It looks like you are getting a gamma of about 0.67 with this development (time, temperature, and developer). That is reasonable (maybe a bit higher than some would like), and the fog level does not sound unreasonable, so you seem to have a good starting point for developing the film. Now you want to determine the speed. You can do that from the curves with an incident light meter reading, but it gets pretty fussy. You also run into inaccuracies due to the warm up and cool down time of the enlarger bulb and possibly from the reciprocity characteristics of the film. It is better to take pictures with a camera. The lazy way would be simply to take some bracketed exposures of a high contrast scene and determine which exposure gave you the best (zone placements reasonably correct) result. Another way is to take bracketed pictures of a paper gray scale (the Macbeth color chart has one, and so do many of the Kodak Photoguides).
My uneducated guess is that I want to lower the values of my VI & up....
I'm (again, uneducated guess) thinking that I need to dilute my developer out a BIT more.. not half again..I'm at 1+9 now.. I'm thinking of going to 1+12...
Then fussing with the development times to get the proper separation in tones.
Does that jive with your statement re: gradients? (this is sort of the same trouble I'm having with the Kodak sensitometry workbook... it tells me what I SHOULD have, but does not tell me which variables have the most direct effect on the outcomes I wish to alter)...
A gradient of 1.00 what gradient might be considered "normal". . . ?
right... so the gamma would "normally" be closer to the low 60's, mid 50's... to reproduce an average scene with out introducing a whole lot of snark... yes?
And determining the speed.. yeah, I'll start out by shooting some sheets bracketed around zone 1, and see that I'm getting something that my densitometer says is .1 or so higher than film base plus fog. The plus side of this is that I will just meter the gray card, stop down 4 stops, bracket, which means I'll be working from the shutter I really want to be clicked into. If I can land my grubby hands on a paper gray scale I'll shoot that! I know someone who's got a MacBeth color chart.
I use a gray Sturdy Board about 22x28 inches then wait for
Originally Posted by Pastiche
about 15 minutes of clear blue sky. Doubling of zone five with
a change in f stops will keep shutter speeds reasonable
and serve as a check of f stop accuracy.
Sometimes I shoot only zones 3 through 7. Below 3 and
above 7 lies very little print image detail.
Sturdy Board is a crafts shop item. Dan
thanks for describing your process Dan.
Even lighting IS so critical... I think I'd use a north facing wall and stay in the shade. Metering for every exposure & then making the adjustments necessary.
Today I'm doing some tests on getting my development dilutions straightened out... I want a curve with a little less slope (gradient).
I'll post some curves this afternoon/evening.
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I'd think a 5 to 10 minutes shoot would do for all
Originally Posted by Pastiche
zones. Avoid near twilight for the series as the
level of light drops rapidly. Dan
Point noted Dan.
Here are the curves for my last test of this film/developer
All curves are:
ERA 100 shot at 50 ISO
Developed in Dektol at three different dilutions: 1+9, 1+11, 1+14
According to the Kodak guide to sensitometry, the total span of densities between the lowest and the highest densities "should" be about 1.30
It looks as though the process that most closely resembles that is this film/ISO combo in Dektol 1+11 (1:12), 5 min. Rotary process, 68 deg. F.
The question that lingers in my mind is - these curves seem to be telling me that my effective ISO is actually not 50, but something close to ... 12.
(iso 50 minus two stops... = 12, right...)
I'm arriving at that conclusion because the toe on the curve seems to hover at .2, and only rises to .1 above that around step #3... or be it, two stops more exposure. Yes??
I usually just null the densitometer on the base + fog. If you include it in your curve, you have to go and subtract it back for anything you do with your curve. Also, if the density is high what are you going to do about it? Send the film back and say it's old? Who is going to take it back .
Last edited by ic-racer; 03-18-2009 at 07:13 PM. Click to view previous post history.
Err.. I think I've made a mistake..
The speed point for this process seems to be at about step "II" on the step wedge.. which amounts to one stop more exposure.
WHEN I get off to trying film speed testing I'll use ISO 25 as my "center point", and bracket around it two stops in either direction.
Originally Posted by ic-racer
I realized that I was noting the wrong numbers on the spread sheet that is generating the curves...
I THINK that I've now gotten fb+f numbers that seem reasonable.
Now that I've pretty much settled on the 1:12 dilution for dektol I'll run a blank sheet through it to see what I get (I'm just not quite trusting the 21st step on the tablet as being perfectly opaque.
Next up -
Run a blank sheet through the process.
Then think about ISO testing...
Then, then I'll start wondering about moving the image further into the straight line portion and away from the toe... or I might just give up at that point and keep on keepin on