# Trying to figure out exposure for Stouffer TP120-31

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• 12-11-2013, 07:57 PM
Bill Burk
Quote:

Originally Posted by qualsound
yes i think i underexposed the film quite a bit.

Maybe one f/stop underexposed, but still you have enough curve family information to make processing decisions.

Again the only thing you miss out on, is a few more steps of information that you could have had in the highlight densities on the right side of the graphs.

And the underexposure does not in any way impact the speed of your film that is revealed by the curve family.
• 12-12-2013, 12:15 AM
wiedzmin
Bill,

but why for HP5 effective film speed is so low ~10 for 400 iso film (summary tab)?

Tomasz
• 12-12-2013, 07:21 AM
qualsound
Hi Bill Burk!

Thank you for your explanation! I read Ralphs instructions on that excel sheet once again...and came to the conclusion, that i missed one IMPORTANT point!...to change the EI --> 2/3 less speed in this field,...so 400 --> 250 for HP5 and 125 --> 80 for FP4. Then i had to change the logH min until the curve, the red and black line intersected...! i think i can use these results now... Bill what is your opinion on the filmspeed and development times provided by the excel sheets for fp4 and hp5 (i attached them once again after changing the parameters i described above).

Thank you for your help! Best regards, christoph.

P.S.: So tomasz, stating that from above is the answer to your question "but why for HP5 effective film speed is so low ~10 for 400 iso film (summary tab)?"
Have you got a similar problem...so maybe that is the solution...! ;-)
• 12-12-2013, 09:43 AM
qualsound
what i am able to read out of that excel sheets is:

FP4
N+3: iso 125 ??? @ ???
N+2: iso 125 @ 16'40"
N+1: iso 100 @ 11'30"
N: iso 80 @ 8'
N-1: iso 50 @ 5'30"
N-2: iso 40 @ min 5'
N-3: iso 40 @ min 4'20"

HP5
N+3: iso 400 ??? @ ???
N+2: iso 400 ??? @ 15'50"
N+1: iso 320 @ 12'50"
N: iso 250 @ 8'50"
N-1: iso 200 @ 7'
N-2: iso 160 @ min 5'50"
N-3: iso 125 @ min 5'10"

Bill Burk your opinion on my conclusion is very much appreciated! Thank you for your help!

Best regards, Christoph.
• 12-12-2013, 06:36 PM
wiedzmin
Christoph,

Quote:

P.S.: So tomasz, stating that from above is the answer to your question "but why for HP5 effective film speed is so low ~10 for 400 iso film (summary tab)?"
yes I think that was it. Are you going to perform real film speed test based on WBM 2?
• 12-13-2013, 01:41 AM
Bill Burk
Quote:

Originally Posted by qualsound
Bill Burk your opinion on my conclusion is very much appreciated! Thank you for your help!

Best regards, Christoph.

Looks good to me at first glance.

I'm graphing your HP5 to double-check.
• 12-13-2013, 07:44 AM
qualsound
Bill Burk,

I looked at the results closer now and made a few corrections concerning dev.time and filmspeed (see below) Why is it that at n+3 both, fp4 and hp5 go beyond their actual box speed of 125 and 400 (i printed the curves from the excel sheet on a dina4 paper and extended the curves by hand, considering they grdually went higher, until they intersected with the lines at +2 and +3)?
Bill you wrote i have to take the filmspeed results with caution...why is that...and how can i determine the correct film speeds and dev.times then...if my results should be too far off?

@tomasz: i will wait what bill suggests and see then what to do next...what about the results of your test?

FP4
N+3: iso 160 @ 23'
N+2: iso 125 @ 17'30"
N+1: iso 100 @ 11'35"
N: iso 80 @ 8'
N-1: iso 64 @ 5'30"
N-2: iso 50 @ min 4'55"
N-3: iso 40 @ min 4'30"

HP5
N+3: iso 640 @ 20'30"
N+2: iso 400 @ 16'30"
N+1: iso 320 @ 12'15"
N: iso 250 @ 8'50"
N-1: iso 200 @ 7'
N-2: iso 160 @ min 5'50"
N-3: iso 125 @ min 5'10"
• 12-14-2013, 12:49 AM
Bill Burk
Hi Christoph,

This is your data as I would interpret it. Notice the ASA triangle. The tip of the triangle at the toe of the curve that fits that triangle, is where I marked 400, the ISO speed of that film. The other speeds marked are based on the point where their curves reach 0.10 above Base+Fog. The relative speeds can be read directly above that point off the chart pasted in the middle of the graph.

HP5
N+1 CI .72: ei 640-800 @ 16'
N CI .60: ei 400 @ 11'
N-2 CI .45: ei 320 @ 8'
N-3 CI .37: ei 250 @ min 5'30"
CI .25: ei 200 @ min 4'

http://www.beefalobill.com/images/hp5curv.jpg
• 12-14-2013, 12:58 AM
wiltw
Quote:

Originally Posted by qualsound
what i still don't know is which bar (number) on the step wedge (either 21 or 31) represents medium gray...so that i could take a spotmeter reading off of that to determine expousre...

'Middle grey' by definition is the center of the range of densities, the midpoint between 'black' and 'white'. So on the 21 step wedge it would be #11 (plos and minus 10 steps to either side), and on the 31 step wedge it would be #16 (plus and minus 15 steps to either side), logically speaking!

So try spotmetering that step!
• 12-14-2013, 01:10 AM
Bill Burk
But for the purpose of sensitometry, it's more important to select an exposure that gives you as much data as you need. In the graph I just posted, you can see my normal exposure "ruler" at the top of the sheet.

Christoph gave his film about four stops less exposure than I usually do. So you can see some wasted sample points where the toe is flat. If you gave four stops more exposure the next time you do a test, you will get a lot more information on the right-hand side of the graph.

You can see that I wasn't able to accurately measure Contrast Index (CI) on the 4 and 5.5 minute curves because one of the measurement points I needed (marked with a "C") is off the chart.

So Christoph, whatever you did before... Give four more f/stops of exposure next time.
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