Testing Film without an enlarger

[Dean Cookson]

Hopefully there's an obvious solution I'm missing to my problem...

I want to do a film test of FP4+ in pyrocat-HD (2:2:100) which are both new materials for me. I've got everything I need to develop the film, I've got a step tablet and I've got a densitometer that will let me read both straight B&W and the blue channel. The only thing I don't have is an enlarger to contact print the step tablet onto the film (although I do have an electronic enlarger timer)...

Any suggestions on the best way to expose the film? Would a 100 watt bulb plugged into the enlarger timer and hung over the contact printer do the trick? Maybe one of you in the Bay Area be willing to expose 5 sheets that I supply in return for a couple pints at your favorite local brew pub? :-)

Thanks for any suggestions.

[Donald Miller]

I would think that your camera and lens would be more accurate then a enlarger timer and light bulb. I would tape a step tablet onto a sheet of film and expose it in camera.

[Michael Mutmansky]

Dean,

A bare lightbulb with a timer will make a suitably accurate device for testing film, as long as the exposure is normalized with a meter and you can be absolutely certain that the conditions in the room will not change sufficiently to cause exposure deviations. Other approaches may not find a bare lamp suitable.

The real benefit to an enlarger is the aperture, which makes the adjustment of the light level relatively easy, and also the light isolation that it provides, which minimizes room conditions. Otherwise, the enlarger is essentially a lamp and a timer.

I once made an exposure unit for contact printing by using a clean paint can from the home center, and a ceramic lamp socket. I drilled a hole in the bottom, and epoxied a piece of PVC pipe to the bottom around the hole, and securred a filter holder to it for contrast control. I then hung it from the ceiling to do proof prints. I recall that I used this to test film until I put together a real enlarger, and it worked well, producing consistant results for my needs.

Before that, I took a shop light, a box, and a piece of opal acrylic and made a rough enlarger out of my camera. In that case, I did not trust the lamp to rapidly heat up and cool off, so I used the shutter on the lens to set the exposure time. That approach worked well, and had all the benefits of the enlarger, but required a little more work. I removed the film back, and placed the acrylic and cardboard 'mixing chamber' on the opening, and then wrapped the entire assembly in dark towels to make it light tight. I used a footswitch to turn on the lamp for only a few seconds (to avoid heat problems) and after a few seconds, fired the shutter.

Now, I use an enlarger, because it is easiest, but I don't think it is any more accurate or precise than the other methods I used.

---Michael

[phil sweeney]

You did not say what paper you will be printing to!

I have done what you are describing as follows (from my notes): 250W photoflood with dimmer (or variac) and electronic timer. On white card turn lamp down and then up until reading 7EV on my digital pentax. Expose at 0.1 seconds. Since you must be planning on BTZS tests be aware there are problems with these tests and staining developers. Even Phil Davis will tell you the results are "iffy." However I have been told that folks using a UV densitometer do very well.

Honestly, at least for starters (i.e., finding an N negative), I would expose 3 films at 125 ISO (or 100) in the camera of a normal scene and develop at 3 different times. See the AZO forum for more. I only mentioned 100 or 125 ISO because I know many folks end up using those speeds for those combinations.

I rate FP4 at 100 for pyrocat (metol version) 7 minutes in tray 2-2-100 for AZO.

[Michael Mutmansky]

Several notes based on Phil's comments:

I do not recommend using a dimmer because this will change the warm-up and cool-down curve of the lamp. This will be a problem that will result in erronious speed ratings. It is better to enclose the lamp and use ND filters (as I mentioned above) to cut the output than it is to use a dimmer.

It also changes the color temperature of the lamp, which can affect the daylight speed as it will depart further from the full voltage rated temperature of the lamp. If you use a blue coated photoflood, this will probably not be too much of an issue.

I also do not recommend using an exposure time shorter than 1/2 of a second. The reason is that the shorter the lamp is turned on, the less time the lamp will be at full output, which is where the light level is set to determine ASA. At 1/10 of a second, the lamp may only be 1/2 the brightness of full output and then the power is cut, at which time it dims to blackness.

It is more accurate to use as long of an exposure as possible without getting into the reciprocity failure range of the film. Doing that won't improve the precision of the test much, but is should improve the accuracy. If you are planning to shoot with long exposures anyway (stopped down a lot, typically in non-sunny-f16 conditions) it is not inconsistant to actually test a bit into the reciprocity failure range so that your test results actually reflect the shooting conditions that you will be making your negatives under. That's for each person to decide, though. I'm not recomending you do that, but it is a valid way to test the film.

As far as testing goes, a single sheet exposed and developed at the 'N' development time will tell you if you have the exposure right, and also if you are on target for the range of times for development. If not, adjust both and as long as you are not too far off on the exposure, you can do the full set of exposures.

---Michael