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Cold Light for B&W?



 
 
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  #1  
Old August 6th 04, 02:30 PM
jjs
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Default Cold Light for B&W?

Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region - therefore causing lesser sharp prints?


  #2  
Old August 6th 04, 03:03 PM
Jean-David Beyer
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Default Cold Light for B&W?

jjs wrote:
Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region - therefore causing lesser sharp prints?


I do not think so. There is a lot of uV produced by the mercury vapor arc
in the tube, but the tubes are internally coated with phosphors that
convert most of that to visible light with a spectrum decided by the
manufacturer. Some put out a quite blue light, most put out bluish white,
and some put out green (I have seen green only in dual-tube heads where a
blue tube and a green tube, whose brightness is individually controlled
for VC papers).

I think there would be little point putting out uV light since if it is
too far in the uV, the glass in the optical system would absorb it.

Actually, provided the uV wavelength is long enough to get through the
glass of the optical system and the gelatine holding the silver grains, if
the light were truely monochromatic, I would imagine the prints could be
sharper because of the shorter wavelength than normally used. For best
results, you would want a lens designed for monochromatic light of the
same wavelength. And, most important, you would need a way to see it so
you could focus it.

And all this is probably inconsequential, since you need only around 10
line-pairs/millimeter at the paper to make a sharp image.

So if you really care, stick a #47B filter in your enlarger and use white
light. Also stick a #47B in your focusing magnifier when you focus. It may
be hard to see. I have such a filter for my magnifier, but it is too dim
to focus by.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 09:55:00 up 2 days, 1:30, 3 users, load average: 4.32, 4.24, 4.18

  #3  
Old August 6th 04, 03:03 PM
Jean-David Beyer
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Default Cold Light for B&W?

jjs wrote:
Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region - therefore causing lesser sharp prints?


I do not think so. There is a lot of uV produced by the mercury vapor arc
in the tube, but the tubes are internally coated with phosphors that
convert most of that to visible light with a spectrum decided by the
manufacturer. Some put out a quite blue light, most put out bluish white,
and some put out green (I have seen green only in dual-tube heads where a
blue tube and a green tube, whose brightness is individually controlled
for VC papers).

I think there would be little point putting out uV light since if it is
too far in the uV, the glass in the optical system would absorb it.

Actually, provided the uV wavelength is long enough to get through the
glass of the optical system and the gelatine holding the silver grains, if
the light were truely monochromatic, I would imagine the prints could be
sharper because of the shorter wavelength than normally used. For best
results, you would want a lens designed for monochromatic light of the
same wavelength. And, most important, you would need a way to see it so
you could focus it.

And all this is probably inconsequential, since you need only around 10
line-pairs/millimeter at the paper to make a sharp image.

So if you really care, stick a #47B filter in your enlarger and use white
light. Also stick a #47B in your focusing magnifier when you focus. It may
be hard to see. I have such a filter for my magnifier, but it is too dim
to focus by.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 09:55:00 up 2 days, 1:30, 3 users, load average: 4.32, 4.24, 4.18

  #4  
Old August 6th 04, 03:27 PM
Nicholas O. Lindan
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Default Cold Light for B&W?

"jjs" wrote

Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region


There is no need for suspicion. Tubes not made for polycontrast printing
produce light at the bluish end of the spectrum. Special tubes are now
made for use with polycontrast filters and these do not have a blue
spectrum.

- therefore causing lesser sharp prints?


There was some hysteria about this 5-10 years ago, caused by an
article in one of the Photo/Darkroom/Techniques magazines. The claimed
effect has never been duplicated. It turned out to be yet another whale
of a tale.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
  #5  
Old August 6th 04, 03:39 PM
jjs
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Default Cold Light for B&W?


"Nicholas O. Lindan" wrote in message
hlink.net...
[...]
- therefore causing lesser sharp prints?


There was some hysteria about this 5-10 years ago, caused by an
article in one of the Photo/Darkroom/Techniques magazines. The claimed
effect has never been duplicated. It turned out to be yet another whale
of a tale.


Ah, so very good to know! Thank you, Nicholas! (I still use tungsten bulbs.
)


  #6  
Old August 6th 04, 08:06 PM
Michael Scarpitti
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Default Cold Light for B&W?

"jjs" wrote in message ...
Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region - therefore causing lesser sharp prints?


Perhaps you've confused actinic light (violet) with visual focus.
Light sources rich in violet may yield blurry prints because you can't
see that actinic light as vividly when you focus, and since lenses
focus each wavelength a little different, you may end up with a
differntial between the visual focus (yellow-green) and the actinic
focus (violet).

So, the anser is yes, but not for the reasons you may have imnagined.
  #7  
Old August 6th 04, 11:59 PM
Dan Quinn
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Default Cold Light for B&W?

"jjs" wrote

I still use tungsten bulbs.


The article referred to was one of the many written by Ctein for,
amoung others, Phototechniques.
In a very few words, it is at end the light that reaches the paper
and the color correction of the lens which determine the exact
best focus. Tungsten sources are not excluded.
The problem is due to the print paper's extrem sensitivity to the
deep blue and long UV portion of the spectrum. To focus, visible
light is required but it is the deep blue and UV which account
for a large part of the exposure.
So, no problem with a well corrected lens. To help, add a between
light and lens UV filter; UV, as in Skylight, Haze.
My personal read on the subject is to keep it in mind. Check the
print against what was seen when focusing. The paper makes a
difference.
Many poo-poo Ctein's work with this subject but I think it a
valuable contribution; very methodical painstakeing time consuming
research. A good read but be very focused.
If from a practicle view point it has no application with this
or that individual the article is informative and "if the shoe fits"
put it on. What you see MAY not be what you get. Dan
  #8  
Old August 7th 04, 12:36 AM
Paul Atreides
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Default Cold Light for B&W?

In article ,
"jjs" wrote:

Is there any truth to the suspicion that cold-light heads have a lot of
light close to UV which coincides with the extra sensitivity of some B&W
papers in the same color-region - therefore causing lesser sharp prints?


One unit I personally tested was the ZBE variable contrast Cold light
lamp house. Tested it using Forte paper, very flat mid- tones sort of
ran them all together.
--
To win one hundred victories in one hundred battles is not the
measure of skill. To subdue the enemy without fighting is the
measure of skill. Sun Tzu
  #9  
Old August 7th 04, 06:07 AM
John
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Default Cold Light for B&W?

On Fri, 6 Aug 2004 09:39:51 -0500, "jjs"
wrote:


"Nicholas O. Lindan" wrote in message
thlink.net...
[...]
- therefore causing lesser sharp prints?


There was some hysteria about this 5-10 years ago, caused by an
article in one of the Photo/Darkroom/Techniques magazines. The claimed
effect has never been duplicated. It turned out to be yet another whale
of a tale.


Ah, so very good to know! Thank you, Nicholas! (I still use tungsten bulbs.
)


The article was by Ctein. Theoretically it's correct but
nobody I know was able to determine the practical degree of the
problem.


Regards,

John S. Douglas, Photographer - http://www.darkroompro.com
Please remove the "_" when replying via email
  #10  
Old August 7th 04, 06:07 AM
John
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Default Cold Light for B&W?

On Fri, 6 Aug 2004 09:39:51 -0500, "jjs"
wrote:


"Nicholas O. Lindan" wrote in message
thlink.net...
[...]
- therefore causing lesser sharp prints?


There was some hysteria about this 5-10 years ago, caused by an
article in one of the Photo/Darkroom/Techniques magazines. The claimed
effect has never been duplicated. It turned out to be yet another whale
of a tale.


Ah, so very good to know! Thank you, Nicholas! (I still use tungsten bulbs.
)


The article was by Ctein. Theoretically it's correct but
nobody I know was able to determine the practical degree of the
problem.


Regards,

John S. Douglas, Photographer - http://www.darkroompro.com
Please remove the "_" when replying via email
 




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