The Paper Negative

[mysteryscribe]

I got to tell you about the camera I shot this with. Okay the frame is a polaroid 250 zeise range finder ect... the back is one i made to shoot 2x3 film or in this case paper negs. But the really interesting thing is that the polaroid focuses by racking the lens in and out on the camera frame, but I put a lens with a moveable front element.

So set the lens on infinity and the camera focuses it down to five feet or so. But even then you can rotate the front element like with a modern slr and the lens focuses close.

How close I have no idea, I haven made a shot that put it out of focus yet. My only regret is that I didn't buy a better lens for this camera. It has a very cheap f11 anastigmat lens. Probably the worst one kodak made. Still it does okay with a f90 pinhole stuck inside the lens.

 

[mysteryscribe]

yep forty five minutes for the paper... the film was two minutes....

Oh yeah my Time setting stopped working as it often does when I do stupid things. But at the last mintue I figured out something. I set the camera up left the dark slide in... opened the lens on bulb... used a rubber band to hold it open so I didn't have to stand there... set the kitchen timer... pulled the dark slide... took the timer and went to watch law and order. It worked as you see above.... Stupidity is the mother of invention....

 

[JamesD]

LOL Hey, if it works....

The information on the lens is interesting. The one I'm planning to use in my upcoming view camera project is a Kodak f/4.5. I'm using a bellows, but the ability to alter the focus of the lens itself to focus closer might come in handy, I suppose.

 

[mysteryscribe]

ah yes the bellows does the real focus. If you bellows is long enough you don't need the moving front glass. You can just keep racking the bellows out.

I have a 3x4 press cam made from another 250 polaroid that has a kodak anastigmat 4.5...

Some of the stuff on the retro camera is paper negs shot with it. It is a really nice lens. It's from the thirties. I have several bellows from old polaroids around. I gave some thought to making a box view with them. You know like the really early ones from the turn of the century. I still might do that. I have learned a lot about light leaks over the last couple of years. Had them about everywhere you can have one I think.

 

[JamesD]

For my project, I'm going to devise my own bellows. Should be interesting--perhaps the most interesting part of the project. Of course, that allows me to make the bellows as long as I like; I might make a couple of interchangeable ones ranging from "normal" to "extra long."

Longer bellows means closer focus, right?

 

[mysteryscribe]

yes the closeness of the focus it like that some of the older roll film cameras had an extention bellows on front. Not sure just how they worked but it was something like my movable lens camera. You would rack it out as far as it would go, the switch to another moving bed to rack it some more.

 

[mysteryscribe]

I just finished shooting a paper negative in my studio. It ran for 90 minutes exposure and was perfect, as much as I can manage anyway. The secret seems to be in adding enough light to make the light active not passive. I'm not sure I said it right, but it's the only way I can describe it.

And of course I'm not sure that it really works that way... This is purely antidotal evidence your honor.

 

[JamesD]

A threshold, then, perhaps in addition to the reciprocity failure? I shall have to research this!

 

[mysteryscribe]

so how is this for freaky

 

[Hertz van Rental]

FYI:
Film and paper can both be 'flashed' to boost film sensitivity.
The proper name for it is latensification and it is an applied use of reciprocity effects.
The mechanism whereby a latent image is formed is a little complicated (and it's still only a theoretical model proposed by Gurney and Mott in 1938 ) but to put it simply, a latent image only forms if enough energy is put into the system to effect electron movement.
Even simpler: consider trying to push a car. It's very difficult to get it moving and takes a great deal of initial effort. But once you do start it rolling it becomes considerably easier.
Latent image formation is a bit like that. In order to get an image to form you need to input enough energy in to overcome the emulsion's resistance to change (hysteresis).
At low light levels this doesn't happen - particularly in shadow areas.
'Flashing' film/paper puts that extra bit of energy into the system to get it moving.
Flashing can actually be done before, during or even after exposure to give pretty much the same results.
Because it increases the sensitivity of the film/paper to low levels of illumination the effect is generally more marked in shadow areas - which is why it has the effect of reducing image contrast (flare does exactly the same thing for the same reason, by the way).
The level of sensitisation is affected by the amount of 'flash' you subject the emulsion to. The more you give it the more energy is put into the system and the more sensitive the emulsion becomes.
Up to a point.
Too much 'flash' and you will begin to fog the emulsion, which is not what you want.
In practice 'flashing' prior to exposure - pre-flashing - is by far the easiest thing to do.
It is best done in the darkroom using an enlarger.
You need to stop down the enlarger lens to the max and move the head to the top of the column - the dimmer the light the better. A piece of ground glass or tracing paper in the neg carrier will help give an even illumination.
Then you do a test strip with a range of exposures and process.
You examine the results and find the exposure time that just starts to register - and choose the exposure before that. This means that you will give the emulsion the maximum amount of light possible without fogging it.
Naturally this will also mean you have achieved maximum sensitivity.
Once the emulsion has been flashed it will be OK for maybe 30 minutes or more before use. It's difficult to be exact as ambient temperature has an effect (colder will slow things down).
If you do flash before use, always leave the emulsion for the same amount of time before use every time you do it. This leads to consitency and predictable results.
If you find that contrast is too low then reduce the flash exposure a little and try again.

The downside is that, as flashing increases sensitivity, any light leak in the darkroom or shortcoming in the safelight will be enhanced and may pose problems.
Also the base level fog of film and paper increases over time (and is affected by storage conditions). Flashing will also enhance this and it might become intrusive.

Without spending a lot of time and effort - and a densitometer - flashing is largely a matter of trial and effort. But the method outlined above does work and is the easiest one I have found.

 

[mysteryscribe]

yeah what he said..

 

[mysteryscribe]

okay if a simple 60watt light bulb will make the paper neg act as it should, i wonder how small a light is needed to 'boost' it. A camp lanter, a flash light, a pinlight a candle. hmmm interesting thoughts. Not sure a I want to go with an exposure longer than two hours. The paper rose above was about 90 minutes.

I do have a 15watt light bulb from a fishtank light I bought to use as a back light for my scanner. I wonder.....................

 

[Hertz van Rental]

Work out what the exposure was and then give the emulsion a flash of around 5% of that exposure beforehand. It's a reasonable starting point for a little trial and error.

 

[mysteryscribe]

Flashing paper isnt what I am interested in. What I am really intersted in is how much booster light is needed for the images to read reasonably true to the meter. So far 60watts does it. I have a 25 and 15 watt bulbs I think I'll give them a shot over the next couple of days. Just to see how low the boost light can be and still combat the other problems of a iso 5 media.

The reason the ones today took so long was I had the overhead light out. Got a pure 60watt boost, at about four feet from the vase. I think i will switch out the bulbs to keep the distance at about four feet or less. Just an interesting test. I know i couldn't get much of anything from the dim studio light from the two small windows. So this will be interesting. I may have to go back and shoot a base just to be sure I wasn't guilty of being sloppy at first.

 

[JamesD]

You rock!

Interesting that you can flash after exposure. Seems like the "photonic data" which doesn't cause the emulsion to change would be lost... But you've been at this much, much longer than I have, so I'll take your word for it til I can try it myself (and find out that you're right).

Also, that's the first time, I think, that I've seen a starting figure (5%, you mention). Actually, that's the first time I've seen a lot of the specifics you outline. Is there a printed or web reference with even more detail? I find it all quite facinating.

Thanks again,
-James