Topic: Colour pinholes and Portra reciprocity

[Ezzie]

I must admit I have been apprehensive about using colour film for pinhole photography, never really having done much long exposures in colour.

Reciprocity figures for C-41 films seem to be less accesible too, which does not help.

I looked up Ektar, and even Kodak themselves recommend experimentation, rather than giving hard figures - evidently due to risk of colour cast et al. Further comments discouraged me to try it out as a first.

For another favourite film of mine, Portra, I found this on LFPF, which is easy enough to understand, but maybe not something you carry around in the field: http://www.largeformatphotography.info/forum/showthread.php?106441-Portra-160-and-400-Reciprocity-Failure

So I applied the formula and made a table I can carry around on my phone instead.

Notes:

• The time for 1 second is not quite right, due to the natural logorithm of 1 being 0. So the resulting correction ending up a negative.
• I have converted stops to seconds, and calculated the resulting actual exposure times, so no need to start adding one to the other
• I have yet to try this out in real life, but hope to within a week or so

[02Pilot]

I'll be interested to see your results. What sort of exposure times are you anticipating, based on the camera and the conditions you expect to be shooting in?

FWIW, I've shot Ektar in one of my pinholes a few times to good effect. I've just used the basic exposure calculation without reciprocity factored in and added a second or so if I'm up past 10-15 seconds. That said, I've only shot it in fairly bright conditions, so I've never had to consider really long exposures. I did not have a problem with color casts, which Ektar can of course be prone to with overexposure, but it did come out very saturated, even for Ektar.

[Ezzie]

For other films I usually end up with exposures in the 8-15 second region midday, and 5-10 minutes in  the early morning and just after sunset. Corrected for reciprocity. The longer the better really, I like cloud trails, calmed water, and other smearing effects.

[Francois]

I can't believe they even went through the trouble of figuring out the non-linear regression curve!

[astrobeck]

One thing I've noticed with shooting color in pinhole is the color shifts go to blue.
Instant Fuji film is probably the very worst.

Ektar is prone to going a bit Cyan and not always consistent in doing so.

A few seconds doesn't matter much, but once you go over the 30 second mark, things get "cool".

I don't have enough experience with Portra to say....

Looking very forward to your photos!!!!   

[DonkeyDave]

Portra goes cyan too, and the sky can go a bit yellowy/green at times

[Cadha13]

I got some pretty good images on Portra 160 on my 6x6 pinhole. Like 5-10 second exposures in 4 PM sun.

I have mine ready with some Portra 400 this week's challenge. 

[Ezzie]

These are Portra 400, with an ND8 filter (3-stops). 2, 6 and 8 minutes respectively. I have corrected for neutral gray as best I could, because the colour cast was quite considerable. In general, the longer the exposure the bluer the cast. Also note that the ambient light got warmer as the evening got on. The shortest exposure being taken first, the longest last.

But, the positive thing is that the table seems to work. Mid-frame, and no vignetting the exposure seems well within a half stop accurate. Portra will easily handle a latitude of 2 stops overexposure, so no problems there.

DIY 6x24 pinhole camera:

Skasen #1 by Eirik0304, on Flickr

Skasen #2 by Eirik0304, on Flickr

Skasen #3 by Eirik0304, on Flickr

[Francois]

Now that is quite comb and soothing.
Still shot with the wine box?

[Ezzie]

Yup, though I have had a few malfunctions. Need to adjust the film gate, it has a tendency to open up and let the film slip inwards towards the lens.

[KevinAllan]

Ezzie, I took your table with me on my last pinhole outing, when I shot the two images in the weekend thread. But the sun was so bright that the metered exposure was 1/8 second ... so no adjustment needed but probably gave extra exposure anyway since accurately timing a 1/8mode is exposure in bulb mode is pretty difficult !

My ND filter is a square type which I can't easily use with the pinhole (unless I just hold it) but I have a 52mm pola which could be fitted, and I'll take that with me next time.

[Ezzie]

Thanks Kevin.

I use a square Lee type filter on the 6x24. The face of the camera is big enough to allow me to fix four screws and to slip the filter underneath the heads. To make a tight fit I added heatshrink to the screws. I will take a picture of the rig for you to see.