The Kodak safelight test

[Firestarter]

After adding some extra safelights to my darkroom I thought it best to retest my overall safe lighting and levels etc.
I decided to use the Kodak test as linked to here......

https://www.kodak.com/uploadedfiles..._motion_products_filter_K4_Safelight_1106.pdf

After doing the test it looks like I am all good but one thing I was wondering about is why Kodak specify a density of 0.25 to 0.50 for the enlarger exposure ?
Other tests I have done in the past only say to pre expose the paper to its minimum exposure threshold.

 

[MattKing]

Most likely because the test is designed so that it will produce repeatable results for labs that already make use of densitometers for process control purposes.
"Minimum Exposure Threshold" is relatively hard to measure repeatably. 0.25 - 0.50 is easy.
I just use "light grey".

 

[Jim Jones]

A safelight test that is little more complicated but more informative than the Kodak test is to first make strips of varying white light exposures in one direction across a piece of photo paper, and then make strips of varying safelight exposures at right angles to the first strips.

In detail, raise the enlarger head to its maximum height and stop the lens down to its minimum opening. There should be no negative in the negative holder. In total darkness place a sheet of fresh paper in the easel. Cover the 1/6 of the bottom of the paper. Make a 1 second exposure. Cover 1/6 more of the paper and make another 1 second exposure. Cover 1/6 more, and make a 2 second exposure. Repeat the process with 8 and 16 second exposures. I find it easier as well as quicker to move the covering material up at the 1, 1, 2, 4, and 8 second intervals. This will also eliminate any error due to the intermittency effect and light lag in the enlarger lamp. Now place the enlarger and paper under the safelight and cover 1/6 of one side of the paper. Turn the safelight on. After 1 minute, cover another 1/6 of the paper. At additional 1, 2, 4, and 8 minutes expose more 1/6 strips. After 16 minutes of safelight exposure turn off the safelight and develop the paper in darkness.

With your darkroom setup you may not need the longer enlarger and safelight exposures. You may also want more precision than provided by these one stop increments. If so, make the exposure steps of 1, 0.4, 0.6, 0.8, 1.2, 1.6, 2.4, 3, and 5 units. Yes, that’s too complicated for me, too.

Analyzing the results of this test may aid one in predicting the effect of pre-exposing film or paper to alter the toe of the characteristic curve of those materials. The results of this surprised me.

 

[Firestarter]

Thanks guys. Matt, I just wanted to be sure I wasn't making a mistake with the density as it sounded fairly heavy. So I could probably do the test again using a lighter tone to be sure the safelights are not affecting my very light tones ?

Jim...I might give that a shot at some stage also, this test seems to check the safelights at the paper flash point, is that correct ?

 

[Jim Jones]

Firestarter, it checks the effect of the safelight at many of the values in the white light exposure. The results aren't what one might intuitively expect. For example, a light fogging exposure can slightly emphasize cloud texture, although burning in (especially with a high contrast filter) when printing on variable contrast paper) is more versatile.

 

[ic-racer]

After doing the test it looks like I am all good but one thing I was wondering about is why Kodak specify a density of 0.25 to 0.50 for the enlarger exposure ?
Other tests I have done in the past only say to pre expose the paper to its minimum exposure threshold.

How are you ascertaining your 'minimum exposure threshold? One way is to observe a density of 0.25 to 0.5 on the paper with your eye or machine.