frankmcelhinney 10:50am, 23 July 2013
When using MULTIGRADE IV RC to make paper negatives at what point does reciprocity failure take effect (i.e. what length of exposure)? Is there a power value or some other means of calculating the compensation required for this reciprocity failure?
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Barnaby Nutt PRO 5 years ago
Please post the reply when you get it. I guess the answer is on the data sheet that comes with the paper...
frankmcelhinney 5 years ago
placid casual:

Based on my experience so far, reciprocity is a non-issue with this paper.
alienmeatsack PRO 5 years ago
Even with longer exposures in the 40-60 hour time frame?
This is from Andrew Sanderson's website and may be helpful
frankmcelhinney 5 years ago
Just to re-iterate, based on my experience reciprocity is a non-issue with this paper. I double checked with Harman (technical) who replied: "For our papers - provided the exposures are within say a couple of hours, there is no real adjustment you'd need to make to whatever your initial metered reading is telling you to expose to."

Alienmeatsack - For exposures of 40-60 hours? I've only ever done those kinds of exposures with pinhole cameras outdoors. In this scenario an image is burned directly into the paper. Chemical developer would turn the paper black. The only way to retrieve an image in this case is to scan the paper as soon as it comes out of the camera, preferably in a darkened room. Maybe you are working with a very faint controlled light source in which case you might still be able to develop the paper normally but, as to reciprocity in that very specific case? I'm afraid you'd just need to go ahead and experiment, (and do please share your findings if you go down that route)!
alienmeatsack PRO 5 years ago
The longest exposure I've done on film has been an overnight exposure with a pinhole camera in my garage. The film was pretty low speed and pretty much failed due to the length of the exposure. I had blocked the one window in the room so the only light was very low ambient light that came through the cracks in the garage door. The final exposure time was around 12 hours.

I would love to try some 1-2 day exposures outside, but the weather has not been really cooperative. It's been "too nice" and too sunny. But I do plan on trying this when we have a few days in a row that are overcast so the exposure is not too much and I can actually shoot overnight and into the next day or so. Because it's such a long investment of time, it makes it kind of difficult to just do a quick test. :D

I was hoping that I could use the Obscura and some of the MGIV paper since it is supposed to hold up better then film would for longer exposures like this.

My goal is, once we have some good dreary days, to do a set of exposures over the course of the day time and then over night, possibly starting and stopping the exposure in place so it's only exposed during the darkness. I figure since this will require a stable safe place for the camera, I can just do the first run through or two on my back porch. I was thinking I'd make a simple mount to hold the camera in place against one of the walls that was under the back porch covering... Doing so preferably on a surface that isn't going to move and birds can't reach to rest and poop on. (This has happened to me before when doing longer exposures.)

When I did some metering recently at night during an average moon lit setting, I was getting estimated exposure times of 40-50 hours. So I'd need to ensure that the camera stayed in place and avoided moisture and critters during it's time there. And since that exposure is going to change as the moon moves acvross the sky, clouds come and go, etc, it will be interesting (and frustrating) to guess the final perfect exposure time needed.

Ive considered doing this first run in the house in a closet that I can have total control of the light and ensure that its safe for it's 1-2 day stay as it exposes. I may try this first and see what I get before I try an outdoors shot. This way I can also cut it in pieces and develop it several methods to figure out what is going to yield the best results for the more "final" shots.

I will definitely post the results once I've done some shots.
frankmcelhinney 5 years ago
You definitely need to use a stop/start method if you want any details of what is happening during night time. If you have a single continuous exposure covering both day and night then any night time details such as moon trails would be lost (overcome by the much stronger day light).

Good luck with it all!
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