Re: critique on infra article and more questions

["David J. Romano" <romano@xxxxxxxx>]

"Christina Z. Anderson" wrote:

> Thanx for the interest in critiquing my infrared article.  I received about
> 25 requests for it (was very surprised)(whew) and have received back about 4
> critiques of it.  Please continue to send me back your input.
>      Bertha raised an interesting question.  Does putting a red filter on
> your lens INCREASE the amount of infrared light available to the film?  From
> what I understand of filters this is not so, it just decreases the visible
> light it blocks.

Nothing can increase the amount of IR reaching the film, only decrease it. The
spectral data for the Kodak #25 and #29 both show that there is only 90%
transmission at 700nm. I don't know if this is the red dye itself, or if it
includes the glass or gelatin it is mounted in. So, if you you do use a filter,
you actually do REDUCE the amount of IR reaching the film by at least 10%. This
amount to less than one fifth of a stop though, so it is of no consequence. Most
importantly, it will increase the proportion of IR to visible, as George stated.

>
>      Is there truly no difference with Konica with the 15, 25 and 29 filter?

In theory, there would be a difference between them if the film was at all
sensitive to yellow light, which I'm sure it is, because the 15 filter would
pass it, while the 29 would not. However, and I quote, "In theory, there is no
difference between practice and theory, but in practice, there is".

>
>      Do fluorescent lights in the darkroom that take a while to subside
> truly not fog infra film if you turn them off and immediately start
> developing, e.g. in trays in the dark?

I use fluorescents in my darkroom, very close to where I load film on the
developing reels. I've never had a problem, but then again, the light fixture is
behind me and I could be blocking any residual IR radiation with my body.

>
>      Should I not even recommend Rodinal as an infrared developer because
> the grain is golfball size?

I would not make that recommendation, or none like it. You could create a list
of developeres and their reported characteristics to give the students some idea
of the choices they have, at least for a starting point. Some may like the
effects of one developer over another. If some students use one developer,
filter, paper, etc. and other students use others, they will all benefit by
seeing the differences in each others' images.  There are so many different ways
of doing things in photography, and that is the beauty of it.

Rodinal may be grainy, but it it sharp. I think one of the reasons for this is
that it doesn't have any sodium sulfite, although someone should correct me if
I'm wrong about that. Personally, I shoot Kodak's 35mm IR because I like the
grain. I even enlarge it to sizes of 9x13 inches, or even 13x20 inches. I
develop in HC-110, or Edwal FG-7 with out the sodium sulfite added. Sodium
sulfite will help keep development times short and film speed up, but it reduces
image sharpness. To me, sharpness is usually much more important that
graininess.

>

Dave

>
>      It is so nice to have you experts here to bounce these concerns off of.
> I do not want to xerox these notes for 40 students if there is wrong info on
> them.
> Chris
>
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