Ilford FP4 - Reciprocity

[stephen_vaughan3]

Would be grateful if anyone is able to share their experience with

regard to exposure adjustment for reciprocity failure, with Ilford

FP4.

Is the table provided by Ilford accurate?

Are any adjustments to development needed?

 

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The exposure reading is, for example, 30 secs @ f/32. The adjustment

needed according to Ilford would be 150 secs @ f/32.

 

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Many thanks!

 

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PS - I'm shooting on 10x8/processing in Pyro PMK (if that makes any

differen

[mark_parsons1]

I shoot FP4 and HP5 and find that the reciprocity info from Ilford is

pretty good. The problem comes when you are making an exposure which

is longer than the Ilford chart covers (not sure but I think it goes

to 30 sec. max?). Then you have to extrapolate from the chart and

use your gut. When in doubt I error on the side of more exposure -

it seems hard to over expose when you get into really long times.

This weekend we were making an exposure on a foggy morning deep in

the forest and the meter said 1 min. so we gave 10 min, and the negs

look fine. You're "supposed" to reduce development when reciprocity

comes into play but I almost never do. Maybe this is because the

types of scenes where long exposures are necessary are by nature

fairly low in contrast to begin with, but I find that normal

development gives me the results I want. (I'm using D-76 1:1, by the

way. No experience w/ pyro.)

 

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Good luck!

[floren_pge]

You can actually extrapolate the rest of the times for the graph

using a number of statistical software. Plug in the numbers from the

Ilford chart and let the program graph it. The program can then

extend the graph indefinitely. It will also give a formula for the

graph. I extrapolated the new times for FP4 up to 1 hour (I don't

have the corrected times in front of me) using a program called

Cricket. I then tested the corrected times for 1, 2, 4, 8, 15, 30,

and 60 minutes. All the exposures came out correct. I heard MS Excel

can also extrapolate data but I've never tried it.

 

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I also don't change the development times when I use ID11 1:1.

[david_carper]

If you wish to calculate a corrected exposure time based on the

ILFORD chart, use the formula

 

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Ec=Em^1.48

 

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Where Ec is the corrected exposure, and Em is the measured exposure,

in seconds. Measured exposures of one second or less do not require

any compensation.

 

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Note that this formula is based on the chart. The chart was

determined from experimentation. Times calculated past the chart

should be good estimates, but are not based on ILFORD experiments.

 

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David Carper

ILFORD Technical Service

[jnorman1]

doing HABS/HAER work, i have often found myself in some pretty

ridiculous exposure situations, in the middle of abandoned tunnels,

dark buildings, bridge abutment housings, unlighted machinery rooms,

etc. as mark mentioned above, it is pretty hard to overexpose in

those kinds of situations. if my meter reads 30 secs or 2 minutes,

or some such, i just wave my finger in the air to see which way the

exposure is blowing, and open the shutter. i wander around a little

while and come back and close it. i have never once had a bad neg

using that technique, and oddly, there doesnt ever seem to be any

noticeable difference between negatives exposed for wildly differing

amounts of time. i used to obsess about this kind of thing, but long

experience has taught me i dont need to worry about it.

[dave_anton]

Stephen, as the previuos answer said, it is difficult to overexpose

the film with long exposures. I also use PMK with FP4 on 810.

Normally I guess a longer time when my meter indicates more than 1

min, and my negs always turn out fine. Somethng to keep in mind is to

make sure the film is settled in the holder before exposing the film.

[pete_andrews]

Ilford's recommendation has seemed reasonably accurate to me, but

then I rarely expose beyond a few seconds.<br>BTW, reciprocity failure

increases contrast, because it affects the shadows much more than the

highlights. This increase in contrast is the opposite to what most

people expect, and the instinctive response is to give a fuller

development. In fact, you should downrate the film, and pull the

development slightly to get the shadow detail back and keep the

highlights in check.

[ed b.]

I have made an exposure calculator for reciprocity failure that also

indicates development compensation factors. I intended it for use

with pinholes, but it will work for any long exposure. The times are

for T-Max 100 and Tri-X, but there is a blank field so you can add

your own favorite film. Anyone can print it out and either paste it

onto some matte board or laminate it in plastic.

 

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http://unblinkingeye.com/Articles/Pinhole/Calculate/calculate.html

[john_hennessy]

This is what I use for HP5+ in PMK

 

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Meter Adj -Dev %

1" 1.2" �

2" 3" �

3" 5" �

4" 7" �

6" 12" �

8" 19" 5

15" 50" 10

22.5" 1'30 12

30" 2'25" 14

45" 4'10" 16

1' 6'20" 18

1.5' 14' 20

2' 28' 24

3' 1°30' 27

4' 2°10' 30

 

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The beauty of reciprocity "failure" is that often with such long

exposures, you also face low contrast. Thus, if you think that +3 is

all you can coax out your developer but this table calls for -20%

development, just ignore the -20% and you'll get maybe a +4

development.

[john_hennessy]

I typed in a nice table from the one on my light meter but it was

rendered as a string of unintelligible numbers here.

 

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If anyone wants my numbers, e-mail me and I'll send a text file.

[pete_andrews]

I wonder if it's possible to submit a table in HTML to this forum?

<center><table BORDER COLS=3 WIDTH=80%>

<tr><td><center><b>Row 1, column 1</td>

<td>Row1, column 2</td><td>Row 1, column 3</b></center></td></tr>

<tr><td><center><b>Row 2, column 1</td>

<td>Row2, column 2</td><td>Row 2, column 3</b></center></td></tr>

</table></center>

<br>If this came out OK, you can see how it was done with the 'view

page source' option, but formatting a table by hand is a real pain.

[pete_andrews]

Hmmph! Nearly right, but the text formatting needs to be done for each

box individually. Very labourious.

[davidspady]

For a close approximation on how many stops to increase the exposure by, use the following method:

 

Find out: two to the power of which number is close to the metered exposure time in seconds. Take that number and divide it in two to determine how many stops to increase the exposure by.

 

Example:

 

Metered Exposure = 9 seconds.

 

2^3 = 2*2*2 = 8 (which is close to 9)

 

So take 3 (from 2^3) and divide it by 2 to get 1.5. So for an 9 second metered exposure, you should add 1.5 stops for a correct exposure.

 

Another example:

 

Metered Exposure = 50 seconds.

 

2^5 = 32 (add 5/2 = 2.5 stops)

2^6 = 64 (add 6/3 = 3 stops)

 

Since 50 is somewhere in the middle of 32 and 64 seconds, add between 2.5 and 3 stops of exposure. In reality, if the curve is extrapolated as an exponential, the correct exposure would be +2.7 stops. So the approximation is pretty good -- and very easy. It works with Ilford Pan-F, FP4, and HP5 and any other film with a similar reciprocity failure curve.