Thanks so much, Richard, for all the good info. I know how much time &
effort it takes to think about & type it in all that, and I really
appreciate it!
However, I am still confused about the comment in your prior post in
response to Mark's:
"You can loose nearly one stop by developing in either Kodak Microdol-X or
Ilford Perceptol (they are identical). When used full strength these
extra-fine-grain developers loose about 3/4 stop when compared to D-76. The
results will be normal contrast negatives."
in light of your more recent one in repsonse to my post:
Thanks again, sorry to be so dense!
-Adrienne Moumin
*************************************** on the web at: www.picturexhibit.com
Additional work at Art@Large, NYC: http://tinyfineart.com/artists3/amou/amou.htm ***************************************
From: "Adrienne Moumin" <photowonder2010@xxxxxxxxxxx> Subject: [pure-silver] Developer and Neg Density Date: Thu, 22 Jun 2006 17:41:04 -0400
Mark Blackwell's question about neg density brought to mind something that's
been on my mind since I set up my darkroom 1-1/2 yrs ago.
I have a Saunders LPL 4550XLG enlarger w/the color module, and it has been a
stretch to get used to it since I've almost always printed on condensor
enlargers. I consistently find that the light is alot less contrasty than I
am used to, as well as somewhat dimmer.
I use Edwal FG-7 w/ 10% sodium sulfite for fine grain. I didn't realize different developers influenced neg density the way Richard mentioned. I'm wondering whether I should also try D-76 for the extra 3/4 stop.
Thanks in advance for any advice,
Adrienne Moumin
PS-Christina, welcome back, and I love your work too!
*************************************** on the web at: www.picturexhibit.com
Additional work at Art@Large, NYC: http://tinyfineart.com/artists3/amou/amou.htm ***************************************
-----much snippage here-----
You can lose nearly one stop by developing in either Kodak Microdol-X or Ilford Perceptol (they are identical). When used full strength these extra-fine-grain developers loose about 3/4 stop when compared to D-76. The results will be normal contrast negatives.
Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx
------------------------------
From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> Subject: [pure-silver] Re: Developer and Neg Density Date: Thu, 22 Jun 2006 15:21:58 -0700
Standard developers will all deliver the same contrast if the development time is correct. There ARE special developers for very high (like lith) and very low (like POTA or Technidol) contrast but otherwise its a matter of time. Kodak time/temperature charts are given for a contrast index suitable for contact printing or diffusion enlargers. That should work OK for your enlarger because most color heads are diffusion sources. In a condenser enlarger these negatives may take one grade softer paper to print with the same tone rendition. Not a bit deal with modern VC papers. The difference in _effective_ contrast is due to something called the Callier Effect. Callier discovered that the grains of silver scattered some of the light striking them. In a condenser enlarger the light is _collimated_ that is, it reaches the film in parallel rays. Some of this light is scattered out of the optical path, that is, away from going to the lens, so the densities appear to be higher. A diffuse source has ligth coming from all directions, or, more exactly, from most of a hemisphere. Some of this light is also scattered away from going toward the lens but light from other angles is scattered _toward_ the lens, so, the densities appear to be less than with a condenser source. The amount of Callier effect, sometimes also called Q factor, varies with the granular structure and thickness of the silver layer. Generally, it is somewhat greater for coarse grain film than for fine grain film. Color film, where the image is composed of very small dye particles, which are also transparent, has almost no Callier effect, so color negatives or slides print with about the same contrast regardless of the type of light source. In any case, the contrast of the negative can be exactly compensated for by changing the grade of printing paper. In his well known book _Controlls in Black and White Photography_ Dr. Richard Henry shows tests he made of printing with both types of sources. In one case the negative contrast was adjusted and prints made on the same grade paper, in the other test the same negative was used and paper grade changed. In both cases the two curves lie exactly on top of each other. In its data sheets for film Kodak usually gives a correction factor for negatives for condenser printing. Ilford curves are evidently compromise values which will print within about one half paper grade on either type. Agfa seems to have used diffuse values. While the ISO does not specify a contrast index or average contrst in the speed standard for B7 &W sill film, it does specify a range of density to be obtained from a range of exposure, which amounts to the same thing. The effective contrast of the standard is about right for contact printing and diffusion enlarging. Since the speed is valid for only this value changing contrast by varying development also affects effective film speed. A reduction in contrast results in a reduction of effective film speed, conversely, increasing development to increase contrast also increases effective film speed. Note there that one can NOT "push" film without increasing contrast or "pull" it without decreasing contrast. As a rule of thumb, the amount of increase or decrease of development time for a one paper grade difference in contrast varies with the type of film. For conventional type emulsions it is about +/- 25% to 33%, for Tabular grain films, its less, around 15% to 25%. This more rapid change in contrast with development for tabular grain films accounts for some of the troubles people have with T-Max contast. Of course, the variation will also be greater with temperature variations and variations in agitation.
--- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx
------------------------------
Date: Thu, 22 Jun 2006 22:39:57 -0400 From: "Mark Blackwell" <markb1958@xxxxxxxxxxx> Subject: [pure-silver] Re: Suggestions needed from the real experts here
----- Original Message ----- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Thursday, June 22, 2006 5:17 PM Subject: [pure-silver] Re: Suggestions needed from the real experts here
>
> ----- Original Message -----
> From: "Mark Blackwell" <markb1958@xxxxxxxxxxx>
> To: <pure-silver@xxxxxxxxxxxxx>
> Sent: Thursday, June 22, 2006 8:34 AM
> Subject: [pure-silver] Re: Suggestions needed from the real experts here
>
>
>> Yes I sure it is, but that for this batch isn't really an option. I
>> called Kodak this morning. For those interested for Tri X its 10% and
>> for T Max its 5%. Took about 2 mins off and we will see on the contrast.
>> I knew that there was a general rule of thumb, but couldn't remember what
>> it was.
>>
>> When I print them we will see but the negs at least look workable.
>>
> Is this developing time? If so, its way off. The change in time for a
> given change in contrast varies with the film and is less for T-Max than
> conventional grain films but, on average, its around 25% to 33% reduction
> for a one paper grade difference in contrast. This is equivalent to about
> 3/4 stop speed to maintain equal densities. To push or pull film the
> difference is a little greater. Again, it varies with the film but for
> conventional films, and most, but not all, developers its about 1.4X the
> time for pushing or about 0.7x for pulling. A 5 or 10 per cent change in
> time will have very little effect on either contrast or equivalent speed.
> OTOH, Tri-X has probably more than ten stops of overexposure latitude so
> 2 stops with normal contrast development will still give you perfectly
> good tone rendition in the print. It will just take longer to expose the
> prints.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
Thanks for the help Richard. Next time I might just develop normally and
test that out too. In fact sometime soon I might do it on purpose to see
what happens I am sure it won't be the last time the dummy behind the
viewfinder makes a mistake. LOL A drop in contrast might actually help this
particular subject, but a higher contrast paper is an option if needed. I
ended up using recommended development time x .80 for the Tri X and x .90
for a role of T Max that was also done the same way per kodak
recommendation. Even if it was bad advise, its worth knowing that too.
One thing I will say that I was a bit surprised at these days. First the Kodak site had a phone number to call with a question. Second someone answered the phone promptly, politely and answered my question. No long waits. Only one or two menu items to get to a person. I like a lot of different bw films, but I am going to buy a lot more Kodak because of the fact that they took my call and answered a question.
------------------------------
From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> Subject: [pure-silver] Re: Suggestions needed from the real experts here Date: Thu, 22 Jun 2006 21:01:44 -0700
----- Original Message ----- From: "Mark Blackwell" <markb1958@xxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Thursday, June 22, 2006 7:39 PM Subject: [pure-silver] Re: Suggestions needed from the real experts here
>>> prints. >> >> --- >> Richard Knoppow >> Los Angeles, CA, USA >> dickburk@xxxxxxxxxxxxx > Thanks for the help Richard. Next time I might just > develop normally and test that out too. In fact sometime > soon I might do it on purpose to see what happens I am > sure it won't be the last time the dummy behind the > viewfinder makes a mistake. LOL A drop in contrast might > actually help this particular subject, but a higher > contrast paper is an option if needed. I ended up using > recommended development time x .80 for the Tri X and x .90 > for a role of T Max that was also done the same way per > kodak recommendation. Even if it was bad advise, its > worth knowing that too. > > One thing I will say that I was a bit surprised at these > days. First the Kodak site had a phone number to call > with a question. Second someone answered the phone > promptly, politely and answered my question. No long > waits. Only one or two menu items to get to a person. I > like a lot of different bw films, but I am going to buy a > lot more Kodak because of the fact that they took my call > and answered a question. For some reason I forgot about Kodak's customer service, its among the few left where the people actually know something about the product. In the USA the number is 1 800 242 2424, professional photo products are at extension 19. If you cut back development by only 10 or 15 percent you will get about normal contrast negatives which will be rather dense. They should print well. Depending on the subject some overexposure is sometimes benificial. C.1940 a group at Kodak Research Labs, led by Loyd A. Jones, conducted very extensive research into the tone rendition of film and paper. Jones had been working since the 1920's (perhaps even before) on means of measuring film speed that would have some significance to the practicing photographer. Earlier methods were of interst to emulsion researchers but of limited practical application to pictorial photography. Jones's method was eventualy adopted by Kodak as its standard internal method and "Kodak" speeds began to be published c.1940. A modification of this sytem was adoped C. 1943 as the orignal ASA system. In their research into tone rendition and film speed Jones's object was to find the minimum exposure which would yield an "excellent" print. The reason for minimizing the exposure was because films of the time became grainier and lost some sharpness with density. This is still true but not to such an extent. It was thought that the thinest negative which would yield "excellent" tone rendition was the optimum. What Jones found was that after a certain minimum exposure was reached the tone rendition did not change for increased exposure over a very wide range. So, while minimum exposure has some benifit in minimizing grain and maximizing sharpness it does not have much effect on tone rendition provided that the exposure is enough. The criteria Jones settled on for his speed method was to set the minimum density which was to have any detail at a point on the toe where the gradient was 0.33 of the straight line portion. In practice, this proved very difficult to measure, so when the ASA revised the speed method in 1958, they adopted a method used by the Germans. This DIN standard was not the one from the 1930's but a newer method. The speed point was defined as a fixed density above gross fog and support density when the film was given a standard series of exposures and developed to a specified contrast. The ASA in testing this method found that the difference between speeds given by it and by the Jones minimum gradient method were very close provided a correction factor was applied to move the speed point up the toe. The ASA found after surveying a large number of films on the market at the time that if the speed from the DIN method was corrected by multiplying by 0.8 it would agree in nearly all cases with the Jones method. In addition, the original ASA speed standard for some reason included a 2x safety factor. This turned out to be a blunder since most exposure errors are in the direction of over rather than under exposure, so when one used the ASA speed one got rather dense negatives. When the new method was adopted in 1958 the fudge factor was dropped and all films doubled in speed overnight. The point of this is to show that overexposure by 2 or even more stops does not wreck the tone rendition of the resulting print. It may take longer to expose but the results will be the same. As far as minimum exposure goes, its of some value for small format negatives, mainly 35mm. By the time one gets to 2-1/4 x 2-1/4 there is probably little gain and none for larger sizes. For underexposure you are generally cooked. Since the film speed gives about the minimum exposure that will yield good tone rendition any further reduction is likely to result in empty shadows or distorted mid grays if contrast is increased in an attempt to make the shadows look right.
--- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx
------------------------------
End of pure-silver Digest V3 #168 *********************************
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