Christina's IR Info

[WR <rivelli@xxxxxxxxxxxxxxxxxxx>]

Chris, thanks for sending me a copy. Looks like you are being very 
thorough in trying to address possible IR problems. There's a lot of 
material to cover, but for now here are my thoughts on the questions 
which were raised.

1. Putting a color filter over the lens will DECREASE the amount of 
visible light rays that hit ANY film. A green filter will pass all 
the green light and block some of the red and blue. A red filter will 
allow the red light to go through and will block some of the blue and 
green. A lighter red filter, like a # 23A will block less B and G 
than a deep red like a # 29. Virtually all color filters will pass 
the infrared rays [the only exception I can think of is the
  # 18A which blocks most of the wavelengths above 800 or so]. Purely 
IR filters, such as the # 87 series and the # 88A will transmit ONLY 
IR, no visible light. IR films are sensitive to visible light AND to 
IR rays. We need to filter out some or all of the visible light in 
order to get the "IR effects" that we like.

2. This leads to an answer to the second question: Yes, there is a difference
in using the 15, 25 and 29 filters with Konica, but it can be very 
subtle. As you know, the film's sensitivity peaks at 750nm [hence the 
name]. Since different color filters pass certain wavelengths in 
different degrees, they can be used for different effects. I have 
tested Konica 750 with the # 3, 8, 12, 15, 23A, 25, 87 and 89B. I 
like the results with the # 12 and # 15 best.
Incidentally, whatever filter factors are recommended, test for 
yourself. [It could be that 12+ stops is the correct compensation for 
the # 87C]. There are a lot of variables involved.

3. As for fluorescent lights in the darkroom that take a while to 
subside, I don't wait more than a minute or so after turning them off 
to begin loading film holders or developing tanks and have had no 
problems.

4. Rodinal is a wonderful developer, but it does not produce "fine 
grain" with soft edges. It produces sharp grain. The individual 
photographer has to decide whether he or she likes the results. As 
usual, my solution is TEST FOR YOURSELF.

  BTW, what age are your students and what is their level of 
photography experience?

Cheers, Bill

             William Rivelli
WILLIAM RIVELLI PHOTOGRAPHY

rivelli@xxxxxxxxxxxxxxxxxxx
     www.rivelli-william.com
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