster film will be more susesptible to bleeding from longer exposures. I'd treat each film separately and go for what would give you a proper exposure. then compare the negs and the prints afterwards. Regardless of keeping the dof fixed, you are going to see noticeable differences in the final results from the film speeds. Most film manufacturers will claim that the technology has advanced so that 400 speed is very sharp, and it has, but they continue to make the slower speeds for a reason. especially in the professional series. Most macro shots look best when the image is sharp, especially on enlargement. Having spent 22 years in the field and doing a lot of experiments, I'd always opt for the slowest film i can get my hands on.

Oh yeah, one more point. Keep your professional films in the refrigerator till about 1/2 hour before use. after you expose the film, put it back in the fridge till your ready to develope. that will minimize any colour shifts. professional films werent designed to keep long and do not react well with higher temps.