about the paper negative

[mysteryscribe]

I have been going a little mad shooting paper negatives in a large format camera. I found something rather interesting but can't put a handle on it. I know about retroprocity (sp) but I can get a good paper negative at normal exposure down to about a minute, then it goes nuts. I mean really nutso.

After a minute I finally cranked the iso down to 1. I usually use five, Still couldnt get enough light on the paper. Then I added stops and i cant get a handle on it. It's making me crazy. I dont think I have made a single decent negatative longer than a minute exposure. Outside it works fine, its just in the studio that I can't make it work. Pin holes at fifteen minutes outside work peachy keen, but in the studio even with a decent lens I get bumpkus.

Anybody familier with paper negs from the camera.

 

[terri]

I'm not, but this is an intriguing problem and hopefully, someone will weigh in here who can shed some insight. I'll move this thread over to the darkroom forum if you'd like, you might get more views over there. Let me know!

Good to see you posting again, mystery, even if you had to be driven mad in order to do so. :mrgreen:

 

[Unimaxium]

There's a characteristic with any kind of film (or paper) called reciprocity failure. Basically, as times get really short or really long, reciprocity becomes no longer a linear relationship and the times needed for a proper exposure differ from what is expected. For example, if hypothetically a scene requires 1 minute at f/8, then it might need 2.5 or 3 minutes at f/11. I have absolutely no experience shooting with paper, so I don't know how much it's affected compared to film, but this might be what you're experiencing. Maybe someone else can chime in with more experience.

 

[mysteryscribe]

actually I am familier with the phenomina and i'm sure thats what it is. What I was hoping is that someone had some idea what formula might be for working with it. It gets so involved that I cant get a pattern in it at all. Sometimes I give it five stops extra and it looks two stops thin... I do it again with the two stops and it looks three stops thin. I have no idea what is going on. I know there and no significant light leaks because the paper is not fogged at all. If it was that the paper would be black on brown from lack of exposure.

It may become moot because the unreliability of it.

No thanks miss terry I like it right cherr just fine honey lamb. It your crew of wackos don't know about paper negatives no way anyone else will.

By the way i got this really cool lens off a plate film camera had to fix the sticking but now that I have that done it is amazing a wallensak biomat with the old us fstop numbers. Hope that confuses you lol

 

[stingray]

retroprocity (sp)

he does know i think, just spelt it real crazy.
Presumably there's some sort of documentation on the paper negs you're using that would have a reciprococity (sp as well ) graph on it... unless you coated it yourself?
sounds like a really interesting problem and I look forward to seeing when someone like Hertz posts and fills us in on the exact science of it all!
Good luck..

 

[Torus34]

Reciprocity failure coupled with the color temperature of indoor lighting.

 

[mysteryscribe]

so spelling does count lol....

Actually I'm not sure color temperature comes into exposure in black and white film. I know it does weird stuff to wedding photos shot from the rear of the church with natural daylight.

I cranked my meter down to iso 1 but that wasn't enough and no matter what I did to increase the exposure it never seemed to be enough. I just switched over to shoot film for the test shot. I'm still curious as heck since I would like to shoot some low low light studio stuff with paper negs. So when the whiz kids get a chance maybe they can direct me to the right place.

It is pretty obvious that the paper is the problem but somebody somewhere has to have taken the time to work it out. Unless...

One of the articles I read said something about light loss in the camera after a certain period of time. It is a possibility I suppose since I can't get a print to check for contrast. I could have a leak in the lens. It is almost, if not, a hundred years old.
I have pretty much given up on paper in this lens. I have a couple of pin hole cameras around I think later this week I'll give one a try on some very very low light still life stuff and see what happens when the lens is out of the equation.

 

[Hertz van Rental]

The first problem is that printing paper is designed to do a rather different job than film so it tends to behave differently when being used as a 'film substitute'.
Firstly, manufacturers do not bother with working out the ISO of printing paper. It's a bit of a moveable feast anyway as it depends upon a variety of factors.
The slowest film I have come across is Lith film at 5 ISO and paper - under average lighting conditions - seems to be a little slower. Taking a starting point somewhere between 2 and 4 ISO would seem reasonable.
Secondly, the colour response of paper is different to film. Graded paper is mostly blue sensitive - once you get to green it records much less, and longer wavelengths don't at all. They are probably more sensitive down into the UV as well.
Multigrade will respond to colour in a slightly different way as it contains a mixture of two emulsions - one sensitive to blue, the other to green.
I would imagine from this (and this is conjecture) that the colour temperature of your light source may have some effect on exposure. Daylight (or lights at 50,000K or above) would give the best results. I wouldn't have thought, though, that colour temp would have much effect until it gets below 3000K - considering that most enlargers use light bulbs running not much above this.
Third, paper has a paper base (well, d'uh!) and this is white so light will be reflected from this during exposure. Any light-coloured or reflective surfaces inside the camera will bounce this back and possibly cause fogging of one kind or another.
Fourthly, paper uses almost the entire exposure range of the emulsion from Dmax to Dmin so there is no 'latitude' like you get in film.

Moving on to exposure:
The biggest problem is hysteresis.
This is what causes reciprocity failure at low levels of exposure.
Any system is reluctant to change and resists it until the energy being put into the system is higher than the energy of resistance.
If you have every tried to push a car on a flat surface you will have come across this. Getting the car moving is the hard part - once you have it moving it seems easier to push.
Emulsion works in a similar way. You need to put enough energy (light) in to the system to start the process of exposure. If the initial energy level is insufficient then no exposure will take place - no matter how long you expose it for.
It's like trying to move the car by pushing gently. You can lean against it for as long as you like but it won't move.
As the ISO of the paper is low it needs far more energy than film to get things going. From this it can be seen that you need to do two things - illuminate your subject as brightly as possible, and use the widest aperture you can.
If you are using a large format camera with a darkslide you can use the darkslide to make a test strip. Pull the slide out in measured increments, doubling the exposure each time. Just like printing. This is by far the best way to assess exposure.

As to the rest I'm afraid you are pretty much on your own. Little or no work has been done on printing paper as film so everything will be trial and error.
I have always used paper as the neg in my pinhole cameras and - by bearing the above limitations and points in mind - I have generally managed to get useable negs.
But paper does have quite severe limits.

 

[mysteryscribe]

Now that makes sense.... Most likely it got to a certain point for the light I had and no matter how much more exposure I gave it, no significant chages were made to the image. The duration of exposure after a certain point might be useless. Thanks hertz

The light temperature thing wouldnt really come into it as I am using daylight to expose but subdued. Like I said there was a very specific point at which is goes nutso. Otherwise it is fairly predictable.

 

[Torus34]

OK, OK you guys! [& gals?]

All this talk enticed me into making a pinhole camera for 8x10" paper negatives. FL is about 11". Pinhole is 0.029" dia. Paper will be an Ilford SW VC RC.

It will be interesting to see if this old dog can learn some new tricks. [Kinda interesting that a pinhole camera is new for me. Something Zen going on here. . .] Details and findings later.

My earlier post to this thread on color temperature refered to the difference in the color temperature of the light out of doors (5800K) to that of indoor lighting [3200 or thereabouts.] The light sensitivity of paper is not panchromatic to the extent of that found in modern films. VC papers are even stranger.

Anyone here remember orthochromatic films?

 

[mysteryscribe]

remember it but never used it. I have made and sold pin hole polaroid cameras and shot a few of them but never for such long exposures. My pinhole drill is ,0177 of an inch and .15mm (I think)My next problem is for some reason the paper devolper I am using wont deverlop film at all. LOL
always something.