Diffuser for Beseler PM1A Color Analyzer

Hello,

 

I have a Beseler PM1A Color Analyzer which came with a B&W enlarger that i purchased. On pages 13-14 of the manual (http://looscanons.com/php/download.php?f=beseler/pm1A.pdf) it describes how to calculate the exposure for an unknown negative by way of an aperture adjustment and from known settings. This requires the use of the "light integrator"/diffuser (originally sold with the analyser) in the light path in the last step of the estimate. Unfortunately mine is missing. Is there anything that I can use as a substitute? Any advice is most welcome!

 

Thank you!

its just a white ground glass you put in the filter holder under the lens.

I just looked at my PM4L, same as yours but with memory moduels. The filter is a thin white plastic.

Thanks. Have you ever tried setting exposures this way? I tried experimenting with a single piece of tissue on a second known negative and it resulted in an estimate of more exposure than that used for the first. I had already printed from the second and had noted that it in fact required required less exposure to get a good print - so I guess the density of the filter must be critical. Edited December 16, 2018 by Xícara de Café

Plastic from a very thin white plastic shopping bag however shows that 1/2 a stop less exposure is required on negative 2. This looks more in line with the test prints that I did.

 

To give the details of these two negatives - to get a good print for both, I set and noted the following settings:

 

Negative 1: f/8 and 2.75 seconds (white channel null reading at 58)

Negative 2 f/8 and 2.25 seconds (white channel null reading at 56)

 

Squeezing in another beginner's question if i may, if my reference negative has an exposure time of 10 seconds and I note that my unknown/test negative requires 1 stop less exposure, does that equate to a reduction by a half of the exposure time at the same aperture (ie. 5 seconds)?

Edited December 16, 2018 by Xícara de Café

You can make an integrating sphere -- Cut a ping pong ball in half and place this hemisphere over the probe entrance. In lieu of this, cut a hole in a ping pong ball, just large enough to allow the probe to enter. This should work just fine!

I recommend a piece of plastic cut from a translucent milk or juice container.

 

The original diffuser was a flat round piece of roughened plastic. Almost identical to the plastic used for milk containers. Not domed or hemispherical, and with a much higher transparency than a ping-pong ball.