Old fashioned film ???

Ole · Jun 19, 2005

jjstafford said:
Your experience? You said that Efke 25 is red-blind, and I asked if you have ever developed it under red safelight. You clearly have not or you wouldn't dare say that.

I wasn't born yesterday.

I have answered this already. I do not use a weak green safelight with EFKE 25, because i can use a STRONG red one.

The burden of evidence is on you, since my opinion (for a change) tallies with not only the manufacrurer's specifications, but also with all photographic literature from Willi Beutler's 1947 "Dunkelkammerpraxis" to the present day. You are the one claiming increased red sensitivity, you prove it.

jjstafford · Jun 19, 2005

Ole said:
I have answered this already. I do not use a weak green safelight with EFKE 25, because i can use a STRONG red one.

This is quite a wonderful bit of news!

All APUG users should be indebted to you for that informaion. Now all of them can load and develop Efke 25 in bright red light. Perhaps Efke will pick up on this as an advertised advantage. I'll pass on this information to Efke so that they can confirm this and recognize you as the authoritative source.

jjstafford · Jun 19, 2005

Ole said:
I have answered this already. I do not use a weak green safelight with EFKE 25, because i can use a STRONG red one.

This has been a profitable thread so far.

John at J&C says: "They are not Orthochromatic though and do see the red part of the spectrum to some degree. Above approximately 650nm they are approaching zero sensitivity. The question is not one of the brightness of the red light but it's wavelength. Even a dim red light at 600nm will fog the film. A bright red ight at 675nm will have little effect. [...]"

Now add to this the fact that the young, healthy human eye cannot see above about 640nm, and the aged eye even less (you are over fifty, no?), then we have an interesting situation. It appears that you (Ole) have two special advantages; first, your eyesight is not typical because you can see farther into red than most mortals, and second, you have a red light source you should share with the rest of us.

Please post the source for this red light and be our hero!

Sincerely,
John

eatfrog · Jun 19, 2005

jjstafford said:
..to some degree. Above approximately 650nm they are approaching zero sensitivity.

So what, where is this extended red sensitivity you started all this fuss about? It is sensitive to red, to some degree, yes. But not as much as Tri-X, and certainly not more so than Tri-X, which is what you stated earlier.

I do certainly not understand your attityde, and why you try to change the subject from the red sensitivity to some darkroom light when you notice that you were wrong.
You have no right to be rude to Ole, who has been clear and nice in his posts, contrary to yourself.
Why would he lie about him developing with a red light? If it works, it works.

jim appleyard · Jun 19, 2005

jjstafford said:
Ole - Respectfully, I am not looking for disagreements.

Oh, really?

Ole · Jun 20, 2005

jjstafford said:
Please post the source for this red light and be our hero!

Sincerely,
John

I use an old-fashioned red bulb, 25W I think, at the other end of the darkroom. It is a lot brighter than the near-invisible green light I use otherwise - but terms like "strong" and "bright" are relative.

It is surprising to many how much light it really takes to fog film, human eyes are certainly far more sensitive to low light levels than 25 ISO film!

No simple light filter is perfect, an certainly not HAMA's coloured light bulbs. But with a little forethought it is very easy to avoid fogging: Remove film from holder in darkness, start developing in darkness, do not turn on light until you are getting close to the expected end of development. In most cases you will find that the colour of the light matters not at all - it might just as well be white as long as it's weak enough. But when some films have reduced sensitivity in some part of the spectrum, I consider it a good idea to exploit this by using a light sorce which is centered around this part of the spectrum. So whether or not I can see farther into the red than the EFKE PL25 film can is irrelevant, since neither I nor the film can see the longer wavelengths that the lightbulb gives off. Good enough reason for me to use red light when developing these films by inspection.

the young, healthy human eye cannot see above about 640nm, and the aged eye even less

Where did you find that information? I couldn't find it? Most sources seem to agree that the visible spectrum extends to just short of 700nm, with people operated for cataracts seeing as far as 780nm. No, I haven't had cataracts, so I don't expect to see into the IR.

jjstafford · Jun 20, 2005

Thanks for the reply, Ole. John of J&C replied privately to me to clarify. I am quoting it here in order to be fair to the facts so we can all benefit. '"I read the thread through this morning. I thought your question was "could the film be handled in the darkroom under a red safelight". To which my answer applies. If your talking development by inspection then after several minutes of development in the dark the films sensitivity decreases and visible light can be used to inspect the film for short periods of time without fogging."'

John's clarification makes perfect sense and is in accord with your experience. I'm not at all unhappy to be corrected regarding the red sensitivity. It is important to have the facts out there, challenged and reaffirmed. Thanks for your persistence, Ole.

Now, if I could get the straight poop on compartive green and blue sensitivity I would be happy, since that is my main concern.

My figures regarding the sensitivity of the human eye are taken from the recently published studies by Margaret Livingstone.

Ole · Jun 20, 2005

I did find a nice page with curves of the sensitivities of the various receptors in the eye just before my PC crashed...

Those curves explain why we normally use green light for film (max. sensitivity of the eye), and why astronomers like red light (rods are not sensitive, so dark-adaptation is unaffected), and why I get away with using a relatively bright red light with orthopanchromatic film: The sensitivity of the eye is higher than that of the film, even if the sensitivity of the eye has dropped to about 10% of max. The film's sensitivity has dropped even more. Doing other films with the same red light might be a bad idea as the total intensity must be increased so much due to the reduced sensitivity that the film would be more easily fogged than with a green light of the same perceived brightness!

I must admit that much of the time I use white light for DBI; my darkroom isn't totally lightproof and after about five minutes I can generally see what's going on, after ten minutes I can see if the negative is done or not. Since no lightmeter I have tried shows the slightest sign of a twitch of the needle, I assume that the light level is nevertheless too low to register on film.
"Safelight" for film development is something I use only at night or in the winter.

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