Does photo paper have an ISO rating?

[keithwms]

Again I wonder about hypering the paper. Is that nutty?

Just to add to my prior suggestion of pulling the darkslide in increments to do an exposure check: you could then take this graded exposure sheet and develop it in increments in direction perpendicular to your exposure steps, just by pulling it out of the developer at successive time intervals. So then you have constructed an exposure vs. development matrix and you can just pick which square works best.

The big wildcard, I think, is the colour temp of the light you use. Methinks that could affect the "speed" of the paper substantially.

 

[removed account4]

i had thought this as well, and asked in another thread ( about hypering film ) but
no one answered / knew ...
sounds like something worth looking into!

john

ps. group - paper negative formed

 

[fschifano]

I'm sure it does. While I have not attempted to measure it for in camera use, I do have some anecdotal observations to report. The liner of the light mixing box in my enlarger had yellowed with age. When I relined it with new material, I immediately noticed that the light striking the baseboard was considerably less yellow. All of the papers I'd tested for speed with a step wedge required about 1 stop less exposure for a given density. Contrast grade changed too. Negatives that required #3 filter now need a #2 filter.

 

[Kimberly Anderson]

Is that why many easel's baseboards are yellow? Does that have anything to do with printing times/contrast filters?

 

[keithwms]

Hmm hadn't thought about that Michael, that makes sense. A yellow baseboard reflects yellow light, to which the paper would be mostly insensitive.

 

[Photo Engineer]

I have baseboards in many colors including black, white and yellow. I think Mr. Saunders liked yellow. His were among the first to be that color IIRC. He used to make special order easels for EK, and I had the opportunity to meet him once and used several of his yellow easels. But since paper is not sensitive to yellow light, it is black as far as the paper is concerned.

PE

 

[BetterSense]

I shot my first negative with my foamcore camera, at one minute, and it was way overexposed. It's sunny today again so if I try today I'll go less. I'm thinking 15 seconds actually, because it looks more than one stop overexposed to me. But with reciprocity I'm not sure if I should try 30 seconds first. I intentionally shot myself skylined for a really high-contrast scene so I could adjust exposure, but I'm thinking the blue light from the sky just blew out the scene.

 

[keithwms]

Before declaring this is "way overexposed" I'd suggest contact printing it. You may be surprised.

(N.b. I do think it is overexposed, but not quite as much as you may think).

 

[BetterSense]

How can I know how long to expose it for contact printing? Last night I did a test strip of the paper, to see how much exposure I got by briefly flashing the bathroom lights, then moving the covering a bit and flashing again. So the strip goes from 9 flashes on one end to no flashes on the other. It turns out 1 flash is dark grey and 2 flashes is fully black. I suppose I can use the white, dark grey, and black sections from the test strip to do a test-contact print on more strips of paper. I will use my enlarger for it this time, but do you suggest a ballpark exposure for the test-strip contact print? I will probably start at f/8, 30 sec, but I have to wait till it gets dark anyway because the bathroom door leaks a lot.

 

[removed account4]

it sounds like your bathroom light is very bright,
and your bathroom is very small ...

when i use my enlarger to make contact prints from paper,
i have it wide open and usually it is about 10-15 seconds.
that is for double weight (fiber ) paper.
is the ilford mg you are using fiber or rc?

john

 

[BetterSense]

It's MGIV RC

It's a very very small bathroom with 5 incandescent lights over the mirror. I wish I had thought to unscrew about half of them before I tested. I just shot another negative at around 20 seconds and it looks like it turned out ok even though I didn't have the camera braced very well. My scanner really is rubbish and it looks better in person. This after inverting. I think I really should do something about my paper flatness issue.

 

[BetterSense]

Well the last photo I took had pretty decent exposure at 15 seconds. After exposure, I metered the scene with my Program Plus on Auto. It selected 1/60s at f/16, with 200 film.

I have a pretty good knowledge that my camera is f/300 because I measured the pinhole with my enlarger. Difference between f/16 and f/300 is four stops slower lens=less light.

Now the difference between 1/60 and 15 is about 10 stops slower=more light. The difference is 6 stops.

6 stops slower than 200 is ISO 3. Who knows how accurate this is due to reciprocity, but it's something to start with.

 

[Joe VanCleave]

I haven't observed appreciable reciprocity failure with paper negatives in exposures many minutes long.

A convenient method of metering for pinhole, if you have a handheld meter, is to set your meter to your working EI (exposure index); I rate my grade 2 paper at EI=3. Then meter the scene, and refer to the f/stop of your pinhole divided by 10. That is, if it's an F300 pinhole, then look for the recommended exposure time opposite F30 on the meter scale (you do this because most light meters don't read above about F128). Then simply multiply this recommended time by 10, to yield your actual exposure time.

As a hypothetical example for an f/300 camera, I set my meter's EI to 3, meter the scene, then refer to the recommended time opposite f/30, which may read, say, 5 seconds. Simply multiply this time by 10, resulting in a recommended exposure time of 50 seconds.

Since this exposure time is well in the range of the times one may encounter in projection enlargement in the darkroom using photo paper, don't worry about reciprocity failure.

If your negative comes out appreciable underexposed using this method, it means that your working Exposure Index is too high, or you aren't developing long enough, or both. You can therefore use this method to dial in your working EI for your paper and processing methods.

I've found that I typically develop my paper negatives for 3-4 minutes, rather than the 1-2 minutes I may use for developing prints, but do so using a more dilute solution, so I can pull it at the right time.

~Joe

PS: Regarding your posted image, is the fogging coming from the camera, the makeshift darkroom, or both?

 

[BetterSense]

I have no idea at this point. It could be either.

 

[keithwms]

Yeah, it looks like some fog; take care that with these long exposures, you need to fuss over all light leaks. You could do a normal exposure with your "lens" covered to see if you have leaks and where they are.

 

[Joe VanCleave]

Of course you want to test your camera for leaks, but I'd recommend starting with your darkroom setup. You want to know right up front if your box of paper has been fogged in the darkroom when it's been opened; not knowing this will throw off all subsequent tests.

If you have a changing bag, try removing one sheet of paper from the box in the bag, then remove that paper in the dark room. Then do the fog test for darkroom leaks. There's two ways to do this; the easy way is to simply keep one part of the paper covered by an opaque object (a coin, etc.) and leave the paper exposed in the darkroom under "safe" lights for at least 5 minutes. Then process the paper normally. The other way is to faintly flash the paper with white light (like from an enlarger for a few seconds at the smallest aperture setting), then do the same test with a coin over the paper; this second method is more sensitive for subtle leaks or fogging from safelights.

With either test, if you notice a density difference on the paper between the covered and uncovered parts of the paper, then you have a fogging issue.

There's also the possibility that the paper in the box is already fogged. The only easy way I know to test for this is to put the box of paper, scissors and a daytank in the changing bag; remove one sheet, cut off a strip and place it into the daytank; seal the box of paper and daytank before removing your arms. Then process the paper in the daytank. You can then compare the density of the paper strip and try comparing its tone against the backside of the paper strip, which should be pretty close to the same shade of white.

Once you know that your darkroom and safelights are good, then you can proceed with testing your camera for leaks. I've found with pinhole cameras you can often see the leak by illuminating one side with a bright articulating desk lamp in an otherwise dark room, and put your face up close to the insides of the camera, checking the corners and edges and seams for light. Of course, you can't check the camera's door or lid this way, unless the camera is big enough to fit inside(!), so you'll have to do a leak test by loading a sheet of paper into the camera (in your now safely-proven darkroom) and leave the camera, shutter closed, out in the bright daylight direct sun for an hour, changing the orientation occasionally. You should see fogging on the paper after processing.

~Joe

 

[BetterSense]

I think it was my camera. I looked in the loading slot and ran a high-powered flashlight around. Not only did the flashlight penetrate the foamcore even through both sides painted black, there were several seams with more pronounced leaks. I covered the entire thing in aluminum foil, and now the flashlight doesn't shine through even a little bit. Although my camera now looks like Sputnik.

 

[keithwms]

Good job. You can also apply that sticky felt stuff from a craft store to the innards of your camera.

 

[BetterSense]

Yay I think the aluminum foil was the ticket, and I had a fogging problem all along. I'm starting to notice bizarre contrast issues with the paper though. The bridge, being red, is underexposed, while the blue sky and rocks are completely blown out. I'm sure this scene would have turned out more normal with film, but then, maybe it wouldn't be as cool either.

 

[keithwms]

Yep welcome to The Contrast Issue. Now you can go back through some of the discussions and see if any of that works for you. I'd say, try preflashing first and foremost, and expect it to increase the sensitivity of your paper by a stop or so.

The other thing, which is blazingly obvious but seldom stated, is that you can meter the contrast of your scene and know straight away whether a paper neg is going to work under "normal" exposure. In a low contrast scene you can get wonderful results. In a an 8 stop scene, well... and of course you can filter blue if that might tighten up the contrast in your scene.

 

[martymarty]

There is a paper ISO rating and a film ISO rating. They are not related.

Ilford MGIV paper has an ISO of about 25. It is not orthochromatic though and has two contrasts at two wavelengths. Graded papers often can be used more effectively than MG papers.

PE

I am a research engineer, NOT a photographer so I don't know where to find
a source of photo sensitive paper that will mail to Israel :

50 sheets of matte photo-sensitive paper ISO/APA 4 , Black/White
(payment will be made via VISA credit card)

If ISO/APA 4, Black/White is not available please indicate which low sensitivity
ISO number is available. ( for example ISO/APA 10 )
-------------------
the reason for such low light sensitivity paper:
to be used for photos of sun's path through the sky taken using a pin hole camera;
the exposure will be taken over a period of 6 months
the exposed photo paper will the be transferred to a computer via a flat-bed scanner

Thanks for whatever help you can offer.


martymarty

 

[Photo Engineer]

Taking pinhole photos outdoors must consider the UV content of the light and this is not done with papers. You will have to test and find out which paper is suitable. You may need a UV filter.

PE

 

[IanPhoto]

In regards to the ISO question, I have been using Adorama paper at ISO 18 in an old lens that is f14 wide open. I further add ND filters so I can get to a slow enough speeds that I can handle with my packard shutter, 2-5 seconds is what I usually target. Today I tried out my new aero ektar f2.5/speed graphic, bracketing with speeds of 1/60, 125 and 250. Everything underexposed. PE said earlier in the post that paper is not meant for exposures under 1/50th or something like that. It follows that the faster your exposures are the more important it is to flash the paper first. Now I'm wondering if even though I flashed, if there is a certain amount of time during the image taking exposure that it takes the paper emulsion to "wake up" and start reacting - in other words a reciprocity factor is needed for exposures faster than 1 second or so. As always more tests are needed..

 

[Joe VanCleave]

Yay I think the aluminum foil was the ticket, and I had a fogging problem all along. I'm starting to notice bizarre contrast issues with the paper though. The bridge, being red, is underexposed, while the blue sky and rocks are completely blown out. I'm sure this scene would have turned out more normal with film, but then, maybe it wouldn't be as cool either.

With paper negatives you have to expect the sky to be blown out to white. This is what I call the "19th century" look. Knowing this will happen, it's best to purposefully compose your scene with this in mind.

Those of us who've been practicing with paper negatives for some time tend to employ a variety of methods for reducing contrast. Among them are:

1) Use RC paper of a fixed contrast grade, rather than VC paper. I've been using Freestyle Photo's Arista grade 2 RC paper, rated at ISO12.

2) Use a dilute developer and develop by inspection, pulling the negative when the shadows begin to show adequate detail but before the highlights get excessively dense.

3) Pre-flash the negative prior to loading the film holders, with a faint gray exposure. This will have a tendency to increase shadow detail without significantly increasing highlight density.

4) Use a yellow filter over VC paper. I haven't personally done this, and it does decrease the paper's speed significantly.

 

[Joe VanCleave]

One exception to the typical white skies with paper negatives is if you're using a very wide angle pinhole camera. The light falloff toward the edges and corners can serve to give you back some sky detail you'd otherwise be missing; especially if you compose purposefully with this in mind.