Measure exposure time - photo resistor

On: Fri, Apr 26, 02 12:42:05 PM

Thilo K. wrote:

Hello. Iīve heard one can measure the relative energy of a lightbeam per mmē or mē by using a photo resistor. I bought one 2 years ago. What I can do very well is measuring the ratio - you know which one :) - but not the energy to figure out the exposure time. Do you know how to get the needed time ? Besides, the value of the resistor is indirect proportional to brightness. Since there is no value given that represents "darkness", there has only been successful measurement of the ratio so far. Any suggestions ?


Jean Dufrasne - Sun, Apr 28, 02 02:03:20 PM

Hi Thilo, Found on the Steve Michael's site. Steve uses a solar cell but maybe you can use your photoresistor just by changing scale on your VOM (select Resistor instead of Volt) and apply the same formula ? Can somebody confirm this ? See you. Jean.

Thilo K. - Tue, Apr 30, 02 01:52:50 PM

Hi Jean, thank you very much for the URL. Occasionally, I saw it a week ago. We have also had some email exchange. But - ultimately - he seeks for the right time by "trial and error". Something that isnīt bad at all as a matter of course. But what I want is to determine how long it takes by using a formula, which is physically correct without experimental factors; that means there should be no correction, no enhancement - at least no great one - neccessary, if a setup is changed. Can you help ? Something different: You might be using PFG-01. So maybe as you know, color changes from green to red in reflection holograms if the exposure time is increased. Do I expose the film long enough, if the picture is almost red ?

Dooley - Tue, Apr 30, 02 03:17:47 PM

It is my understanding that if the pfg01 hologram is developed using jd2 that the longer you expose it will turn green and eventualy blue. Also it is hard to controll all of the factors as the humidity as well as temperature affect the exposure time. Lately with the d&s laser system running at aprox. 27mW and the pfg01 with jd2 dev. I have been exposing for 10 seconds. With the pfg03 and jd4 dev. 10 sec. is also a good time for my particular set up. I came to this conclusion by many trials and a detailed logbook for each exposure.

Thilo K. - Wed, May 01, 02 06:14:56 AM

Hello Dooley, what kind of entries did you add to your 'detailed logbook' and how did you get them ?

Thilo K. - Wed, May 01, 02 06:29:18 AM

Additionally, some information that might be useful: developer: Neutol P(Laser): as itīs used it is within the bounds of 5mW and 8mW film: PFG-01 one-beam-reflection exposure time: 30s

Use this form to add your comments to the current forum entry above
Your Name:
The Text...

HTML, or
Plain text

Action or

| Main Index | Reload | Help? |